JP2000357574A - Terminal strength estimation method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a terminal strength estimation method capable of accurately estimating a terminal strength with a small deviation from an actual measurement. SOLUTION: A database on work hardening by bending of a material constituting a terminal is prepared. The database on the work hardening comprises data showing mechanical properties when the work hardening occurs in the case of applying the bending similar to bending in actual terminal manufacturing to the terminal-constituting material. Data on a stress-strain characteristic of the terminal-constituting material are acquired by a normal tensile test. By adding the database on the work hardening to the stress-strain correlation acquired by the tensile test, a stress-strain characteristic model of the terminal- constituting material after the occurrence of the work hardening can be obtained. Based on the obtained stress-strain characteristic model, the strength of the terminal made of the material is analyzed by a finite element method.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a terminal for connecting an electric signal of an automobile or industrial equipment and electric / electronic equipment mounted thereon and an electric wire for supplying electric power from a power source, and particularly to a bending process The present invention relates to a terminal strength prediction method for predicting the strength of a terminal manufactured by the above method.

[0002]

2. Description of the Related Art Conventionally, in designing a terminal as described above, it has been necessary to sufficiently evaluate not only the electrical properties of the terminal material but also the mechanical properties. This is because if the strength of the terminal is low, sufficient contact pressure for obtaining a stable contact resistance cannot be obtained, but if the strength of the terminal material is too high, bending becomes difficult.

Therefore, it has been necessary to design and develop the terminal from both the selection of the material and the processing technique so that the strength of the manufactured terminal is increased to some extent while using a material excellent in workability. At this time, if the designed terminals are manufactured one by one and the mechanical characteristics such as strength are evaluated, a large cost and time are required for the terminal design.

For this reason, in the terminal design, generally, C
A method is used in which the strength of a terminal is predicted by structural analysis using AE (computer-aided engineering), the terminal is actually produced for a good prediction result, and the terminal strength is confirmed.

[0005]

When performing a structural analysis by a computer using CAE, it is necessary to input data relating to a material (for example, a copper alloy) constituting a terminal. Specifically, it is necessary to input data relating to the stress-strain characteristics of the material constituting the terminal. here,
Conventionally, a JIS No. 5 test piece of a material constituting a terminal is pulled by a tensile tester, and data on the stress-strain characteristics obtained thereby is used.

[0006] However, when CAE analysis is performed using data on stress-strain characteristics obtained by a tensile test, the result of the analysis may differ greatly from an actually measured value (a value measured by actually manufacturing a terminal). was there.

SUMMARY OF THE INVENTION The present invention has been made in view of the above problems, and has as its object to provide a terminal strength prediction method capable of accurately predicting a terminal strength with a small deviation from an actually measured value.

[0008]

According to a first aspect of the present invention, there is provided a method for estimating the strength of a terminal formed by bending, comprising the steps of: A work hardening information preparing step of preparing information on hardening; and a calculating step of calculating the strength of the terminal in consideration of the information on the work hardening.

According to a second aspect of the present invention, in the method for predicting strength of a terminal according to the first aspect of the present invention, the calculating step includes a step of obtaining stress-strain characteristic information on a material constituting the terminal by a tensile test. Taking into account the information about the work-hardening to the stress-strain characteristic information, obtaining a stress-strain characteristic model for the material after the work-hardening has occurred, and determining the strength of the terminal based on the stress-strain characteristic model. Analysis step for analyzing.

According to a third aspect of the present invention, in the terminal strength prediction method according to the second aspect of the present invention, the stress-strain characteristic model is obtained by expanding an elastic region in the stress-strain characteristic information.

In this specification, the term "strength of a terminal" is an index indicating a reaction force to a predetermined displacement when the terminal is given a predetermined displacement.

[0012]

Embodiments of the present invention will be described below in detail with reference to the drawings.

FIG. 1 is a flowchart showing the procedure of a method for estimating the strength of a terminal according to the present invention. First, a database of work hardening of a material constituting a terminal by bending is prepared (step S1). The work hardening database is constructed from data indicating the mechanical properties when the work hardening occurs when the terminal forming material is subjected to the same bending work as in the actual manufacturing of the terminal. The data indicating such mechanical properties can be obtained by various methods. In the present embodiment, data is obtained by a method as shown in FIG. 2 as an example.

FIG. 2 is a diagram showing an example of a method for acquiring data indicating mechanical properties of a terminal constituent material which has undergone work hardening due to bending. Terminal material 1
Is subjected to bending in advance, and work hardening is caused by the bending. This bending is for bending only a part of the plate material. It is desirable that the bending speed at the time of bending is approximately equal to the bending speed at which an actual terminal is formed. Then, one side of the straight portion (unbent portion) of the bent plate 1 is restrained and fixed by the restraining member 2, and the other side is restrained and pressed by the pressing member 3. Then, the plate 1 is deformed as shown by the arrow A2. At this time, since the linear portion of the plate 1 is restrained, the bent portion of the plate 1, that is, the portion where the work hardening occurs, is deformed.

As the data indicating the mechanical properties of the work-hardened material, the correlation between the displacement of the deformed plate 1 and the reaction force is obtained. The displacement of the plate 1 is determined by the pressing member 3
The moving distance or the deformation angle of the linear portion pressed by is measured by a micrometer or the like. Further, the reaction force is obtained by measuring the force that the pressing member 3 receives from the plate 1 using the force gauge 4. As described above, since the deformed portion is the bent portion of the plate material 1, the displacement of the plate material 1 is the displacement of the portion where the work hardening occurs as it is. Therefore, by performing such a measurement, a correlation between the displacement and the reaction force of the terminal constituent material having undergone work hardening is obtained.

[0016] Such measurement is performed for various materials.
In addition, various combinations of plate thickness and bending radius at the time of bending are performed, and data showing the mechanical properties of the terminal constituent materials that have undergone work hardening are accumulated to construct a database of work hardening due to bending. .

In the method shown in FIG. 2, the size of the plate 1 is considerably larger than the actual terminals, and the bending is simple bending. Therefore, the above measurement is relatively easy. The time and cost required to create a database on work hardening due to processing is significantly less than when actually manufacturing and evaluating terminals.
In addition, the method of acquiring data indicating the mechanical properties of the terminal constituent material in which the work hardening has occurred is not limited to the method shown in FIG. Anything should do.

Returning to FIG. 1, in addition to preparing a database of work hardening by bending, data on stress-strain characteristics of the material constituting the terminal is obtained by a tensile test (step S2). Here, the correlation (so-called stress-strain curve) between the stress and the strain of the terminal constituting material is obtained by a tensile test based on a standard such as JIS. The correlation between the stress and the strain obtained by the tensile test based on the standard is specific to the material, and if there is existing data, it may be used as it is.

Next, a stress-strain characteristic model for the terminal constituent material after the work hardening is created from a database of work hardening by bending for the terminal constituent material and a stress-strain correlation obtained by a tensile test. (Step S3). This model creation is performed by a computer incorporating a data conversion program converting data of stress-strain correlation obtained by a tensile test using a database of work hardening by bending. FIG. 3 is a diagram illustrating a stress-strain characteristic model of a terminal constituent material after work hardening has occurred. In the figure, the horizontal axis represents strain, and the vertical axis represents stress.

SS1 in FIG. 3 indicates the stress-strain curve of the terminal component material obtained by the tensile test, that is, the stress-strain correlation of the terminal component material that does not undergo work hardening due to bending. By adding a work hardening database to this stress-strain correlation, SS2 in the figure can be obtained.
It is possible to obtain a stress-strain characteristic model of the terminal constituent material after the work hardening as shown in FIG. Specifically, it corresponds to the terminal thickness, bending angle, and bending radius of the terminal to be produced in the correlation between the displacement and the reaction force for the terminal constituent material in which work hardening has occurred, which constitutes the content of the work hardening database. By correcting and converting the stress-strain curve SS1 based on the data, it is possible to obtain the stress-strain characteristic model SS2 for the terminal constituent material after the work hardening.

Next, based on the stress-strain characteristic model SS2 obtained as described above, the strength of the terminal made of the material is analyzed (step S4). This analysis is a so-called finite element analysis, and is executed by a computer incorporating a finite element method program.

FIG. 4 is a diagram showing an analysis result of the finite element analysis. This figure shows the correlation between the displacement of the terminal and the reaction force, with the horizontal axis representing the displacement and the vertical axis representing the reaction force. In FIG. 4, R1 indicated by a dotted line is obtained by measuring the displacement and the reaction force of the actually manufactured terminal. The other solid lines show the calculation results obtained by the analysis. Of these analysis results, R
2 shows the result of analysis based on the stress-strain curve SS1 in FIG. 3, that is, the stress-strain correlation of the terminal constituent material in which the work hardening due to bending has not occurred. R2, which is the analysis result, greatly deviates from R1, which is the measurement result of the actual terminal.

On the other hand, the analysis result R3 is a result of analysis based on the stress-strain characteristic model SS2 in FIG. As shown in FIG. 4, the analysis result R3 is equal to the analysis result R2.
Is closer to R1 which is the measurement result of the actual terminal.

As described above, by performing an analysis based on the stress-strain characteristic model SS2 obtained by adding the work-hardening database to the stress-strain correlation of the terminal constituting material obtained by the tensile test, Analysis results close to the measurement results for the actual terminals are obtained. In other words, it can be said that accurate prediction of the terminal strength with less deviation from the actual measurement value than before can be performed. The reason why an analysis result close to the actually measured value is obtained as described above will be described below.

The tensile test is a test for pulling a test piece at a relatively low strain rate specified by JIS standards, that is, a material test under static conditions. on the other hand,
In actual production of terminals, bending is performed at a relatively high strain rate. That is, the degree of processing (degree of processing) differs between the tensile test and the bending processing, and it is considered that the difference in the degree of processing affects the work hardening. The work hardening occurring in the actual bent portion of the terminal is caused by the relatively high-speed bending.

Therefore, the stress-strain correlation of the terminal material determined by the tensile test (stress-strain curve SS1)
Does not include the factor of the effect of work hardening caused by bending (the effect of the degree of work).
On the other hand, the stress-strain characteristic model SS2 obtained by adding the work-hardening database to the stress-strain correlation by the tensile test shows the effect of the work-hardening caused by the bending, that is, the effect of the tensile test and the bending. It can be said that this is a stress-strain curve of the terminal constituting material in consideration of the factor of the difference in the working degree.

Therefore, performing the analysis based on the stress-strain characteristic model SS2 means that the analysis is performed based on data taking into account the effect of work hardening caused by bending (the effect of the degree of work). An analysis result close to the measurement result of the actual terminal can be obtained.

In FIG. 3, the stress-strain curve SS1 of the terminal constituting material obtained by the tensile test and the stress-
When compared with the strain characteristic model SS2, the Young's modulus of both is almost the same, but the stress-strain characteristic model SS2
Can be regarded as an expansion of the elastic region in the stress-strain curve SS1. That is, it is considered that the effect of work hardening caused by bending is to enlarge the elastic region.

Therefore, assuming that the terminal constituting material is a perfect elastic body and performing the same analysis as above based on the stress-strain characteristic model SS3 in which the elastic region of the stress-strain curve SS1 is infinitely enlarged, FIG. The analysis result of R4 was obtained.
When the analysis result R4 is compared with the measurement result R1 of the actual terminal, the difference between the two is large in a region where the displacement is large, but they are almost the same in a region with a displacement of 0.8 mm or less. This means that the stress-strain curve SS
The effect of work hardening caused by bending can be considered by enlarging the elastic region in 1;
As a result, it is shown that it is possible to accurately predict the terminal strength with less deviation from the actually measured value than before.

[0030]

As described above, according to the first aspect of the present invention, since the strength of the terminal is calculated in consideration of the information on the work hardening of the material constituting the terminal, the work hardening is performed by bending. It is possible to accurately predict the strength of the terminal where the occurrence has occurred, and to reduce the deviation from the actually measured value.

According to the second aspect of the present invention, stress-strain characteristic information on the material constituting the terminal is obtained by a tensile test, and information on work-hardening is added to the stress-strain characteristic information to obtain work-hardening. Since the stress-strain characteristic model of the material after the occurrence of the stress is obtained and the strength of the terminal is analyzed based on the stress-strain characteristic model, it is necessary to perform the analysis based on the data considering the influence of work hardening. Therefore, it is possible to accurately predict the terminal strength with little deviation from the actually measured value.

According to the third aspect of the present invention, the stress-strain characteristic model is obtained by enlarging the elastic region in the stress-strain characteristic information. And the terminal strength can be accurately predicted.

[Brief description of the drawings]

FIG. 1 is a flowchart showing a procedure of a terminal strength prediction method according to the present invention.

FIG. 2 is a diagram illustrating an example of a technique for acquiring data indicating mechanical properties of a terminal constituent material in which work hardening has occurred.

FIG. 3 is a diagram illustrating a stress-strain characteristic model of a terminal constituent material after work hardening has occurred.

FIG. 4 is a diagram showing an analysis result of finite element analysis.

[Explanation of symbols]

 REFERENCE SIGNS LIST 1 plate material 2 restraining member 3 pressing member 4 force gauge SS1 stress-strain curve SS2, SS3 stress-strain characteristic model R1 measurement result R2, R3, R4 analysis result

Claims (3)

[Claims] 1. A method for predicting the strength of a terminal manufactured by bending, comprising: a work hardening information preparing step of preparing information on work hardening of a material forming the terminal; A calculating step of calculating the strength of the terminal by taking into account information on hardening. 2. The method for predicting the strength of a terminal according to claim 1, wherein the calculating step comprises: obtaining stress-strain characteristic information on a material constituting the terminal by a tensile test; A step of obtaining a stress-strain characteristic model of the material after work-hardening in consideration of information on hardening, and an analysis step of analyzing the strength of the terminal based on the stress-strain characteristic model. A method for predicting the strength of a terminal, characterized in that: 3. The terminal strength prediction method according to claim 2, wherein the stress-strain characteristic model is obtained by enlarging an elastic region in the stress-strain characteristic information.