JPH06323962A - Fatigue strength evaluation device - Google Patents

Abstract

PURPOSE:To reduce measurement work and save the time and labor used for designing structures by calculating with the use of analysis method such as finite element method about what part of mechanical structure impressed by repeated load a stress concentration is caused, measuring the strain data only at the particular part, and calculating the stress data. CONSTITUTION:Constituted of are a structure design means 1 using a CAD, a strength analysis means 2 for analyzing the structure strength by operation using the structure design data, gauge putting location selection means 3 for detemining an optimum gauge putting location on the structure based on the analysis result, an automatic gauge putting means 4 for putting gauges on the structure by using the location data, a strain waveform measuring means 5 for giving load on the structure put by gauges and measuring the strain waveform, a stress calculation means 6 for calculating stress waveform of the structure by using the obtained strain waveform data, and a fatigue strength evaluation means 7 for evaluating the fatigue strength of the structure by operation using time obtained stress data.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a fatigue strength evaluation apparatus by stress measurement using a strain gauge.

[0002]

2. Description of the Related Art Generally, when examining the fatigue strength of a mechanical structure to which a repeated load is applied, stress data is calculated from strain data obtained by attaching a strain gauge to the mechanical structure, and calculating the stress data and the mechanical structure. The fatigue limit is evaluated by comparing it with the fatigue limit of an object.

When a load is repeatedly applied to the mechanical structure, stress is distributed to each part of the mechanical structure. At this time, the only part that causes fatigue fracture is the part where stress concentration occurs and exceeds the fatigue limit, and the other parts are irrelevant. However, it is not possible to determine which portion the stress concentration is occurring unless a strain gauge is attached, strain data is measured, and then stress data is calculated.

Therefore, it is necessary to measure strain data and calculate stress data at a large number of measurement points, which requires a large amount of measurement work time and labor, which increases the time spent for designing a structure and labor costs. However, there is a problem that the manufacturing cost of the structure increases.

[0005]

SUMMARY OF THE INVENTION The present invention has been made in view of the problems of the prior art as described above, and a finite element is used to determine which part of a mechanical structure to which a repeated load is applied causes stress concentration. Calculate using the analysis method such as the method, measure strain data only for that part and calculate stress data to reduce the measurement work and try to reduce the time and labor spent on the structure design That is the purpose.

[0006]

SUMMARY OF THE INVENTION The present invention comprises a design means for a structure using CAD, and a strength analysis means for analyzing the strength of the structure by calculation using the structure design data of the design means, A gauge sticking place selecting means for obtaining an optimum sticking position of the gauge on the structure necessary for detecting the stress of the structure based on the analysis result by the analyzing means, and position data selected by the selecting means. A gauge automatic sticking means for sticking a gauge on the structure using the strain gauge, a strain waveform measuring means for measuring a strain waveform by applying a load to the structure to which the gauge is stuck, and strain waveform data obtained by the measuring means. A stress calculating means for calculating the stress waveform of the structure by using the above, and a fatigue strength for evaluating the fatigue strength of the structure by calculating using the stress data obtained by the calculating means. More the value means.

[0007]

In the above structure, it is estimated by stress analysis by the finite element method in which part of the mechanical structure where stress is repeatedly applied, where stress concentration occurs, and strain data is measured and stress data is measured only for that part. By calculating, it becomes possible to efficiently evaluate the fatigue strength of the mechanical structure without measuring the strain of the portion unrelated to the fatigue fracture.

[0008]

An embodiment of the fatigue strength evaluation device of the present invention will be described in detail below with reference to the drawings.

The bearing case of the fully-automatic washing machine is repeatedly loaded during the dehydration operation, and fatigue strength becomes a problem. In order to estimate the part of the bearing case where the stress is highest, it is necessary to perform strength analysis by the finite element method.

FIG. 1 is a block diagram showing the basic configuration of the apparatus of this embodiment. In the figure, 1 is CAD (Computer Aide)
d Design) means for designing a structure (a bearing case 8 of a fully automatic washing machine in the embodiment) using the device, and 2 uses the structure design data of the design means 1 to analyze the strength of the structure by calculation. Strength analysis means 3, 3 is a gauge sticking location selecting means for obtaining an optimum sticking position of a strain gauge as a sensor necessary for detecting the stress of the structure on the structure based on the analysis result by the strength analysis means, Reference numeral 4 is a gauge automatic sticking means for actually sticking a gauge onto the structure using the position data selected by the gauge sticking place selecting means 3, and 5 is a load applied to the structure to which the strain gauge is stuck. Strain waveform measuring means for measuring the strain waveform, 6 is a stress calculating means for calculating the stress waveform of the structure by using the strain waveform data obtained by the strain waveform measuring means 5, and 7 is the stress calculating It is a fatigue strength evaluation means for evaluating the fatigue strength of the structure by calculation using the stress data obtained by the means 6. The operation of the apparatus of this embodiment having the above configuration will be described with reference to the flowchart of FIG.
A structure (product) is designed using the device, and three-dimensional data for strength analysis is created based on the design data. FIG. 3 shows an example of the three-dimensional data created in step S1. Next, strength analysis is performed in step S2,
Estimate stress concentration points. Then, in step S3, the minimum necessary gauge attachment location is selected based on the result of step S2. In this embodiment, as shown in FIG.
We decided to attach the strain gauges 1 to G4 to the selected locations.

Here, the judgment as to whether or not the stress is concentrated is made based on whether or not a stress of X (X is an arbitrary preset value)% or more of the maximum stress value is generated as a standard. That is, if a stress of X% or more of the maximum stress value is generated, it is regarded as a stress concentration point. The ratio X% to the maximum stress value, which is the criterion for judgment, is arbitrarily determined depending on the product.

Next, in step S4, a strain gauge is actually attached to the location selected in step S3 using an automatic attachment machine (not shown). In the case of the present embodiment, the bearing case is generally made of a flat plate member, and the principal stress generated by the repeated load is not limited to a fixed direction, and a correct principal stress waveform cannot be obtained only by strain measurement in one direction.

Therefore, in order to treat the stress two-dimensionally and measure it as a plane stress, strain waveforms in three directions orthogonal to each other are calculated. That is, step S5 is performed according to the mounted strain gauge.
At, the strain data εa to εc (see FIG. 5) are actually measured.

Then, in step S6, the step S5 is executed.
The principal stress is calculated by the equation 1 using the data of εa to εc actually measured in (1).

[0015]

[Equation 1]

The strain waveform measured by the strain gauge in this way is captured as digital data by an FFT analyzer (not shown). Then, this distortion waveform data is transferred to an EWS (Engineering Work Station) (not shown),
The principal stress waveform is calculated by an automatic processing program that executes the calculation of the above mathematical expression 1. FIG. 6 is a plot diagram of the main stress waveform thus obtained. In the figure, σw is the stress amplitude,
σm is the average stress, and σmax is the maximum principal stress.

Next, the fatigue strength of the bearing case is evaluated by the design SN curve (see FIG. 7) in which the safety factor is taken into consideration in the SN curve of the material. That is, the equivalent stress amplitude σe considering the average stress σm in the stress amplitude σw in FIG. 6 is calculated by the modified Goodman equation 2.

[0018]

[Equation 2]

If the equivalent stress amplitude σe obtained by the equation 2 is equal to or less than the fatigue limit (the value at which the design SN curve of the bearing case in FIG. 7 is saturated), the result is that the bearing case is not destroyed by fatigue. Then, the fatigue strength evaluation of the bearing case is completed (step S7).

When it is evaluated in step S7 that the bearing case is broken due to fatigue, the process returns to step S1 to correct the design of the bearing case, and the evaluation algorithm of steps S2 to S7 is repeated again to finally The design change will be repeated many times until the result of not breaking due to fatigue strength is output.

[0021]

The present invention is constructed as described above, and the strength analysis by the finite element method is carried out in order to grasp the fatigue strength of which part of the mechanical structure is subjected to repeated load and the stress concentration. By estimating the point to be measured by, the strain data is measured only for that portion, and the main stress waveform is calculated and calculated from the strain waveforms in three directions in order to treat the stress as a planar stress. It is possible to efficiently evaluate the fatigue strength of mechanical structures without measuring strain in parts, and it is possible to significantly reduce the amount of measurement work, reducing the time, labor, and costs associated with designing structures. The effect that can be reduced can be expected.

[Brief description of drawings]

FIG. 1 is a functional block diagram showing a fatigue strength evaluation device of the present invention.

FIG. 2 is a flowchart showing a processing operation of each component of FIG.

FIG. 3 is a diagram showing three-dimensional data of a product designed by the product design means of FIG.

FIG. 4 is a diagram in which the gauge attachment locations selected by the gauge attachment location selection means in FIG. 1 are shown in black.

5 is a graph of 3 measured by the distortion waveform measuring means of FIG.
It is a figure which shows the distortion waveform of a direction.

6 is a diagram showing a stress waveform calculated by a stress waveform calculation means of FIG. 1 based on the strain waveform of FIG.

FIG. 7 is a diagram showing an S-N curve used for evaluating fatigue strength.

[Explanation of symbols]

 1 Product Design Means 2 Strength Analyzing Means 3 Gauge Adhesion Place Selection Means 4 Gauge Automatic Adhesion Means 5 Strain Waveform Measuring Means 6 Stress Calculating Means 7 Fatigue Strength Evaluating Means

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[Procedure amendment]

[Submission date] June 30, 1993

[Procedure Amendment 2]

[Document name to be amended] Statement

[Name of item to be corrected] 0002

[Correction method] Change

[Correction content]

[0002]

2. Description of the Related Art Generally, when examining the fatigue strength of a mechanical structure to which a repeated load is applied, stress data is calculated from strain data obtained by attaching a strain gauge to the mechanical structure, and calculating the stress data and the mechanical structure. Fatigue strength is evaluated by comparing the fatigue limit of an object.

[Procedure 3]

[Document name to be amended] Statement

[Correction target item name] 0010

[Correction method] Change

[Correction content]

FIG. 1 is a block diagram showing the basic configuration of the apparatus of this embodiment. In the figure, 1 is CAD (Computer Aide)
d Design) means for designing a structure (a bearing case 8 of a fully automatic washing machine in the embodiment) using the device, and 2 uses the structure design data of the design means 1 to analyze the strength of the structure by calculation. Strength analysis means 3, 3 is a gauge sticking location selecting means for obtaining an optimum sticking position of a strain gauge as a sensor necessary for detecting the stress of the structure on the structure based on the analysis result by the strength analysis means, Reference numeral 4 is a gauge automatic sticking means for actually sticking a gauge onto the structure using the position data selected by the gauge sticking place selecting means 3, and 5 is a load applied to the structure to which the strain gauge is stuck. Strain waveform measuring means for measuring the strain waveform, 6 is a stress waveform calculating means for calculating the stress waveform of the structure by using the strain waveform data obtained by the strain waveform measuring means 5, and 7 is the stress It is a fatigue strength evaluation means for evaluating the fatigue strength of the structure by calculation using the stress data obtained by the waveform calculation means 6. The operation of the apparatus of this embodiment having the above configuration will be described with reference to the flowchart of FIG. 2. First, in step S1, a structure (product) is designed using the CAD apparatus described above, and strength is determined based on the design data. Create 3D data for analysis. FIG. 3 shows an example of the three-dimensional data created in step S1. Next, in step S2, strength analysis is performed to estimate stress concentration points. And step S3
Then, the minimum necessary gauge attachment location is selected based on the result of step S2. In this embodiment, as shown in FIG. 4, G1 to G4 are selected as the selected locations and strain gauges are attached.

[Procedure amendment 4]

[Document name to be amended] Statement

[Correction target item name] Explanation of code

[Correction method] Change

[Correction content]

[Explanation of Codes] 1 Product Design Means 2 Strength Analysis Means 3 Gauge Adhesion Location Selection Means 4 Gauge Automatic Adhesion Means 5 Strain Waveform Measurement Means 6 Stress Waveform Calculation Means 7 Fatigue Strength Evaluation Means

Claims (1)

[Claims] 1. A structure design means using CAD, a strength analysis means for analyzing the strength of the structure by calculation using structure design data of the design means, and a result of analysis by the analysis means. And a gauge on the structure using a gauge sticking place selecting means for obtaining an optimum sticking position of the gauge on the structure necessary for detecting the stress of the structure, and the position data selected by the selecting means. A gauge automatic sticking means for sticking, a strain waveform measuring means for measuring a strain waveform by applying a load to the structure to which the gauge is stuck, and a stress of the structure using the strain waveform data obtained by the measuring means. A stress calculation means for calculating the waveform by calculation,
A fatigue strength evaluation device comprising a fatigue strength evaluation means for evaluating the fatigue strength of the structure by calculation using stress data obtained by the calculation means.