Method for evaluating bond strength

Abstract

To provide a method for evaluating bond strength capable of accurately reproducing bond strength between joint members using the CZM model.SOLUTION: A method for evaluating bond strength between joint members 11 and 12 includes the steps of: setting a first CZM model setting a first damage starting point P1 and a second CZM model setting a second damage starting point P2 with a displacement larger than a displacement of the first damage starting point P1 of the first CZM model, according to stress-displacement line figure measuring the bond strength in a shear direction between the joint members 11 and 12; creating a combined CZM model by combining the first CZM model and the second CZM model in the stress-displacement line figure; and evaluating the bond strength between joint members 11 and 12 using the combined CZM model.SELECTED DRAWING: Figure 3

Description

Technical Field

[0001] The present invention relates to a method for evaluating joint strength.

Background Art

[0002] For example, for the evaluation of the sealing performance at the bonding part, stress and damage degree evaluation by the finite element method (FEM) are used. Patent Document 1 proposes a method for evaluating the bonding strength of a bonded body based on the allowable shear stress of the bonded body by a tensile test using a plurality of test bodies with different side restraint lengths and the shear stress of the bonded body by the finite element analysis method.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] However, when using the cohesive zone model (CZM model), in the relationship between stress and displacement, it is common to use a model having a simple triangular shape, and the slope up to the damage initiation point cannot be changed. For example, when conducting a test to measure the bonding strength between bonded members joined to each other, many of the test results show behavior such as plastic deformation at the interface before damage initiation, and many have a changing slope. Therefore, even when using the commonly used triangular CZM model, it is difficult to accurately reproduce the bonding strength between the bonded members.

[0005] In view of such points, the present invention is made, and an object thereof is to provide a method for evaluating joint strength that can accurately reproduce the joint strength between bonded members using the CZM model.

Means for Solving the Problems

[0006] In view of the above problems, the method for evaluating the bonding strength according to the present invention is a method for evaluating the bonding strength between bonded members using a CZM model. Based on the stress-displacement diagram obtained by measuring the bonding strength in the shear direction between the bonded members, a first CZM model with a first damage initiation point set and a second CZM model with a second damage initiation point set having a displacement amount larger than the displacement amount of the first damage initiation point of the first CZM model are set. In the stress-displacement diagram, a combined CZM model obtained by combining the first CZM model and the second CZM model is created, and the bonding strength between the bonded members is evaluated using the combined CZM model.

Advantages of the Invention

[0007] According to the present invention, the bonding strength between bonded members can be accurately reproduced using the combined CZM model.

Brief Description of the Drawings

[0008]

Figure 1

Figure 2

Figure 3

Embodiments for Carrying Out the Invention

[0009] Hereinafter, with reference to FIGS. 1 to 3, the method for evaluating the bonding strength between bonded members according to the present embodiment will be described.

[0010] In this embodiment, as shown in Fig. 3(a), for a joined body 10 in which two joining members 11 and 12 such as a base material and a sealing material are joined by an adhesive or the like, the joining strength in the shearing direction between the joining members 11 and 12 is evaluated. First, the joined body 10 is prepared, and in step S1 of Fig. 1, an interfacial strength measurement test is carried out. Specifically, as shown in Fig. 3(a), one joining member 11 is fixed, and a load is applied to the other joining member 12 so that a shearing stress acts on these interfaces. At this time, the stress acting on the interfaces between the joining members 11 and 12 and the displacement of the joining member 11 when this stress acts are measured.

[0011] Next, in step S2 of Fig. 1, a displacement-stress diagram is obtained from the interfacial strength measurement test. Specifically, as shown in Fig. 2(a), a waveform W1 can be obtained. Next, in step S3 of Fig. 1, the displacement amount a at the first damage initiation point P1 is obtained, and in step S4, the displacement amount b at the second damage initiation point P2 is obtained.

[0012] Specifically, on the waveform (displacement-stress curve) W1, tangents L1 and L2 having different slopes are set. The slope of the tangent L1 is larger than the slope of the tangent L2, and the shape of the waveform W1 is approximated by these two tangents L1 and L2. Here, the intersection point of the two tangents L1 and L2 is the first damage initiation point P1. The stress value of the tangent L2 at the displacement amount at which the joined state of the joining members 11 and 12 is released (the displacement amount when the stress of the waveform W1 rapidly decreases and becomes 0 MPa) is the second damage initiation point P2. Here, the total displacement amount of the joining member 11 at the second damage initiation point P2 is a + b mm, the displacement amount at the second damage initiation point P2 is the displacement amount of the joining member 11 from the first damage initiation point P1, and is b mm.

[0013] Next, in step S5 of Fig. 1, based on the stress-displacement diagram in which the joining strength in the shearing direction between the joining members 11 and 12 is measured, a first CZM model in which the first damage initiation point P1 is set and a second CZM model in which a second damage initiation point P2 having a displacement amount b larger than the displacement amount a of the damage initiation point of the first CZM model are set.

[0014] Specifically, a first CZM model showing the state of FIG. 3(a) is created. As shown in FIG. 3(c), the first CZM model is a triangular diagram with the slope of the tangent line L1 inclined from the origin and having the first damage start point P1 (displacement a mm, stress A MPa) as its vertex. Next, a second CZM model showing the state of FIG. 3(b) is created. As shown in FIG. 3(c), the second CZM model is a triangular diagram having a side inclined from the displacement amount (displacement b mm, stress B MPa) to the second damage start point P2 (displacement a + b mm, stress B MPa).

[0015] Next, proceed to step S6, and in the stress-displacement diagram, create a combined CZM model by combining the first CZM model and the second CZM model shown in FIG. 3(c). Specifically, the combined CZM model is obtained by adding the stresses at the same displacement amounts of the first CZM model and the second CZM model.

[0016] Finally, proceed to step S7, and using the combined CZM model, analyze the bonding strength between the bonding members 11 and 12 under the same conditions as the interface measurement test conditions in step S1. As a result, as shown in FIG. 2(b), a waveform (displacement-stress curve) W2 can be obtained. Finally, compare the waveform (displacement-stress curve) W1 obtained in the interface measurement test with the waveform W2 obtained from the analysis result to verify the accuracy of the analysis. To improve the accuracy of the analysis, the displacement amount a at the first damage start point P1 obtained in step S3 and the displacement amount b at the second damage start point P2 obtained in step S4 can be changed to different values to improve the accuracy of the analysis.

[0017] In this way, by defining the second CZM model newly emerging at the second damage start point P2 from the position of the first CZM model, it becomes possible to represent a stress-displacement curve having a second slope (tangent line L2) directed from the first damage start point P1 to the second damage start point P2. Using the CZM model, the bonding strength between the bonding members can be accurately reproduced.

[0018] As described above in detail, the embodiments of the present invention have been described in detail. However, the present invention is not limited to the above embodiments, and various design changes can be made without departing from the spirit of the present invention described in the claims.

[0019] In this embodiment, the model was such that the joining member 11 itself was displaced. However, for example, even if the joining position between the joining members 11 and 12 is displaced without displacing the joining members 11 and 12, the same result can of course be obtained.

Explanation of Reference Numerals

[0020] 11, 12: Joining members, P1: First damage start point, P2: Second damage start point

Claims

【Claim 1】 An evaluation method for evaluating the bonding strength between bonded members joined to each other using a CZM model, comprising: Based on a stress-displacement diagram obtained by measuring the bonding strength in the shear direction between the bonded members, a first CZM model in which a first damage initiation point is set and a second CZM model in which a second damage initiation point having a displacement amount larger than the displacement amount of the first damage initiation point of the first CZM model are set; In the stress-displacement diagram, a combined CZM model obtained by combining the first CZM model and the second CZM model is created; An evaluation method for bonding strength, characterized in that the bonding strength between the bonded members is evaluated using the combined CZM model.

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