Apparatus and method for testing the shock resistance of a test object in a liquid in the absence of explosives

Abstract

A device (20) for testing the shock resistance of a test object (22) in a liquid (24) in the absence of explosives is disclosed. The device comprises a volume (26) filled with the liquid (24), wherein the volume (26) is designed to accommodate the test object (22). The device further comprises a shock device (28) designed to generate a pressure wave (30) in the volume (26) in order to test the shock resistance of the test object (22).

Description

[0001] The invention relates to conducting shock tests on objects, e.g., electrical components, in a liquid without the use of explosives. By using the liquid, e.g., water, the shock resistance of the objects in the liquid can be tested. In particular, the shock resistance of the objects underwater can be simulated.

[0002] For military equipment on ships, it is often necessary to demonstrate shock resistance under water blast. This is usually done through experiments in water, in which the parts to be tested, such as acoustic sensors, are exposed to a detonation pressure wave. Such experiments are conducted, for example, by the German Federal Defense Technical Services. Such a procedure is very complex, due to the handling of the explosives, for example, and usually does not allow for testing during development.

[0003] The object of the present invention is therefore to create an improved concept for conducting shock tests under water.

[0004] This object is achieved by the subject matter of the independent patent claims. Further advantageous embodiments are the subject matter of the dependent patent claims.

[0005] Embodiments show a device for testing the shock resistance of a test object in a liquid, in particular water, in the absence of explosives. In other words, the device physically simulates an explosive load on the test object. The device comprises a volume filled with a liquid, e.g. water, wherein the volume is designed to accommodate the test object. The volume can be a box of any size. The use of a box makes it possible to carry out the tests in a hall. Defined conditions can be set in the hall. In particular, it is possible to eliminate weather influences such as rain or wind in the hall. This facilitates the tests compared to tests carried out outdoors. In principle, however, it is also possible for the volume to be defined by the bottom of a body of water.The test object can be positioned in the volume using a test object holder. It is also possible for the test object to be positioned in the volume without a corresponding holder. In particular, the test object then lies on the bottom of the liquid-filled volume.

[0006] Water or a water-like liquid, for example, is suitable for simulating the underwater splash behavior. A water-like liquid is defined as a liquid with properties similar to those of water. Particularly suitable for this application are liquids with a similar speed of sound and / or density to water. Some oils, in particular, meet these requirements.

[0007] The device further comprises a shock device. The shock device is configured to generate a pressure wave in the volume to test the shock resistance of the test object. The following embodiments will present two options for configuring the shock device, each generating the pressure wave in different ways.

[0008] The idea now is to replace explosives in underwater shock resistance tests of test objects by generating the necessary pressure wave using other means. This eliminates the need for explosives experts to conduct or at least supervise the test. Instead, the test can, in principle, be performed by anyone without any knowledge of explosives using the device or method. Likewise, it is not necessary to conduct the tests in water; another liquid, particularly a water-like liquid, can also be used.

[0009] In one embodiment, the volume is defined by the walls of a box. In particular, the box completely encloses the liquid. The shock device has a holding element that is designed to keep the box suspended above the floor and to drop the box at a specific time in order to generate the pressure wave in the volume when the box hits the floor. The forces when the box hits the floor can destroy the box. This is not a problem, since the relevant pressure wave travels through the volume in fractions of a second and the test object is exposed to the influence of the pressure wave before liquid escapes from the box. However, it must be ensured that the test object itself does not hit the floor and break there. In this respect, it is advantageous if the test object is arranged in a receptacle and not directly on the floor of the box.If the box breaks, the test object can be washed out of the box with the escaping liquid. Advantageously, the area of ​​the floor around the impact point of the box is softer than the impact point itself. If the test object hits the softer area of ​​the floor during the washout, the risk of damage to the test object is further reduced.

[0010] In an alternative embodiment, the shock device comprises a (first) plate and a holding element. The plate advantageously has a density of more than 4000 kg / m 3 , more preferably more than 7000 kg / m 3This makes it possible to use flatter plates with the same mass and the same base area. Flat plates are usually easier to handle, for example by means of the holding element, than thick plates. Furthermore, it is advantageous if the plate (or the falling box) is magnetic. The holding element is designed to hold the plate suspended above the volume and to let the plate fall onto the liquid at a specific time in order to generate the pressure wave in the volume when the plate hits the liquid (or the liquid surface). When using a magnetic metal plate, the holding element can have an (electro) magnet to hold the plate and let it fall at that time. The plate is preferably made predominantly or entirely of a metal, for example steel.Metals appear to be suitable materials for forming a heavy, rigid mass capable of generating a shock wave that mimics the shock wave of explosives.

[0011] The holding element can, like the holding element in the previous embodiment, be a crane, for example. A crane allows the panel or box to be picked up from any position within its reach and can bring the panel or box into the drop position and drop it at a specific time.

[0012] It has been found that increasing the thickness (and thus the mass) of the plate results in a longer pressure wave duration. With a maximum pressure wave duration of less than one millisecond (typically between 0.1 and 0.2 ms), increased mass can significantly increase the energy acting on the test object.

[0013] The impact of the plate on the liquid can occur immediately. However, in embodiments it is also possible and advantageous if the shock device comprises a further (second) plate arranged on the liquid surface, wherein the holding element is designed to let the (first) plate fall onto the further (second) plate at the specific point in time. The further plate has the technical effect that the liquid surface is kept still and thus disturbances such as small waves that would lead to a weakening of the pressure wave are reduced or completely eliminated. Nevertheless, the plate still impacts the liquid surface. The impact on the liquid typically occurs immediately after the impact on the further plate.

[0014] For example, the falling plate pushes a volume of air ahead of it. This volume of air would influence the liquid surface shortly before impact, particularly partially displacing it. To mitigate or eliminate this effect, it is advantageous to cover the liquid surface with a suitable, second, thin plate. For example, the additional plate has a thickness of a maximum of 1 cm, preferably a maximum of 0.5 cm, more preferably a maximum of 0.25 cm or 0.1 cm.

[0015] The additional plate can, for example, float on the liquid surface. However, the additional plate is preferably arranged on the liquid surface, for example on spring elements. This makes it possible, for example, to manufacture the additional plate, at least predominantly, from the same material as the plate. This avoids or at least reduces an impedance jump between the plate and the additional plate. This means that there is no or only slight attenuation of the possible pressure wave due to the additional plate. In other words, the coupling of the pressure into the liquid is not significantly disrupted. The same effect, i.e. the disruption-free coupling of the pressure wave into the liquid, is achieved if the additional plate is manufactured predominantly from a material that has the same or a similar acoustic impedance as the liquid, i.e. essentially has the acoustic impedance of the liquid.For example, a plastic material, such as polypropylene, can be used as the material. The acoustic impedance of the plate preferably has a maximum deviation of 15%, preferably a maximum of 10%, and more preferably a maximum of 5% from the acoustic impedance of the liquid. When speaking of acoustic impedance, reference is made, for example, to the acoustic sound characteristic impedance.

[0016] In exemplary embodiments, the plate has one or more openings. The opening(s) allow an air layer that forms between the falling plate and the liquid surface or the other plate shortly before impact, and which can, for example, reduce the impact velocity or influence the liquid surface, to escape at locations other than the edge of the plate. Thus, the air layer can escape more quickly and has less impact on the coupling of the pressure wave into the liquid.

[0017] In further embodiments, the shock device is designed to allow the plate to impact the liquid parallel to the liquid surface with a maximum deviation of 0.1°. The smaller the deviation, the better the coupling of the pressure wave into the liquid. With regard to the falling box, it is advantageous if the side of the box, i.e., the side that first hits the ground, has a maximum deviation of 0.1° from the ground upon impact.

[0018] In exemplary embodiments, the shock device comprises guide rails. The guide rails are designed to guide the plate or box during the fall onto the liquid surface. The guide rails can guide the plate or box, for example, using a ball bearing or a dovetail guide. The guide rails provide an option for allowing the plate to impact the liquid parallel to the liquid surface or for allowing the box to impact the liquid parallel to the ground.

[0019] In further embodiments, the shock device has a precision control. The precision control has a plurality of distance meters which are designed to measure the distance between the plate and the liquid surface or the further plate (or the falling box and the ground) at various points. Thus, the orientation of the plate in relation to the liquid surface or the further plate (or the falling box to the ground) can be determined by means of the distance meters. This means, for example, that it is possible to determine the inclination of the plate (or the box) vectorially, i.e. in terms of amount and direction. The precision control further comprises a position control which is designed to align the plate based on the measured values ​​of the plurality of distance meters such that the plate impacts or impacts parallel to the liquid surface with a deviation of a maximum of 0.1°.to align the box in such a way that the box hits the ground parallel with a maximum deviation of 0.1°.

[0020] Embodiments further show that the shock device is designed to generate a plane pressure wave. Plane waves are characterized by the fact that the energy of the pressure wave spreads evenly through the liquid and impinges on the test object. A spherical wave would no longer have the same energy as a plane wave, especially in the edge areas of the test object.

[0021] Further embodiments show the shock device with an acceleration device. The acceleration device is designed to allow the plate to impact the liquid surface at a speed that is greater than the drop height, or to allow the box to impact the ground at a speed that is greater than the drop height. This means that the plate or box is not accelerated exclusively by gravitational acceleration, but additionally by the acceleration device before it impacts the liquid surface or the ground.

[0022] Furthermore, exemplary embodiments show the device with the receptacle for positioning the test object in the volume. Furthermore, the device has a sound reflector, in particular a spherical or cylindrical one, which is designed to reflect the pressure wave in a focused manner onto the receptacle. This allows the energy of the pressure wave to be focused on the test object and thus increased.

[0023] With regard to the above statements, the following considerations should be made. In fluids, pressure waves (unlike pressure waves in air) cause material movement to be small relative to the pressure. This results from the impedance equation. p=ρ∗c∗Δv which relates the pressure p to the density ρ of the liquid (=1000kg / m 3in the case of water), the speed of sound c in the liquid (=1500 m / s in water) and the material velocity jump Δv. Thus, a velocity change of only Δv = 10 m / s causes a pressure peak of approximately 150 bar in water, a value that is within the range of typical pressures in impact tests. This means that, with the force of gravity alone, a plate striking the liquid surface can generate a pressure of approximately 150 bar if water is used as the fluid.

[0024] However, to generate a pressure of 150 bar, optimal conditions must be established. This means that the plate should impact parallel to the liquid surface, and the liquid surface should not exhibit any disturbances; in other words, it should be steady, for example by using the additional plate. Furthermore, it is advantageous if the plate is manufactured with a certain degree of precision so that the surface impacting the liquid surface is also flat. However, the pressure can be increased, for example if the reflector is used or if the plate already has an initial velocity before (free) fall. If a pressure of 150 bar is still to be achieved, the described conditions can be reduced by using the described means for increasing the pressure. Otherwise, all statements regarding the falling plate apply analogously to the alternative embodiment of the falling box.

[0025] In further embodiments, the device comprises a buffer element. The buffer element is designed to decelerate the plate after impact with the liquid. This prevents, for example, the plate from impacting the test object and destroying or at least damaging it.

[0026] Embodiments further show that the plate is larger than the maximum size of the test object for which the device is designed. For example, this ensures that the test object is reached by the plane wave across its entire width. The size is understood to be, for example, the diameter or the area of ​​the surface of the plate that impinges on the liquid surface. The test object or the holder for the test object should now be arranged such that the test object lies completely within a vertical projection of the plate into the volume. The maximum size of the test object should therefore also advantageously be selected such that the test object lies completely within the projection.

[0027] Analogously, a method for testing the shock resistance of a test object in a liquid (20) in the absence of explosives is disclosed, comprising the following steps: a) providing a volume filled with the liquid, wherein the volume is designed to accommodate the test object; b) generating a pressure wave in the volume to test the shock resistance of the test object. In particular, the pressure wave in step b) can be generated by means of a plate falling onto the liquid, and the plate falling onto the liquid in a negative pressure environment. Using the negative pressure environment reduces the air layer that forms between the plate and the liquid surface when the plate falls. However, if the air pressure is too low, measures must be taken to ensure that the liquid remains liquid. For example, the volume can be completely enclosed.If the volume is completely enclosed by a casing, it is advantageous to use an additional plate, which forms part of the casing. The additional casing can be connected to the additional plate and consist primarily of a flexible material, such as rubber or a similar plastic. Using the additional plate ensures that only a single impedance jump occurs when the plate hits the liquid surface.

[0028] Furthermore, it is possible to adjust the strength of the pressure wave by adjusting or varying the impact speed of the plate on the liquid surface.

[0029] Preferred embodiments of the present invention are explained below with reference to the accompanying drawings. Fig. 1: a schematic perspective view of an apparatus for testing the shock resistance of a test object in a liquid in the absence of explosives according to an embodiment; Fig. 2: a schematic perspective view of a device for testing the shock resistance of a test object in the liquid in the absence of explosives according to a Fig. 1 alternative embodiment; Fig. 3: a schematic perspective view of a plate of the device according to Fig. 1, where Fig. 3a and Fig. 3b each present different possibilities for how openings in the slab can be provided; and Fig. 4: a schematic side view of the device according to Fig. 1, where Fig. 4b in addition to Fig. 4a has a reflector for focusing a pressure wave onto the test object.

[0030] Before exemplary embodiments of the present invention are explained in more detail below with reference to the drawings, it is pointed out that identical, functionally identical or equivalent elements, objects and / or structures in the different figures are provided with the same reference numerals, so that the description of these elements shown in different exemplary embodiments is interchangeable or can be applied to one another.

[0031] Fig. 1 shows a schematic perspective view of a device 20 for testing the shock resistance of a test object 22 in a liquid 24 in the absence of explosives. The device 20 comprises a volume 26 filled with the liquid 24, wherein the volume 26 is configured to accommodate the test object 22. By way of example, the volume 26 is configured in a box 27. The shock device 28 can generate a pressure wave 20 in the volume 26 in order to test the shock resistance of the test object 22. The shock device 28 comprises a plate 32 and a holding element 34. The holding element 34 can hold the plate 32 above the volume 26 and drop it onto the liquid 22 (or the liquid surface) at a specific time. The impact of the plate 32 onto the liquid 24 generates the pressure wave 30 in the volume 26. The impact position 32' of the plate 32 on the liquid surface is shown in dashed lines.The fall distance is shown schematically by means of a movement arrow 36.

[0032] It should be noted that the device 20 can also take on a cylindrical shape instead of the square or cuboid shape shown throughout.

[0033] Fig. Figure 2 shows a schematic perspective view of the device 20 for testing the shock resistance of a test object 22 in the liquid 24 in the absence of explosive in a Fig. 1 alternative embodiment. As already mentioned in Fig. 1, the volume is defined by the walls of the box 27, but is shown more schematically here. The volume, ie, the interior of the box 27, is advantageously completely filled with the liquid 24. The shock device 28 has the holding element 34. In contrast to the embodiment according to Fig. 1, however, the holding element 34 does not hold a plate here, but rather the entire box 27 suspended above the floor 38. A solid, thick steel base beneath the box, for example, is suitable as the floor. The holding element 34 can drop the box 27 at a specific time to generate the pressure wave in the volume when the box 27 hits the floor 38.

[0034] Fig. Figure 3a shows the plate 32 in a schematic, perspective view. The plate 32 has an opening 40. The opening cuts out an area in the underside of the plate that impinges on the liquid, which advantageously corresponds to at least 1%, at least 5%, or at least 10% of the total area of ​​the underside of the plate. The opening makes it easier for an air layer that builds up between the plate and the liquid surface shortly before impact with the liquid surface to dissipate. This means that the air can escape not only to the outside but also through the opening 40. If the test object is small compared to the plate, this embodiment of the plate also makes it possible to focus the wavefront on the test object. Thus, the energy can be increased compared to the energy of the plane wave that would impinge on the small test object.

[0035] Fig. 3b discloses the plate 32 with, in contrast to the embodiment of Fig. 3a, a plurality of openings 40. The openings 40 can be arranged in any desired manner. This means, for example, that the openings 40 can be arranged randomly or symmetrically. Examples are shown in Fig. 3b shows 12 openings 40. However, any number of openings greater than or equal to 1 can be used to make it easier for the air layer to escape. Advantageously, the openings in total leave out an area of ​​the underside of the plate, which advantageously corresponds to at least 1%, at least 5% or at least 10% of the total area of ​​the underside of the plate. The openings 40 therefore reduce the impact area of ​​the plate 32 on the liquid surface, as a result of which the pressure wave receives less energy. A balance must therefore be struck between the influence of the air layer and the size of the openings. In principle, it is also possible to design the opening(s) 40 larger than 10% of the total volume. For example, the total area of ​​the plate must then be selected to be correspondingly larger in order to bring the corresponding energy into the liquid.

[0036] Fig. Figure 4a shows a schematic sectional view of the device 20 in various embodiments. For reasons of clarity, the holding element has been omitted. As already shown in Fig. As shown in Figure 1, the device 20 comprises the volume 26 filled with the liquid 24. The volume 26 is delimited by the box 27. The plate 32 is held by the holding element (not shown). When the plate 32 is released, it is guided to the liquid surface 24' by means of optional guide rails 42. Two guide rails 42, 42' are shown as examples. Advantageously, at least one additional guide rail is arranged outside the viewing plane.

[0037] An optional additional plate 44 is arranged on the liquid surface 24'. The additional plate 44 is optionally mounted on spring elements 46. The spring elements 46 are preferably dimensioned such that the additional plate 44 submerges even with a small force. Thus, the impact of the plate 32 on the liquid surface 24' is virtually unaffected by the additional plate 44.

[0038] The device 20 optionally further comprises one or more buffer elements 48. For example, a circumferential buffer element 48 can be provided, or the buffer elements can be arranged at various positions within the volume. The buffer elements can decelerate the plate 32 after impact with the liquid. For example, a collision between the plate 32 and the test object 22 is thus prevented.

[0039] Fig. 4b discloses in addition to Fig. 4a an optional sound reflector 50. The sound reflector 50 can reflect an incident pressure wave, in particular a plane wave, in a focused manner onto the test object 22. The test object 22 is arranged, for example, by means of a receptacle 52 above the reflector, ie between the reflector and the liquid surface, in particular at a focal point of the reflector.

[0040] The device 20 also optionally has an acceleration device 54. The acceleration device can cause the plate to impact the liquid surface at a speed that is higher than the drop height. The acceleration device 54 can be a passive acceleration device. A suitable passive acceleration device, for example, is a preloaded spring that accelerates the plate 32 after it has been triggered, i.e., dropped, to a greater speed than would be possible solely through gravity. The acceleration device 54 can also be an active acceleration device. An electric motor, for example, is suitable as an active acceleration device. For example, an electric motor 54, 54' can be provided for each guide rail 42, 42', which accelerates the plate 32 along the guide rails.The electric motor is also a design to enable position control of the plate 32 relative to the liquid surface 24'.

[0041] It should be noted that the Fig. 4a and Fig. 4b, the optional features of the device 20 can be used individually or in any combination.

[0042] Although some aspects have been described in connection with a device, it should be understood that these aspects also represent a description of the corresponding method, so that a block or component of a device can also be understood as a corresponding method step or as a feature of a method step. Analogously, aspects described in connection with or as a method step also represent a description of a corresponding block, detail, or feature of a corresponding device.

[0043] The above-described embodiments are merely illustrative of the principles of the present invention. It is understood that modifications and variations of the arrangements and details described herein will be apparent to others skilled in the art. Therefore, it is intended that the invention be limited only by the scope of the following claims and not by the specific details presented in the description and explanation of the embodiments herein. List of reference symbols: 20 Device 22 test object 24 Liquid 26 volumes 27 boxes 28 Shock device 30 pressure wave 32 plate 32' Impact position of the plate 34 Holding element 36 Movement arrow 38 hard surface 40 Breakthrough 42 guide rail 44 more records 46 spring element 48 Buffer element 50 sound reflector 52 Holder for the test object 54 Accelerator

Claims

[1] Device (20) for testing the shock resistance of a test object (22) in a liquid (24) in the absence of explosives, having the following features: - a volume (26) filled with the liquid (24), wherein the volume (26) is designed to receive the test object (22); - a shock device (28) designed to generate a pressure wave (30) in the volume (26) in order to test the shock resistance of the test object (22). [2] Device (20) according to claim 1, wherein the shock device (28) comprises a plate (32) and a holding element (34), wherein the holding element (34) is designed to hold the plate (32) above the volume (26) and to allow the plate (32) to fall onto the liquid (24) at a certain time in order to generate the pressure wave (30) in the volume (26) by impact of the plate (32) on the liquid (24). [3] Device (20) according to claim 2, wherein the shock device (28) comprises a further plate (44) arranged on the liquid surface, wherein the holding element (34) is adapted to allow the plate (32) to fall onto the further plate (44) at the specific time. [4] Device (20) according to one of claims 2 or 3, wherein the plate (32) has one or more openings (40). [5] Device (20) according to one of claims 2 to 4, wherein the shock device (28) is designed to cause the plate (32) to strike the liquid (24) parallel to the liquid surface with a maximum deviation of 0.1°. [6] Device (20) according to one of claims 2 to 5, wherein the shock device (28) comprises guide rails (42) adapted to guide the plate (32) during the fall onto the liquid surface. [7] Device (20) according to one of claims 2 to 6, wherein the further plate (44) consists predominantly of the same material as the plate (32) or wherein the further plate (44) consists predominantly of a material whose impedance substantially corresponds to the impedance of the liquid (24). [8] Device (20) according to one of claims 2 to 7, wherein the shock device (28) has a precision control, wherein the precision control has a plurality of distance meters which are designed to measure the distance between the plate (32) and the liquid surface or the further plate (44) at different points and wherein the precision control comprises a position control which is designed to align the plate (32) based on the measured values ​​of the plurality of distance meters such that the plate (32) impacts the liquid surface in parallel with a deviation of a maximum of 0.1°. [9] Device (20) according to one of claims 2 to 8, wherein the shock device (28) comprises an acceleration device (54) which is designed to cause the plate (32) to impact the liquid surface at a speed which is higher than the drop height. [10] Device (20) according to one of claims 2 to 9, wherein the device comprises a receptacle (52) for positioning the test object (22) in the volume (26) and wherein the device comprises a sound reflector (50) which is designed to reflect the pressure wave (30) in a focused manner onto the receptacle (52). [11] Device (20) according to one of claims 2 to 10, wherein the device comprises a buffer element (48), wherein the buffer element (48) is designed to brake the plate (32) after impact with the liquid (24). [12] Device (20) according to one of the preceding claims, wherein the shock device (28) is designed to generate a plane pressure wave (30). [13] Apparatus (20) according to any one of the preceding claims, wherein the plate (32) is larger than the maximum size of the test object for which the apparatus is designed. [14] Device (20) according to claim 1, - wherein the volume (26) is defined by walls of a box (27); - wherein the shock device (28) has a holding element (34) which is designed to keep the box (27) suspended above the ground and to let the box (27) fall at a certain point in time in order to generate the pressure wave (30) in the volume (26) by impact of the box (27) on the ground. [15] Method for testing the shock resistance of a test object (22) in a liquid (24) in the absence of explosive, comprising the following steps: a) providing a volume filled with the liquid (24), wherein the volume (26) is designed to receive the test object (22); b) Generating a pressure wave (30) in the volume (26) to test the shock resistance of the test object (22). [16] Method according to claim 15, wherein the pressure wave (30) in step b) is generated by means of a plate (32) falling onto the liquid (24), and wherein the plate (32) falls onto the liquid (24) in a negative pressure environment. [17] Method according to one of claims 15 or 16, wherein a strength of the pressure wave (30) is adjusted by adjusting the impact speed on the liquid surface.

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