Method of separating bonded elements of a vehicle

Abstract

A vehicle has first and second elements, for example a frame 110 and a battery pack 115, bonded by at least one adhesive joint where at least one of the elements comprises an electrically conductive m

Description

FIELD OF THE INVENTION The invention relates to vehicles comprising elements bonded together using adhesive and provided with an integrated cutting wire. The invention also relates to methods of manufacture of such vehicles, and to methods of separating bonded elements of a vehicle using an integrated cutting wire. BACKGROUND Mechanical fasteners, such as nuts and bolts, are very commonly used across vehicles for their strength and ease of unfastening for maintenance. However, mechanical fasteners have substantial downsides. For example, where large elements are joined together, this may require many mechanical fasteners that require significant time and effort fastening and unfastening during maintenance. Additionally, mechanical fasteners are often inefficient at transmitting or reacting to loads that are applied perpendicularly to their main axis (i.e. shear loads), meaning the number and sizing of fasteners has to be increased to prevent all possible failure modes including bolt shear failure, joint slip failure, and failures at the edge of the bolt holes. An alternative means of joining elements of a vehicle is by adhesive. However, adhesive is typically seen as a semi-permanent means of joining elements of a vehicle, which is not conducive to maintenance that involves separating the joined elements. Adhesive, however, provides advantages in that it can be scaled up to join larger elements without significantly increasing the time to join the elements. Adhesive may also improve handling of impact loads from different directions. It is therefore desirable to provide a means of benefitting from the advantages of adhesives for joining elements of a vehicle while facilitating maintenance that involves separating the joined elements. SUMMARY OF INVENTION The invention provides configurations and methods to ensure that an integrated cutting wire that is heated by an electric current does not form a short circuit with electrically conductive material of adhesively bonded elements in a vehicle as the cutting wire cuts through an adhesive joint of the bonded elements. Elements bonded together by an adhesive joint with an integrated cutting wire greatly simplify the separation of elements and so facilitates effective maintenance of the vehicle. The integrated cutting wire is an electrically conductive wire. The wire may be a metal wire, preferably a nichrome wire, or stainless steel. Metal wires are particularly suitable for cutting adhesive joints and / or heating. The wire can be heated before and during cutting to allow the wire to better cut through the adhesive. A convenient way of achieving this may be to join one end of the wire to the first element or the second element at an electrical connection point, wherein the electrical connection point electrically connects the wire to at least part of a circuit for heating the wire. For example, a metal anchor point may electrically connect the wire to the circuit. In this way, a technician may use the circuit to heat the wire, for example by retrieving the second end of the wire and completing a circuit to resistively heat the wire, before and / or during cutting the adhesive joint. In another example, both ends of the cutting wire may be exposed or accessible, and where a technician can connect the two ends of the cutting wire (e.g. by using crocodile clips) to an external circuit to resistively heat the wire. In accordance with a first aspect of the invention, there is provided a vehicle comprising: a first element bonded to a second element by at least one adhesive joint between a surface of the first element and a surface of the second element, the first element and / or the second element comprising an electrically conductive material; and an electrically conductive wire comprising a first portion configured to cut the at least one adhesive joint and a second portion configured to be connected to at least part of a circuit for heating the electrically conductive wire; wherein the surface of the first element and / or the surface of the second element further comprises a non-electrically conductive layer to prevent at least the first portion of the electrically conductive wire from contacting the electrically conductive material of the first element and / or the second element as it is pulled through the at least one adhesive joint. The first portion of the electrically conductive may be arranged between the surface of the first element and the surface of the second element. The electrically conductive wire may be arranged adjacent to the at least one adhesive joint. As the electrically conductive cutting wire is being resistively heated (with an electrical current) and being pulled through the adhesive joint, the cutting wire may be pulled toward a surface of the first element and / or the second element such that the electrical current passing through the cutting wire could contact electrically conductive material in the first element and / or second element accidentally and form a short circuit. In the present invention, any electrically conductive material in the first element and second element is shielded from contact with the electrically conductive cutting wire when it is being resistively heated. Preferably, the surface of the first element and / or the surface of the second element comprises aluminium or an aluminium alloy, and wherein the non-electrically conductive layer comprises an anodised layer of the aluminium or aluminium alloy. Anodisation creates and / or increases the thickness of an electrically insulating oxide layer on the surface of the electrically conductive aluminium material, thus eliminating conductivity into a first element and / or second element. Advantageously, it has also been found that anodisation can also increase the surface roughness of a bonding surface such that adhesion with the adhesive joint is promoted. It should be understood that the electrically conductive material of the first element and / or the second element may be in the region or at the interface of the at least one adhesive joint such that contact between the electrically conductive wire and the electrically conductive material during when an electrical current is passing through the wire would cause shorting of an electrical circuit. The non-electrically conductive layer therefore eliminates the risk of shorting between an active electrically conductive wire and the electrically conductive material of the first and / or second element. Preferably, the non-electrically conductive layer comprises a coating. The coating may comprise an electrodeposition coating, or e-coating. The non-electrically conductive coating may also be applied in a way to promote adhesion with the adhesive joint. For example, the surface roughness of the coating may be increased or a particular coating composition may be used. The coating may also be applied on top of an anodised layer of aluminium and / or aluminium layer for additional adhesion promotion and electrical insulation. In accordance with a second aspect of the invention, there is provided a vehicle comprising: a first element bonded to a second element by at least one adhesive joint between a surface of the first element and a surface of the second element, the first element and / or the second element comprising an electrically conductive material; an electrically conductive wire comprising a first portion configured to cut the at least one adhesive joint and a second portion configured to be connected to at least part of a circuit for heating the electrically conductive wire; and a locating element arranged to at least partially position the electrically conductive wire between the surface of the first element and the surface of the second element to prevent the first portion of the electrically conductive wire from contacting the electrically conductive material of the first element and / or the second element as it is pulled through the at least one adhesive joint. It will be appreciated that the features of the first and second aspects of the invention are compatible, and the invention according to the first aspect may be provided with the features of the second aspect, including all of the optional features discussed below, and the invention according to the second aspect may be provided with the features of the first aspect, including all of the optional features discussed above. For example, a vehicle may use the non-electrically conductive layer in some regions or for some adhesive joints and may use the locating element in other regions or for other adhesive joints. Alternatively, the vehicle may use the non-electrically conductive layer and the locating element together in the same region of the same adhesive joints, as these will both lead to improved cutting of the adhesive joints. It should be understood that the electrically conductive material of the first element and / or the second element may be in the region or at the interface of the at least one adhesive joint such that contact between the electrically conductive wire and the electrically conductive material during when an electrical current is passing through the wire would cause shorting of an electrical circuit. The locating element can ensure that the cutting wire is directed away from the bonded surfaces of the first element and the second element. The locating element may be arranged to ensure that the initial position of a pulling portion of the wire is in a substantially central position between the first and second element surfaces, or otherwise in a position spaced from the first and second element surfaces. For example, the locating element may arrange the pulling portion of the wire at a position between the surface of the first element and the surface of the second element that is substantially equidistant from the surface of the first element and the surface of the second element. It has been found that the initial position of a pulling position of the cutting wire can effectively determine a preferential direction of travel of cutting as the wire is pulled through the at least one adhesive joint. Typical adhesives are good thermal insulators and do not readily dissipate thermal energy across the bulk of the adhesive material. As such, heat generated by resistively heating the electrically conductive wire can be concentrated in the adhesive material in the vicinity of the cutting wire and allow the cutting path (of the wire being pulled through the adhesive joint) to remain along a central portion of the adhesive joint away from the surface of the first element and the surface of the second element. Furthermore, materials such as aluminium or other metallic alloys in the first and / or second elements may act as effective heat sinks, which mean that any heat from the resistively heated cutting wire that is thermally conducted toward the first and / or second elements may be quickly dissipated across the first element and / or second element, which leaves the adhesive material near the interface(s) with the surface of the first element and / or the surface of the second element to remain relatively cool and harder to cut. The locating element may comprise at least two pieces of material (e.g. a hard plastic) with respective semicircular cut-outs, which are arranged adjacently to the adhesive joint to provide a gap and entry / exit for the second portion of the wire to pass in and out of. In another example, the locating element may comprise an open ring shape (e.g. a C-shaped ring). Other designs of locating elements would be readily apparent to the skilled person. Preferably, the locating element comprises a guide arranged to provide a gap in line with a side of the at least one adhesive joint. The guide may comprise a length that is equal or greater than a length of the at least one adhesive joint such that the electrically conductive wire may be fully guided as it is pulled through the at least one adhesive joint. Alternatively, the guide may be shorter than the length of the adhesive joint but provide more than an initial positioning of the wire. Preferably, the electrically conductive wire further comprises a third portion of the electrically conductive wire arranged to pass through the gap, and wherein the guide is arranged such that the electrically conductive wire is progressively pulled through the gap as it is pulled through the at least one adhesive joint. The third portion may be the pulling portion of the wire. The third portion of the wire may be arranged away from the guide and only brought into the guide when a user wishes to cut the adhesive joint. Alternatively, the third portion of the wire is provided in the gap of the guide during installation / manufacture such that the third portion is easily accessed and ready for the heating and cutting process. Preferably, a width of the gap is less than a width of the at least one adhesive joint between the surface of the first element and the surface of the second element. In this way, the guide can ensure that any lateral displacement (i.e. travel of the cutting wire that deviates from a main cutting path along the adhesive joint) of the cutting wire does not cause the cutting wire to come into contact with the surface of the first element and / or the surface of the second element. As should be understood, the gap of the guide may be entirely arranged over the at least one adhesive joint without revealing any material of the first element and / or the second element through the gap. Preferably, the width of the gap is adjustable. In other words, the gap may be adjusted to increase or decrease a distance between the guide portions (and the permissible lateral displacement of the wire in the cutting process). As an example, the gap may be between 4 to 6 mm. An electrically conductive cutting wire may have a diameter of 1 to 2 mm. Preferably, the locating element is adjacent to the third portion of the electrically conductive wire. In this way, the third portion of the cutting wire can effectively ensure that the first cutting portion of the wire is correctly positioned before the wire is pulled through the at least one adhesive joint. The locating element may be at least partially embedded in the at least one adhesive joint. For example, a portion of the locating element may be provided in the adhesive joint as it is formed (i.e. when the two surfaces of the first and second elements are brought together and bonded with the adhesive material) to provide a permanent fitting. The locating element may be detachable from the vehicle. The locating element may be a separate or temporary piece that is attached to the vehicle before and during an adhesive joint is cut. The locating element may comprise a non-electrically conductive material. For example, the locating element may comprise a non-electrically conductive surface at an interface with the first or second element, and / or a non-electrically conductive surface facing the cutting wire. Typically, the locating element will be formed of a non-electrically conductive material, such as a plastic. Preferably, a part of the electrically conductive wire is joined to the first element or the second element. The part of the electrically conductive wire may be an end of the wire that is joined to an anchor point of the first element or the second element. The anchor point may be an electrical connection point. In this way, the electrically conductive wire can be readily connected to a circuit for heating the wire. For example, a metal anchor point may electrically connect the wire to the circuit. In this way, a technician may use the circuit to heat the wire, for example by retrieving an end of the wire and completing a circuit to resistively heat the wire, before and / or during cutting the adhesive joint. Preferably, the part of the wire is anchored to the first element or the second element, such that the wire may be pulled through the at least one adhesive joint to cut the at least one adhesive joint while anchored to the first element or the second element. An anchor will typically comprise a mechanical fastener, such as bolt or rivet to anchor the wire in place. Preferably, the electrically conductive wire comprises a fourth portion that is embedded in the at least one adhesive joint. Part of the electrically conductive wire may fix or anchor one end of the wire in place and the fourth portion of the wire may fix or anchor the other end of the wire in place. Embedding the fourth portion of the wire in the adhesive joint can ensure that the cutting wire is in a correct position for cutting. In particularly preferable embodiments, the at least one adhesive joint comprises areas arranged on surfaces at different angles. Where mechanical fasteners may be used, it becomes particularly difficult to allow mechanical fasteners to be secured along different axes, as this would generally require clearance around the secured elements from multiple different directions to fasten and unfasten the mechanical fasteners. An adhesive joint extending across surfaces at different angles can be conveniently cut using the integrated cutting wire, which may bend or be manipulated along different directions to cut a more complex adhesive joint. Where the adhesive joint is elongate, the different areas on surfaces at different angles may be different areas of the adhesive joint along the elongate direction of the joint, or they may be different areas generally perpendicular to the elongate direction of the joint. In other cases, different ones of the adhesive joints may be arranged on surfaces at different angles but nonetheless cut by the same integrated cutting wire. As indicated above, generally, the at least one adhesive joint is elongate, preferably having a length of at least 30 cm, preferably at least 50 cm, more preferably at least 100 cm, most preferably at least 200 cm. As described above, an advantage of adhesive joints is that they can be conveniently scaled up in size without significantly increasing the time to separate the joined elements. Elongate adhesive joints are also generally easier to cut. Where a plurality of adhesive joints are provided, each adhesive joint may individually be elongate or the adhesive joints together may be elongate, e.g. extending along an elongate track of the adhesive joints. The width of each adhesive joint may be less than 15 cm, preferably less than 10 cm, more preferably less than 5 cm. The thickness of each adhesive joint may be no more than 10 mm, preferably no more than 5 mm, more preferably no more than 3 mm. Preferably, the thickness of each adhesive joint is in the range 0.5 mm to 5 mm, preferably 1 mm to 3 mm. Where the at least one adhesive joint is elongate, preferably the wire extends along substantially the entire length of the or each elongate adhesive joint. For example, the first portion of the wire may be joined at one end of the least one adhesive joint, and the second portion of the wire may be accessible at an opposing end of the at least one adhesive joint. Preferably, the at least one adhesive joint substantially surrounds an area within which the third portion of the wire is joined to the first element or the second element. The cutting wire of the present invention is particularly useful for cutting adhesive joints that surround a central area, since the wire may be anchored or otherwise joined within the surrounded area. Examples of such use cases include electronics enclosures, such a battery tray closed by a lid in which an adhesive joint is applied along the periphery of the tray surrounding the tray centre, or a battery pack secured to the frame of a vehicle by an adhesive joint along the periphery of the battery pack. In these use cases, without an integrated cutting wire, it would be difficult to suitably arrange a cutting wire across the adhesive joint into the surrounded centre area without the present integrated cutting wire that is already joined within the surrounded area. In many embodiments, the adhesive joint may define a path and the wire is arranged to substantially follow the path of the at least one adhesive joint. For example, the adhesive joint may be provided along a path at the interface between the first and second elements, and so to ensure that the wire may cut each part of the path, the wire may be arranged on one side of the adhesive joint to follow the path, e.g. generally in parallel with the path of the adhesive joint. To hold the wire in place as it follows this path, the wire may be joined to the first element or the second element at a plurality of locations as it follows the path of the at least one adhesive joint, wherein preferably the wire is joined to the first element or the second element at each of the plurality of locations by a patch of adhesive. As indicated above, the invention is particularly useful in cases in which a first side of the adhesive joint is substantially enclosed between the first element and the second element, and wherein the third portion of the wire may be joined to the first element or the second element on a side of the adhesive joint. This allows the third portion of the wire to be anchored or otherwise joined within enclosed housings or other inaccessible regions of the vehicle, but still allows for the adhesive joint to be cut by the present wire arranged across the joint between the inaccessible enclosed region and an external region. Preferably, at least 60% of a length of the wire, preferably at least 70%, more preferably at least 80%, more preferably at least 90%, most preferably at least 95% of the length of the wire, is provided on a first side of the adhesive joint, wherein preferably the first side of the adhesive joint is substantially enclosed between the first element and the second element. In this way, the majority of the wire may be secured out of the way during normal use and prevented from becoming damaged. The adhesive used for the adhesive joint may preferably be a paste-like, ductile structural adhesive with polyurethane chemistry and is applied by coating an element with the surface to be coated facing upwards. The adhesive may be applied with a thickness of at least 3 mm for example, which will compensate for any roughness in the surface of first or second element. In accordance with a third aspect of the invention, there is provided a vehicle according to the first aspect and the second aspect. In accordance with a fourth aspect of the invention, there is provided a method of manufacturing a vehicle comprising: providing a non-electrically conductive layer on at least a surface of a first element and / or a surface of a second element of the vehicle, the first element and / or the second element comprising an electrically conductive material, wherein the at least one surface of the first element and / the second element is a bonding surface of the first element and / or the second element to be in contact with at least one adhesive joint; providing an electrically conductive wire having a first portion for cutting, a second portion for connecting to at least part of a circuit for heating the electrically conductive wire; and bonding the first element to the second element using the at least one adhesive joint, wherein the non-electrically conductive layer prevents at least the first portion of the electrically conductive wire from contacting the electrically conductive material of the first element and / or the second element as it is pulled through the at least one adhesive joint. The electrically conductive wire may be arranged in the vehicle to be adjacent to the at least one adhesive joint. This method corresponds to a method performed on a vehicle according to the first aspect of the invention. All of the preferred features described above may be implemented in this context. Preferably, providing a non-electrically conductive layer comprises anodising and / or coating the surface of the first element and / or the surface of the second element. In accordance with a fifth aspect of the invention, there is provided a method of manufacturing a vehicle comprising: providing a non-electrically conductive layer on at least a surface of a first element and / or a surface of a second element of the vehicle, the first element and / or the second element comprising an electrically conductive material, providing an electrically conductive wire having a first portion for cutting and a second portion for connecting to at least part of a circuit for heating the electrically conductive wire; bonding the first element to the second element using the at least one adhesive joint; and providing a locating element according to the second aspect to at least partially position the electrically conductive wire between the surface of the first element and the surface of the second element to prevent the first portion of the electrically conductive wire from contacting the electrically conductive material of the first element and / or the second element as it is pulled through the at least one adhesive joint. The electrically conductive wire may be arranged in the vehicle to be adjacent to the at least one adhesive joint. This method corresponds to a method performed on a vehicle according to the second aspect of the invention. All of the preferred features described above may be implemented in this context. Preferably, the method further comprises arranging a third portion of the electrically conductive wire to pass through the locating element. In accordance with a sixth aspect of the invention, there is provided a method of manufacturing a vehicle according to the fourth aspect and the fifth aspect. This method corresponds to a method performed on a vehicle according to the first aspect and the second aspect of the invention. All of the preferred features described above may be implemented in this context. Bonding the first element to the second element using the at least one adhesive joint may involve pressing two elements together while the adhesive sets. This may simply involve lowering one element onto the other element or else by pressing one element into the other element so that the weight of one element works to press and counteract any hydraulic force generated by the adhesive squeeze out. However, preferably mechanical fasteners are used, which may be used to clamp the two elements together, while the adhesive sets. These mechanical fasteners may clamp the two elements together during the bonding in order to counteract the hydraulic force generated by the adhesive squeeze out. Such mechanical fasteners could be driven to hard stop through compression limiters so as to control the adhesive gap to an exact dimension and avoid hard contact between the first element and the second element. For example, where the mechanical fasteners include bolts, a 3 mm spacing element may be placed on one or more of the bolt shafts between the first element and the second element to ensure an adhesive joint thickness of 3 mm. The mechanical fasteners could also exclusively provide the means to hold the first element and / or the second element in place whilst the adhesive rigidities, thus enabling subsequent vehicle handling operations whilst the adhesive achieves its full strength. In accordance with a seventh aspect of the invention, there is provided a method of separating a first element from a second element of a vehicle according to the first, second or third aspects, the method comprising: heating the electrically conductive wire by using the at least part of the circuit to pass an electric current through the electrically conductive wire; and retrieving the electrically conductive wire and pulling the electrically conductive wire through the at least one adhesive joint. This method corresponds to a method performed on a vehicle according to the first, second or third aspects of the invention. All of the preferred features described above may be implemented in this context. In addition to the heating of the wire, the adhesive joint may also be heated. Heating the adhesive joint may further soften the adhesive, while heating the wire cause the wire to soften the adhesive as it comes into contact with the adhesive. The adhesive may be heated by placing a heat source in contact with the opposing surface of the peripheral flange. The wire may be heated by a resistive process by passing an electric current through the wire, as described above. If the wire is anchored at one end to the first element or second element, the anchor point could include an electrical connection to the vehicle ground or to a dedicated circuit of the vehicle that is accessible in the vehicle when the battery is being serviced. When the wire is pulled through the at least one adhesive joint, the wire may be pulled manually or assisted by tools. If an integral cutting wire is used, only one end of the wire will need to be pulled with the other remaining anchored in place. Once the wire has been pulled through the full path of the adhesive joint(s), the adhesive will be cut. If any mechanical fasteners are used, they may also be disengaged. For example, if a battery pack is bolted to a frame, then the bolts may be removed to allow the battery pack to be extracted. The invention is suitable for any elements of a vehicle connected by an adhesive joint. The invention finds particular use when relatively large parts are joint in such a way that opposing sides of the joint are not both readily accessible to a technician. In particular, in some preferable embodiments, the first element is a vehicle frame and the second element is a battery pack. The one or more adhesive joints may be located along a peripheral edge portion of the battery pack. The one or more adhesive joints substantially surround a centre region of the battery pack. The battery pack may comprise one or more peripheral flanges configured to form at least part of an interface with the frame, and the one or more adhesive joints may be located along one or more of said peripheral flanges. In these embodiments, the integrated cutting wire may allow the battery pack to be removed from the vehicle frame for servicing or replacement. The vehicle frame will generally correspond to the so-called body in white (BIW), in which the frame defines at least the cabin of a passenger vehicle. However, the frame could also be a component that will later be assembled into the vehicle body or BIW. For example, the frame may comprise a floor frame, which may define the rocker and / or door sill portions of the vehicle body, which generally define the plane of the floor of the vehicle. The battery pack may thus be mounted within this floor frame before the floor frame is joined up with one or more other frame portions defining the vehicle body or BIW. In other preferable embodiments, the first element is a housing of a battery pack of the vehicle and the second element is a closure for closing the housing of the battery pack. For example, the first element may be a tray of a battery pack, which may generally comprise a base and a plurality of peripheral walls defining the tray, and the second element may comprise a lid bonded to the tray, for example bonded to the peripheral walls, by the at least one adhesive joint for closing the tray. In these embodiments, the cutting wire may allow the closure of the battery pack to be removed to open the battery pack and allow access to the housing for maintenance of the contents of the battery pack. There may be provided a battery pack for an electric vehicle, the battery pack comprising a housing, preferably a tray, and a closure for closing the housing, preferably a lid for closing the tray, the closure being bonded to the housing by at least one adhesive joint, wherein a first portion of the wire is joined to the housing or the closure, and wherein a second portion of the wire is accessible for pulling the wire through the at least one adhesive joint to cut the at least one adhesive joint. This battery pack may be provided with any of the preferable features described above in connection with the first, second or third aspects of the invention. In other preferable embodiments of the first, second or third aspects of the invention, one of the first and second elements is a panel, wherein preferably the other of the first and second elements is a vehicle frame or second panel. For example, one of the elements may be a sacrificial panel for protecting valuable elements of a structure or vehicle from debris, abrasion, impact, weather, etc. A particularly preferred example is an underbody panel for an automotive vehicle, the underbody panel facing a road in use. This may protect a high voltage battery pack, or other underbody structures, from impact or debris. Advantageously, the cutting wire may be used to remove the underbody panel from the vehicle to replace in case of damage. In other embodiments, one of the first and second elements is a first body structure part of the vehicle and the other of the first and second elements is a second body structure part of the vehicle. For example, the invention may be used for sections of a vehicle body structure that may require repair / replacement in case of crash, such as crash rails or bumper beams. While some particularly preferred uses for the first, second or third aspects of the invention have been provided above, it will be appreciated that there are many different possible use cases for the invention. For example, the invention may be used for any electrical enclosure that requires robust mechanical retention and / or high IP rating and infrequent access for service, or any mechanical assembly, such as gearbox or transmission housings or electric motor housings. The invention may also be used for screens or other interfaces of a vehicle centre console, for example. Other uses may include see-through surfaces in vehicles or car interior surfaces. BRIEF DESCRIPTION OF DRAWINGS The invention will now be described with reference to the accompanying drawings, of which: Figure 1A and 1B show a perspective and cross-sectional view of a vehicle frame and a battery pack; Figures 2A and 2B show a perspective and cross-sectional view of a vehicle frame and a battery pack; Figure 2C shows a locating element; Figure 3 shows another cross-sectional view of a vehicle frame and a battery pack; Figure 4 shows another cross-sectional view of a vehicle frame and a battery pack; Figure 5 shows a top view of part of a vehicle body including a mounted battery pack; Figure 6 shows a schematic cross-section through the vehicle body and battery pack of Figure 5; Figure 7 shows a schematic top view of the battery pack of Figure 5 with the vehicle body omitted; Figures 8A to 8E show five alternative schematic cross-sections through a vehicle body with a mounted battery pack; Figure 9 shows an enlarged detail of a schematic cross-section through a vehicle body with a mounted battery pack; Figure 10 shows a schematic top view of a mounted battery pack with the vehicle body omitted; Figure 11 shows a schematic top view of a mounted battery pack with the vehicle body omitted; Figure 12 is a schematic cross-section through a vehicle body and battery pack according to another embodiment; Figure 13A is a schematic cross-section through a batter pack according to another embodiment; and Figure 11B is an enlarged portion of Figure 13A; Figure 14 is a schematic top view of the embodiment of Figure 13A; Figure 15 is a schematic top view of a variant of the embodiment of Figure 13A; and Figure 16 is a schematic top view of another variant of the embodiment of Figure 13A. DETAILED DESCRIPTION Figures 1A and 1B show a perspective view of a vehicle frame 110 and a battery pack 115 in a to-be-assembled configuration and a cross-sectional side view of a vehicle frame 110 and a battery pack 115 in an assembled configuration. The vehicle frame 110 is a first element and the battery pack 115 is a second element of a vehicle. In this example, the battery pack 115 has a trapezoidal prism shape with side surfaces 120 that are configured to bond to corresponding surfaces 125 in the vehicle frame 110. A surface 125 of the vehicle frame 110 is bonded to a surface 120 of the battery pack 115 by using adhesive strips 130 to form an adhesive joint between the two surfaces. Each side surface 120 includes a first adhesive strip 130a across a portion in the upper half of the side surface and a second adhesive strip 130b across a portion in the lower half of the side surface. The multiple adhesive strips across a single side surface ensures that sufficient adhesion is provided in the adhesive joint. However, it should be understood that different numbers and patterns of adhesive strips may be used according to design or operational requirements. For example, a single adhesive strip may be used for each adhesive joint. Each of the side surfaces 120 further includes electrically conductive wires 135 which act as integrated cutting wires for the adhesive joint. A cutting wire 135 is connected to the side surface 120 at two anchor points 140, where each end of the wire is attached to a respective anchor point 140. The anchor points 140 electrically connects the wire 135 to a circuit that allows an electrical current to flow through and resistively heat the wire 135. In this specific example, both ends a wire 135 are fully connected to two anchor points in a respective side surface 120. In another example, a wire may only have one end connected to a single anchor point in the battery pack (not necessarily on a side surface) and where the other open end of the wire is connectable to an electrical circuit when a user wishes to heat the wire and cut the adhesive joint. In yet another example, both ends of the integrated cutting wire may be open ends that are configured to be electrically connected to a circuit for heating the wire when a user intends to cut the adhesive joint. A cutting portion of each wire is arranged along a length of a respective adhesive strip 130 and a pulling portion of the wire is arranged to pass across a width of the adhesive strip to a top or bottom surface of the battery pack 115. This allows the cutting portion of the wire to be on the opposite side of an adhesive strip to the second portion such that the cutting portion will cut through the adhesive strip when it is pulled from the pulling portion on the respective top or bottom surface of the battery pack. In the example of Figures 1A and 1B where both ends of the wire are connected to respective anchor points, a first end of a wire is connected to a first anchor point and a first cutting portion of the wire is arranged along a side an adhesive joint away from the top or bottom surface of the battery pack. At an end of the adhesive joint, the wire is arranged to pass across a width of the adhesive joint to a top or bottom surface of the element and loop back on itself at the top or bottom surface to form a pulling portion of the wire. The remaining length of the wire is then arranged to pass back along the side of the adhesive joint (which further forms the first cutting portion) and that the second end of the wire is connected to a second anchor point. In use, the pulling portion is pulled by a user when the cutting wire is heated such that the first portion cuts through the adhesive joint as the wire is anchored at the anchor points. Accordingly, the cutting portion of a wire is positioned on an “inner” side of an adhesive strip (e.g. towards the centre a side surface I the side of the adhesive strip away from the top or bottom surface where the pulling portion is configured to be accessed or pulled) in order for the wire to cut through an adhesive strip as it is pulled along the adhesive joint. In the specific example of Figures 1A and 1B, each adhesive strip 130 has two corresponding cutting wires 135. This ensures that each cutting wire has a shorter length, which reduces the risk of the wire snapping. It should be understood that different configurations would be apparent to the skilled person and a single cutting wire for each adhesive strip can also be used. In another example, a single cutting wire may be used for multiple adhesive strips across the entire adhesive joint between the first element and the second element of a vehicle. The side surfaces 120 of the battery pack 115 in Figures 1A and 1B comprise a non-electrically conductive layer, such as aluminium or an aluminium alloy that has been anodised to form an electrically insulating layer or an e-coating. The adhesive strips 130 are arranged on the non-electrically conductive layer across the lengths of the respective side surfaces 120. The top and bottom surfaces of the battery pack 115 may also be coated or anodised in a similar manner. In this way, when an electrical current is passed through the anchor points into the wire 135, any portions of the wire that may come into contact with the side, top or bottom surfaces of the battery pack 115 do not short the electrical circuit. The bonding surfaces 125 of the vehicle frame 110 also comprise a non-electrically conductive layer by anodisation and / or coating. As will be appreciated, a non-electrically conductive layer would not be required on or around the side surfaces of the battery pack or the bonding surfaces of the vehicle frame is there are no electrically conductive components or areas that the cutting wire may be exposed to during the heating and cutting operation. For example, the vehicle frame and / or a battery pack casing may made of a plastic or other non-electrically conductive material. In addition, the vehicle frame 110 may also include integrated cutting wires in a similar way to those described for the battery pack 115. It should be understood that the integrated cutting wires may be provided on the battery pack 115 and / or the vehicle frame 110 according to design and manufacturing requirements. Figures 2A and 2B show a perspective view of a vehicle frame 210 and a battery pack 215 and a cross-sectional side view of a vehicle frame 210 and a battery pack 215 in an assembled configuration. The vehicle frame 210 is a first element and the battery pack 215 is a second element of a vehicle. The assembly 200 of the vehicle frame 210 and the battery pack 215 is similar to that described above in reference to Figures 1A and 1B, where the one or more adhesive strips are provided between side surfaces of the battery pack 215 and the bonding surfaces of the vehicle frame 210 to form an adhesive joint 220, and one or more cutting wires 225 are integrated in the adhesive joint 220. The assembly 200 further comprises an initial locating element 230 which is arranged on a top surface of the vehicle frame 210 and the battery pack 215 over the adhesive joint 220 such that the pulling portion 225b of a cutting wire (the portion which passes a width of the adhesive joint 220 is accessible through the initial locating element 230. The cutting portion 225a of the cutting wire is arranged in the adhesive joint 220 along a side of an adhesive strip away from the top surface. Figure 2C shows a top view of the initial locating element 230 having two rectangular sections 235, each with a substantially semicircular cut-out 240 along one side. One section 235a of the initial locating element 230 is arranged on the vehicle frame 210 and the other section 235b is arranged on the battery pack 215 with the respective semicircular cut-outs facing each other. The two sections 235 are positioned such that a gap 245 is provided over the adhesive joint 220 and to allow the wire 225 to pass in and out of the locating element 230. The two semicircular cut-outs 240 provide a substantially circular hole 250 for the second portion 225b of the wire to initially located in the adhesive joint 220 before a heating and cutting procedure. To perform a cutting operation, an electrical current is passed through the cutting wire 225 to heat the wire and a tool 255 is used to pull the wire through the adhesive joint by the pulling portion 225b of the wire. The gap 245 comprises a short linear portion to provide an initial cutting direction of the wire. As the wire 225 is pulled, the cutting portion 225a cuts through the adhesive joint. Other shapes and designs of an initial locating element would be apparent to the skilled person. For example, an open ring shape (C-shaped element) may be used. The initial locating element 230 may be glued on the respective surfaces of the assembly 200 during manufacture or may be a temporary element that is added to the assembly before a cutting operation. In yet another example, the initial locating element may also have an L-shaped profile where a portion of each half section is embedded into the adhesive joint. Figure 3 shows another cross-sectional side view of the assembly 200, where initial locating elements 230 are provided on both the top surfaces and the bottom surfaces of the vehicle frame 210 and battery pack 215 respectively. Figure 4 shows another assembly 400 of a vehicle frame 410 and a battery pack 415 in an assembled configuration. The assembly 400 of the vehicle frame 410 and the battery pack 415 is similar to that described above in reference to Figures 1, 2 and 3 above, where the one or more adhesive strips are provided between side surfaces of the battery pack 415 and the bonding surfaces of the vehicle frame 410 to form an adhesive joint 420, and one or more cutting wires are integrated in the adhesive joint. Similar to the assembly 200 of Figures 2A and 2B, the assembly 400 of Figure 4 includes a locating element 425 arranged on a top surface of the vehicle frame 410 and the battery pack 415 over the adhesive joint 420 such that a second pulling portion of a cutting can be accessible through the locating element 425. However, the locating element 425 in this example has a length that is substantially the same as or greater than a corresponding length of one or more adhesive strips that are configured to be cut by a respective cutting wire. As such, the locating element 425 acts as a guide for the full length of the cutting operation of a wire. The locating element 425 includes two rectangular strips of non-electrically conductive material, such as plastic. One rectangular strip 425a is arranged on the vehicle frame 410 and the other rectangular strip 425b is arranged on the battery pack 415 to form a gap 430 over the adhesive joint. The gap 430 defines the limits of movement of the cutting wire as it is pulled through the adhesive joint. Locating elements 425 can be provided on the top surface and / or the bottom surface of the assembly 400 over an adhesive joint in a similar way as shown in Figure 3. Locating elements 425 may also be a permanent component in the assembly (e.g. glued to a surface or at least partially embedded in the adhesive joint) in a similar way to that described above in reference to the assembly 200 of Figure 2. As will be appreciated, other shapes and designs of the locating element 425 would be readily apparent to the skilled person. It should be understood that the examples of Figures 1 to 4 can be used separately or in combination to ensure that a cutting wire does not come into contact with electrically conductive material in the first element and / or the second element as it is being electrically heated and pulled through an adhesive joint. For example, a locating element in the form of a guide may be used in combination with a coated battery pack. Figures 5 to 16 show different exemplary arrangements of a vehicle having a first element and a second element that can be bonded with an adhesive joint. Figure 5 shows part of a vehicle body 1. The vehicle body comprise a frame 10. This frame could be the so-called body in white (BIW). In Figure 5, a floor frame section is shown, which comprises opposing longitudinal structural members 11a, 11b, which correspond to the rockers or door sill regions of the vehicle body. This floor frame could be part of the BIW, or could be a separate frame part that is to later be assembled into the BIW. The longitudinal structural members 11a, 11b extend along the longitudinal length of the cabin of the vehicle, between the front and rear wheels, and typically include crash absorbing structured designed to absorb side impact crashes. The frame 10 also includes a front transverse structural member 12 that extends between the longitudinal structural members 11a, 11b just behind the front wheel area of the body, and a rear transverse structural member 13 that extends between the longitudinal structural members 11a, 11b just ahead of the rear wheel area of the body. The transverse and longitudinal structural members thus delimit a floor portion of the vehicle body. The floor portion of the vehicle body generally defines a plane of the floor, which is substantially parallel to the ground. The transverse and longitudinal structural members also define a generally rectangular-shaped opening with truncated comers 14 through the floor portion in the vertical direction, in which the battery pack 20 is located. The front transverse structural member 12 is coupled to a front crash structure 2 and is designed to transmit front impact forces along the longitudinal structural members 11a, 11b and around the battery pack 20. Likewise, the rear transverse structural member 13 is coupled to a rear crash structure 3 and is designed to transmit rear impact forces along the longitudinal structural members 11a, 11b and around the battery pack 20. As mentioned above, the battery pack 20 is located in the opening 14 through the frame 10. The battery pack comprises a main housing 21 in which a plurality of battery modules is located, along with other battery components. The battery pack 20 generally corresponds in shape to the shape of the opening 14 through the frame 10. The battery pack is generally planar, having a width in the transverse direction that is similar in dimension to the width of the frame, and a length in the longitudinal direction that is similar in dimension to the length of the frame, but is relatively small in the vertical direction, being intended to sit substantially within the floor of the vehicle. At the peripheral edge of the battery pack 20, surrounding the main housing 21, is a peripheral flange 22. In this example, the battery pack is to be inserted into the frame from beneath the frame, and so the flange 22 extends out from the lower face of the battery pack away from a central axis of the battery pack that is perpendicular to the general plane of the battery pack. The flange has a smaller thickness in the vertical direction than the main housing 21 of the battery pack. Therefore, when inserted from below the frame 10, the peripheral flange 22 may engage the transverse and longitudinal structural members, 11a, 11b, 12, 13, along respective sides of the battery pack 20, while much of the main housing 21 sits inside the opening 14, substantially between the transverse and longitudinal structural members, 11a, 11b, 12, 13. Figure 6 shows a cross-section through the frame in a plane extending along the vertical and transverse directions, and shows the main housing of the battery being located between the longitudinal structural members, 11a, 11b, with the upper face of the flange 22 and the vertical side walls of the housing 21 forming an interface with the frame 10. The battery pack 20 in this example is mounted within the frame 10 using an adhesive joint 30, which is shown in Figures 6 and 7. As can be seen in Figure 6, the adhesive joint is positioned on the upper surface of the peripheral flange 22 of the battery pack and bonds the peripheral flange to lower faces of the lateral structural members 11a, 11b. The lower faces of the transverse and longitudinal structural members 11a, 11b, 12, 13 define as a complementary rim about the opening 14 that engages with the peripheral flange. While this interface between the upper surface of the flange 22 and the lower surface of the transverse and longitudinal structural members 11a, 11b, 12, 13 is shown as flat surfaces, it will be appreciated that any complementary interfaces may be used. Figure 7 shows a top view of the battery pack 20, with the frame 10 omitted, so that the path followed by the adhesive joint 30 can be seen. As shown in Figure 7, the main housing of the battery pack has a footprint that is generally rectangular, with truncated comers, to match the shape of the opening 14 through the frame. Around the entire periphery of this main housing 21, the peripheral flange 22 extends from the lower surface of the battery pack, so that there is a step down from the upper surface of the battery pack to the upper surface of the peripheral flange 22. The adhesive joint 30 is provided in one continuous path that extends around the entire peripheral flange 22 of the battery pack 20 so as to surround the main housing 21. This enables the battery pack to be bonded to the frame 10 about the entire periphery of the battery pack. The adhesive used for the adhesive joint 30 may be a ductile structural adhesive with polyurethane chemistry. The material of the battery case housing 21 and the flange 22 may be a composite material comprising a resin matrix, reinforcement fibres and metallic inserts. The frame 10 may be made of an assembly of aluminium alloys. While these materials are typical, in principle, any combinations of materials for the battery pack and frame may be used with an adhesive suitable for bonding those materials. It should be therefore be understood that the bonding surfaces (i.e. the surfaces in contact with the adhesive) of the frame 10 and the battery pack 20 may each include electrically conductive material and conduct electricity and short a circuit if exposed to an electrical current. Figures 6 and 7 also show that the vehicle has been provided with an integrated cutting wire 60 for cutting the adhesive joint. In this embodiment, an integral cutting wire 60 is provided on the battery pack. This wire may be made of stainless steel or nichrome and may be 1 to 2 mm in diameter, for example. The wire could have a circular cross-section or even a square or rectangular cross-section to define sharper cutting edges. Alternatively, the wire could be a braided cutting wire. Most of the length of the wire extends along the peripheral flange 22, positioned between the main housing 21 and the adhesive joint 30. The wire may be weakly adhered to the flange 22 by small dots of adhesive. A clearer example of this is provided in Figure 10, described below. A first end 61 of the cutting wire 60 is fixedly anchored to the battery pack. In this example, the first end is anchored next to the lower left corner of the main housing 21, as shown in Figure 10. The cutting wire follows a path, clockwise in Figure 7, extending completely around the main housing 21. When the wire reaches the anchor point again, the second end 62 of the wire passes across the adhesive joint 30 to be accessible by a technician. In order to cut the adhesive, a technician need only retrieve the second end of the wire 62 and pull the wire through the adhesive joint, following the path of the adhesive joint around the battery pack 20. In the example, there is a single cutting wire 60 that extends around the main housing 21. In other examples, multiple cutting wires 60 may be used such as one or more cutting wires arranged on each side of the main housing. Providing multiple cutting wires allows the one or more adhesive joints 30 to be more easily cut and also allows shorter wires to be used, which reduces the risk of snapping. Similarly, the adhesive joint 30 may be formed using sets of multiple adhesive strips arranged between a bonding surface of the battery pack 20 and a bonding surface of the frame 10 (see Figure 11 for example). In an example, each set or pair of adhesive strips may be arranged with a respective cutting wire around the entire adhesive joint. Figures 5 to 7 illustrate one possible interface and mounting arrangement for the battery pack 20 and frame 10, but various other mounting arrangements are possible. Some alternative configurations will now be described with reference to Figures 8Ato 8E, each of which is an alternative cross-section through the frame 10 in a plane extending along the vertical and transverse directions. Each of these may also be provided with an integrated cutting wire, as will be described. The differences between these alternative embodiments and that of Figures 5 to 7 will now be described. Figure 8A shows an embodiment in which the frame 10 is further provided with a flange 16 that projects from the side walls of the transverse and longitudinal structural members 11a, 11b, 12, 13 partially into the opening 14 for engaging an upper surface of the main housing 21 of the battery pack 20. This defines a substantially stepped interface between the battery pack 20 and the frame 10. The battery pack is additionally bonded to the frame 20 by a second adhesive joint 31 that is positioned between the lower surface of the flange 16 of the frame 10 and the upper surface of the main housing 21 of the battery pack. This second adhesive joint may be provided to extend around the entire periphery of the upper surface of the main housing 21 or may only extend partially around the periphery. This second adhesive joint increases the strength of the bond between the battery pack 20 and the frame 10. In this embodiment, a first cutting wire 60 is provided for cutting the first adhesive joint, provided between the battery pack flange 22 and the lower surfaces of the structural members 11a, 11b, and a second cutting wire 70 is provided for cutting the second adhesive joint 31, provided between the flange 16 of the frame 10 and the upper surface of the main housing 21 of the battery pack. The first cutting wire 60 is anchored to the battery pack flange 22 and extends around the main housing 21 of the battery pack in the same way as described with respect to Figure 7 so as to be in substantially the same plane of the adhesive joint 30. The second cutting wire 70 may be anchored to the upper surface of the main housing 21 of the battery pack and extend around the main housing 21 in the same plane as the second adhesive joint 31. Removal of this battery pack may therefore involve retrieving the second end of the first cutting wire 60 and pulling this through the first adhesive joint 30, following the path of the adhesive joint around the frame from the outside of the vehicle, before retrieving the second end, i.e. the non-anchored end, of the second cutting wire 70 through the opening 14 through the floor of the frame and pulling this through the second adhesive joint 31, following the path of the adhesive joint around the frame from the inside of the vehicle. Figure 8B shows an embodiment in which the interface between the frame 10 and the battery pack 20 is the same as that of Figures 5 to 7. However, in this embodiment, a second adhesive joint 31 is provided between the vertical side wall of the main housing 21 of the battery pack 20 and the inner side walls of the transverse and longitudinal structural members 11a, 11b, 12, 13, which face into the opening 14. Not only does this second adhesive joint increase the strength of the bond between the battery pack 20 and the frame 10, but arranging two adhesive joints on surfaces that define an angle to one another ensures that the adhesive joints will experience the same force in different relative directions. For example, a side impact force may produce a shear force on the first adhesive joint 30, but a compressive force on the second adhesive joint 31. This decreases the risk that both adhesive joints would fail as a result of the same impact. In this embodiment, the cutting wire 60 is anchored to the upper surface of the main housing 21 of the battery pack and extends around the perimeter of the upper surface of the main housing 21. The second end of the cutting wire may then be arranged to pass through both the first and second adhesive joints, between the sidewall of the main housing 21 and one of the structural members 11a, 11b and then between the upper surface of the flange 22 of the battery pack and the lower surface of said structural member. To remove the battery pack, a technician may then retrieve the second end of the cutting wire 60 and pull the cutting wire through both adhesive joints, following the path of the adhesive joints around the battery pack 20. Figure 8C shows an embodiment in which the interface between the battery pack 20 and the frame 10 is the same as that described with reference to Figure 8A, with a flange 16 that projects from the side walls of the transverse and longitudinal structural members 11a, 11b, 12,13 partially into the opening 14. However, in this embodiment, there is no adhesive joint provided along the interface between the flange 16 and the upper face of the main housing 21 of the battery pack. Instead, the interface between the flange 16 and the upper face of the main housing 21 is provided with a number of mechanical fasteners 40a, 40b. Only two mechanical fasteners are shown in the cross-section of Figure 8C, but it will be appreciated that mechanical fasteners may be provided in a number of places around the interface between the battery pack 20 and the frame 10. In this embodiment, the mechanical fasteners comprise bolts. Threaded bolt shafts are provided that project out of the upper face of the main housing 21 of the battery pack. These bolt shafts are received in corresponding holes through the flange 16 and are secured with nuts so that the battery pack is bolted to the frame. While bolts are described as the mechanical fasteners in this embodiment, it will be appreciated that any type of mechanical fastener may be used, including clips, pins or rivets, among others. In this embodiment, the use of mechanical fasteners 40a, 40b in addition to the adhesive joint 30 between the flange 22 of the battery pack 20 and the frame ensures that the battery mount is more resilient to the different failure modes affecting each joint type individually. Mechanical fasteners may also be useful for seating the battery pack and holding the battery pack in place while the adhesive dries. In this embodiment, the cutting wire 60 may again be anchored to the battery pack flange 22 and extend around the main housing 21 of the battery pack in the same way as described with respect to Figure 7 so as to be in substantially the same plane of the adhesive joint 30. In this embodiment, separating the battery pack from the frame will require both cutting the adhesive joint using the cutting wire and unfastening the mechanical fasteners 40a and 40b. However, due to the provision of the adhesive joint, fewer mechanical fasteners may be used than would otherwise be necessary to withstand the same impact forces. As will be appreciated, mechanical fasteners may assist in positioning the frame and battery pack before the adhesive joint is formed. As another example, a similar effect can be achieved without mechanical fasteners using dowel pins or the like. Figure 8D shows an embodiment in which a substantially continuous floor surface 15 extends between the transverse and longitudinal structural members 11a, 11b, 12, 13 so that there is no opening through the frame in the vertical direction. In this embodiment, the battery pack is mounted to the frame by an adhesive joint 30 that is again provided in one continuous path that extends around the entire peripheral flange 22 of the battery pack 20 so as to surround the main housing 21. Additionally, mechanical fasteners 40a, 40b are again provided in the form of bolts, with the threaded bolt shafts being provided to project out of the upper face of the main housing 21 of the battery pack, but in this embodiment being received in corresponding holes through the substantially continuous floor surface 15. The cutting wire of this embodiment may be provided in the same manner described above, and separation of the battery pack from the frame may be the same as for Figure 8C. Figure 8E shows an embodiment that differs from that of Figure 8D in that the interface between the battery pack and the frame along which the adhesive joint is provided includes portions arranged at an oblique angle relative to the horizontal plane. In particular, instead of the peripheral flange 22 extending in the horizontal plane, in this embodiment, a flange 22a is provided at an angle that slopes down in the direction away from the main housing 21 of the battery pack. As shown in Figure 8E, this means that the angle that the flange makes to the horizontal (i.e. the plane of the floor and the battery pack) on the left side of Figure 8E is one rotated anticlockwise by about 10°, and on the right side of Figure 8E is one rotated clockwise by about 10°. While not shown in this Figure, the flange along the front and rear edges of the battery pack 20 is similarly sloped down and way from the main housing 21 of the battery pack. The lower face of the transverse and longitudinal structural members 11a, 11b, 12, 13 is inclined in a complementary manner, i.e. sloping downward in the direction away from the centre of the frame. The adhesive joint 30 is provided between the inclined upper surface of the flange 22a and the inclined lower surface of the transverse and longitudinal structural members 11a, 11b, 12,13. This interface shape means that a side impact force will place the adhesive joint partly in compression instead of in pure shear, meaning it is less likely to fail. Again, a cutting wire 60 is provided that is capable of cutting through this angled adhesive joint, being anchored to the angled flange 22a between the adhesive joint 30 and the main housing 21 of the battery pack and following the path of the adhesive joint around the main housing 21. It will be appreciated that the various features described above with respect to the alternative cross-sections could be combined as desired. For example, the inclined flange 22a of Figure 8E could be provided in any of the embodiments of Figures 6 or 8A to 8D. Similarly, the second adhesive joint 31 on the vertical sidewalls in Figure 8B could be provided in any of the other embodiments. Figure 9 shows an enlarged portion of a frame and battery pack constructed in substantially the same way as described with reference to Figures 5 to 7. However, in this embodiment, a conduit 50 has been provided across the adhesive joint 30. This conduit may be a small tube made of soft and thin rubbery or polymeric material, for example EPDM or ABS, approximately 2 mm in diameter, that extends across the adhesive joint 30. In this embodiment, the conduit follows a path starting at a first end 51, which is located at the very outer edge of the peripheral flange in the opening into the gap between the flange and the lower face of the longitudinal structural member, so as to be accessible from the outside of the frame. The conduit extends from this first end 51 across adhesive joint, towards the centre of the battery pack. The conduit follows the interface between the frame 10 and the battery pack 20 until it reaches the opening through the frame. The second end 52 of the conduit is thus accessible near the upper surface of the main housing 21 of the battery pack 20 through the opening 14 through the frame 10. As will be described in more detail below, this conduit may be used in removing the battery pack from the frame. In particular, the integrated cutting wire may be arranged to pass between the first and second end 51, 52, along the conduit 50. With the wire so arranged, the technician may pull the wire through the adhesive joint, following the path of the adhesive joint around the battery pack 20, to cut the adhesive joint to allow for removal of the battery pack. The conduit 50 may therefore be provided to allow the integrated cutting wire to be more readily accessible. In another example, the conduit 60 may include a slit across its length to allow the cutting wire 60 to be pulled out of the conduit 50 in use to cut through the adhesive joint 30. In this case, the conduit 50 may serve as an initial locating element for the wire 60. In yet another example, the cutting wire 60 may cut through the conduit 50 before being pulled through the adhesive joint 30. Figure 10 schematically shows a top view of a battery pack to more clearly illustrate the integrated cutting wire 60. This battery pack is substantially square in profile, and again comprises a main housing 21 that holds the battery modules and the like, and a peripheral flange 22 extending therefrom. Once again, an adhesive joint 30 is provided that extends along this peripheral flange 22, surrounding the main housing 21 of the battery pack 20. In this embodiment, an integral cutting wire 60 is provided on the battery pack. Again, this wire may be made of stainless steel or nichrome and may be 1 mm in diameter, for example, and could have a circular cross-section or a square or rectangular cross-section to define sharper cutting edges. Alternatively, the wire could be a braided cutting wire. Most of the length of the wire extends along the peripheral flange 22, positioned between the main housing 21 and the adhesive joint 30. The wire may be weakly adhered to the flange 22 by small dots of adhesive 63 positioned at a plurality of locations around the path followed by the cutting wire 60. This may be the same adhesive as the adhesive used for the joint 30, or could be a different adhesive. A first end 61 of the cutting wire 60 is fixedly anchored to the battery pack. In this embodiment, the first end is anchored next to the top right corner of the main housing 21, as shown in Figure 10. This anchor point preferably electrically connects the cutting wire to part of a circuit that may be used to resistively heat the cutting wire. The cutting wire follows a path, anticlockwise in Figure 10, extending completely around the main housing 21. A short section of the wire overlaps itself after having completed one full path around the main housing 21 and then the second end of the wire 62 passes through a conduit 50 that is provided across the adhesive joint 30. The free second end is thus provided at the outer edge of the battery pack 20, where it may be accessed by a technician. In order to cut the adhesive, a technician need only retrieve the second end of the wire 62, complete the circuit to the second end of the wire in order to resistively heat the wire, and pull the wire through the adhesive joint, following the path of the adhesive joint around the battery pack 20. To complete the circuit a second connection point may be provided elsewhere on the battery housing 21, which electrically connects to the anchor point. In some embodiments, electric current from the battery modules in the battery pack may be used to resistively heat the wire 60. An alternative embodiment is shown in Figure 11. This embodiment differs from Figure 10 in that four separate adhesive joints are provided along respective edges of the battery pack corresponding respectively to the edges of the transverse and longitudinal structural members 11a, 11b, 12, 13. In this embodiment, the second end of the wire 62 may simply be provided through the gap between two adjacent adhesive joints, to allow second end of the wire to be accessible along the outer edge of the battery pack 20. As explained above, a single cutting wire 60 is provided in the example of Figure 11 that extends around the main housing 21. Other examples include using multiple cutting wires 60 corresponding to each of the separate adhesive joints 30a, 30b, 30c, 30d. The above embodiments have illustrated embodiments in which the invention is used to provide a means of separating a vehicle battery pack from a vehicle frame. Other embodiments illustrating the invention in other contexts will now be described. Figure 12 shows an embodiment in which the invention is implemented in the context of a sacrificial underbody panel of an electric vehicle, although in principle the invention may be used to join a sacrificial underbody panel to other types of vehicle, or to join other types of panels to vehicle frames. In this embodiment, the vehicle comprises a battery pack 20 mounted to a vehicle frame in the same manner as described with respect to Figures 5 to 7. In particular, a first adhesive joint 30 is provided joining the battery pack 20 by flanges 22 to the lower face of structural members 11a, 11b of the vehicle frame. This embodiment differs from that of Figures 5 to 7 in that a sacrificial underbody panel 80 is applied over the lower facing surface of the battery pack 20. The underbody panel 80 is a flat sheet of a suitable material such as aluminium or carbon fibre reinforced polymer. The interface between the battery pack 20 and the underbody panel 80 is defined by a raised ridge 23 on the lower face of the battery pack. This ridge 23 is provided generally in the region of the peripheral flange 22 and so extends generally around the periphery of the lower face of the battery pack 20. The underbody panel 80 is bonded to this ridge 23 by a second adhesive joint 31 located between the ridge 23 and the upper-facing surface of the sacrificial underbody panel 80. The purpose of this raised ridge 23 is to space the sacrificial underbody panel 80 from the main housing 21 of the battery pack to improve the operation of the sacrificial underbody panel 80. A cutting wire 60 is provided in the space between the sacrificial underbody panel 80 and the lower face of the battery pack 20 in the area located surrounded by the second adhesive joint 31. The cutting wire 60 is anchored to the underbody panel 80 at an anchor point in the space between the sacrificial underbody panel 80 and the lower face of the battery pack 20 in the area surrounded by the second adhesive joint 31. As with the previous embodiments, the cutting wire 60 may be arranged to follow the path of the adhesive joint, optionally secured to the underbody panel 80 by dots of adhesive in the same manner described with reference to Figure 10. Again, having followed the full path of the adhesive joint, a second free end of the wire 60 may be arranged to cross the adhesive joint so as to be accessible to a technician from the edge of the battery pack, between the flange 22 and the underbody panel 80. Figure 13A shows an embodiment in which the first element is a battery pack housing and the second element is a closure 24, i.e. a lid, for the battery pack housing. In this embodiment, the main body 21 and the flange 22 of the battery pack define an open tray, open through the lower surface shown in the Figure. This tray is closed by a lid 24, which has a shape and size that follows the perimeter of the tray defined by the flange. The lid 24 is secured to the tray by an adhesive joint 30 that is provided between the flange and the lid, and which extends around the entire periphery of the battery pack. Figure 14 shows a schematic plan view of the lid 24, showing the arrangement of the adhesive joint 30 and the cutting wire 60. As shown in this Figure, in this embodiment, the adhesive joint 30 extends around the periphery of the battery pack lid 24, surrounding a centre region of the lid. The cutting wire 60 is arranged so that it follows a path of the adhesive joint around the periphery of the lid, offset so as to be parallel to the path of the adhesive joint. Although not shown in this Figure, the cutting wire may be held in place using small dots of adhesive, in the manner described above with reference to Figure 10. In this embodiment, the first and second ends 61, 62 of the wire are arranged to each extend across the adhesive joint, so that the adhesive joint holds these sections of the wire in place. The first and second ends 61, 62 of the wire are arranged to cross the adhesive joint in substantially the same place on the battery lid 24. As shown in Figure 13B, in this embodiment, a barrier 25 is located between the adhesive joint 30 and the cutting wire 60. This barrier may be an elongate strop formed of a foamed material, for example. Figure 14 shows that the barrier 25 is arranged between the wire 60 and the adhesive joint 30 and follows the paths of the wire 60 and the adhesive joint 30 as they extend around the periphery of the battery lid 24. A small gap is provided in the barrier 25 for the wire to pass through where the first and second ends 61, 62 of the cutting wire 60 extend across the adhesive joint 30. It will be appreciated that a barrier of this sort may be used in any of the preceding embodiments to protect the wire from adhesive squeeze out during formation of the adhesive joint 30. In order to remove the battery lid 24 from the tray in this embodiment, the technician may retrieve the first and second ends 61, 62 of the wire 60. One end may then be anchored in place, while the other end is pulled around the path of the adhesive joint, through the adhesive joint to cut through the adhesive. This action of pulling the wire to cut the adhesive joint will also cut the foam used to form the barrier between the adhesive joint 30 and the wire. In each of the above embodiments, a single cutting wire has been provided that extends all of the way around the perimeter of the joined elements. However, this is not essential and indeed may not be practical if other parts of the vehicle obstruct part of the periphery of the elements. Figure 15 shows a variant in which multiple cutting wires are provided. This variant is shown in the context of the battery tray and lid just described, but it will be appreciated that this may apply to any of the above embodiments. Figure 15 shows a battery pack lid 25, which generally has a square shape in this schematic depiction. A separate adhesive joint 30a, 30b, 30c, 30d is provided along each peripheral edge of the lid. Together, the adhesive joints substantially surround a centre region of the lid. A respective cutting wire 60a, 60b, 60c, 60d is provided along each edge of the lid, inset from the respective adhesive joint 30a, 30b, 30c, 30d. A first end of each wire 60a, 60b, 60c, 60d is anchored to the lid 24 at a respective anchor point 61a, 61b, 61c, 61 d located at one end of the respective adhesive joint 30a, 30b, 30c, 30d. From the anchor point, each wire 60a, 60b, 60c, 60d follows the path of the respective adhesive joint 30a, 30b, 30c, 30d to the opposite end of the adhesive joint. In this embodiment, each wire extends beyond the end of the respective adhesive joint 30a, 30b, 30c, 30d, and then turns and extends towards the edge of the battery pack lid 24 so that the second end of the wire is accessible by a technician. While not shown, again, the wires may be held in place by small dots of adhesive, for example, along the paths of the wires 60a, 60b, 60c, 60d. In this embodiment, a technician may sequentially retrieve the second end of each wire 60a, 60b, 60c, 60d and pull that wire through the respective adhesive joint 30a, 30b, 30c, 30d towards the respective anchor point 61 a, 61 b, 61 c, 61 d to cut the adhesive joint. In another variant, shown in Figure 16, the first and second ends of each wire may cross over the respective adhesive joint 30a, 30b, 30c, 30d generally at opposing ends of the respective adhesive joint 30a, 30b, 30c, 30d, and a technician may retrieve the opposing ends of each wire and pull them towards each other to cut the adhesive joint.

Claims

1. A vehicle comprising:a first element bonded to a second element by at least one adhesive joint between a surface of the first element and a surface of the second element, the first element and / or the second element comprising an electrically conductive material; andan electrically conductive wire comprising a first portion configured to cut the at least one adhesive joint and a second portion configured to be connected to at least part of a circuit for heating the electrically conductive wire;wherein the surface of the first element and / or the surface of the second element further comprises a non-electrically conductive layer to prevent at least the first portion of the electrically conductive wire from contacting the electrically conductive material of the first element and / or the second element as it is pulled through the at least one adhesive joint.

2. The vehicle according to claim 1, wherein the surface of the first element and / or the surface of the second element comprises aluminium or an aluminium alloy, and wherein the non-electrically conductive layer comprises an anodised layer of the aluminium or aluminium alloy.

3. The vehicle according to any of claims 1 or 2, wherein the non-electrically conductive layer comprises a coating.

4. A vehicle comprising:a first element bonded to a second element by at least one adhesive joint between a surface of the first element and a surface of the second element, the first element and / or the second element comprising an electrically conductive material;an electrically conductive wire comprising a first portion configured to cut the at least one adhesive joint and a second portion configured to be connected to at least part of a circuit for heating the electrically conductive wire; anda locating element arranged to at least partially position the electrically conductive wire between the surface of the first element and the surface of thesecond element to prevent the first portion of the electrically conductive wire from contacting the electrically conductive material of the first element and / or the second element as it is pulled through the at least one adhesive joint.

5. The vehicle according to claim 4, wherein the locating element comprises a guide arranged to provide a gap in line with a side of the at least one adhesive joint.

6. The vehicle according to claim 5, wherein the electrically conductive wire further comprises a third portion arranged to pass through the gap, and wherein the guide is arranged such that the electrically conductive wire is progressively pulled through the gap as it is pulled through the at least one adhesive joint.

7. The vehicle according to claims 5 or 6, wherein a width of the gap is lessthan a width of the at least one adhesive joint between the surface of the first element and the surface of the second element.

8. The vehicle according to claim 7, wherein the width of the gap is adjustable.

9. The vehicle according to any of claims 6 to 8, wherein the locating element is adjacent to the third portion of the electrically conductive wire.

10. The vehicle according to any of claims 4 to 9, wherein the locating element is at least partially embedded in the at least one adhesive joint.

11. The vehicle according to any of claims 4 to 10, wherein the locating element is detachable from the vehicle.

12. The vehicle according to any of the preceding claims, wherein a part of the electrically conductive wire is joined to the first element or the second element.

13. The vehicle according to any of the preceding claims, wherein the electrically conductive wire comprises a fourth portion that is embedded in the at least one adhesive joint.

14. A vehicle according to any of claims 1 to 3 and any of claims 4 to 13.

15. A method of manufacturing a vehicle comprising:providing a non-electrically conductive layer on at least a surface of a first element and / or a surface of a second element of the vehicle, the first element and / or the second element comprising an electrically conductive material, wherein the at least one surface of the first element and / the second element is a bonding surface of the first element and / or the second element to be in contact with at least one adhesive joint;providing an electrically conductive wire having a first portion for cutting and a second portion for connecting to at least part of a circuit for heating the electrically conductive wire; andbonding the first element to the second element using the at least one adhesive joint,wherein the non-electrically conductive layer prevents at least the first portion of the electrically conductive wire from contacting the electrically conductive material of the first element and / or the second element as it is pulled through the at least one adhesive joint.

16. The method of claim 15, wherein providing a non-electrically conductive layer comprises anodising and / or coating the surface of the first element and / or the surface of the second element.

17. A method of manufacturing a vehicle comprising:providing a non-electrically conductive layer on at least a surface of a first element and / or a surface of a second element of the vehicle, the first element and / or the second element comprising an electrically conductive material;providing an electrically conductive wire having a first portion for cutting and a second portion for connecting to at least part of a circuit for heating the electrically conductive wire;bonding the first element to the second element using the at least one adhesive joint; andproviding a locating element according to any of claims 4 to 14 to at least partially position the electrically conductive wire between the surface of the first element and the surface of the second element to prevent the first portion of the electrically conductive wire from contacting the electrically conductive material ofthe first element and / or the second element as it is pulled through the at least one adhesive joint.

18. The method of claim 17, further comprising arranging a third portion of the electrically conductive wire to pass through the locating element.5 19. A method of manufacturing a vehicle according to claims 16 and 17.

20. A method of separating a first element from a second element of a vehicleaccording to any of claims 1 to 14, the method comprising:heating the electrically conductive wire by using the at least part of the circuit to pass an electric current through the electrically conductive wire; and10 retrieving the electrically conductive wire and pulling the electricallyconductive wire through the at least one adhesive joint.

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