JPH11148875A - Residual stress analyzing apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To estimate a stress distribution in the area other than a measurement point by simulating a residual stress measurement experiment by notching in the finite element method, using a ratio of an actually measured value of the residual stress and an analyzed value as a correction coefficient, and multiplying a residual stress distribution according to the finite element method by the coefficient. SOLUTION: A plurality of nodes of the same coordinate axis are generated on a notched plane, and a finite element is formed in a partial structure. After a boundary condition is designated so that each node behaves in the same manner, an analysis with a load and a compulsory shift applied is carried out, and an internal force distribution when the analysis is completed is stored. The boundary condition of each node is released, and then an analysis is carried out wherein an internal force when the analysis is completed is applied as a load. A residual stress by the finite element method is calculated with the use of a change of a strain at this time at a free strain measurement position as a free elastic strain. A ratio of an actually measured residual stress and the calculated residual stress is obtained as a correction coefficient, and a stress distribution value in the partial structure is multiplied by the correction coefficient and stored in an analysis result data file. Accordingly, not only an average residual stress of the area of interest, but a local residual stress can be obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an analyzer for predicting a residual stress distribution in a structure.

[0002]

2. Description of the Related Art If a residual stress exceeds a specified value when a structure is completed, the structure cannot be used or a great deal of effort is required to remove the residual stress and deformation caused by the residual stress. In order to avoid this, the residual stress is measured by a test specimen or analyzed by a finite element method.

[0003] Methods for measuring residual stress can be broadly classified into mechanical measurement methods and physical measurement methods. The former is to divide a portion holding the residual stress, measure the deformation when the residual stress is released in the portion, and calculate the residual stress by using the elastic mechanics. The latter is an X-ray method or a magnetic method. These utilize the X-ray diffraction phenomenon of the crystal and the magnetic properties of the material, and in this case, there is no need to divide the material.

For measuring the residual stress of a plate or the like, a mechanical measuring method is often used. In this method, a cut is made in a portion where the residual stress is to be measured, the stress in that portion is completely released, and the residual stress is determined from the strain generated at that time. In this method, the measured residual stress is the average value of the cut area. Further, the size of the cut area cannot be reduced as much as possible because a strain gauge must be attached to the test piece in advance and the test piece must be fixed with a jig when making the cut. Therefore, the measured values of the residual stress are obtained at certain intervals.

The above-described method of measuring residual stress by the notch method is described in "Generation of Residual Stress and Countermeasures" (Shigeru Yoneya, 1979,
(Yokendo).

[0006]

In the actual measurement of the residual stress by the notch method, the measured residual stress value is the average value of the notch region, and it is not possible to evaluate the local residual stress in the notch region. Also, the measured values of the residual stress are not continuous but discrete at a certain interval.

An object of the present invention is to correct a measured value of an average residual stress in a cut area measured by a cut method into a local stress distribution, and to predict a residual stress distribution at a position other than a measurement point. It is to provide a device.

[0008]

In order to achieve the above object, the present invention simulates in detail a residual stress measurement experiment by a notch method by a finite element method, and obtains a measured value of a residual stress and an analysis value by a finite element method. The ratio is obtained as a correction coefficient, and the obtained value is multiplied by the residual stress distribution obtained by the finite element method to predict the local stress distribution and the residual stress distribution at positions other than the measurement point.

More specifically, the specimen is divided into several regions (referred to as "substructures"), and a partial structure having a cut surface at a boundary is stored in a storage device.
For each substructure, a node is generated inside the substructure.
At this time, a plurality of different nodes having the same coordinate value are generated on the boundary formed by the cut surfaces. Create a finite element in the substructure from the generated nodes. Boundary conditions are specified so that the nodes generated on the cut surface have the same behavior, an analysis is performed under load and forced displacement, and the internal force distribution at the end of the analysis is stored in the storage means.

Next, for a node on which a boundary condition is designated so as to take the same behavior on the cut surface, the designation is removed, and
An analysis is performed in which the internal force at the end of the analysis obtained earlier is applied as a load. The change in strain at the release strain measurement position at this time is stored in the storage device. The change in strain at the release strain measurement position obtained here is calculated as the release elastic strain and the residual stress by the finite element method.

That is, the measured value of the residual stress by the incision method and the whole structure are divided into a plurality of regions with the cut surface as a boundary, and an element division having two nodes having the same coordinates on the boundary is performed. Sometimes, these nodes take the same behavior, and after the end of the load, the following advantages are obtained by the analysis results corrected by the ratio of the analysis results simulating the same conditions as the cutting method by using the means to set them to behave independently. Can be pulled out.

It is possible to know not only the average residual stress distribution in the cut area but also the local residual stress distribution in the cut area. Since the values are corrected in consideration of the experimental results, good agreement with the experimental results can be obtained.

[0013]

Embodiments of the present invention will be described below. FIG. 1 is a configuration diagram of hardware according to the present embodiment. In FIG. 1, a display device 101, an input device 102, a CPU 103, a RAM 104, and a disk device 110 are provided via a common bus 100. CPU 103 is the disk device 11
0 is a central processing unit for executing the operation program 111 stored in the RAM 104 in the RAM 104. The disk device 110 also stores a structural shape data file 112 of a structure to be analyzed, an analysis input data file 113 created by executing the operation program 111, and an analysis result data file 114 at the same time.

FIG. 2 shows a test piece used for calculating a residual stress from a measurement result of elastic strain released by making a cut. In the figure, a hatched area 210 indicates a scheduled cutting position. Reference numeral 220 denotes a strain gauge for measuring the release strain.

The operation flow of this embodiment will be described with reference to the analysis example of the test piece shown in FIG. First, when the operation program 111 of the present apparatus is started, the processing of the STP 10 is performed in the main routine shown in FIG. 3, and the contents of the structural shape data file 112 are read. The structural shape data read from the structural shape data file 112 includes:
The dimensions of the structure, the position of the cut surface in the overall structure,
The position where the strain gauge is attached is recorded. Further, in the structural shape data file 112, as shown in FIG. 4, partial structure data 510 in the format of FIG. 5 regarding a partial structure divided so as to have a cut surface as a boundary is recorded.

Next, the processing shifts to the analysis input data setting routine of STP20 in FIG. 3, and the analysis input data setting routine STP20 shown in FIG. 6 is executed. First, STP2
In step 1, with reference to the data 510, nodes having different node numbers at the same position on the cutting plane are generated. Specifically, as shown in FIG. 7, a node having the same position as the node generated on the No. 1 plane of the partial structure is set to the N of the partial structure.
o. Duplicate on two sides. Similarly, a node having the same position as the node generated on the No. 3 plane of the partial structure is duplicated on the No. 4 plane of the partial structure. Hereinafter, the same processing is performed on data 510.
This is performed for all the boundary surfaces recorded in.

Next, the process proceeds to STP22, where nodes are generated in the partial structure, and a finite element composed of those nodes is generated in STP23. Next, the processing shifts to STP24, and the setting of the nodes for restricting the displacement and the nodes to which the load is applied is performed with reference to the structural shape data 112. Next, the process proceeds to STP25, in which boundary conditions for a plurality of different nodes existing on the cut surface are set. Specifically, among a plurality of different nodes having the same coordinates, only one node is given an independent degree of freedom, and the other nodes are set to have the same displacement as the node given the independent degree of freedom. Next, the data generated in STP 26 is recorded in the structure analysis input data file 113, and the process returns to the main routine.

Next, the processing shifts to STP30 in FIG. 3, and a structural analysis routine STP30 shown in FIG. 8 is executed. In the structural analysis routine, the analysis conditions recorded in the structural analysis input data file 113 in STP 31 are read. Next, in STP32, the load on the test piece recorded in the structural analysis input data file is set in the form of a load vector. Next, the rigidity matrix of the entire test piece is created in STP33, and the displacement of the node is calculated by solving the rigidity equation in STP34.

Next, the internal force is calculated in STP35, and STP3 is calculated.
The convergence is determined for the load vector set in 6.
If not converged, the process returns to STP32, and if converged, the process proceeds to STP37. In STP37, a determination regarding the end of the analysis step for the entire load history is made. If all the load steps have not been completed, the process returns to STP32, and if completed, the process proceeds to STP38. At STP38, the internal force vector is recorded in the internal force vector recording file, and the process returns to the main routine.

Next, the processing shifts to STP40 in FIG. 3, and a release strain calculation routine STP40 shown in FIG. 9 is executed. In this routine, the analysis conditions recorded in the analysis input data file 113 in STP41 are read. Next, the setting is made for a plurality of different nodes having the same coordinates, giving independent freedom to only one node, and canceling the setting that the other nodes take the same displacement as that, and canceling the setting The coordinates are set so as to have independent degrees of freedom if the node numbers are different. Next, the process proceeds to STP42, where a load vector is set. ST
In P38, the internal force vector recorded in the internal force vector recording file is read and set as the load vector.

Next, a rigidity matrix of the entire test piece is prepared in STP43, and the displacement of the node is calculated by solving a rigidity equation in STP44. Next, the internal force is calculated in STP45, and the convergence is determined for the load vector set in STP46. If not converged, the process returns to STP42, and if converged, the process proceeds to STP47. STP4
In step 7, the release strain at the position where the strain gauge is attached to the specimen is calculated. The residual stress at the position where the strain gauge is attached is calculated using the released strain, and the process returns to the main routine.

Next, the processing shifts to STP50 in FIG. 3, where data correction and interpolation are performed. In STP50, the ratio between the actually measured residual stress value and the residual stress value at the position where the strain gauge is attached by the analysis obtained in STP30 is calculated as a correction coefficient in the partial structure. Next, the coordinate of the integration point existing in the partial structure and the value obtained by multiplying the stress value at the integration point by the correction coefficient are recorded in the analysis result data file 114 as the residual stress value. Experimental data corrected by the finite element method is recorded in the analysis result data file.

[0023]

As described above. According to the present invention, the partial structure shape data stored in the storage means, the data in which the partial structure numbers correspond to the group numbers, the residual stress and residual deformation data calculated for each group, the residual stress and the residual stress for each group, The calculation of the entire structure is performed by the structural element reflecting the residual deformation data. The same structural element can be used for partial structures belonging to the same group. Therefore, the calculation time can be reduced as compared with the case where the entire structure is divided into elements and analyzed by the finite elements of dimensions used for the analysis of the partial structure. Further, when the structural elements used for calculating the entire structure are recorded in the database, it is not necessary to generate the structural elements again, so that the calculation time can be further reduced as compared with the above.

As described above, according to the present invention, a plurality of nodes having the same coordinates are generated on a cut plane, one node is assigned to each of the partial structures bounded by the cut plane, and further cuts are formed. Generates nodes in regions other than the plane, generates finite elements from these nodes, and gives independent degrees of freedom to only one node for different nodes having the same coordinates on the cut plane, and the others are dependent on it An analysis is performed to simulate a load under a condition in which a degree of freedom is set. An analysis simulating a residual stress measurement experiment by a notch method is performed by performing an analysis in which independent degrees of freedom are set for all nodes after an analysis simulating a load.

It is possible to know not only the average residual stress distribution in the cut area but also the local residual stress distribution in the cut area. Since the values are corrected in consideration of the experimental results, good agreement with the experimental results can be obtained.

[Brief description of the drawings]

FIG. 1 is a configuration diagram of hardware according to an embodiment of the present invention.

FIG. 2 is a diagram showing a structure of a test body according to one embodiment of the present invention.

FIG. 3 is a flowchart of a main routine in one embodiment of the present invention.

FIG. 4 is a diagram showing division by a partial structure in one embodiment of the present invention.

FIG. 5 is a table showing a relationship between a cut surface and a boundary surface of a partial structure in one embodiment of the present invention.

FIG. 6 is a flowchart of an analysis input data setting routine according to an embodiment of the present invention.

FIG. 7 is a diagram illustrating setting of a node on a boundary surface of a partial structure according to an embodiment of the present invention.

FIG. 8 is a flowchart of a structural analysis routine according to another embodiment of the present invention.

FIG. 9 is a flowchart of a release strain calculation routine according to another embodiment of the present invention.

[Explanation of symbols]

101: display device (CRT display), 102: input device (keyboard, mouse), 103: CPU, 10
4 RAM, 110 disk device, 210 cut surface, 220 strain gauge.

Claims (1)

[Claims] In a residual stress analysis apparatus for simulating a residual stress measurement by a notch method by a finite element method, a plurality of nodes having the same coordinates are generated on a cut surface to form a partial structure having the cut surface as a boundary. Setting means for allocating one node at a time, means for generating nodes in an area other than the cut plane, means for generating a finite element from the generated nodes, and different nodes having the same coordinates on the cut plane. Means to give independent degrees of freedom to only one node, means to set the degrees of freedom dependent on others, means to simulate load loading using the set data, and analysis to simulate load loading A residual stress analysis device simulating a residual stress measurement by a notch method for performing an analysis in which independent degrees of freedom are set for all nodes after the step (c).