Method for monitoring the temperature of a welded joint of a continuous carbon fiber reinforced thermoplastic composite material

Abstract

The application discloses a kind of continuous carbon fiber reinforced thermoplastic composite welding joint temperature monitoring method, to the upper joint pair and the lower joint pair of direct welding of ultrasonic wave are carried out surface treatment, then fixed electrode, and put into temperature control box;Signal processing end is used to collect and analyze the signal obtained by electrode, compared with the temperature-resistance curve obtained by experiment, to realize the temperature monitoring of welding joint.The application does not increase additional structure, cost is lower, operation is convenient, and under the premise of stable and reliable, the internal temperature of welding joint is monitored using the performance of material itself.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of temperature monitoring, and particularly relates to a continuous carbon fiber reinforced thermoplastic composite welding joint temperature monitoring method. BACKGROUND

[0002] In actual application, the joint connected by welding is weaker than the material itself in strength, and when a large load is borne, damage first occurs in the joint part. Since the material itself is thermoplastic, temperature monitoring in the service process has a great influence on the structural reliability, and has a great influence on the safety of the joint in use. Meanwhile, the thermoplastic matrix has poor thermal conductivity, and the temperature change of the welding interface is difficult to obtain through the measurement of the surface temperature.

[0003] According to the prior art, a thermocouple or other sensors can be arranged to monitor the temperature of the welding joint, and other instruments such as infrared thermometers can be used. However, the additional sensors will bring additional costs, and it is difficult to realize firm fixation, and the measurement of the internal temperature of the joint may affect the structure of the joint; the use of infrared thermometers and other instruments is costly, and it is difficult to achieve real-time internal monitoring of the welding joint. SUMMARY

[0004] The technical problem to be solved by the application is to provide a continuous carbon fiber reinforced thermoplastic composite welding joint temperature monitoring method to solve the technical problem that the internal temperature of the continuous carbon fiber reinforced thermoplastic composite welding joint cannot be measured.

[0005] The application adopts the following technical solutions:

[0006] The continuous carbon fiber reinforced thermoplastic composite welding joint temperature monitoring method comprises the following steps:

[0007] S1, surface treatment is performed on the upper and lower bonding pairs completed by ultrasonic direct welding, then electrodes are fixed, and the electrodes are placed in a temperature control box;

[0008] S2, signals obtained by the electrodes are collected and analyzed by a signal processing end, and compared with a temperature-resistance curve obtained by experiment, so as to realize temperature monitoring of the welding joint.

[0009] Specifically, in step S1, the matrix of the upper and lower bonding pairs is made of continuous carbon fiber reinforced thermoplastic composite material.

[0010] Further, the volume fraction of carbon fibers in the continuous carbon fiber reinforced thermoplastic composite material is 20% to 60%.

[0011] Further, the continuous carbon fiber reinforced thermoplastic composite material includes polyethylene, polyether ether ketone, polyphenylene sulfide and / or polyethylene terephthalate.

[0012] Specifically, in step S1, the surface treatment is specifically:

[0013] Clean the extrusion around the welding interface of the upper joint pair and the lower joint pair.

[0014] Further, the conductive paint is applied on the interface of the upper joint pair and the lower joint pair after the extrusion is cleaned, and then the electrodes are connected respectively.

[0015] Specifically, in step S1, the electrodes are fixedly connected to the upper joint pair and the lower joint pair by mechanical pressing.

[0016] Specifically, in step S1, the electrodes are symmetrically placed and located at one end of the upper joint pair and the lower joint pair.

[0017] Specifically, in step S2, the resistance value is recorded once every 5℃ change in temperature, and the temperature of the temperature control box needs to be kept unchanged for 1 minute when recording the resistance each time.

[0018] Specifically, in step S2, the actual measured signal is compared with the interface resistance and temperature change curve to obtain the real-time temperature inside the welded joint.

[0019] Compared with the prior art, the present application has at least the following beneficial effects:

[0020] The continuous carbon fiber reinforced thermoplastic composite material welding joint temperature monitoring method of the present application directly monitors the internal temperature of the welded joint by monitoring the change of the interface resistance or voltage during the service process of the welded joint, avoiding damage to the structure of the welded joint caused by excessive high or low temperature; the carbon fiber reinforced material changes the resistance when the environmental temperature changes, and the fixed electrode method is used to monitor the temperature of the welding interface after the formation of the conductive network, the temperature-resistance fitting curve has high linearity, high monitoring sensitivity and rapid response to temperature change.

[0021] Further, the carbon fiber has excellent conductivity, and the natural conductive network formed after welding is used for interface monitoring, which is the core of the present application; at the same time, the thermoplastic composite material reinforced by carbon fiber has the advantages of light weight, high modulus, high strength, designability, high temperature resistance, excellent thermal stability, fatigue resistance, corrosion resistance, good processability and wide application.

[0022] Further, the volume fraction of the continuous carbon fiber reinforced thermoplastic composite material matrix fiber is between 20% and 60%, and too low or too high fiber volume fraction will lead to the reduction of the performance of the joint pair.

[0023] Further, the continuous carbon fiber reinforced thermoplastic composite matrix includes polyethylene, polyether ether ketone, polyphenylene sulfide and / or polyethylene terephthalate and other common thermoplastic materials.

[0024] Further, after welding, under the combined action of welding heat and welding pressure, the thermoplastic matrix will melt and extrude, and part of the fibers will also move. Removing excess polymer can expose the fibers wrapped in the polymer, increase the contact area of the monitoring head and the conductive network when monitoring the resistance or voltage signal.

[0025] Further, a conductive paint is provided between the upper and lower joint pairs to maximize the electrical contact between the welding interface and the copper foil and increase the stability of the conductive network.

[0026] Further, the electrode and the conductive network are connected by mechanical pressure to ensure close contact between the electrode and the conductive network.

[0027] Further, the electrodes are symmetrically arranged along the length direction of the joint pair, which can fully reflect the characteristics of the conductive network formed by ultrasonic welding and improve the monitoring accuracy.

[0028] Further, the temperature is recorded every 5℃ change, which is used to obtain a more uniform interface temperature gradient and make the fitting result more accurate; when recording the resistance, the temperature of the temperature control box should be kept stable for 1 minute, the purpose is to make the interface temperature and interface resistance stable before measurement, so as to obtain more accurate corresponding relationship between the two.

[0029] Further, by comparing the actual measured signal with the interface resistance and temperature change curve, the real-time temperature inside the welded joint can be obtained.

[0030] In summary, the present application can monitor the internal temperature of the welded joint without adding additional structure, with low cost, convenient operation, stable and reliable performance, and using the performance of the material itself.

[0031] The technical solutions of the present application will be further described in detail below by means of the accompanying drawings and examples. DETAILED DESCRIPTION

[0032] Figure 1 It is a schematic diagram of the welding joint temperature monitoring principle of the present application;

[0033] Figure 2 It is a schematic diagram of the interface monitoring method in the ultrasonic welding process;

[0034] Figure 3 It is a diagram of the interface resistance changing with temperature measured in the gradient temperature experiment;

[0035] Wherein: 11. upper joint pair; 12. lower joint pair; 13. conductive network; 14. electrode; 15. signal processing end; 21. temperature control box; 25. resistance meter; 26. wire. DETAILED DESCRIPTION

[0036] The technical solutions in the embodiments of the present application will be clearly and completely described below with reference to the drawings in the embodiments of the present application. Obviously, the described embodiments are some of the embodiments of the present application, rather than all the embodiments of the present application. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative work fall within the scope of protection of the present application.

[0037] In the description of the present application, it should be understood that the terms "center", "longitudinal", "transverse", "upper", "lower", "front", "rear", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer", "one side", "one end", "one edge" and the like indicate the orientation or positional relationship based on the orientation or positional relationship shown in the drawings, and are only for the convenience of describing the present application and simplifying the description, and do not indicate or imply that the device or element referred to must have a particular orientation, be constructed and operated in a particular orientation, and therefore cannot be understood as a limitation on the present application. In addition, in the description of the present application, unless otherwise specified, the meaning of "a plurality of" is two or more.

[0038] In the description of the present application, it should be noted that unless otherwise specified and limited, the terms "mounting", "connection", "connection" should be understood broadly, for example, it can be fixedly connected, or it can be detachably connected, or integrally connected; it can be mechanically connected, or it can be electrically connected; it can be directly connected, or it can be indirectly connected through an intermediate medium; it can be the communication inside two elements. For those skilled in the art, the specific meaning of the above terms in the present application can be understood according to the specific circumstances.

[0039] It should be understood that when used in the present specification and the appended claims, the terms "include" and "contain" indicate the presence of described features, whole, steps, operations, elements and / or components, but do not exclude the presence or addition of one or more other features, whole, steps, operations, elements, components and / or sets thereof.

[0040] It should also be understood that the terms used in the present application are only for the purpose of describing specific embodiments and are not intended to limit the present application. As used in the present application specification and the appended claims, unless otherwise specified in the context, the singular form "a", "an" and "the" is intended to include the plural form.

[0041] It should be further understood that the term "and / or" as used herein in the specification and in the claims, if any, means any combination of one or more of the associated listed items can be present, and includes multiples of any item or mixture of items. It should also be understood that, depending on the particular context, the term "at least" can sometimes be used in the specification and / or claims to indicate that a feature can be present once or more than one time.

[0042] The various structural diagrams according to the disclosed embodiments of the present application are shown in the accompanying drawings. These diagrams are not drawn to scale, in which certain details are shown in a somewhat exaggerated manner for the purpose of clarity and understanding, and certain details can be omitted. The shapes of various regions, layers and the relative size and positional relationship therebetween shown in the drawings are merely exemplary, and in actuality, they can be deviated due to manufacturing tolerances or technical limitations, and regions / layers with different shapes, sizes and relative positions can be additionally designed by those skilled in the art according to actual needs.

[0043] The present application provides a continuous carbon fiber reinforced thermoplastic composite material welding joint temperature monitoring method, electrodes are laid at both ends of the joint formed after welding, wherein the electrodes are in contact with the conductive network formed by welding, and the electrodes are connected to a signal processing end, when the temperature changes, the resistance of the conductive network will also change accordingly due to the comprehensive influence of the thermoplastic matrix and carbon fiber on the temperature change, the electrical signal obtained by monitoring the signal processing end can monitor the welding joint temperature, and give an early warning to dangerous working temperature to avoid the influence of too high or too low temperature on the normal work of the welding joint.

[0044] Please refer to Figure 1 The theoretical basis of the present application is as follows:

[0045] The two workpieces to be welded are arranged in an upper joint pair 11 and a lower joint pair 12, the lower surface of the upper joint pair 11 is in contact with the upper surface of the lower joint pair 12 to form a conductive network 13, one end of the upper joint pair 11 and the connection of the lower joint pair 12, and one end of the lower joint pair 12 and the connection of the upper joint pair 11 are respectively provided with electrodes 14, and the two electrodes 14 are respectively connected to a signal processing end 15 of a resistance meter.

[0046] After the process of welding the carbon fiber reinforced thermoplastic composite material, the thin thermoplastic matrix is melted and extruded, the carbon fiber structures of the upper and lower workpiece welding interfaces are in contact, and a conductive loop of black is formed Figure 1 When the temperature changes, the resistance of the conductive loop will also change accordingly due to the comprehensive influence of the thermoplastic matrix and carbon fiber on the temperature change, which can be measured by a resistance or voltage monitoring system, and the temperature measured by this method is the internal temperature of the welding joint.

[0047] The present application provides a continuous carbon fiber reinforced thermoplastic composite material welding joint temperature monitoring method, which comprises the following steps:

[0048] S1, surface treatment is performed on the joint pair after direct welding, the excess extrudate around the welding interface is cleaned, and conductive paint is applied on the treated interface, and the electrode connected with the signal processing end is fixed.

[0049] The monitoring method is aimed at carbon fiber reinforced materials with thermoplastic polymer matrix, which can be repeatedly heated and melted, and can flow after softening at high temperature, including but not limited to polyethylene, polyether ether ketone, polyphenylene sulfide, polyethylene terephthalate and other polymers, in order to meet the requirement that the matrix can be melted and fused during welding; the reinforcing carbon fiber has good electrical conductivity and excellent performance, and the continuous carbon fibers of the two joint pairs will be in contact during welding, forming a conductive network. The mechanical and chemical changes of the matrix and carbon fiber when the temperature changes will jointly affect the resistance of the conductive network. It should be noted that the load borne by the welded joint will also affect the conductive network, so the temperature monitoring method is mainly applied to the welded joint bearing non-changing load.

[0050] After welding is completed, under the combined action of welding heat and welding pressure, the thermoplastic matrix will melt and extrude, and part of the fibers will also move in position. Removing excess polymer can expose the fibers wrapped in the polymer, increasing the contact area of the monitoring head and the conductive network during resistance or voltage signal monitoring. Similarly, arranging an extremely thin electrode and applying conductive paint on the electrode and the monitoring site can also increase the electrical contact of the conductive network at the electrode and the joint interface, avoiding the influence on the interface resistance or voltage monitoring due to poor contact between the electrode and the conductive network. As an alternative, the combination of an extremely thin electrode and conductive paint can also be replaced by a conductive adhesive with stronger adhesion. In this solution, after cleaning the excess polymer, a layer of conductive adhesive can be applied directly on the cleaned interface, and the wire is inserted into the adhesive layer before the adhesive solidifies. After the adhesive solidifies, the connection of the monitoring circuit is completed. Mechanical pressing can also ensure the close contact between the electrode and the conductive network.

[0051] S2, collect and analyze the obtained signal, and compare it with the temperature-resistance curve obtained by experiment, so as to obtain the temperature of the welded joint at this time.

[0052] The actual measured signal is compared with Figure 3 The interface resistance and temperature change curve in the middle can obtain the real-time temperature of the welding interface.

[0053] The present application utilizes the characteristic that the resistance of carbon fiber in the conductive network changes with temperature, and meanwhile, can be applied to other welding processes that can form a conductive network in the welding process, such as induction welding, resistance welding, etc., while the first two patents are mainly applied to the monitoring field of ultrasonic welding of continuous carbon fiber reinforced thermoplastic composites. According to the above difference points, the effects produced are also different. The present application mainly focuses on the temperature monitoring of the welded joint, and the first two patents mainly focus on the interface monitoring and welding quality detection of ultrasonic welding.

[0054] The temperature monitoring method using the characteristic that the resistance of carbon fiber reinforced material changes with temperature is not limited to the case of direct connection between carbon fiber reinforced materials, but can also be applied to the connection between thermoplastic composites using continuous carbon fiber structure (such as carbon nanotubes, graphene, etc.) as interface reinforcing material as reinforcing phase.

[0055] Meanwhile, due to the different changes of carbon fiber and thermoplastic matrix caused by temperature change, the response of the material resistance to temperature change is not monotonic, and in actual use, the temperature measurement interval needs to be clearly defined, or the temperature change trend needs to be roughly defined, so as to accurately measure the temperature change within a certain temperature range.

[0056] In order to make the purpose, technical scheme and advantages of the embodiments of the present application clearer, the technical scheme in the embodiments of the present application will be described clearly and completely below in combination with the drawings in the embodiments of the present application. Obviously, the described embodiments are part of the embodiments of the present application, not all the embodiments. The components of the embodiments of the present application described and shown in the drawings herein can be arranged and designed in various different configurations. Therefore, the following detailed description of the embodiments of the present application provided in the drawings is not intended to limit the scope of the claimed present application, but only represents selected embodiments of the present application. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative labor belong to the scope of protection of the present application.

[0057] In the embodiments 1 and 2 of the present application, a continuous carbon fiber reinforced polycarbonate composite plate with a length of 101.6 mm, a width of 25.4 mm and a thickness of 2 mm is used, wherein the volume fraction of carbon fiber is 20% to 60%.

[0058] Please refer to Figure 2 The upper joint pair 11 and the lower joint pair 12 are placed in the temperature control box 21, and the electrodes 14 at the connection between the upper joint pair 11 and the lower joint pair 12 and the electrodes 14 at the connection between the lower joint pair 12 and the upper joint pair 11 are respectively electrically connected to the signal processing end 15 of the resistance meter 25 through the wires 26.

[0059] The application will be described in detail below with reference to the drawings.

[0060] Example 1

[0061] In the temperature range of 25-85℃, the isothermal differential temperature change experiment was conducted on the test piece to determine the relationship between the interface resistance and the joint temperature.

[0062] No reinforcing phase was arranged at the welding interface, and the two composite plates were directly welded by ultrasonic welding, with the welding parameters being a welding pressure of 2 bar and a welding time of 1.2 s. After the test piece was cooled to room temperature, the excess extrudate in the front and rear directions of the welding interface was removed to expose the surface carbon fibers. After the excess mixture was removed, conductive silver paint was applied to the interface, the two sides of the conductive silver paint were parallel to the length direction of the composite plate, and after the conductive silver paint was solidified, 0.1 mm copper foil connected with wires was covered on the conductive silver paint area and fixed with adhesive tape. The two wires were respectively connected to the positive and negative electrodes of the resistance meter to monitor the size of the interface resistance.

[0063] The treated test piece was placed in a temperature control box for resistance measurement experiment at a specific temperature, and the resistance value was recorded once every 5℃ change in temperature. Each time the resistance was recorded, the temperature of the temperature control box needed to be kept unchanged for 1 minute. The starting temperature was 25℃, and the ending temperature was 85℃. The monitoring method is shown in the schematic diagram of Figure 2 .

[0064] The initial resistance was measured to be 0.878Ω, and the interface resistance continued to increase with the increase of temperature. When the welding joint was stable at 85℃, the interface resistance was 1.024Ω.

[0065] In the temperature range of 25-85℃, the isothermal differential temperature change experiment was conducted on the test piece to determine the relationship between the interface resistance and the joint temperature.

[0066] Example 2

[0067] In the temperature range of 85-105℃, the isothermal differential temperature change experiment was conducted on the test piece to determine the relationship between the interface resistance and the joint temperature.

[0068] Without setting any reinforcing phase at the welding interface, the two composite plates are welded together by ultrasonic direct welding, and the welding parameters are as follows: welding pressure: 2 bar; welding time: 1.2 s. After the test piece cools to room temperature, the excess extrudate in the front and rear directions of the welding interface is removed, the surface carbon fibers are exposed, conductive silver paint is applied on the interface after cleaning the excess mixture, the two sides of the conductive silver paint are parallel to the length direction of the composite plate, after it solidifies, 0.1 mm copper foil connected with the wires is covered on the part where the conductive silver paint is applied and is fixed, and the two wires are respectively connected to the positive and negative electrodes of the resistance meter to monitor the size of the interface resistance.

[0069] The treated test piece is placed in a temperature control box for resistance measurement experiment at a specific temperature, and the resistance value is recorded once every 5℃ change in temperature. Each time the resistance is recorded, the temperature of the temperature control box needs to be kept unchanged for 1 minute. The starting temperature is 85℃, and the ending temperature is 105℃. The monitoring method is shown in Figure 2 .

[0070] The initial resistance is measured to be 1.026Ω, and the interface resistance continues to decrease with the increase of temperature. When the welding joint is stable at 105℃, the interface resistance is 0.867Ω. This is because the carbon fibers compounded in the resin matrix have a negative temperature coefficient effect, which promotes the local fiber charge thermal activation hopping at this high temperature, weakens the influence of the fiber tunneling effect on the conductivity, and thus enhances the conductivity of the entire fiber conductive network.

[0071] Combining the two examples, the interface resistance-temperature change curve from 25℃ to 105℃ is shown in Figure 3 .

[0072] Example 3

[0073] In the temperature range of 15-75℃, the test piece is subjected to random temperature change experiment to verify the relationship between the interface resistance and the joint temperature:

[0074] In this example, the test sample is connected by ultrasonic direct welding, and the welding parameters are as follows: welding pressure: 2 bar; welding time: 1.2 s. After the test piece cools to room temperature, the excess extrudate in the front and rear directions of the welding interface is removed, the surface carbon fibers are exposed, conductive silver paint is applied on the interface after cleaning the excess mixture, the two sides of the conductive silver paint are parallel to the length direction of the composite plate, after it solidifies, 0.1 mm copper foil connected with the wires is covered on the part where the conductive silver paint is applied and is fixed, and the two wires are respectively connected to the positive and negative electrodes of the resistance meter to monitor the size of the interface resistance.

[0075] It is placed in an environment with random temperature changes, and the temperature change interval is 15-75℃. The change of its interface resistance is continuously measured within 10 minutes, and the change of the environmental temperature is recorded.

[0076] The measured resistance change trend is consistent with the temperature change trend, the resistance-temperature correspondence relationship in example 1 is used to process the resistance change curve, the obtained temperature change curve is highly consistent with the actual temperature change curve, and the error is small.

[0077] In summary, the continuous carbon fiber reinforced thermoplastic composite welding joint temperature monitoring method has the advantages of simple sensor or instrument installation process, simple operation, low cost, high efficiency and stability, no damage to the welding joint structure, high sensitivity, simple installation, simple material, low cost, high efficiency and stability, no additional structure, wide application range, and wide application prospect with the wide application of the carbon fiber reinforced thermoplastic composite welding.

[0078] The above content only illustrates the technical idea of the present application, and cannot limit the protection scope of the present application, and any modification made according to the technical idea of the present application on the basis of the technical scheme falls within the protection scope of the claims of the present application.

Claims

1. A method for monitoring the temperature of a continuous carbon fiber reinforced thermoplastic composite welded joint, characterized in that, The method comprises the following steps: S1, surface treatment is performed on the upper and lower bonding pairs after ultrasonic direct welding, then electrodes are fixed and placed in a temperature control box, the matrix of the upper and lower bonding pairs is made of continuous carbon fiber reinforced thermoplastic composite material, and the volume fraction of carbon fiber in the continuous carbon fiber reinforced thermoplastic composite material is 20%-60%; The electrodes are fixedly connected to the upper and lower bonding pairs in a mechanical pressing manner, and the electrodes are symmetrically placed at one end of the upper and lower bonding pairs; S2, signals obtained by the electrodes are collected and analyzed by a signal processing end, and compared with a temperature-resistance curve obtained by experiments, so that temperature monitoring of the welded joint is realized.

2. The continuous carbon fiber reinforced thermoplastic composite welded joint temperature monitoring method according to claim 1, characterized in that, The continuous carbon fiber reinforced thermoplastic composite material comprises polyethylene, polyether ether ketone, polyphenylene sulfide and / or polyethylene terephthalate.

3. The continuous carbon fiber reinforced thermoplastic composite welded joint temperature monitoring method according to claim 1, characterized in that, In step S1, the surface treatment specifically comprises: The extrudates around the welding interfaces of the upper and lower bonding pairs are cleaned.

4. The continuous carbon fiber reinforced thermoplastic composite welded joint temperature monitoring method according to claim 3, characterized in that, Conductive paint is applied on the cleaned interfaces of the upper and lower bonding pairs, and then the electrodes are connected.

5. The continuous carbon fiber reinforced thermoplastic composite welded joint temperature monitoring method according to claim 1, wherein, In step S2, the resistance value is recorded once every 5℃ of temperature change, and the temperature control box temperature needs to be kept unchanged for 1 minute when recording the resistance value each time.

6. The continuous carbon fiber reinforced thermoplastic composite welded joint temperature monitoring method according to claim 1, characterized in that, In step S2, the actually measured signal is compared with the interface resistance and temperature change curve, so that the real-time temperature inside the welded joint is obtained.

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