JP2014215290A - Residual stress estimation method, strain estimation method, residual stress estimation system, strain estimation system, and program - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method which allows residual stress to be estimated with high accuracy without requiring large-scaled transfer of a device or a member even when processing strain is generated.SOLUTION: A residual stress estimation method includes: a relationship acquisition step S101 for acquiring a relationship between inherent strain and a physical amount related to residual strain for a residual stress estimation object; measurement steps S102 and S104 for measuring the physical amount related to the residual strain before and after processing the residual stress estimation object; an inherent strain estimation step S105 for determining an inherent strain estimation value for the residual stress estimation object and an estimation value of inherent strain generated by processing, on the basis of the relationship between the inherent strain and the physical amount related to the residual strain, and the physical amount related to the residual strain obtained by measurement; and a residual stress estimation step S106 for estimating residual stress for the residual stress estimation object on the basis of the inherent strain estimation value for the residual stress estimation object and the estimation value of the inherent strain caused by processing.

Description

  The present invention relates to a residual stress estimation method, a strain estimation method, a residual stress estimation system, a strain estimation system, and a program.

It is important to accurately estimate the residual stress generated in a structure or the like in order to accurately grasp the strength or life of the structure or the like. Several techniques have been proposed to estimate such residual stress.
For example, Non-Patent Document 1 discloses a cutting surface force method and an inherent strain method as methods for estimating the residual stress. In the cutting surface force method, a target object for residual stress measurement is cut, and the relaxation strain at the time of cutting is measured at a measurable position. Then, from the obtained relaxation strain, the cutting surface force (the force acting on the cutting surface in the state before cutting) is obtained. Furthermore, from the obtained cutting surface force, a relaxation strain or a relaxation stress at a point not measured is obtained. Such cutting is repeated until the strain and stress at each point are not relaxed, and the residual stress is estimated by taking the total relaxation amount.
In the inherent strain method, as in the case of the cutting surface force method, the target object for residual stress measurement is cut, and the relaxation strain at the time of cutting is measured at a measurable position. However, unlike the case of the cutting surface force method, in the inherent strain method, a relaxation strain and a relaxation stress at a point that is not directly measured without using a cutting surface force are obtained from the obtained relaxation strain, and a residual stress is estimated.

  Further, Non-Patent Document 2 discloses a surplus removal method as a method for estimating residual stress. In the surplus removal method, a surplus weld is removed from the target member for residual stress measurement, and a strain change at the time of surplus removal is measured in the vicinity of the weld line. Then, the most probable value of the inherent strain distribution is obtained from the obtained strain change using the least square method or the minimum norm method. Further, by performing the elastic finite element analysis using the most probable value of the obtained inherent strain distribution as the initial strain, the three-dimensional residual stress distribution generated in the member is obtained.

Yukio Ueda and 3 others, “Measurement Principle Based on Finite Element Method of Residual Stress and Reliability of Estimated Values”, The Shipbuilding Society of Japan, 1975, No. 138, p. 499-507 Katsuhiko Kumagai and two others, “Analysis-Assisted Nondestructive Evaluation of Welding Residual Stress by Removing Overfilling (Concept Proposal and Analytical Demonstration with Butt Welded Plate)”, Transactions of the Japan Society of Mechanical Engineers, A, 1999, Vol. 65 629, p. 133-140

In order to accurately estimate the residual stress using the methods described in Non-Patent Documents 1 and 2, when performing processing such as cutting of members and removal of surplus, a new plastic strain (working strain) is obtained. ) Must be processed so that it does not occur.
However, although machining can be performed with high accuracy, processing distortion occurs. On the other hand, in electropolishing, although processing distortion does not occur, it is difficult to perform processing with high accuracy, and since an electrolytic solution is used, it cannot be applied to a place where wetting is not allowed. Furthermore, in the electrolytic polishing, for example, a considerable time is required when cutting a thick plate member.

  In addition, a method has been proposed to determine the residual stress from the residual strain measured by the diffraction method instead of the release strain, but in order to improve the estimation accuracy of the residual stress, a high-energy sync that can measure the residual strain to the inside of the member. It is necessary to perform tron X-ray diffraction and neutron diffraction. For this reason, a large-scale apparatus is required, and there are only a limited number of cases where the method can be applied. For example, it is necessary to detach a member from an actual machine and transfer it to a facility capable of measuring residual strain.

  The present invention has been made in view of such circumstances, and the object thereof is to estimate the residual stress more accurately even when a large strain of apparatus or member is not required and a processing strain occurs. An object of the present invention is to provide a residual stress estimation method, a strain estimation method, a residual stress estimation system, a strain estimation system, and a program.

  The present invention has been made to solve the above-described problems, and the residual stress estimation method according to an aspect of the present invention is a relationship for acquiring the relationship between the inherent strain and the physical quantity related to the residual strain in the residual stress estimation object. An acquisition step, a measurement step for measuring a physical quantity related to the residual strain before processing the residual stress estimation object and a physical quantity related to the residual strain after processing, and the intrinsic strain obtained in the relation acquisition step. Based on the relationship with the physical quantity related to the residual strain and the physical quantity related to the residual strain obtained in the measurement step, the estimated value of the inherent strain in the object to be estimated for the residual stress and the inherent strain generated in the processing A natural strain estimation step for obtaining an estimated value of the residual stress estimation target obtained by the natural strain estimation step. Estimates of Zumi, and, based on the estimated value of the specific resulting strain in the processing, characterized by comprising: a residual stress estimation step of estimating the residual stresses in said residual stress estimation object.

  Further, the residual stress estimation method according to an aspect of the present invention is the above-described residual stress estimation method, and the relation acquisition step is set for each of a plurality of settings of the inherent strain in the residual stress estimation object. Obtain the elastic strain obtained by using the finite element method with the inherent strain as the initial strain, and obtain the relationship between the inherent strain and the residual strain based on the relationship between the set inherent strain and the obtained release strain. It is characterized by.

  Further, the strain estimation method according to one aspect of the present invention includes a relationship acquisition step of acquiring a relationship between the inherent strain in a strain estimation object and a physical quantity related to the residual strain, and residual strain before processing the strain estimation object. A measurement step for measuring a physical quantity related to the physical strain and a residual strain after processing, a relationship between the intrinsic strain obtained in the relation acquisition step and a physical quantity related to the residual strain, and a measurement step obtained An inherent strain estimation step for obtaining an estimated value of the inherent strain in the strain estimation object and an estimated value of the inherent strain generated in the processing based on a physical quantity related to the residual strain. .

  Further, the residual stress estimation system according to one aspect of the present invention includes a relationship acquisition unit that acquires a relationship between an inherent strain and a physical quantity related to residual strain in a residual stress estimation object, and before processing the residual stress estimation object. A measurement unit that measures a physical quantity related to residual strain and a physical quantity related to residual strain after processing; a relationship between the intrinsic strain acquired by the relation acquisition unit and a physical quantity related to residual strain; and the measurement unit measures An inherent strain estimator that obtains an estimated value of the inherent strain in the residual stress estimation object and an estimated value of the inherent strain generated by machining based on the physical quantity related to the residual strain, and acquisition of the inherent strain estimator The residual stress estimation based on the estimated value of the inherent strain in the residual stress estimation object and the estimated value of the inherent strain generated in the machining. Characterized by comprising the residual stress estimation unit for estimating a residual stress in the object, the.

  In addition, the strain estimation system according to one aspect of the present invention includes a relationship acquisition unit that acquires a relationship between an inherent strain in a strain estimation object and a physical quantity related to the residual strain, and residual strain before the strain estimation object is processed. The measurement unit that measures the physical quantity related to the physical strain and the residual strain after processing, the relationship between the intrinsic strain acquired by the relationship acquisition unit and the physical quantity related to the residual strain, and the residual strain measured by the measurement unit And an intrinsic strain estimating unit that obtains an estimated value of the inherent strain in the strain estimation object and an estimated value of the inherent strain generated in the processing based on the physical quantity.

  A program according to an aspect of the present invention includes a relationship acquisition step of acquiring a relationship between an intrinsic strain and a physical quantity related to a residual strain in a residual stress estimation object in a computer included in the residual stress estimation system; A measurement step for measuring a physical quantity related to a residual strain before processing an estimation target object and a physical quantity related to a residual strain after processing, and a physical quantity related to the intrinsic strain and the residual strain obtained in the relation acquisition step. Based on the relationship and the physical quantity related to the residual strain obtained in the measurement step, the inherent strain for obtaining the estimated value of the inherent strain in the residual stress estimation object and the estimated value of the inherent strain generated in the processing An estimation step and an intrinsic strain of the residual stress estimation object obtained in the intrinsic strain estimation step. Value, and, based on the estimated value of the specific resulting strain in the processing, a program for executing, and residual stress estimation step of estimating the residual stress in the residual stress estimation object.

  Further, a program according to an aspect of the present invention includes a relationship acquisition step of acquiring a relationship between a physical quantity related to an inherent strain and a residual strain in a strain estimation target object in a computer included in the strain estimation system, and the strain estimation target object. A measurement step for measuring a physical quantity related to the residual strain before processing and a physical quantity related to the residual strain after processing; a relationship between the intrinsic strain obtained in the relationship acquisition step and a physical quantity related to the residual strain; and Based on the physical quantity related to the residual strain obtained in the measurement step, an estimated value of the inherent strain in the strain estimation target object, and an inherent strain estimation step for obtaining an estimated value of the inherent strain generated in the processing, This is a program to be executed.

  According to the present invention, it is possible to estimate the residual stress with higher accuracy even when a large-scale device or member does not need to be transferred and a processing strain occurs.

It is a flowchart which shows the procedure of the process which performs the residual stress estimation method in one Embodiment of this invention. It is a schematic external view which shows the shape of the welding flat plate made into analysis object in this embodiment. It is a schematic external view which shows the shape of the member set to the model in this embodiment. It is explanatory drawing which shows the shape of the member before the surplus removal in this embodiment. It is explanatory drawing which shows the shape of the member after the surplus removal in this embodiment. It is a graph which shows the inherent distortion assumed to the model in this embodiment. It is a graph which shows the residual stress distribution obtained from the correct intrinsic strain. It is explanatory drawing which shows the position of the measurement point set to a member in this embodiment. It is a graph which shows the residual stress calculated | required without considering process distortion. It is a graph which shows the magnitude | size for the contribution of a process distortion among residual stresses. It is a graph which shows the magnitude | size of the release distortion accompanying the removal of surplus. It is a graph which shows the magnitude | size of the variation | change_quantity of the residual strain which a process distortion exerts. It is a graph which shows the value of the residual stress when processing distortion generate | occur | produces. It is a schematic block diagram which shows the function structure of the residual stress estimation system in this embodiment. It is a schematic block diagram which shows the function structure of the distortion estimation system in this embodiment.

Embodiments of the present invention will be described below with reference to the drawings.
In the following description, a matrix is expressed by enclosing it with “[” and “]”, and a vector or matrix for one row or one column is expressed with “{” and “}”.
FIG. 1 is a flowchart showing a processing procedure for performing a residual stress estimation method according to an embodiment of the present invention. The process shown in the figure may be performed by a person, or the residual stress estimation system described later may perform the process shown in the figure automatically or semi-automatically. Here, a case where a person (operator) performs the processing of the same figure using a computer or a strain measuring device will be described as an example.

In the process of FIG. 1, the worker first acquires the relationship between the inherent strain and the physical quantity related to the residual strain in the residual stress estimation object (the object for which the residual stress is estimated) (step S101). . Step S101 corresponds to an example of a relationship acquisition step.
The physical quantity related to the residual strain here is a physical quantity indicating a phenomenon related to the residual strain. Examples of physical quantities related to residual strain include, but are not limited to, residual strain, residual stress, or a combination thereof. The residual stress is a stress generated in the residual stress estimation object due to the residual strain, and corresponds to an example of a physical quantity related to the residual strain.
Hereinafter, a case where the relationship between the inherent strain and the residual strain is acquired in step S101 will be described as an example.

  More specifically, in step S101, the operator uses the set inherent strain as an initial strain for each of a plurality of settings of the inherent strain in the residual stress estimation object, and uses a finite element method (FEM). The elastic strain obtained using is obtained. Then, the operator acquires the relationship between the set inherent strain and the obtained elastic strain as the relationship between the inherent strain and the residual strain.

The relationship between the inherent strain and residual strain obtained in step S101 will be further described. First, the case where the influence of the processing strain is not considered will be described, and then the case where the influence of the processing strain is considered will be described.
In general, the elastic strain {ε _e } is expressed as in Equation (1) using an elastic response matrix [R _e ] and an inherent strain vector {ε _e ^* }.

The i-th column of this elastic response matrix [R _e ] has a unit inherent strain shown in Formula (2) in which the i-th component of the inherent strain vector {ε _e ^* } is 1 and all other components are 0. Can be determined based on

Here, “ ^T ” indicates transposition of a vector or a matrix.
Specifically, the unit inherent strain shown in Expression (2) is given to the finite element model as an initial strain, and an elastic strain vector based on the initial strain is obtained. By obtaining elastic strain vectors for various unit intrinsic strains, an elastic response matrix [R _e ] that is a relationship between the intrinsic strain and the elastic strain vector can be obtained.

From equation (1), the elastic strain {ε _eb } before processing the stress estimation object is obtained using the elastic response matrix [R _b ] before processing and the inherent strain vector {ε ^* _b } before processing. It can be shown as equation (3).

Also, from the equation (1), the elastic strain {ε _ea } after processing the stress estimation object is obtained by processing the elastic response matrix [R _a ] after processing and the inherent strain vector {ε ^* after processing ^. _a } and can be expressed as in equation (4).

  The processing performed here can be various processing that changes the material characteristics of the stress estimation object. For example, the geometric shape of the stress estimation object may be changed, for example, by cutting the stress estimation object or removing a bead when the stress estimation object is a welding member. . Alternatively, the Young's modulus may be changed by heating the stress estimation object.

Here, {ε ^* _b } = {ε ^* _a } = {ε ^* } under the condition that the inherent strain is unchanged before and after processing. Under such conditions, the release strain vector {Δε _e } generated during the processing is expressed as an equation (5) as an elastic strain difference {ε _ea } − {ε _eb } before and after the processing.

However, [R] (= [R _a ] − [R _b ]) is an elastic response matrix that relates the release strain and the intrinsic strain.
If the measurement error that occurs when measuring the release strain using a strain gauge is {Δε _err }, the measurement release strain vector {Δε _em } is expressed as in equation (6).

Here, the measured release strain vector is a vector indicating a measurement value of the release strain.
Using the least square method, the most probable value {ε _est ^* } of the estimated value of the inherent strain is expressed as shown in Equation (7).

However, [R] ⁺ is a Moore-Penrose generalized inverse matrix of the elastic response matrix [R], and is expressed as in Equation (8).

In the equation (7), the inherent strain is derived under the condition that the inherent strain is unchanged before and after the machining.
On the other hand, when a new inherent strain (hereinafter referred to as “processing strain”) {ε _p ^* } is generated during processing, Equation (4) becomes Equation (9).

Further, the measured release strain vector {Δε _em } is expressed as in Equation (10) by adding the influence [R _a ] {ε _p ^* } of processing strain to the right side of Equation (6).

For this reason, when the processing strain {ε _p ^* } is relatively large, using Equation (7) cannot lead to a correct solution in principle even if the release strain can be measured with high accuracy. Therefore, Equation (3) and Equation (4) are modified so that the processing strain {ε _p ^* } can be evaluated. First, the term of processing strain {ε _p ^* } is added to equation (3) to obtain equation (11).

Further, the term of processing strain {ε _p ^* } is added to the equation (4) to obtain the equation (12).

By evaluating the processing strain {ε _p ^* } separately from the processed inherent strain {ε ^* _a }, the initial intrinsic strain can be set to {ε _b ^* } = {ε ^* _a } = {ε ^* }. it can. Therefore, Expression (13) can be obtained by combining Expression (11) and Expression (12).

However, the elastic response matrix [R _ab ] is expressed as in Expression (14).

In step S101, the worker obtains this elastic response matrix [R _ab ]. Specifically, first, as described with reference to the equations (1) and (2), each of the elastic stress matrices [R _a ] and [R _b ] is converted into a finite element model with the unit inherent strain as an initial strain. The elastic response matrix [R _ab ] is obtained based on the equation (14).
Further, the operator obtains the Moore-Penrose generalized inverse matrix [R _ab ] ⁺ of the elastic response matrix [R _ab ] as described with reference to the equations (7) and (8).

If the surface is a target of residual stress estimation, residual strain can be measured nondestructively for each of before and after processing, for example, by X-ray diffraction. The estimated value {ε _est ^* ε _{p_est} ^* } of the initial inherent strain that existed before the processing and the inherent strain generated by the processing is the measured residual strain {ε _ebm ^* ε _{p_eam} ^* } ^T taking into account the measurement error. From this, it can be obtained based on equation (15).

By obtaining the estimated value {ε _{p_est} ^* } of the processing strain, the processing strain can be excluded from factors that adversely affect the estimation accuracy when the residual stress is estimated. Thereby, only the measurement error of the residual strain has an adverse effect on the estimation accuracy, and the residual stress can be estimated with high accuracy.

After step S101, the operator measures the residual strain {ε _ebm } before processing the residual stress estimation object (step S102).
The method for measuring the residual strain here may be any method that can measure the residual strain itself (not the amount of change in the residual strain) at a predetermined location of the residual stress measurement object. For example, the residual strain at the measurement position set on the surface of the residual stress measurement object may be measured by X-ray diffraction. Alternatively, when the residual stress measurement object is a magnetic material and the characteristics are known, the residual strain may be measured using a magnetostriction method.

  Note that the physical quantity measured in step S102 may be a physical quantity related to the residual strain, and is not limited to the residual strain. For example, both residual strain and residual stress can be calculated from the current value in the magnetostriction method. Therefore, the relationship between the inherent strain and the residual stress may be acquired in step S101, and the residual stress may be measured by calculating the residual stress from the current value in the magnetostriction method in step S102.

After step S102, the operator processes the residual stress estimation object (step S103).
Similarly to the above, the process performed in step S103 can be various processes that change the material characteristics of the stress estimation object. For example, the geometric shape of the stress estimation object may be changed, for example, by cutting the stress estimation object or removing a surplus when the stress estimation object is a welding member. Alternatively, the Young's modulus may be changed by heating the stress estimation object.

Then, the operator measures the remaining after processing the residual stress estimation object strain {epsilon _eam} (step S104).
As in the case of step S102, the method for measuring the residual strain in step S104 may be any method that can measure the residual strain itself at a predetermined location of the residual stress measurement object. A method by X-ray diffraction or a magnetostriction method may be used. Various methods such as a method to be used can be used.
Steps S102 and S104 correspond to an example of a measurement step.

After step S104, the operator uses the relationship between the inherent strain obtained in step S101 and the residual strain, and the residual strain obtained in step S102 or step S104. An estimated value of strain and an estimated value of machining strain are obtained (step S105). Step S105 corresponds to an example of an intrinsic strain estimation step.
More specifically, the operator uses the elastic response matrix [R _ab ] (or generalized inverse matrix [R _ab ] ⁺ ) derived in step S101 and the residual strain measurement value before processing obtained in step S102. {Ε _ebm } and the residual strain measurement value {ε _ea } after processing obtained in step S104 are applied to the equation (15) to estimate the intrinsic strain {ε _est ^* } in the residual stress estimation object. And an estimated value {ε _{p_est} ^* } of the processing strain.
The processing in step S105 corresponds to an inverse problem analysis for obtaining the inherent strain at an arbitrary position from the measured value of the residual strain at a predetermined position.

Then, based on the estimated value {ε _est ^* } of the inherent strain and the estimated value {ε _{p_est} ^* } of the processing strain obtained in step S105, the worker _calculates the residual stress in the residual stress estimation object. Estimate (step S106). Step S106 corresponds to an example of a residual stress estimation step.
Specifically, the operator gives the estimated value {ε _est ^* } of the inherent strain and the estimated value {ε _{p_est} ^* } of the processing strain to the finite element model as the initial strain, and the residual stress in the residual stress estimation object. Residual stress is estimated by performing forward problem analysis to calculate.
After step S106, the process of FIG.

  In the calculation in step S105, a plurality of physical quantities related to residual strain may be used. For example, both residual strain and residual stress may be calculated from X-ray diffraction or magnetostriction. As described above, by using a plurality of physical quantities related to the residual strain, it is expected that the number of data when performing inverse problem analysis is increased and the solution is stabilized.

  Next, an execution example of the residual stress estimation method by simulation will be described. The inventor of the present application has confirmed the effectiveness by executing the residual stress estimation method of the present invention by numerical simulation. In the simulation, the welded flat plate was simulated by a finite element model, and the residual stress was estimated for the case where the surplus was removed as processing.

Specifically, the simulation was performed according to the following procedure.
(1) A certain inherent strain distribution is set (assumed) as a correct answer for the model, and a correct residual stress distribution is calculated from the correct intrinsic strain distribution.
(2) The residual strain at the measurement position is obtained from the correct answer of the inherent strain, and the measurement error is added to simulate the measured value of the residual strain.
(3) From the residual strain measurement values obtained in (2), an estimated value of intrinsic strain is obtained by inverse problem analysis, and further, an estimated value of residual stress is obtained by forward problem analysis.

FIG. 2 is a schematic external view showing the shape of a welded flat plate to be analyzed. The welded flat plate shown in the figure is formed by welding two identically shaped stainless steels, and is a butt welded flat plate with no constraint on the periphery. There is a weld line in the x-axis direction shown in the figure, and the portion P11 is an extra portion. Assuming that this welded plate is line-symmetric with respect to the weld line, an analysis was performed using a half model (portion y ≧ 0).
In the following, the x-axis direction shown in the figure is the plate width direction of the stainless steel plate, the y-axis direction is the length direction, and the z-axis direction is the plate thickness direction.

FIG. 3 is a schematic outline view showing the shape of a member (stainless steel plate having a welded portion) set as a model (finite element model). As described above, the model of the member shown in FIG. 3 is a half model (portion y ≧ 0) of the welded plate shown in FIG. The left end of the member shown in FIG. 3 is a weld line, and an extra portion P11 is shown.
Further, the size of the member shown in FIG. 3 is a plate width (weld line length) of 60 millimeters (mm), a length of 240 millimeters, a plate thickness of 10 millimeters, and a surplus piece width of 8 millimeters. Is 0.3 mm in height. The Young's modulus of stainless steel was E = 2.0 × 10 ^ 5 (10 5) megapascal (MPa), and the Poisson's ratio was v = 0.265.
The total number of nodes of the model was 3349, and the total number of elements was 2544.

  FIG. 4 is an explanatory view showing the shape of the member before the removal of the surplus. In the state before the removal of surplus shown in the figure, the member set in the model has a surplus portion P11 as in FIG.

  FIG. 5 is an explanatory view showing the shape of the member after removing the excess. In the state after the removal of the surplus shown in the figure, the surplus portion (P11 in FIG. 4) of the member set in the model is lost. In addition, when removing the surplus, a processing strain is applied to the region A21.

FIG. 6 is a graph showing the inherent strain assumed in the model. The horizontal axis in the figure indicates the position in the length direction (y direction) of the member, and the vertical axis indicates the strain. Lines L11, L12, and L13 indicate the x-direction component, the y-direction component, and the z-direction component of the inherent strain, respectively. In this simulation, the inherent strain assumed for the welded flat plate in Non-Patent Document 2 is used.
Hereinafter, the inherent strain assumed in the model is referred to as “correct natural strain”.
In the following, when the residual stress distribution is shown, the residual stress distribution in the y direction is shown at the center (x = 30 mm) of the weld line on the bottom side (z = 0 mm) where the measurement position is not set.

FIG. 7 is a graph showing the residual stress distribution obtained from the correct intrinsic strain. The horizontal axis in the figure indicates the position in the length direction (y direction) of the member, and the vertical axis indicates the stress. Lines L21, L22, and L23 indicate the x-direction component, the y-direction component, and the z-direction component of the residual stress, respectively.
Specifically, the residual stress was calculated by giving the correct intrinsic strain as the initial strain to the finite element model shown in FIG.
Hereinafter, the residual stress obtained from the correct intrinsic strain is referred to as “correct residual stress”.

FIG. 8 is an explanatory diagram showing the positions of the measurement points set on the member.
As shown in the figure, in the plate width direction of the member, x = 3.75 millimeters, 11.25 millimeters, 18.75 millimeters,..., 56.25 millimeters and 8 rows at 7.5 millimeter intervals. Set the measurement point. In the length direction, three measurement points are set at intervals of 2 millimeters, such as y = 10 millimeters, 12 millimeters, and 14 millimeters. Thus, 8 × 3 = 24 measurement points are set on the surface of the member.

  Residual strains are calculated for each of these measurement points before and after removal of surplus by simulating the measurement of residual strain by X-ray diffraction. Specifically, the residual strain distribution at each measurement position is obtained from the correct intrinsic strain by the elastic calculation using the finite element method, the measurement error is added, and the measurement strain information (measurement value of the residual strain) is calculated. For the measurement error, a random value according to a normal distribution with an average of 0 and a standard deviation of 500 microstrain (μ strain) is used as the measurement error.

When obtaining the estimated value of the inherent strain from the measured value of the residual strain, the singular point analysis is used in the inverse problem analysis so that the inherent strain distribution of the entire member can be appropriately obtained from the measured value of the residual strain at a part of the member. A solution optimization method and a solution stabilization method using artificial noise were applied. Moreover, as will be described below, the unknowns were reduced by approximating the inherent strain as a function.
Then, the estimated accuracy was evaluated by comparing the obtained residual stress estimated value with the correct residual stress.

Here, reduction of unknowns by function approximation of intrinsic strain will be described.
When the three-direction components of the inherent strain are obtained for each node, the number of unknowns to be obtained is three times the total number of nodes. Then, the number of unknowns becomes enormous and it becomes difficult to obtain an appropriate solution.
Therefore, with respect to welding inherent strain (inherent strain generated by welding), as shown in Equation (16), the solution space of the inherent strain is appropriately limited by linear combination of logistic functions, and the unknowns are reduced.

Here, the subscript s indicates a plate width direction (weld line direction, x direction), a length direction (y direction), and a plate thickness direction (z direction). {A _si } is an unknown coefficient vector. In addition, p and q _i are set so that the four basic terms on the right side of the equation (16) are substantially equally spaced in the range of z ≦ 40 mm, considering that the existence region of the inherent strain is about 40 mm at most. It is a constant determined so as to be distributed. Specifically, the values of p and q _{1 to} q ₄ were set as in Expression (17).

Furthermore, assuming a thin welded plate, the inherent strain is assumed to be uniformly distributed in the thickness direction and constant in the weld line direction.
Thus, the number of unknowns becomes 12 by approximating the inherent strain with four logistic functions in each of the three directions of x, y, and z. Even if the inherent strain is constant in the thickness direction, the residual stress can be distributed in the thickness direction.

On the other hand, as shown in FIG. 5, the processing strain applied by the processing for removing the surplus is constant on the surface of the region A21 from which the surplus has been removed. Specifically, the intrinsic strain of the three-direction (x, y, z) component is applied to each of five points of y = 0, 2, 4, 6, 8 millimeters on the surface of the member (z = 10 millimeters). Thus, the number of unknown processing strains is 15.
By effectively deleting the number of unknowns, it is possible to reduce the load of performing the inverse problem analysis in step S105 and improve the accuracy of the analysis results.

  At the time of removal of the surplus, the estimation accuracy is evaluated on the assumption that the inherent strain of the x direction component of −500 microstrain is uniformly generated on the surface of the processed part after removal of the surplus (region A21 in FIG. 5). Comparison was made with the case where processing strain was not taken into consideration.

FIG. 9 is a graph showing the residual stress obtained without considering the processing strain. Here, as shown in the above equation (7), the inverse strain analysis is performed based on the amount of change in the residual strain before and after the machining to calculate the inherent strain, and the forward stress analysis is performed from the inherent strain to obtain the residual stress. .
The horizontal axis in FIG. 9 indicates the position in the length direction (y direction) of the member, and the vertical axis indicates the stress. A line L31 indicates the value of the correct residual stress. A line L32 indicates an estimated value of the residual stress when no processing strain occurs. A line L33 indicates an estimated value of the residual stress when a processing strain occurs. Note that, in the line L32, the residual stress is obtained in consideration of the measurement error of the residual strain. On the other hand, in the line L33, the residual stress is obtained without taking into account the measurement error of the residual strain (that is, assuming that there is no measurement error).

When processing distortion does not occur, relatively good estimation accuracy can be obtained even if there is a measurement error so that the difference between the line L32 and the line L31 is small.
On the other hand, when machining distortion occurs, it is difficult to obtain a highly accurate solution even if there is no measurement error so that the line L33 is greatly different from the line L31.

  FIG. 10 is a graph showing the magnitude of the contribution of processing strain in the residual stress. The horizontal axis in the figure indicates the position in the length direction (y direction) of the member, and the vertical axis indicates the stress. Lines L41, L42, and L43 indicate the magnitudes of contributions of machining strain among the x-direction component, the y-direction component, and the z-direction component of the residual stress, respectively.

The assumed processing strain value is relatively smaller than the welding inherent strain, and the amount that directly contributes to the residual stress is only about a few mechanical pascals as shown in FIG.
Further, the release strain associated with the removal of surplus is, for example, as shown in FIG. 11 at the center of the upper surface of the member (x = 30 millimeters, z = 10 millimeters).

FIG. 11 is a graph showing the magnitude of the release strain associated with the removal of surplus. The horizontal axis in the figure indicates the position in the length direction (y direction) of the member, and the vertical axis indicates the strain. Lines L51 and L52 indicate the magnitudes of the x-direction component and the y-direction component, respectively, of the release strain associated with the removal of surplus. As shown in FIG. 11, the release strain accompanying the removal of the excess is in the range of approximately ± 20 microstrain.
On the other hand, the amount of change in strain exerted by processing strain accompanying removal of surplus is, for example, as shown in FIG. 12 at the center of the upper surface of the member (x = 30 mm, z = 10 mm).

FIG. 12 is a graph showing the magnitude of the amount of change in residual strain exerted by processing strain. The horizontal axis in the figure indicates the position in the length direction (y direction) of the member, and the vertical axis indicates the strain. Lines L61 and L62 respectively indicate the magnitudes of the x-direction component and the y-direction component of the amount of change in residual strain exerted by the residual strain. As shown in FIG. 12, the amount of change in strain exerted by machining strain is a relatively large value. For this reason, if the residual stress is estimated without considering the influence of the processing strain, the estimation accuracy may be significantly reduced.
On the other hand, if the method of the present invention considering the processing strain is used, the estimation accuracy can be greatly improved.

  FIG. 13 is a graph showing the value of residual stress when machining strain occurs. In the figure, the horizontal axis indicates the position in the length direction (y direction) of the member, and the vertical axis indicates the residual stress. Line L71 indicates the value of the correct residual stress. Line L72 shows the residual stress estimate by the method of the present invention. Line L73 shows the residual stress estimated value by the method which does not consider a process distortion similarly to line L33 (FIG. 9). In line L72, the residual stress is obtained by taking into account the residual strain measurement error. On the other hand, in the line L73, the residual stress is obtained without taking into account the measurement error of the residual strain (that is, assuming that there is no measurement error).

  The line L73 is significantly different from the line L71, while the line L72 has a smaller difference from the line L71. In this way, in the method that does not consider the processing strain, the estimation accuracy of the residual stress is greatly lowered even when there is no measurement error. On the other hand, the reliability of the solution is greatly improved by using the method of the present invention. Can be improved.

  As described above, in the relationship acquisition step, the relationship between the inherent strain and the residual strain in the residual stress estimation object is acquired. In the measurement step, the residual strain before processing the residual stress estimation object and the residual strain after processing are measured. Based on the relationship between the inherent strain and residual strain obtained in the relationship acquisition step and the residual strain obtained in the measurement step, the inherent strain in the target object for estimating the residual stress is estimated in the inherent strain estimation step. The estimated value and the estimated value of the inherent strain generated by the machining are obtained. Further, in the residual stress estimation step, the residual stress estimation target is obtained based on the estimated value of the inherent strain in the residual stress estimation object obtained in the inherent strain estimation step and the estimated value of the inherent strain generated by machining. Estimate the residual stress in the object.

  Thereby, the residual stress can be obtained in consideration of the processing strain, and the residual stress can be obtained with high accuracy even when the processing strain occurs. Further, as a method for measuring the residual strain, a method that does not require a large-scale apparatus such as an X-ray diffraction method or a magnetostriction method can be used. As described above, the residual stress estimation method according to the present embodiment does not require a large-scale apparatus or member transfer, and can estimate the residual stress more accurately even when machining strain occurs.

In the relationship acquisition step, the elastic strain obtained using the finite element method is determined for each of the multiple settings of the inherent strain in the residual stress estimation object, using the set inherent strain as the initial strain, and the set inherent strain is determined. Based on the relationship between the strain and the obtained elastic strain, the relationship between the inherent strain and the residual strain is acquired.
Thus, the relationship between the inherent strain and the release strain can be obtained by solving the forward problem analysis for obtaining the elastic strain from the initial strain using the finite element method. In this respect, the relationship between the inherent strain and the release strain can be obtained relatively easily.

The present invention can also be implemented as a strain estimation method for estimating intrinsic strain and machining strain. Specifically, the processes in steps S101 to S105 may be performed in FIG. 1, and the process in step S106 may not be performed.
Alternatively, the present invention can be implemented as a residual strain estimation method for estimating residual strain. Specifically, in step S106 in FIG. 1, the residual strain in the residual stress estimation object may be measured instead of or in addition to the residual stress in the residual stress estimation object.
It is also possible to implement the present invention as a residual stress estimation system.

FIG. 14 is a schematic block diagram showing a functional configuration of the residual stress estimation system in the present embodiment. In the figure, a residual stress estimation system 100 includes a relationship acquisition unit 101, a measurement unit 102, an inherent strain estimation unit 103, a residual stress estimation unit 104, and a result output unit 105.
The residual stress estimation system 100 is configured by combining, for example, a computer and a residual strain measuring device, and estimates residual stress from measured values of residual strain before and after processing on a residual stress estimation object.

The relationship acquisition unit 101 acquires the relationship between the inherent strain and the residual strain in the residual stress estimation object. The relationship acquisition unit 101 performs the process of step S101 in FIG.
The measuring unit 102 measures the residual strain before processing the residual stress estimation object and the residual strain after processing. The measurement unit 102 performs the processes in step S102 and step S104 in FIG.
Note that the residual stress estimation system 100 may automatically perform processing on the residual stress estimation object, for example, by controlling a numerically controlled machine tool.

The inherent strain estimation unit 103 is based on the relationship between the inherent strain and the residual strain acquired by the relationship acquisition unit 101, and the residual strain measured by the measurement unit 102. Then, an estimated value of the inherent strain generated by machining is obtained. The inherent strain estimation unit 103 performs the process of step S105 in FIG.
The residual stress estimator 104 uses the estimated value of the inherent strain in the residual stress estimation object acquired by the inherent strain estimator 103 and the estimated value of the inherent strain generated in the processing, in the residual stress estimation object. Estimate the residual stress. The residual stress estimation unit 104 performs the process of step S106 in FIG.

  The result output unit 105 has a display screen such as a liquid crystal panel, for example, and displays the estimation result of the residual stress estimation unit 104. However, the method by which the result output unit 105 outputs the estimation result of the residual stress estimation unit 104 is not limited to display. For example, the result output unit 105 may transmit the estimation result of the residual stress estimation unit 104 to another device.

  With the above configuration, the residual stress estimation system 100 can determine the residual stress in consideration of the processing strain, and can accurately determine the residual stress even when the processing strain occurs. Further, as a method for measuring the residual strain, a method that does not require a large-scale apparatus such as an X-ray diffraction method or a magnetostriction method can be used. As described above, the residual stress estimation system 100 can estimate the residual stress more accurately even when a large strain of apparatus or member is not required and a processing strain occurs.

Further, the relationship acquisition unit 101 calculates and sets the elastic strain obtained by using the finite element method with the set inherent strain as the initial strain for each of a plurality of settings of the inherent strain in the residual stress estimation object. Based on the relationship between the inherent strain and the obtained elastic strain, the relationship between the inherent strain and the residual strain is acquired.
Thereby, the relationship acquisition unit 101 can acquire the relationship between the inherent strain and the release strain by solving the forward problem analysis for obtaining the elastic strain from the initial strain using the finite element method. In this respect, the relationship between the inherent strain and the release strain can be obtained relatively easily.

In addition, it is also possible to implement this invention as a distortion estimation system which estimates a natural distortion and a process distortion.
FIG. 15 is a schematic block diagram showing a functional configuration of the strain estimation system in the present embodiment. In the figure, the residual stress estimation system 100 includes a relationship acquisition unit 101, a measurement unit 102, an inherent strain estimation unit 103, and a result output unit 205. In the figure, portions having the same functions corresponding to the respective portions in FIG. 14 are denoted by the same reference numerals (101 to 103), and description thereof is omitted.

  The result output unit 205 has a display screen such as a liquid crystal panel, for example, and displays the estimation result of the inherent strain estimation unit 103. However, the method by which the result output unit 205 outputs the estimation result of the inherent strain estimation unit 103 is not limited to display. For example, the result output unit 205 may transmit the estimation result of the inherent strain estimation unit 103 to another device.

  Alternatively, the present invention can be implemented as a residual strain estimation system that estimates residual strain. For example, the residual strain estimation system may include the strain estimation system described with reference to FIG. 15 and estimate (calculate) the residual strain from the obtained inherent strain and processing strain.

A program for realizing all or part of functions of the residual stress estimation system 100 and the strain estimation system 200 is recorded on a computer-readable recording medium, and the program recorded on the recording medium is stored in the computer system. The processing of each unit may be performed by reading and executing. Here, the “computer system” includes an OS and hardware such as peripheral devices.
Further, the “computer system” includes a homepage providing environment (or display environment) if a WWW system is used.
The “computer-readable recording medium” refers to a storage device such as a flexible medium, a magneto-optical disk, a portable medium such as a ROM and a CD-ROM, and a hard disk incorporated in a computer system. Furthermore, the “computer-readable recording medium” dynamically holds a program for a short time like a communication line when transmitting a program via a network such as the Internet or a communication line such as a telephone line. In this case, a volatile memory in a computer system serving as a server or a client in that case, and a program that holds a program for a certain period of time are also included. The program may be a program for realizing a part of the functions described above, and may be a program capable of realizing the functions described above in combination with a program already recorded in a computer system.

  The embodiment of the present invention has been described in detail with reference to the drawings. However, the specific configuration is not limited to this embodiment, and includes design changes and the like without departing from the gist of the present invention.

DESCRIPTION OF SYMBOLS 100 Residual stress estimation system 101 Relation acquisition part 102 Measurement part 103 Intrinsic strain estimation part 104 Residual stress estimation part 105,205 Result output part 200 Strain estimation system

Claims (7)

In a residual stress estimation object, a relationship acquisition step for acquiring a relationship between the inherent strain and the physical quantity related to the residual strain;
A measuring step for measuring a physical quantity related to residual strain before processing the residual stress estimation object and a physical quantity related to residual strain after processing;
Based on the relationship between the inherent strain obtained in the relationship acquisition step and the physical quantity related to the residual strain, and the physical quantity related to the residual strain obtained in the measurement step, the inherent strain in the residual stress estimation object. And an intrinsic strain estimation step for obtaining an estimated value of the intrinsic strain generated by machining,
Based on the estimated value of the inherent strain in the residual stress estimation object obtained in the inherent strain estimation step and the estimated value of the inherent strain generated in the processing, the residual stress in the residual stress estimation object A residual stress estimation step for estimating
The residual stress estimation method characterized by comprising.   In the relation acquisition step, for each of a plurality of settings of the inherent strain in the residual stress estimation object, an elastic strain obtained by using the finite element method with the set inherent strain as an initial strain is obtained and set The residual stress estimation method according to claim 1, wherein the relationship between the inherent strain and the residual strain is acquired based on the relationship between the inherent strain and the obtained release strain. A relationship acquisition step for acquiring a relationship between the inherent strain in the strain estimation object and the physical quantity related to the residual strain;
A measurement step of measuring a physical quantity related to residual strain before processing the strain estimation object and a physical quantity related to residual strain after processing;
Based on the relationship between the inherent strain obtained in the relationship acquisition step and the physical quantity related to the residual strain, and the physical quantity related to the residual strain obtained in the measurement step, the inherent strain in the strain estimation object is calculated. An inherent strain estimation step for obtaining an estimated value and an estimated value of the inherent strain generated in the machining;
A strain estimation method comprising: In the residual stress estimation object, a relationship acquisition unit that acquires the relationship between the inherent strain and the physical quantity related to the residual strain,
A measuring unit for measuring a physical quantity related to residual strain before processing the residual stress estimation object and a physical quantity related to residual strain after processing;
Based on the relationship between the physical strain related to the inherent strain and the residual strain acquired by the relationship acquisition unit, and the physical quantity related to the residual strain measured by the measurement unit, the estimated value of the inherent strain in the residual stress estimation object, And an inherent strain estimator for obtaining an estimated value of the inherent strain generated by the machining,
The residual stress in the residual stress estimation object is estimated based on the estimated value of the inherent strain in the residual stress estimation object acquired by the intrinsic strain estimation unit and the estimated value of the inherent strain generated in the processing. A residual stress estimation unit,
A residual stress estimation system comprising: A relationship acquisition unit for acquiring the relationship between the inherent strain in the strain estimation object and the physical quantity related to the residual strain;
A measurement unit for measuring a physical quantity related to a residual strain before processing the strain estimation object and a physical quantity related to a residual strain after processing;
Based on the relationship between the inherent strain acquired by the relationship acquisition unit and the physical quantity related to the residual strain, and the physical quantity related to the residual strain measured by the measurement unit, the estimated value of the inherent strain in the strain estimation object, and An intrinsic strain estimator for obtaining an estimated value of the inherent strain caused by machining;
A strain estimation system comprising: In the computer equipped with the residual stress estimation system,
In a residual stress estimation object, a relationship acquisition step for acquiring a relationship between the inherent strain and the physical quantity related to the residual strain;
A measuring step for measuring a physical quantity related to residual strain before processing the residual stress estimation object and a physical quantity related to residual strain after processing;
Based on the relationship between the inherent strain obtained in the relationship acquisition step and the physical quantity related to the residual strain, and the physical quantity related to the residual strain obtained in the measurement step, the inherent strain in the residual stress estimation object. And an intrinsic strain estimation step for obtaining an estimated value of the intrinsic strain generated by machining,
Based on the estimated value of the inherent strain in the residual stress estimation object obtained in the inherent strain estimation step and the estimated value of the inherent strain generated in the processing, the residual stress in the residual stress estimation object A residual stress estimation step for estimating
A program for running In the computer equipped with the strain estimation system,
A relationship acquisition step for acquiring a relationship between the inherent strain in the strain estimation object and the physical quantity related to the residual strain;
A measurement step of measuring a physical quantity related to residual strain before processing the strain estimation object and a physical quantity related to residual strain after processing;
Based on the relationship between the inherent strain obtained in the relationship acquisition step and the physical quantity related to the residual strain, and the physical quantity related to the residual strain obtained in the measurement step, the inherent strain in the strain estimation object is calculated. An inherent strain estimation step for obtaining an estimated value and an estimated value of the inherent strain generated in the machining;
A program for running

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