System for evaluation for evaluating fracture toughness value of joined body on joined interface, fracture toughness value evaluation method, method for predicting lifespan of injection molded joined body, and method of manufacturing injection molded joint body

Abstract

To provide a system for evaluation that can precisely and easily evaluate the fracture toughness value of a joined body on a joined interface.SOLUTION: The present invention relates to a system for evaluation that comprises: a crack gauge which has its surface coated with a random pattern for a DIC method and is stuck on a joined part for evaluation using a tension testing machine for a joined body; a digital camera which photographs a random pattern; software for analysis which analyses the strain of the joined part; and a computer, wherein the computer can send and receive electric signals between the crack gauge and digital camera, and synchronizes a crack progress length at time X when the joined part cracks that the crack gauge outputs with the strain of the joined part that the digital camera photographs at the time X, and the software for analysis evaluates a progress behavior of the crack at the joined part, and calculates a threshold for determining the progress of the crack based upon the strain at the time X.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to an evaluation system for evaluating the fracture toughness value at the bonded interface of a bonded body, a fracture toughness evaluation method, a method for predicting the life of an injection-molded bonded body, and a method for producing an injection-molded bonded body. [Background technology]

[0002] In recent years, various developments have been underway to strengthen the bonding and adhesion of dissimilar materials, one of the key issues in multi-material methods. To popularize lightweight and highly reliable bonded structures, it is important to anticipate fractures (cracks) at the bonded interface, which are likely to be the weakest point. Calculation of fracture toughness values, an energy evaluation method that can consider and predict long-term durability characteristics such as normal fracture, fatigue due to the gradual progression of cracks, and fracture due to heat shock, is required not only for bonded structures but also for bonding and adhesion between individual resin materials.

[0003] Test methods used to calculate fracture toughness at the bonded interface include the double cantilever beam (DCB) test and the end-notched flexure test (ENF) test (both standardized by JIS K 7086). In these test methods, even if the load history shows elastic-plastic behavior, damage may still be progressing inside the test piece. Therefore, the maximum load (P max ), but the limit load (P C It is defined that the fracture toughness value G is used. IC In the following formula (1) for calculating the limit load (P C : the load at the initial stage of crack propagation).

[0004]

number

[0005] As shown in equation (1), the fracture toughness value G IC Limit load P C Since the value of acts as a square, it is an important parameter in the calculation process of the Mode I / Mode II fracture toughness value, and accurate calculation is required. C The 5% offset method is recommended as a method for determining the limit load (the load at the initial stage of crack propagation), but this is a geometric method and it is difficult to accurately evaluate the limit load when there is material nonlinearity, such as in thermoplastic resins.

[0006] Other conventional methods for evaluating crack propagation behavior include the visual inspection method, in which a scale is applied to the side of a test specimen and the evaluation is performed visually; the crack gauge method (see Patent Document 1), in which a crack gauge is used to detect fracture; and the DIC method, in which the strain at the crack tip is evaluated by digital image correlation. [Prior art documents] [Patent documents]

[0007] [Patent Document 1] Japanese Patent Application Publication No. 2-238303 Summary of the Invention [Problem to be solved by the invention]

[0008] However, the visual inspection method cannot accurately evaluate the crack propagation length, making it impossible to calculate fracture toughness values ​​with high precision. Furthermore, while the crack gauge method can accurately evaluate the crack propagation length, the crack gauges themselves are expensive, making it difficult to increase the number of samples for evaluation. Furthermore, the DIC method cannot evaluate the threshold value for determining cracks (fracture strain in the opening direction), making it impossible to calculate fracture toughness values ​​with high precision. It would be useful if fracture toughness could be evaluated easily and accurately.

[0009] The present invention has been made in consideration of the above-mentioned problems of the conventional art, and an object of the present invention is to provide an evaluation system capable of accurately and simply evaluating the fracture toughness value at the bonded interface of a bonded body, a fracture toughness evaluation method capable of accurately and simply evaluating the fracture toughness value, a method for predicting the life of an injection-molded bonded body, and a manufacturing method capable of manufacturing an injection-molded bonded body having a desired life value. [Means for solving the problem]

[0010] One aspect of the present invention that solves the above problems is as follows. (1) A tensile testing machine capable of applying a tensile load to a bonded structure formed by bonding two articles in a direction in which the two articles move away from the bonded portion; A crack gauge having a random pattern for a digital image correlation (DIC) method applied to its surface and attached to the bonded portion of the bonded body when evaluating the bonded portion using the tensile tester; a digital camera that photographs the random pattern applied to the crack gauge; analysis software for analyzing the strain of the joint photographed by the digital camera; a computer that executes at least the analysis software; Equipped with the computer is configured to be able to transmit and receive electrical signals between the crack gauge and the digital camera; an evaluation system for evaluating the fracture toughness value at the bonded interface of a bonded body, the evaluation system synchronizing the crack growth length at time X when a crack occurs in the bonded part, which is output by the crack gauge, with the strain of the bonded part photographed by the digital camera at time X, evaluating the crack growth behavior at the bonded part of the bonded body using the analysis software, and calculating a threshold value for determining crack growth based on the strain at time X.

[0011] (2) A method for evaluating the fracture toughness value at the bonding interface of a bonded structure formed by bonding two articles, comprising the steps of: Step A includes performing, in no particular order, Step A1 of attaching a crack gauge to a side surface of a bonded structure to be evaluated, in which two articles are bonded together, and Step A2 of applying a random pattern for a digital image correlation (DIC) method to the surface of the crack gauge; A step B of applying a tensile load to the bonded body in a direction in which the two articles move away from the bonded portion using a tensile testing machine capable of applying a tensile load to the bonded body in a direction in which the two articles move away from the bonded portion, and acquiring the time X when a crack occurs in the bonded portion and the propagation length of the crack at the time X, which are output by the crack gauge; and A step C of photographing the joint using a digital camera that photographs the random pattern applied to the crack gauge, acquiring strain at the time X and the propagation length of the crack at the time X by a digital image correlation (DIC) method, and calculating a threshold value for determining the propagation of the crack based on the strain; A method for evaluating the fracture toughness value at the bonded interface of a bonded body, comprising:

[0012] (3) A method for evaluating fracture toughness at the bonded interface of a bonded body according to (2), wherein, in the first evaluation of the fracture toughness at the bonded interface of the bonded body, steps A to C are all performed for the crack propagation length that can be obtained by the crack gauge to calculate the average strain value, and in the second or subsequent evaluation of the fracture toughness at the bonded interface of the bonded body, steps A and B are not performed, and a limit load is determined using the average strain value for the crack propagation length obtained in steps A to C for the first time and a digital image correlation (DIC) method, and the fracture toughness value is calculated based on the limit load.

[0013] (4) The method for evaluating the fracture toughness value at the bonded interface of a bonded body according to (2) or (3), wherein the bonded body is made of a nonlinear material.

[0014] (5) A method for predicting the life of an injection-molded joined body by CAE using a fracture toughness value obtained by the method for evaluating the fracture toughness value at the joining interface of a joined body according to any one of (2) to (4) above.

[0015] (6) A step A of obtaining a plurality of fracture toughness values ​​corresponding to each bonded interface for each injection-molded joint molded in accordance with JIS K 7086 standard (double cantilever beam test piece) by the fracture toughness evaluation method for the bonded interface of the joint molded according to (2) or (3). A step B of predicting the life value of an injection-molded joint having the same shape as the injection-molded joint or the life value of an injection-molded joint having an arbitrary shape different from the injection-molded joint by CAE using any of the plurality of fracture toughness values ​​obtained in the step A; and and a step C of determining the state of the joining interface of the injection-molded joined body to be manufactured based on the life value predicted in the step B, A method for producing an injection-molded joint, which produces an injection-molded joint according to the state of the joint interface of the injection-molded joint determined in step C. [Effects of the Invention]

[0016] According to the present invention, it is possible to provide an evaluation system that can accurately and simply evaluate the fracture toughness value at the joint interface of a joint body, a fracture toughness evaluation method that can accurately and simply evaluate the fracture toughness value, a method for predicting the life of an injection-molded joint body, and a method for manufacturing an injection-molded joint body that can produce an injection-molded joint body having a desired life value. [Brief explanation of the drawings]

[0017] [Figure 1] 1 is a conceptual diagram showing the overall configuration of an evaluation system according to an embodiment of the present invention. [Figure 2] FIG. 10 is a side view showing a state in which a tensile load is applied to a joined body by a tensile tester. [Figure 3] FIG. 1A is a side view showing the state in which a crack gauge is attached to the joint of a joint body, and FIG. 1B is a side view showing the state in which a random pattern is further applied to the joint. [Figure 4] 1 is a graph showing the change in strain over time at the bonded portion of a bonded body, as output by a crack gauge. [Figure 5] 1 is a graph showing the change in resistance value of a crack gauge over time (solid line) and the relationship between tensile load and stroke change (opening displacement) (dashed line) in an evaluation using the evaluation method of this embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0018] <Evaluation system for evaluating fracture toughness at the bonded interface of bonded bodies> The evaluation system (hereinafter referred to as the "evaluation system") for evaluating the fracture toughness value at the bonded interface of a bonded body of this embodiment includes a tensile tester capable of applying a tensile load to a bonded body formed by bonding two articles in a direction in which the two articles move away from the bonded portion. For evaluation using the tensile tester, the system also includes a crack gauge having a random pattern applied to its surface for use in the digital image correlation (DIC) method (hereinafter also referred to as the "DIC method") and attached to the bonded portion of the bonded body. The system also includes a digital camera that photographs the random pattern applied to the crack gauge. The system also includes analysis software that analyzes the strain of the bonded portion photographed by the digital camera. The system also includes a computer that executes at least the analysis software. The computer is configured to enable electrical signals to be exchanged between the crack gauge and the digital camera. When evaluating the fracture toughness value at the bonded interface of the bonded body, the crack growth length at time X when a crack occurs in the bonded body, output by the crack gauge, is synchronized with the strain of the bonded body photographed by the digital camera at time X, and the behavior of the crack growth at the bonded body is evaluated using analysis software, and a threshold value for determining crack growth is calculated based on the strain at time X.

[0019] As described above, the DIC method can evaluate the crack propagation region, but accurate evaluation requires a threshold value for determining whether a crack has occurred, and conventionally, no method for calculating this threshold value has been known. In the evaluation system of this embodiment, the crack propagation length at time X when a crack occurs in a joint, as sensed by a crack gauge, is synchronized with the strain of the joint photographed by a digital camera at time X. In other words, by simultaneously detecting the crack tip position and time using a crack gauge and measuring strain using the DIC method, it becomes possible to evaluate the threshold value for determining whether a crack has occurred (opening direction fracture strain), thereby solving the above-mentioned problems. Furthermore, once a threshold for determining cracks is obtained by performing measurements using a crack gauge, the strain at each time point can be obtained from that threshold and images acquired using the DIC method. In other words, measurements using a crack gauge and measurements using the DIC method are performed only the first time, and thereafter measurements using only the DIC method are sufficient, making it possible to accurately evaluate fracture toughness values ​​without using expensive crack gauges. Furthermore, since the above-mentioned processing can be performed on a single computer, there is no need for cumbersome processing such as using multiple computers, and the fracture toughness value can be evaluated easily and accurately.

[0020] First, an example of an evaluation system according to the present embodiment will be described with reference to Fig. 1. The evaluation system 10 shown in Fig. 1 includes a tensile tester 12, a dynamic strain gauge 18, a data collection device 20, a computer 22, and a digital camera 24. The tensile tester 12, the dynamic strain gauge 18, the data collection device 20, and the digital camera 24 are each configured to be able to send and receive electrical signals directly or indirectly to and from the computer 22. In the evaluation system according to the present embodiment, photography software for the digital camera 24 is installed in the computer 22.

[0021] When a tensile test is performed on a joined body formed by joining two articles (joint pieces) using a tensile tester 12, a joined body 14 is placed inside the tensile tester 12 as shown in FIG. 2. More specifically, an engagement portion 26 is provided near one end of the first joining piece 14a of the joined body 14, which is made up of a first joining piece 14a and a second joining piece 14b, and a chuck 30a engages with the engagement portion 26. Similarly, an engagement portion 28 is provided near one end of the second joining piece 14b, and a chuck 30b engages with the engagement portion 28. Specific examples of the engagement portions 26 and 28 include hinges. The chucks 30a and 30b are linearly moved upward and downward, respectively, by a driving device (not shown). That is, a tensile load is applied to the joined body 14 in a direction away from the joint by the upward and downward movement of the chucks 30a and 30b.

[0022] In this embodiment, as shown in FIG. 3(a), a crack gauge 16 is attached to the joint of the bonded structure 14. The crack gauge 16 has a large number of grid circuits installed inside it, and as a crack occurs, multiple wiring grid lines are physically cut in sequence, causing a change in the resistance value of the gauge, making it possible to measure the progression length and propagation speed of the crack. In this embodiment, when a tensile load is applied to the bonded structure 14 and both bonded pieces move up and down, the grid lines are cut in sequence, causing a change in resistance value, making it possible to sense the progression length of the crack. In addition, the crack gauge 16 has, for example, 26 to 46 grid lines.

[0023] Figure 4 shows, as an example, a graph of the change in resistance over time for a crack gauge with 26 grid lines. As shown in the graph in Figure 4, the resistance of the crack gauge increases stepwise as the grid lines in the crack gauge break due to the opening of the joint. This increase in resistance (approximately 40 με) corresponds to the breakage of one grid line, meaning that the crack has grown 1 mm. In other words, by using a crack gauge, it is possible to pinpoint the tip position of the crack with high accuracy. Note that the graph in Figure 4 is merely an example, and the tendency for the resistance to increase will differ depending on the crack gauge.

[0024] In Figure 5, the solid line shows the change in the resistance of the crack gauge over time. The dashed line shows the relationship between the stroke change of the tensile tester and the tensile load during the tensile test, i.e., the load-displacement diagram. In the graph in Figure 4, the horizontal axis represents time, but because the stroke change of the tensile tester changes at a constant rate, it is possible to plot the load-displacement diagram and the change in the resistance of the crack gauge over time on the same axis. For example, when the stroke change of the tensile tester is 5 mm, the tensile load reaches its maximum, but at that point the resistance (voltage) of the crack gauge is zero. Therefore, no cracks have occurred at this point. As the crack then propagates through the joint, the grid lines of the crack gauge are broken, the resistance (voltage) increases, and energy is released, causing the load to decrease.

[0025] Furthermore, as shown in FIG. 3(b), a random pattern 32 for digital image correlation (DIC) is applied to the surface of the crack gauge 16. In FIG. 3(b), the random pattern 32 is applied even to areas where the crack gauge 16 is not attached. Then, a digital camera 24 photographs the random pattern 32, generating an image of the strain distribution occurring at the joint, which is then transmitted to the computer 22. Examples of the form of the random pattern include a geometric pattern in which numerous circles or rectangles are arranged, a random pattern, a regular or irregular grid pattern, and the like. Any form may be used as long as it can be recognized by a digital camera and is applicable to the DIC method.

[0026] In Figure 3, crack gauge 16 is attached to the joint of joined body 14 and a random pattern is applied to its surface, but crack gauge 16 to which random pattern 32 has been applied in advance may also be attached to the joint of the joined body. In other words, the order of attaching the crack gauge to the side of the joined body and applying the random pattern for the digital image correlation (DIC) method to the crack gauge surface is not important.

[0027] The dynamic strain gauge 18 has the function of amplifying and converting the change in resistance value (electrical signal) output from the crack gauge 16 and outputting it externally as a digital signal. In other words, it has the function of converting the input analog signal into a digital signal and outputting it.

[0028] The data acquisition device 20 converts the external output of the tensile tester 12 so that it can be input to the computer 22. The data acquisition device 20 preferably includes an A / D converter to convert the collected interference signals into digital data.

[0029] As described above, the digital camera 24 serves to photograph the random pattern 32 applied to the crack gauge 16. The photographed data (image of strain distribution) photographed by the digital camera 24 is transmitted to the computer 22. Then, the photographed data is converted into strain by analysis software in the computer 22.

[0030] The computer 22 may be, for example, a personal computer. Analysis software is installed on the computer 22, and the computer 22 executes the analysis software. If photography software for the digital camera 24 is installed on the computer 22, the computer 22 executes the photography software when taking a photograph. The analysis software corresponds to a program necessary for evaluating the fracture toughness value in this embodiment, such as converting photographed data taken by a digital camera into strain.

[0031] In the evaluation system of this embodiment, when evaluating the fracture toughness value at the bonded interface of a bonded body, the crack propagation length at time X when a crack occurs in the bonded portion, as output by the crack gauge, is synchronized with the strain of the bonded portion captured by the digital camera at time X. In other words, at the same time, the crack propagation length based on the crack gauge output and the strain distribution image of the bonded portion captured by the digital camera are linked and input into a computer. As a result, the crack tip position based on the crack gauge output and the strain distribution image captured by the digital camera are synchronized, and the crack tip position is identified from the strain distribution image captured by the digital camera. Furthermore, once a threshold value for determining cracks is obtained by measurement using the crack gauge, the strain at each time can be obtained from that threshold value and images captured by the DIC method.

[0032] The true value of the evaluation system of this embodiment can be demonstrated by using the evaluation system of this embodiment described above and executing the method for evaluating the fracture toughness value at the joint interface of the joined body of this embodiment described below.

[0033] <Method for evaluating fracture toughness at the bonded interface of bonded bodies> The method for evaluating the fracture toughness at the bonded interface of a bonded body of this embodiment (hereinafter referred to as the "evaluation method") is a method for evaluating the fracture toughness at the bonded interface of a bonded body formed by bonding two articles together, and includes the following steps A to C. Step A: Step A1, in which a crack gauge is attached to the side of the bonded structure to be evaluated, in which two articles are bonded, and step A2, in which a random pattern for the digital image correlation (DIC) method is applied to the surface of the crack gauge, are performed in any order. Step B: Using a tensile testing machine capable of applying a tensile load in a direction in which the two articles of the bonded structure move away from the bonded portion, a tensile load is applied to the bonded structure in a direction in which the two articles move away from the bonded portion, and the time X when a crack appears in the bonded portion and the length of the crack propagation at time X are obtained as output by the crack gauge. Step C: The joint is photographed using a digital camera that photographs the random pattern applied to the crack gauge, and the strain at time X and the crack propagation length at time X is obtained using the digital image correlation (DIC) method. Based on the strain, a threshold value for determining crack propagation is calculated.

[0034] The evaluation method of this embodiment is an evaluation method that can be applied to the evaluation system of this embodiment described above. That is, it is performed using each element shown in the evaluation system of this embodiment, such as a tensile tester, a crack gauge, a digital camera, and a computer. Each step will be described below.

[0035] [Step A] In Step A, Step A1 of attaching a crack gauge to the joint on the side of a joined body formed by joining two articles to be evaluated, and Step A2 of applying a random pattern for a digital image correlation (DIC) method to the surface of the crack gauge are performed in any order. That is, in Step A, there are two modes: Mode A, in which the crack gauge is first attached to the side of the joined body (Step A1), and then the random pattern is applied (Step A2), and Mode B, in which the random pattern is applied to the crack gauge in advance (Step A2), and then the crack gauge with the random pattern applied is attached (Step A1), and then the crack gauge is attached to the side of the joined body. In either embodiment, a crack gauge with a random pattern applied to its surface is attached to the joint on the side of the joined body. However, in embodiment B, if the random pattern is applied in advance (step A2), the gauge may become contaminated with adhesive or the random pattern may peel off during the process of adhering it to the side of the joined body (step A1), which may result in a decrease in accuracy. Therefore, embodiment A is preferred.

[0036] [Step B] In step B, a tensile testing machine capable of applying a tensile load to the two articles of the bonded structure in a direction that moves them away from the bond is used, and a tensile load is applied to the bonded structure in a direction that moves the two articles away from the bond, and the time X when a crack occurs in the bonded structure and the propagation length of the crack at time X, output by the crack gauge, are obtained. In other words, the propagation length of the crack at time X, the moment when a crack occurs in the bonded structure as sensed by the crack gauge, is obtained; as explained in the evaluation system of this embodiment, the moment when the grid lines of the crack gauge are cut is the moment when a crack occurs in the bonded structure, and this moment is taken as time X, and the propagation length of the crack at time X is obtained.

[0037] [Step C] In step C, the joint is photographed using a digital camera that photographs the random pattern applied to the crack gauge, and the strain at time X and the crack propagation length at time X is obtained using the digital image correlation (DIC) method, and a threshold for determining crack propagation is calculated based on the strain. That is, in step C, the crack at the joint is photographed using a digital camera that photographs the random pattern applied to the crack gauge, and the crack is converted into strain using the DIC method based on the crack. Then, at time X, the crack propagation length obtained in step B is linked to the strain obtained in step C, and a threshold for determining crack propagation is calculated based on the strain.

[0038] As described above, steps B and C are synchronized at time X, and the time X at the moment the grid lines of the crack gauge are cut and the length of the crack tip at time X, as well as the strain distribution image captured by the digital camera, can be obtained. Therefore, the threshold value for determining the crack is known, and the crack growth can then be evaluated using the DIC method. In other words, all of steps A to C only need to be performed the first time, and steps A and B do not necessarily need to be performed from the second time onwards.

[0039] The following describes the first evaluation of fracture toughness value and the second and subsequent evaluations of fracture toughness value using the results of the first evaluation of fracture toughness value. First, in the initial evaluation of the fracture toughness value at the bonded interface of the bonded body, steps A to C are all performed for the crack propagation length that can be measured by the crack gauge, and the average strain value is calculated. The crack propagation length that can be measured by the crack gauge corresponds to the number of grid lines. In other words, if there are 26 grid lines, steps A to C are performed for those 26 lines, and the average strain obtained is calculated. Next, in the evaluation of the fracture toughness value at the bonded interface of the bonded body from the second time onwards, steps A and B are not performed, and the fracture toughness value is calculated based on the average value of strain relative to the crack propagation length obtained in the first steps A to C, and the limit load and crack propagation behavior parameters calculated by the digital image correlation (DIC) method. Note that the crack propagation behavior parameters are the fracture toughness value G IC This corresponds to α1 in equation (1) for calculating

[0040] As described above, the evaluation of fracture toughness can be simplified by performing all of steps A to C only the first time, and not performing steps A and B from the second time onwards, and calculating the fracture toughness based on the average strain versus crack propagation length obtained in steps A to C the first time, and the limit load and crack propagation behavior parameters calculated using the digital image correlation (DIC) method. In addition, the use of expensive crack gauges makes it possible to accurately evaluate the fracture toughness even the first time.

[0041] <Method for predicting the life of injection-molded joints> The method for predicting the life of an injection-molded joint of this embodiment is a method for predicting the life of an injection-molded joint by CAE using the fracture toughness value obtained by the evaluation method of this embodiment described above. For example, a calculation model for structural analysis is created by CAE (computer-aided engineering), and the life can be predicted from the fracture toughness value obtained by the evaluation method of this embodiment, taking into account the propagation of cracks at the joint interface of the injection-molded joint.

[0042] <Method for manufacturing injection-molded joint> The method for producing an injection-molded joined body of this embodiment includes the following steps A to C. A step A is performed by the method for evaluating the fracture toughness at the bonded interface of the bonded body according to the present embodiment described above, for injection-molded joints having any bonded interface molded in accordance with JIS K 7086 standard (double cantilever beam test piece), to obtain a plurality of fracture toughness values ​​corresponding to each bonded interface for each injection-molded joint. Step B: using any of the plurality of fracture toughness values ​​obtained in Step A, predicting by CAE the life value of an injection-molded joint having the same shape as the injection-molded joint, or the life value of an injection-molded joint having an arbitrary shape different from the injection-molded joint. Process C: determining the state of the joining interface of the injection-molded joint to be manufactured based on the life value predicted in Process B Includes: Then, an injection-molded joint is produced in accordance with the state of the joint interface of the injection-molded joint determined in step C. Each step will be described below.

[0043] [Process A] First, in step A, a method for evaluating fracture toughness at a bonded interface of a bonded body according to the present embodiment is used to obtain multiple fracture toughness values ​​corresponding to each bonded interface for injection-molded joints molded in accordance with JIS K 7086 (double cantilever beam test specimen). In step A, the fracture toughness values ​​are obtained for injection-molded joints having a predetermined shape specified by the JIS standard and with a bonded interface of any desired type. In other words, the fracture toughness of an injection-molded joint having a desired bonded interface is evaluated using the method for evaluating fracture toughness at a bonded interface of a bonded body according to the present embodiment. The double cantilever beam test specimen in JIS K 7086 is intended for test specimens of carbon fiber reinforced composite materials, but in process A, it is intended for injection molded joints. That is, the injection molded joint in process A differs from the double cantilever beam test specimen in JIS K 7086 in that it is a carbon fiber reinforced composite material and an injection molded joint, but otherwise is the same. In step A, for each injection-molded joint having any given bonded interface, a plurality of fracture toughness values ​​corresponding to each bonded interface are obtained. For example, if there are two injection-molded joints, injection-molded joint A having bonded interface A and injection-molded joint B having bonded interface B, fracture toughness values ​​are obtained for each of injection-molded joint A and injection-molded joint B. That is, the fracture toughness value corresponding to bonded interface A and the fracture toughness value corresponding to bonded interface B are obtained. As described above, a plurality of fracture toughness values ​​for any bonded interface obtained in step A can be collected and compiled into a database. Then, a fracture toughness value for any bonded interface can be appropriately extracted from the database and used in step B. In this case, step A does not need to be performed every time. The fracture toughness evaluation method has already been explained above, so it will not be described here.

[0044] [Process B] Next, in step B, one of the multiple fracture toughness values ​​obtained in step A is used to predict (1) the life value of an injection-molded joint having the same shape as the injection-molded joint, or (2) the life value of an injection-molded joint having an arbitrary shape different from the injection-molded joint. In step B, the fracture toughness value calculated in step A can be used to predict the life value of an injection-molded joint of any shape. That is, the life value of an injection-molded joint is predicted by the method for predicting the life of an injection-molded joint of the present embodiment described above. In step (1) above, the injection-molded joint having the same shape as the injection-molded joint used to evaluate fracture toughness in step A may be the injection-molded joint itself whose fracture toughness was evaluated in step A, or it may be a newly prepared injection-molded joint having the same shape as the injection-molded joint. In both cases, the injection-molded joint is molded in accordance with JIS K 7086 (double cantilever beam test piece), and the life value is predicted using such an injection-molded joint. On the other hand, in the above (2), the injection-molded joint of any shape different from the injection-molded joint whose fracture toughness was evaluated in step A refers to an injection-molded joint of a different shape and / or size. That is, the life value is predicted for an injection-molded joint of a different shape and / or size from the injection-molded joint used for evaluation in step A. However, the injection-molded joint whose life value is predicted in step B and the injection-molded joint used for evaluation in step A must have the same configuration of the joint interface. The method for predicting the lifespan has already been explained above, so it will not be explained here.

[0045] [Process C] Furthermore, in step C, the state of the bonded interface of the injection-molded joint to be manufactured is determined based on the life value predicted in step B. For example, steps A and B are performed once or multiple times, and if the life value predicted in step B is a desired value, the state of the bonded interface of the injection-molded joint corresponding to that life value is determined. In this way, by determining the state of the bonded interface of the injection-molded joint that has achieved the desired life value (the injection-molded joint that has achieved the fracture toughness value in step A), an injection-molded joint whose bonded interface has the desired life value can be obtained.

[0046] Next, an injection-molded joint is produced according to the state of the joint interface of the injection-molded joint determined in step C. That is, an injection-molded joint can be produced in which the joint interface has a desired life value. [Example]

[0047] The present embodiment will be described in more detail below with reference to examples, but the present embodiment is not limited to the following examples.

[0048] [Example 1] As the first bonding piece, a plate-shaped resin piece (width: 20 mm, total length: 200 mm, thickness: 3 mm) made of PBT resin (glass fiber-reinforced DURANEX (registered trademark) 3300, manufactured by Polyplastics Co., Ltd.) was prepared.

[0049] Next, the crack propagation region of the first bonding piece was subjected to a surface treatment. The surface treatment involved forming a large number of grooves by irradiating with laser light. Specifically, the laser light was irradiated in a diagonal lattice pattern so that the groove width was approximately 100 μm and the spacing between adjacent grooves was 250 μm. The laser light used had an oscillation wavelength of 1.064 μm and a maximum rated output of 25 W (average), with an output of 80%, a frequency of 50 kHz, and a scanning speed of 2500 mm / s.

[0050] Furthermore, the second joining piece was formed by injection molding the same resin as that of the first joining piece over the entire first joining piece.

[0051] Next, a pair of hinges (engagement portions) were prepared to be joined to the outer surfaces of the first and second joining pieces, and the joining surfaces of the hinges were roughened by rubbing them with coarse sandpaper. An adhesive (Metal Lock, manufactured by Cemedine Co., Ltd.) was then applied to the areas of the first and second joining pieces where the hinges would be joined. The hinges were then placed on the adhesive-applied areas of the first and second joining pieces and joined.

[0052] In this manner, a test piece for evaluation was obtained.

[0053] Next, to conduct the DCB test described below, a crack gauge was attached to the side of the evaluation test piece with adhesive (CC-33A (an adhesive recommended by Kyowa Electric Industry)), and then a random pattern for the DIC test (black spots on a white background applied by spraying) was sprayed on top of it.The DCB test described below was then started, and when the crack propagation behavior was evaluated, it was confirmed that the crack gauge was cleaving as the evaluation test piece opened.

[0054] [DCB Test] The DCB test was carried out in accordance with JIS K 7086. The conditions for the DCB test are as follows: (conditions) Evaluation mode: Mode I fracture toughness evaluation (JIS K7087) Tensile testing machine: Shimadzu Corporation, Autograph AG-20KNX Test speed: (from start to crack growth of 20 mm): 0.5 mm / min (After that): 1.0 mm / min Digital camera: Point Grey Research, GRAS-50S5M Evaluation area: 70mm

[0055] In the DCB test, when a tensile load was applied, the progress of the crack that occurred at the bonded interface between the first and second bonded pieces was photographed with a digital camera, and the progress of the crack was determined by analyzing it using the digital image correlation (DIC) method. Then, the fracture toughness value (G IC ) was calculated.

[0056]

number

[0057] 10 Evaluation System 12 Tensile testing machine 14 Zygote 16 Crack Gauge 18 Dynamic strain gauge 20 Data Collection Equipment 22 Computer 24 Digital Camera 26 28 Engagement part

Claims

1. a tensile tester capable of applying a tensile load to a bonded structure formed by bonding two articles in a direction in which the two articles move away from the bonded portion; a crack gauge having a random pattern for a digital image correlation (DIC) method applied to a surface thereof and attached to a joint portion of the joined body when the evaluation is performed using the tensile tester; a digital camera that photographs the random pattern applied to the crack gauge; analysis software for analyzing the strain of the joint photographed by the digital camera; a computer that executes at least the analysis software; Equipped with the computer is configured to be able to transmit and receive electrical signals between the crack gauge and the digital camera; an evaluation system for evaluating the fracture toughness value at the bonded interface of a bonded body, the evaluation system synchronizing the propagation length of a crack at time X when a crack occurs in the bonded part, which is output by the crack gauge, with the strain of the bonded part photographed by the digital camera at time X; evaluating the propagation behavior of the crack at the bonded part of the bonded body using the analysis software; and calculating a threshold value for determining crack propagation based on the strain at time X.

2. A method for evaluating the fracture toughness value at a bonded interface of a bonded body formed by bonding two articles, comprising the steps of: Step A includes performing, in no particular order, Step A1 of attaching a crack gauge to a side surface of a bonded structure to be evaluated, in which two articles are bonded together, and Step A2 of applying a random pattern for a digital image correlation (DIC) method to the surface of the crack gauge; A step B of applying a tensile load to the bonded body in a direction in which the two articles move away from the bonded portion using a tensile testing machine capable of applying a tensile load to the two articles of the bonded body in a direction in which the two articles move away from the bonded portion, and acquiring the time X when a crack occurs in the bonded portion and the propagation length of the crack at the time X, which are output by the crack gauge; and Step C: taking an image of the joint using a digital camera that photographs the random pattern applied to the crack gauge, acquiring strain at the time X and the propagation length of the crack at the time X by a digital image correlation (DIC) method, and calculating a threshold value for determining the propagation of the crack based on the strain; A method for evaluating the fracture toughness value at the bonded interface of a bonded body, comprising:

3. 3. The method for evaluating fracture toughness at a bonded interface of a bonded body according to claim 2, wherein, in an initial evaluation of the fracture toughness at the bonded interface of the bonded body, all of steps A to C are performed for the crack growth length that can be obtained by the crack gauge to calculate an average value of strain, and in second or subsequent evaluations of the fracture toughness at the bonded interface of the bonded body, steps A and B are not performed, but a limit load is determined using the average value of strain for the crack growth length obtained in steps A to C for the initial evaluation and a digital image correlation (DIC) method, and the fracture toughness is calculated based on the limit load.

4. 4. The method for evaluating fracture toughness at a bonded interface of a bonded body according to claim 2, wherein the bonded body is made of a nonlinear material.

5. A method for predicting the life of an injection-molded joint by CAE using a fracture toughness value obtained by the method for evaluating fracture toughness at the joint interface of a joint according to claim 2 or 3.

6. A step A of obtaining a plurality of fracture toughness values ​​corresponding to each bonded interface for each injection-molded joint body, the fracture toughness values ​​being obtained for each injection-molded joint body having any bonded interface molded in accordance with JIS K 7086 standard (double cantilever beam test piece) by the method for evaluating fracture toughness at a bonded interface of a bonded body according to claim 2 or 3; A step B of predicting, by CAE, the life value of an injection-molded joint having the same shape as the injection-molded joint or the life value of an injection-molded joint having an arbitrary shape different from the injection-molded joint, using any of the plurality of fracture toughness values ​​obtained in the step A; and and a step C of determining the state of the joining interface of the injection-molded joined body to be manufactured based on the life value predicted in the step B, A method for producing an injection-molded joint, which comprises producing an injection-molded joint in accordance with the state of the joint interface of the injection-molded joint determined in step C.

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