JP2017187400A - Residual stress estimation method and residual stress estimation device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a residual stress estimation method and residual stress estimation device capable of setting an appropriate analysis range without being influenced by user's experience.SOLUTION: In the present residual stress estimation method, an index reflecting a strain in a crystal lattice in a structure having undergone plastic working is acquired by measuring the structure; a region in which a strain has occurred in the crystal lattice is identified on the basis of the acquired index; and the identified region is set as an analysis range for estimating the residual stress. A measured value related to the residual stress of the structure is acquired, and the distribution of inherent strain in the analysis range is estimated using the measured value so as to approximate the inherent strain of the structure in the set analysis range.SELECTED DRAWING: Figure 4

Description

  The present invention relates to a residual stress estimation method and a residual stress estimation apparatus for estimating a residual stress of a structure based on an intrinsic strain method.

  Residual stress generated in a structure may cause damage such as fatigue cracks, and it is important to grasp the value. As a method for estimating the residual stress of a structure, a method using an inherent strain method is known (for example, see Patent Documents 1 and 2).

  In the conventional method for estimating residual stress based on the inherent strain method, two types of cut pieces are cut out from a structure, the elastic strain or residual stress is measured for each cut piece, and the measured elastic strain or residual stress of the cut piece is measured. The measured value is applied to the inverse analysis processing based on the finite element method. A user inputs, as an analysis range, a range in which the inherent strain is assumed to be generated with respect to the analysis apparatus that executes the reverse analysis process. The analysis apparatus approximates the inherent strain distribution by the least square method using the distribution function defined in the analysis range, and calculates the residual stress of the structure from the obtained inherent strain distribution.

JP 2005-181172 A JP 2003-121273 A

  The estimation accuracy of residual stress is greatly affected by the set analysis range. Therefore, it is important to set the analysis range appropriately. However, conventionally, the user has set the analysis range by trial and error based on experience, and an appropriate analysis range is not always set.

  This invention is made | formed in view of such a situation, The main objective is to provide the residual-stress estimation method and residual-stress estimation apparatus which can solve the said subject.

  In order to solve the above-described problem, the residual stress estimation method according to one aspect of the present invention obtains an index reflecting the distortion of the crystal lattice in the structure by measuring the structure subjected to plastic working. Identifying a region where crystal lattice distortion has occurred based on the index, setting the identified region as an analysis range for estimating residual stress, and residual stress obtained from the structure Estimating the inherent strain distribution in the analysis range so as to approximate the inherent strain of the structure in the analysis range based on the measured value, and in the structure based on the estimated inherent strain distribution Estimating the residual stress.

  In this aspect, the index may be a mechanical property that changes depending on the presence or absence of crystal lattice distortion.

  In the above aspect, the mechanical properties are selected from the group consisting of hardness, Young's modulus, yield point, ultimate strength, breaking strength, breaking elongation, drawing, impact value, fatigue strength, and creep strength. It may be.

  In the above aspect, the index may be a measured value reflecting a distance between the crystal lattices obtained by irradiating the structure with synchrotron radiation or neutrons.

  In the above aspect, the index may be a half width obtained by an X-ray diffraction method or a neutron diffraction method.

  Further, the residual stress estimation device according to one aspect of the present invention includes an acquisition unit that acquires an index that reflects a distortion of a crystal lattice in the structure by measuring the structure subjected to plastic working, and the acquisition unit A setting means for specifying a region where crystal lattice distortion has occurred based on the index obtained by the step, and setting the specified region as an analysis range for estimating residual stress, and a residual stress of the structure An input unit that accepts an input of a measurement value, and a unique value in the analysis range using the measurement value received by the input unit so as to approximate the inherent strain of the structure in the analysis range set by the setting unit An estimation means for estimating the strain distribution, and a display for displaying a residual stress estimation result based on the intrinsic strain distribution estimated by the estimation means. And, equipped with a.

  According to the present invention, it is possible to set an appropriate analysis range without being influenced by the user's experience.

The block diagram which shows the structure of the residual stress estimation apparatus which concerns on embodiment. The figure which shows the structure of a crankshaft. The figure for demonstrating the plastic working with respect to a crankshaft. The flowchart which shows the procedure of the residual stress estimation which concerns on embodiment. The perspective view for demonstrating an example of the cutting piece extract | collected from a structure. The figure for demonstrating extraction of C piece. The figure for demonstrating the analysis range. The graph which shows an example of hardness distribution in the depth direction from the surface of a structure. The graph which shows the result of the tension test implemented with respect to the material of the structure which showed distribution of hardness in FIG. The graph which shows the result (estimated error of residual stress) of an evaluation test. The graph which shows the result (estimation result of the residual stress in a fillet circumferential direction) of an evaluation test. The graph which shows the result (estimation result of the residual stress in a pin peripheral direction) of an evaluation test. The graph which shows an example of distribution in the depth direction of the half value width obtained by X-ray diffraction method.

  Hereinafter, preferred embodiments of the present invention will be described with reference to the drawings.

(Embodiment 1)
The residual stress estimation device according to the present embodiment acquires an index reflecting the distortion of the crystal lattice in the structure, specifies the region where the distortion of the crystal lattice has occurred based on the acquired index, and the specified The region is set as an analysis range, and the residual stress of the structure is estimated based on the inherent strain method for this analysis range.

[Configuration of residual stress estimation device]
FIG. 1 is a block diagram showing a configuration of a residual stress estimation apparatus according to the present embodiment. The residual stress estimation device 1 is realized by a computer 10. As shown in FIG. 1, the computer 10 includes a main body 11, an input unit 12, and a display unit 13. The main body 11 includes a CPU 111, ROM 112, RAM 113, hard disk 115, reading device 114, input / output interface 116, and image output interface 117. The CPU 111, ROM 112, RAM 113, hard disk 115, reading device 114, input / output interface 116, The image output interface 117 is connected by a bus.

  The CPU 111 can execute a computer program loaded in the RAM 113. Then, when the CPU 111 executes a residual stress estimation program 110 that is a computer program for residual stress estimation, the computer 10 functions as the residual stress estimation device 1. The residual stress estimation program 110 is an inverse analysis processing program based on the finite element method, and enables estimation of the distribution state of the inherent strain in the structure.

  The ROM 112 is configured by a mask ROM, PROM, EPROM, EEPROM, or the like, and stores a computer program executed by the CPU 111, data used for the same, and the like.

  The RAM 113 is configured by SRAM, DRAM, or the like. The RAM 113 is used for reading the residual stress estimation program 110 recorded on the hard disk 115. Further, when the CPU 111 executes a computer program, it is used as a work area for the CPU 111.

  The hard disk 115 is installed with various computer programs to be executed by the CPU 111 such as an operating system and application programs, and data used for executing the computer programs. A residual stress estimation program 110 is also installed in the hard disk 115.

  The hard disk 115 is installed with an operating system such as Windows (registered trademark) manufactured and sold by Microsoft Corporation. In the following description, it is assumed that the residual stress estimation program 110 according to the present embodiment operates on the operating system.

  The reading device 114 is configured by a flexible disk drive, a CD-ROM drive, a DVD-ROM drive, or the like, and can read a computer program or data recorded on the portable recording medium 120. The portable recording medium 120 stores a residual stress estimation program 110 for causing the computer to function as a residual stress estimation device. The computer 10 reads out the residual stress estimation program 120 from the portable recording medium 120, and The stress estimation program 120 can be installed on the hard disk 115.

  The input / output interface 116 is, for example, a serial interface such as USB, IEEE1394, or RS-232C, a parallel interface such as SCSI, IDE, or IEEE1284, and an analog interface including a D / A converter, an A / D converter, and the like. It is configured. An input unit 12 including a keyboard and a mouse is connected to the input / output interface 116, and the user can input data to the computer 10 by using the input unit 12.

  The image output interface 117 is connected to the display unit 13 constituted by an LCD, a CRT, or the like, and outputs a video signal corresponding to the image data given from the CPU 111 to the display unit 13. The display unit 13 displays an image (screen) according to the input video signal.

[Principle of residual stress estimation based on intrinsic strain method]
(1) Calculation of residual stress using inherent strain When the inherent strain is ε ₀ , the residual stress σ is expressed by the following equation.
σ = D (ε−ε ₀ ) (1)
However, D is an elastic modulus matrix and ε is the total strain that satisfies the relationship of the following equation.

  Now, when the intrinsic strain is known, the residual stress is obtained as follows.

From the equations (2) and (3), the following equation is given.

  When u is obtained by solving equation (4), residual stress is obtained from equations (3) and (1).

(2) Calculation of inherent strain using measured residual stress N measured residual stresses are represented as σ _m . Correspondingly, N calculated residual stresses obtained from the inherent strain are represented by σ _c , and a residual R with respect to the measured residual stress is defined by the following equation.

In addition, the inherent strain at an arbitrary point is expressed by the following linear function with M distribution function parameters a.
Here, M is a function of coordinates, and may be nonlinear with respect to the coordinates.

If the intrinsic strain is determined by the equation (8), the measured residual stress is obtained by the method (1), and as a result, the following linear relational expression is obtained.

  Substituting equation (9) into equation (7) and determining a so that R is minimized, the inherent strain distribution is determined so that the error between the measured residual stress and the calculated residual stress at the measurement point is minimized. The

[Operation of residual stress estimation device]
Hereinafter, the operation of the residual stress estimation apparatus 1 according to the present embodiment will be described.

  The residual stress estimation device 1 executes a residual stress estimation process as described below to estimate the residual stress of the structure.

  Here, a crankshaft will be described as an example of a structure. FIG. 2 is a diagram showing the configuration of the crankshaft. The crankshaft 200 is configured by connecting a journal shaft 201 and a pin shaft 203 by a crank arm 202. A large stress is likely to be generated at the time of use at the connection point between the journal shaft 201 and the crank arm 202 and at the connection point between the pin shaft 203 and the crank arm 202. If tensile residual stress is generated inside these connection portions, it may cause damage such as fatigue cracks. In order to improve the fatigue life, plastic processing such as roll processing or shot peening is applied to the above-mentioned connection locations, and compressive residual stress is introduced.

  FIG. 3 is a view for explaining plastic working on the crankshaft. FIG. 3 shows the case of roll processing. In the roll processing, the shaft 201 is rotated in a state where the roll 300 is pressed against the connection portion between the journal shaft 201 (or the pin shaft 203) and the crank arm 202. As a result, fillets 204 are formed at the connection locations, and compressive residual stress is applied so as to be distributed in the circumferential direction of the shaft 201.

  Residual stress is estimated using the residual stress estimation apparatus 1 for the structure subjected to plastic working as described above. FIG. 4 is a flowchart showing a procedure of residual stress estimation according to the present embodiment.

  The user cuts the structure, collects a cut piece, and measures the residual stress from the cut piece (step S1). In general, a structure is thinly cut in one direction to obtain a cut piece (T piece), and thinly cut in a direction orthogonal to the one direction to obtain a cut piece (L piece).

  Here, the residual stress is a value obtained by multiplying the elastic strain by the Young's modulus, and measuring the elastic strain is equivalent to measuring the residual stress. Therefore, either elastic strain or residual stress may be measured from the cut piece. In the present embodiment, a case where residual stress is measured will be described.

  FIG. 5 is a perspective view for explaining an example of a cut piece collected from the structure. As shown in FIG. 5, in the case of an axisymmetric structure such as a journal shaft or pin shaft to which compressive residual stress is uniformly applied in the circumferential direction, the T piece is obtained by cutting in the radial direction. If the inherent strain is uniformly distributed in the circumferential direction, the inherent strain does not change no matter which part of the circumferential direction the T piece is obtained. Therefore, only one T piece may be collected. Thereby, since the number of sampling of T piece can be decreased, the work burden of cutting processing and residual stress measurement of a cut piece can be reduced.

  On the other hand, in the axial length direction, the inherent strain distribution is complicated. Therefore, it is necessary to collect L pieces at a plurality of locations in the axial direction.

  When the crankshaft has a curved surface such as a fillet portion, a conical cut piece (hereinafter referred to as “C piece”) cut in the normal direction of the curved surface may be collected instead of the L piece. . Alternatively, only the T piece may be collected without collecting the L piece and the C piece. FIG. 6 is a diagram for explaining the collection of the C piece. In FIG. 6, each figure is a cross-sectional view when the journal shaft is cut in the longitudinal direction of the rotation axis. The C piece 500 is obtained by cutting the structure in the normal direction of the curved surface of the fillet, that is, in the radial direction of the arcuate fillet in the cross section. Since the journal axis has an axisymmetric shape, the cut surface 501 of the C piece 500 extends conically around the rotation center axis of the journal axis. Such C pieces are collected by changing the center angle of the fillet (for example, every 10 ° from 20 ° to 110 °).

  Moreover, when compressive residual stress is uniformly given to the longitudinal direction with respect to the rod-shaped structure long in one direction, only one T piece can be extract | collected at one place of a longitudinal direction.

  The user directly measures the residual stress by X-rays or the like on the cut piece collected as described above. When measuring the elastic strain, the user attaches a strain gauge to the cut piece, further cuts it into a plurality of small pieces, and measures the release strain (elastic strain) of each small piece. In measurement of residual stress or release strain (elastic strain), a plurality of different components are measured.

  Refer to FIG. 4 again. The user inputs a residual stress measurement value to the residual stress estimation apparatus 1. The CPU 111 of the residual stress estimation device 1 receives the measurement value input from the input unit 12 (step S2). The measured values input in this way are used for estimation of residual stress by optimizing the parameters of the distribution function described later.

  Next, the user measures the cut piece and acquires an index reflecting the distortion of the crystal lattice in the structure (step S3). When plastic working is applied to the structure, inelastic strain such as plastic strain and transformation strain is generated in the plastic processed portion. This inelastic strain is microscopically the strain of a crystal lattice (hereinafter referred to as “lattice strain”), among which plastic strain is caused by lattice strain due to lattice defects such as dislocations, and transformation strain is diffusion type. Regardless of the transformation and non-diffusion transformation, it is caused by lattice strain due to the change in crystal structure. Inherent strain occurs due to such inelastic strain, and residual stress is generated inside the structure.

  There is a mechanical property that changes when the above lattice strain occurs. For example, it is known that work hardening or work softening occurs in a metal material. This means that the hardness of the material changes depending on the presence or absence of lattice strain. Therefore, hardness is one of the mechanical properties that changes depending on the presence or absence of lattice strain. Further, it is known that mechanical properties such as ultimate strength, fatigue strength, creep strength, and impact value have a good correlation with hardness. Therefore, these mechanical properties correlated with the hardness also change depending on the presence or absence of lattice strain, and can be used as the above-mentioned index. Such mechanical properties are measured by Young's modulus, yield point, ultimate strength, breaking strength, breaking elongation, and drawing, hardness measured by a hardness test, impact test, as measured by a static tensile / compression test. Impact value, fatigue strength by fatigue test, and creep strength by creep test.

  In the present embodiment, a configuration using Vickers hardness as an index reflecting lattice strain will be described. A user measures the Vickers hardness in each part of the cut piece which cut | disconnected the structure by the Vickers hardness test.

  Next, the user inputs the obtained measurement value to the residual stress estimation apparatus 1 as an index reflecting the distortion of the crystal lattice in the structure. CPU111 receives the parameter | index input from the input part 12 (step S4). The input measurement value (index) is used for setting an analysis range that is a range for estimating the residual stress in the structure.

Here, the analysis range and hardness measurement in the crankshaft will be described. FIG. 7 is a diagram for explaining the analysis range. FIG. 7 shows a cross section along the central axis of the journal shaft 201. When a cold roll process is performed on a connection portion between the journal shaft 201 and the crank arm 202, the roll 300 is inclined at a predetermined angle (hereinafter referred to as a “fillet angle”) with respect to the central axis of the journal shaft 201. Press against the connection (see Figure 3). For this reason, a crankshaft is compressed in the range extended in the fan shape centering on the pressing direction of the roll 300, and plastic distortion arises. The residual stress can be accurately estimated by setting an analysis range that approximates the range in which such plastic strain occurs. As shown in FIG. 7, the analysis range can be defined by angles α ₀ and Δα and a depth Δr in a cross section along the central axis of the journal shaft 201. Further, since it can be estimated that plastic deformation occurs uniformly in the circumferential direction around the rotation axis, setting the analysis range in one cross section can omit setting the analysis range in the other cross section.

  In order to obtain data necessary for setting such an analysis range, the user measures the hardness at a plurality of locations of a cut piece (T piece) cut along the cross section of the structure. The measurement value of hardness thus obtained is input to the residual stress estimation device 1.

  When receiving the input of the measurement value, the CPU 111 sets the analysis range based on the input measurement value (step S5). The setting of the analysis range will be described. FIG. 8 is a graph showing an example of hardness distribution in the depth direction. In FIG. 8, the vertical axis indicates the hardness, and the horizontal axis indicates the depth from the surface of the structure. In the example shown in FIG. 8, the hardness is small at a position close to the surface of the structure, and the hardness increases as the depth increases. The hardness is 309 Hv at a position where the depth is about 12 mm, and the hardness is constant at 309 Hv at a position deeper than that.

FIG. 9 is a graph showing the results of a tensile test (static tensile test and cyclic test) performed on the material of the structure whose hardness distribution is shown in FIG. 8 (hereinafter referred to as “target material”). It is. In FIG. 9, the vertical axis represents stress, and the horizontal axis represents strain. In the figure, the black solid line shows the result of the static tensile test, and the gray solid line shows the result of the cyclic test. Depending on the material, structure, etc., there are metals that harden (work hardening) and those that soften (work softening) when plastic working. As shown in FIG. 9, it can be seen that the target material is softened by repeatedly applying a tensile load and a compressive load (repetitive processing). The tensile strength of the target material is 970 MPa, which corresponds to 309 Hv in terms of Vickers hardness. Referring to FIG. 8 again, it can be seen that the position of about 12 mm from the surface is the boundary between the plastic strain generation region and the non-generation region. The CPU 111 can detect this boundary by comparing the measured value of the hardness for each depth with the hardness of the target material in a state where the plastic processing given in advance is not performed. Alternatively, the change in hardness measurement value may be examined in the order of depth, and the depth at which the measurement value becomes constant may be detected as a boundary. In the example of FIG. 8, plastic strain occurs in the range from the surface to a depth of about 12 mm. Therefore, in this example, the depth Δr of the analysis range can be determined as about 12 mm. The analysis range start angle α ₀ and the analysis range angle Δα are similarly determined.

  By the way, the residual stress of the structure is estimated based on the measured residual stress (or elastic strain) of the cut piece. Therefore, where the measurement point of the residual stress or elastic strain is made has a great influence on the estimation accuracy of the residual stress of the structure. Residual stress can be estimated with high accuracy by using a site where the value of the inherent strain is high, a site where the distribution of the inherent strain changes sharply, and the like as measurement points. Since such a part is included in the analysis range, the user may determine a measurement point within the analysis range. For example, before inputting the measurement value of the residual stress, the input of the index reflecting the lattice strain and the determination of the analysis range are executed, and the determined analysis range is displayed on the display unit 13, and the user displays this analysis range. Referring to the measurement point of residual stress or elastic strain may be determined.

  Next, the CPU 111 determines a distribution function of intrinsic strain (step S6). An arbitrary multi-order polynomial or a trigonometric series can be selected as the distribution function. In this case, the CPU 111 may automatically select a distribution function, or the user may specify a desired distribution function using the input unit 12. Further, a distribution function may be set in advance in the residual stress estimation apparatus 1.

  Next, the CPU 111 optimizes the parameters of the distribution function (step S7). Hereinafter, the process of step S7 will be specifically described.

The CPU 111 first determines H in Expression (9). The procedure is as follows.
(A) As a = [1, 0, 0,..., 0] ^T , ε ₀ = Ma is obtained.
(B) Solve Equation (4) to find u.
(C) ε is obtained by equation (3).
(D) σ is obtained from equation (1).
(E) N values corresponding to the residual stress measurement points are extracted from the components of σ, and set as the first column of H.
(F) a = [0, 1, 0,..., 0] As ^T , the second column of H is similarly obtained by the procedures (b) to (f).

  Next, the CPU 111 determines a so that R in Expression (7) is minimized. Thereby, the parameters of the distribution function are optimized.

  Further, the CPU 111 calculates an estimated value of residual stress (step S8).

  In the process of step S8, first, the CPU 111 obtains an intrinsic strain at an arbitrary point according to equation (8). Further, the CPU 111 solves the equation (4) to obtain u, applies the obtained u to the equation (3) to obtain ε, and applies the obtained ε to the equation (1) to obtain σ.

  Next, the CPU 111 displays the estimated value of the obtained residual stress on the display unit 13 (step S9).

  After step S9, the CPU 111 ends the process.

  By adopting the above-described configuration, it is possible to specify a region where plastic strain occurs using mechanical properties that are indices reflecting crystal lattice strain, and this region can be set as an analysis range. Intrinsic strain is generated due to inelastic strain including plastic strain, and residual stress is generated due to this inherent strain. Therefore, it is estimated that residual stress is generated by setting the region where plastic strain is generated as the analysis range. Therefore, the residual stress is estimated within the range, and the estimation accuracy can be improved. Therefore, the analysis range can be appropriately set without being influenced by the user's experience.

  Conventionally, there is also an apparatus that searches for an analysis range by an optimization process separately from a residual stress estimation device in which a user manually inputs an analysis range. In the residual stress estimation device according to the present embodiment, since the analysis range can be set before the residual stress estimation process, there is no need to search the analysis range by the optimization process, and the amount of calculation in the residual stress estimation process Can be greatly reduced.

(Evaluation test)
The inventor conducted a performance evaluation test of the residual stress estimation method described above. In this evaluation test, the width of the analysis range in the circumferential direction centered on the central axis of the journal axis is constant at α ₀ = −20 ° and Δα = 100 °, and the depth Δr of the analysis range is variously changed to be unique. A numerical experiment of residual stress estimation by the strain method was performed, and the correct value (actually measured value) was compared with the numerical experimental result for each depth Δr. In addition, in the sample (structure) used in this test, the hardness shown in FIG. 8 was measured (that is, the boundary between the region where the plastic strain was generated and the region where the plastic strain was not generated is around 12 mm deep). ). Further, in this test, measured values and estimated values of residual stress were obtained at a plurality of depths at a fillet angle of 40 °. The measured values were measured by a cutting method by drilling the structure to the measurement depth and attaching a strain gauge to the bottom of the hole.

  FIG. 10 is a graph showing the results of this test. In FIG. 10, the vertical axis represents an estimation error (error from an actual measurement value of an estimated value of residual stress), and the horizontal axis represents the depth Δr of the analysis range. As shown in FIG. 10, the case where the depth Δr of the analysis range is 12 mm can be estimated with the highest accuracy. The depth of the range where the plastic strain occurs is about 12 mm, and it can be seen that the residual stress can be estimated with high precision when the analysis range is matched with the range where the plastic strain occurs.

In addition, the estimated value and the actually measured value were compared for each analysis range shown in the following table. 11A and 11B are graphs showing the comparison results. FIG. 11A shows the distribution of residual stress in the circumferential direction (fillet circumferential direction) of the arc-shaped fillet, and FIG. 11B shows the distribution of residual stress in the circumferential direction of the circle (pin circumferential direction) around the journal axis. Is shown.

  In the analysis range 1 (depth is 4 mm), the analysis range is smaller than the range in which plastic strain occurs. As shown in FIGS. 11A and 11B, in the case of such analysis range 1, the residual stress in the vicinity of the surface deviates greatly from the actual measurement value, and the estimation accuracy is poor. On the other hand, when the analysis range is larger than the range in which plastic strain occurs, such as analysis range 2 (depth 30 mm) and analysis range 3 (depth 60 mm), an estimated value of depth 15 mm or more is actually measured. Deviates from the value and the estimation accuracy is poor. It can be seen that in the analysis range 4 (depth is 12 mm) in which the range in which the plastic strain occurs and the analysis range substantially match, the estimated value is in good agreement with the measured value, and the residual stress can be estimated with high accuracy.

(Embodiment 2)
In this embodiment, the half width obtained by the X-ray diffraction method is used as an index reflecting the lattice strain in the structure. When lattice distortion occurs in the structure, the distance between the lattices changes. On the other hand, it is known that the half width obtained by the X-ray diffraction method or the neutron diffraction method spreads in inverse proportion to the distance between the lattices (crystal size). In other words, the half width reflects the distance between the lattices. For this reason, a half width can be measured by irradiating a structure with synchrotron radiation or neutrons, and the half width can be used as an index reflecting lattice strain. The residual stress estimation apparatus according to the present embodiment determines the analysis range using the half width obtained by the X-ray diffraction method. That is, in step S3 shown in FIG. 4, the user measures the half-value width from the cut piece, and in step S4, the CPU 111 accepts an input of the half-value width.

FIG. 12 is a graph showing an example of the distribution in the depth direction of the half width obtained by the X-ray diffraction method. The full width at half maximum of the target material not subjected to plastic working is 2.6. As shown in FIG. 12, the half-value width is large at a position close to the surface of the structure, and the half-value width decreases as the depth increases. The half-value width is 2.6 at a position where the depth is about 12 mm, and the half-value width is 2.6 at a position deeper than that. Therefore, it can be seen that the target material has a boundary between a region where plastic strain is generated and a region where plastic strain is not generated at a position of about 12 mm from the surface. That is, plastic strain occurs in the range from the surface to a depth of about 12 mm. Therefore, in this example, the depth Δr of the analysis range can be determined as about 12 mm. The analysis range start angle α ₀ and the analysis range angle Δα are similarly determined.

  Since the configuration and other operations of the residual stress estimation device according to the present embodiment are the same as the configuration and operation of the residual stress estimation device 1 according to the first embodiment, description thereof will be omitted.

  By setting it as the above structures, the area | region where a plastic strain generate | occur | produces can be specified using the half value width which is the parameter | index reflecting the distortion | strain of crystal lattice, and this area | region can be set as an analysis range. By setting the region where the plastic strain occurs as the analysis range, the residual stress is estimated in the range where the residual stress is estimated to be generated, and the estimation accuracy can be improved.

(Other embodiments)
In the first and second embodiments described above, the configuration in which the residual stress estimation apparatus determines the analysis range based on the index reflecting the distortion of the crystal lattice has been described, but the present invention is not limited to this. The user may determine the analysis range based on an index reflecting the strain of the crystal lattice and input this analysis range to the residual stress estimation device.

  In the first and second embodiments, the residual stress is measured from the cut piece of the structure, and the distribution is performed so that the difference between the measured residual stress and the residual stress calculated by the distribution function is minimized. Although the configuration for optimizing the function parameters has been described, the present invention is not limited to this. As a configuration that measures the release strain (elastic strain) from a cut piece of a structure and optimizes the parameters of the distribution function so that the difference between the measured release strain and the elastic strain calculated by the distribution function is minimized. Also good.

  In the second embodiment, the configuration using the half width obtained by irradiating the structure with synchrotron radiation or neutron has been described, but the present invention is not limited to this. The diffraction angle obtained by the X diffraction method or the neutron diffraction method is a value that directly reflects the distance between crystal lattices. For this reason, you may use this diffraction angle as a parameter | index reflecting the distortion | strain of a crystal lattice.

  The residual stress estimation method and the residual stress estimation apparatus of the present invention are useful as a residual stress estimation method and a residual stress estimation apparatus for estimating the residual stress of a structure based on the inherent strain method.

DESCRIPTION OF SYMBOLS 1 Residual stress estimation apparatus 10 Computer 12 Input part 13 Display part 110 Residual stress estimation program 111 CPU
115 Hard Disk 116 Input / Output Interface 117 Image Output Interface

Claims (6)

Obtaining an index reflecting the distortion of the crystal lattice in the structure by measuring the structure subjected to plastic working; and
Identifying a region where crystal lattice distortion has occurred based on the index, and setting the identified region as an analysis range for estimating residual stress;
Estimating a distribution of inherent strain in the analysis range to approximate the inherent strain of the structure in the analysis range based on a measurement value relating to residual stress obtained from the structure;
Estimating a residual stress in the structure based on the estimated inherent strain distribution;
Having
Residual stress estimation method based on intrinsic strain. The index is a mechanical property that varies depending on the presence or absence of strain in the crystal lattice.
The residual stress estimation method according to claim 1. The mechanical property is a mechanical property selected from the group consisting of hardness, Young's modulus, yield point, ultimate strength, breaking strength, breaking elongation, drawing, impact value, fatigue strength, and creep strength.
The residual stress estimation method according to claim 2. The index is a measurement value reflecting the distance between the crystal lattices obtained by irradiating the structure with synchrotron radiation or neutrons,
The residual stress estimation method according to claim 1. The index is a half width obtained by an X-ray diffraction method or a neutron diffraction method.
The residual stress estimation method according to claim 4. An acquisition means for acquiring an index reflecting the distortion of the crystal lattice in the structure by measuring the structure subjected to plastic working;
A setting unit that identifies a region where crystal lattice distortion has occurred based on the index acquired by the acquiring unit, and sets the specified region as an analysis range for estimating residual stress;
An input unit for receiving an input of a measurement value relating to the residual stress of the structure;
Estimating means for estimating the distribution of the inherent strain in the analysis range using the measurement value received by the input unit so as to approximate the inherent strain of the structure in the analysis range set by the setting means;
A display unit for displaying an estimation result of residual stress based on the distribution of the inherent strain estimated by the estimation unit;
Comprising
Residual stress estimation device.