JP2009174886A - Mechanical characteristics evaluation method with respect to modified portion - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a mechanical characteristics evaluation method for a surface-modified portion, using the surface-modified portion as a measuring object. <P>SOLUTION: The method includes an elastoplasticity analysis step wherein a condition similar to an indenter indentation test to the measuring object which is the surface-modified portion is simulated, and elastoplasticity analysis is performed by using a numerical value showing the mechanical-physical characteristics of the measuring object as a parameter, and correlation between indenter maximum indentation displacement, residual displacement or elastic displacement and the numerical value showing the mechanical-physical characteristic is acquired and arranged to form a database; an indentation test step, wherein the indenter indentation test is performed actually to the measuring object, and the indenter maximum indentation displacement, the residual displacement or the elastic displacement is acquired from a result of the indenter indentation test; and a mechanical-physical characteristic identification step wherein the indenter maximum indentation displacement, the residual displacement or the elastic displacement acquired in the indentation test step is compared with the correlation formed as the database between the indenter maximum indentation displacement, the residual displacement or the elastic displacement and the numerical value showing the mechanical-physical characteristic, and the numerical value showing the mechanical-physiccal characteristics of the measuring object is identified. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a mechanical property evaluation technique for a structure or the like, and more particularly, to a mechanical property evaluation method for evaluating mechanical and physical properties of a surface modification portion of an object to be measured.

  Structures such as power plants and various work plants may experience stress corrosion cracking due to the presence of residual tensile stress due to thermal effects such as welding and the interaction of the corrosive environment of the structure. As a material of such a structure, a metal material having corrosion resistance is used, and further periodic replacement is performed in order to prevent damage to the structure.

  However, for example, a core shroud in a boiling water reactor, its support structure, and a structure such as a control rod drive mechanism housing at the bottom of the reactor cannot be replaced unless it is cut or the like because it is a welded structure. It is a structure used semi-permanently.

  As a means of preventing stress corrosion cracking in advance for structures that are difficult to replace, the surface of the structure is modified by impacting the surface of the structure and improving the tensile stress existing in the structure to compressive stress. There are surface modification means for quality. For example, there are laser peening that uses the impact force of plasma (see Patent Document 1) and water jet peening that uses the impact force at the time of cavitation destruction (see Patent Document 2).

  The effect on the construction site after construction such as laser peening is confirmed by visual inspection, etc. The degree of residual compressive stress existing in the construction site after construction is measured in advance using a test material having a shape equivalent to the actual construction site. Trial construction is performed, and this test material is secured by measuring the magnitude of residual compressive stress using an X-ray diffraction method or the like.

  Here, there are inventions disclosed in Patent Document 3 and Patent Document 4 as methods for measuring material constants and residual strains representing mechanical and physical properties of materials.

  In the invention disclosed in Patent Document 3, an indenter indentation test is performed in advance on an elastoplastic material, a set of curve constants of displacement-load curves obtained based on the indenter indentation test, and yield stress in a plurality of elastoplastic materials. Then, a database of the relationship with the material constant group consisting of work hardening index and work hardening coefficient is created. Also, by obtaining the curve constant set of displacement-load curve obtained based on the indenter indentation test for the material to be investigated, and collating this curve constant set with the curve constant set in the database, the material constant of the material to be investigated is obtained. This is a method for determining a pair.

The invention disclosed in Patent Document 4 is based on the correlation between the indentation depth and hardness obtained by performing an indenter indentation test on a material in advance, and the indenter indentation obtained by performing an indenter indentation test on a material to be investigated. This is a method of determining the residual strain by comparing depth and hardness.
JP 7-246483 A JP-A-6-47667 JP-A-9-288050 JP-A-8-247914

  When surface modification is performed on a structure using surface modification means such as water jet peening, residual compressive stress is generated at a construction site after construction. In addition, the surface modified layer, which is a construction site after peening, changes not only the residual stress but also the values representing mechanical and physical characteristics such as yield stress and longitudinal elastic modulus. The values representing these mechanical and physical characteristics have a great influence on the soundness evaluation of structures after peening.

  It can be considered that the material constants such as yield stress are determined by applying the inventions shown in Patent Documents 3 and 4 to the structure after peening. However, the inventions disclosed in Patent Documents 3 and 4 have not taken into consideration the influence existing in the structure subjected to the surface modification.

  The present invention has been made in view of such circumstances, and an object of the present invention is to provide a method for evaluating mechanical properties of a surface modified portion in consideration of the influence on a construction site after surface modification.

  In order to solve the above-described problems, the mechanical property evaluation method for a surface modified portion according to the present invention includes an indenter indentation test for an object to be measured having a surface modified portion whose surface property has been modified by a surface modifying means. Simulate the same conditions, perform elasto-plastic analysis using the numerical values representing the mechanical and physical properties of the object to be measured as parameters, and express the indenter maximum indentation displacement, residual displacement or elastic displacement and the mechanical and physical properties. An elasto-plastic analysis step that obtains a correlation with a numerical value and creates a database, and an indentation that performs the indenter indentation test on the object to be measured and obtains an indenter maximum indentation displacement, residual displacement, or elastic displacement from the result of the indenter indentation test The indenter maximum indentation displacement, residual displacement or elasticity obtained in the test step and the indentation test step is converted into the database indenter maximum indentation displacement, residual displacement or elasticity. A mechanical / physical property identification step for comparing a correlation between a position and a numerical value representing the mechanical / physical property and identifying the numerical value representing the mechanical / physical property of the object to be measured. It is characterized by that.

  The mechanical property evaluation method for the surface modified portion according to the present invention can accurately perform the mechanical property evaluation of the surface modified portion in consideration of the influence on the construction site after the surface modification.

  An embodiment of a method for evaluating mechanical properties of a surface modified portion according to the present invention will be described with reference to the accompanying drawings.

  The mechanical property evaluation method for the surface modified portion in the present embodiment is a nuclear power plant structure made of austenitic stainless steel as an example, and uses, for example, a surface modifying means such as water jet peening. This is applied to the case where the mechanical and physical characteristics of the peened site where surface modification has been performed are evaluated. This mechanical property evaluation method for the surface reforming part is used for reactor internal structures in nuclear power plants, especially for reactor internal structures that are difficult to remove and evaluate mechanical and physical characteristics. It is effective. The mechanical property evaluation method for the surface modified portion in this embodiment will be described as an evaluation method by identifying residual stress, yield stress, and longitudinal elastic modulus, which are numerical values representing mechanical and physical properties.

[First Embodiment]
An example of an indenter indentation test apparatus used for the mechanical property evaluation method for the surface modified portion in this embodiment will be described.

  The indenter indentation test apparatus is configured such that a measuring unit including an indenter that applies a predetermined load by pushing the indenter into a measurement object and measures the displacement of the indentation point can be inserted into the nuclear reactor. Also, in the reactor, a position control mechanism that controls the position of the measurement unit, a data processing unit that is installed outside the reactor, etc., and that consists of a computer that processes the measurement data of the measurement object obtained from the measurement unit Composed.

  The indenter provided in the measuring unit measures the displacement in the load direction of the indentation point in the measurement object by being pushed into the measurement object by a predetermined load. The indenter is pushed in remotely by using a motor or the like as a drive source. Further, since the indentation load is set according to the hardness of the object to be measured, it is variably configured within a predetermined range.

  The measurement data obtained from the measurement unit is processed by the data processing unit to obtain a displacement-load curve of the object to be measured. In addition, the data processing unit acquires the correlation between residual stress, which is a numerical value representing mechanical and physical characteristics, and each displacement caused by indentation using an analytical method, and executes processing to create a database To do.

  When an indenter indentation test is performed on an object to be measured using such an indenter indentation device, a displacement-load curve representing the relationship between the load applied to the object to be measured and the displacement in the load direction of the indentation point is obtained. It is done. FIG. 1 shows an example of a displacement-load curve.

  In this displacement-load curve, the vertical axis represents the load applied from the indenter indentation test apparatus, and the horizontal axis represents the indentation displacement amount in the load direction. The displacement-load curve has a hysteresis property, and is composed of a displacement-load curve at the time of pushing obtained when the indenter is pushed and a displacement-load curve at the time of drawing obtained when the indenter is drawn.

Displacement - from the load curve can be read indenter Maximum indentation depth _{h max,} the residual displacement _{h r} and the elastic displacement _{h e.} The indenter maximum indentation displacement h _max is the maximum displacement amount during indenter indentation in the indentation displacement-load curve. Further, the residual displacement h _r is the displacement from the previous indenter indentation after indenter drawing. The elastic displacement h _e an elastic displacement amount after indenter drawing, represented by the difference between the residual displacement h _r and indenter Maximum indentation depth h _max.

  Next, a mechanical property evaluation method for the surface modified portion in the present embodiment will be described. In the present embodiment, the mechanical property evaluation method for the surface modified portion is a database of analysis data obtained by using an analytical method such as a finite element method (FEM), and this data is referred to by referring to this database. Evaluate the mechanical and physical properties of the measurement object. FIG. 2 is a flowchart showing the process of analysis data acquisition processing.

In step S1, an elasto-plastic analysis is performed by simulating the same conditions as the test conditions such as the shape and additional load of the indenter used in the indenter indentation test using the indenter indentation test apparatus. The elasto-plastic analysis is performed using at least one of residual stress (σ _r ), yield stress (σ _y ), and longitudinal elastic modulus (E) as a parameter. Hereinafter, an example in which elastoplastic analysis is performed using L (L ≧ 2) residual stresses as parameters will be described.

  In step S2, a displacement-load curve representing the relationship between the applied load and the indentation displacement of the object to be measured is acquired from the analysis result of the elasto-plastic analysis performed in analysis execution step S1. FIG. 3 is a graph showing an example of a displacement-load curve obtained by performing an elasto-plastic analysis. Since the elasto-plastic analysis is performed using L residual stress values as parameters, L displacement-load curves are obtained according to the parameter values.

In step S3, displacement and residual stress as a parameter - from the load curve to determine the value of the residual stress (sigma _r), indenter Maximum indentation depth h _max, the correlation between the residual displacement h _r and the elastic displacement h _e. Further, since the value of the L residual stress as a parameter, the L indenter Maximum indentation depth corresponding to the residual stresses h _max, L sets of data of the residual displacement h _r and the elastic displacement h _e is obtained.

Figure 4 is a diagram showing the values of the L residual stress as a parameter, an indenter Maximum indentation depth h _max, an example of the analysis result of the relationship between the residual displacement h _r and the elastic displacement h _e. The horizontal axis is the value of residual stress, with positive values being tensile stresses and negative values being compressive stresses. The vertical axis indenter Maximum indentation depth h _max, a rate of change of the residual displacement h _r and the elastic displacement h _e, residual stress is a reference value of each displacement amount when the 0 [MPa], changes to the reference value Indicates the percentage. When the rate of change is a negative value, it indicates that the displacement is smaller than the reference value, and when the rate of change is a positive value, it indicates that the displacement is greater than the reference value.

From FIG. 4, the residual stress is small (compressed) indeed indenter Maximum indentation depth h _max and residual displacement h _r present in the object to be measured is smaller than the reference value, the residual stress is large (tensile) indeed made that increased I understand. On the other hand, the elastic displacement h _e, an inverted correlation is the maximum indentation depth h _max and residual displacement h _r indenter, the residual stress is small (the compression) the more elastic displacement h _e is larger than the reference value, It turns out that it becomes small, so that a residual stress becomes large (it becomes tensile).

Incidentally, FIG. 5 is a diagram showing the values of M yield stress as a parameter, an indenter Maximum indentation depth h _max, an example of the analysis result of the relationship between the residual displacement h _r and the elastic displacement h _e. Since the value of the yield stress of the M (M ≧ 2) as a parameter, M-number of indenter Maximum indentation depth corresponding to the value of the yield stress h _max, M sets of data of the residual displacement h _r and the elastic displacement h _e tables Is done.

  The horizontal axis represents the rate of change in yield stress, and the yield stress value of the object to be measured before peening is taken as the reference value, and the rate of change relative to this reference value is shown. When the rate of change is a negative value, it indicates that the yield stress is lower than the reference value, and when the rate of change is a positive value, it indicates that the yield stress is higher than the reference value.

The vertical axis indenter Maximum indentation depth h _max, a rate of change of the residual displacement h _r and the elastic displacement h _e, based on the respective amount of displacement when the yield stress value prior to peening the yield stress of the object to be measured The value represents the rate of change with respect to this reference value. When the rate of change is a negative value, it indicates that the displacement is smaller than the reference value, and when the rate of change is a positive value, it indicates that the displacement is greater than the reference value.

5 that the indenter Maximum indentation depth h _max and residual displacement h _r as the yield stress present in the object to be measured is increased is smaller than the reference value, the yield stress is seen that the larger drops. On the other hand, the elastic displacement h _e, an inverted correlation is the maximum indentation depth h _max and residual displacement h _r indenter, elastic displacement h _e higher yield stress increases is larger than the reference value, the yield stress It turns out that it becomes small, so that it falls.

Figure 6 is a diagram showing the values of the N modulus of longitudinal elasticity as a parameter, an indenter Maximum indentation depth h _max, an example of the analysis result of the relationship between the residual displacement h _r and the elastic displacement h _e. Due to the modulus of longitudinal elasticity of N (N ≧ 2) as a parameter, indenter Maximum indentation depth corresponding to N the yield stress h _max, N sets of data of the residual displacement h _r and the elastic displacement h _e can be obtained.

  The horizontal axis represents the rate of change in the longitudinal elastic modulus, and the longitudinal elastic modulus of the object to be measured before peening is taken as the reference value, and the rate of change relative to this reference value is shown. When the rate of change is negative, it indicates that the longitudinal elastic modulus is lower than the reference value, and when the rate of change is positive, it indicates that the longitudinal elastic modulus is higher than the reference value. Show.

The vertical axis indenter Maximum indentation depth h _max, a rate of change of the residual displacement h _r and the elastic displacement h _e, each displacement amount in the case of the longitudinal elastic coefficient before peening the longitudinal elastic coefficient of the DUT As a reference value, the ratio of change with respect to this reference value is shown. When the rate of change is a negative value, it indicates that the displacement is smaller than the reference value, and when the rate of change is a positive value, it indicates that the displacement is greater than the reference value.

From FIG. 6, the indenter Maximum indentation depth h _max as modulus present in the object to be measured is _increased, the residual displacement h _r and the elastic displacement h _e is smaller than the reference value, the yield stress increases as decreases I understand. Incidentally, this correlation is seen more strongly elastic displacement h _e.

In step S4, from the correlation between the L sets of residual stresses acquired in the data acquisition step S3 and the respective displacements, an L-1 order polynomial approximate expression shown below is obtained using a least square method or the like. An L-1 order polynomial approximate expression expressing the residual stress as a function of each displacement is expressed as follows.
[Equation 1]
σ _r = a _1r + a _2r h _max + a _3r h _max ² + ... + a _Lr h _max ^L-1
[Equation 2]
σ _r = b _1r + b _2r h _r + b _3r h _r ² +... + b _Lr h _r ^L−1
[Equation 3]
_{σ r = c 1r + c 2r} h e + c 3r h e 2 + ··· + c Lr h e L-1
On the other hand, an L-1 order polynomial approximate expression expressing each displacement as a function of residual stress can also be obtained.
[Equation 4]
h _max = d _1r + d _2r σ _r + d _3r σ _r ² +... + d _Lr σ _r ^L-1
[Equation 5]
h _r = e _1r + e _2r σ _r + e _3r σ _r ² +... + e _Lr σ _r ^L-1
[Equation 6]
h _e = f _1r + f _2r σ _r + f _3r σ _r ² +... + f _Lr σ _r ^L−1
[Equation 4] is L-1 order polynomial approximate expression representing the maximum indentation depth h _max indenter as a function of residual stress, Equation 5 is L-1-order representation of the residual displacement h _r as a function of residual stress polynomial approximation, [6] is a polynomial approximation L-1-order representation of the elastic displacement h _e as a function of residual stress.

Incidentally, sigma _r is the residual _{stress, h max} is indenter Maximum indentation depth _h max, _{h r} the residual displacement _h r, _{h e} represents the elastic displacement _{h e.} A _1r , a _2r ,..., A _Lr in [ _Equation 1], b _1r , b _2r ,..., B _Lr in [ _Equation 2], and c _1r , c _2r in [ _Equation 3], .., C _Lr , d _1r , d _2r in [ _Equation 4], d _Lr , e _1r in [ _Equation 5], e _2r ,..., E _Lr , and f in [ _Equation 6] _1r , _f2r ,..., _FLr are constants.

In addition, an M−1 order polynomial approximate expression expressing the yield stress as a function of each displacement using the correlation between the M sets of yield stress and each displacement is expressed as follows.
[Equation 7]
σ _y = a _1y + a _2y h _max + a _3y h _max ² + ... + a _My h _max ^M-1
[Equation 8]
_{σ y = b 1y + b 2y} h r + b 3y h r 2 + ··· + b My h r M-1
[Equation 9]
_{σ y = c 1y + c 2y} h e + c 3y h e 2 + ··· + c My h e M-1
Alternatively, it is also possible to obtain an M−1 order polynomial approximate expression expressing each displacement as a function of yield stress.
[Equation 10]
h _max = d _{1 y} + d 2 _y σ _y + d _{3 y} σ _y ² +... + d _My σ _y ^M−1
[Equation 11]
h _r = e _1y + e _2y σ _y + e _3y σ _y ² +... + e _My σ _y ^M−1
[Equation 12]
h _e = f _1y + f _2y σ _y + f _3y σ _y ² +... + f _My σ _y ^M−1
[Expression 10] M-1 order polynomial approximate expression representing the maximum indentation depth h _max indenter as a function of yield stress, Equation 11] M-1 order, which represents the residual displacement h _r as a function of yield stress polynomial approximation, equation 12] is a polynomial approximation M-1 order, which represents the elastic displacement h _e as a function of yield stress.

Note that σ _r indicates a residual stress. Further, a _1y , a _2y ,..., A _My in [ _Equation 7], b _1y , b _2y ,..., B _My in [ _Equation 8], and c _1y , c _2y in [ _Equation 9], , C _My , d _1y , d _2y ,..., D _My in [ _Equation 10], e _1y , e _2y ,..., E _My in [ _Equation 11], and f in [Equation 12] _{1y, f 2y, ···, f} My is a constant.

Further, an N−1 order polynomial approximation expression in which the longitudinal elastic modulus is expressed as a function of each displacement using the correlation between N sets of longitudinal elastic modulus and each displacement is expressed as follows.
[Equation 13]
E = a _1E + a _2E h _max + a _3E h _max ² +... + A _NE h _max ^N−1
[Formula 14]
_{E = b 1E + b 2E h} r + b 3E h r 2 + ··· + b NE h r N-1
[Equation 15]
_{E = c 1E + c 2E h} e + c 3E h e 2 + ··· + c NE h e N-1
Alternatively, it is also possible to obtain an N−1 order polynomial approximate expression in which each displacement is expressed as a function of the longitudinal elastic modulus.
[Equation 16]
h _max = d _1E + d _2E E + d _3E E ² +... + d _NE E ^N−1
[Equation 17]
h _r = e _1E + e _2E E + e _3E E ² +... + e _NE E ^N−1
[Equation 18]
h _e = f _1E + f _2E E + f _3E E ² +... + f _NE E ^N−1
[Expression 16] is N-1 order polynomial approximation represents the maximum indentation depth h _max indenter as a function of the modulus of longitudinal elasticity, Equation 17] N-1 which represents a residual displacement h _r as a function of the longitudinal elastic modulus following polynomial approximation, equation 18] is a polynomial approximation N-1 order, which represents the elastic displacement h _e as a function of the modulus of longitudinal elasticity.

E represents a longitudinal elastic modulus. In addition, a _1E , a _2E ,..., A _NE in [ _Equation 13], b _1E , b _2E ,..., B _NE in [ _Equation 14], and c _1E , c _2E in [ _Equation 15], , C _NE , d _1E , d _2E in [ _Equation 16], d _NE , e _1E in [ _Equation 17], e _2E ,..., E _NE , and f in [Equation 18] _1E , _f2E ,..., _FNE are constants.

  The acquired polynomial approximation formula is made into a database, and the analysis data acquisition process ends.

  Next, the process of identifying numerical values representing the mechanical and physical characteristics of the object to be measured will be described. FIG. 7 is a flowchart illustrating a process for identifying numerical values representing mechanical and physical characteristics. In the step of identifying numerical values representing mechanical / physical characteristics described below, a case where residual stress is identified among numerical values representing mechanical / physical characteristics will be described.

  In step S11, an indenter indentation test is performed on the peening site (surface modified portion) in the object to be measured using an indenter indentation test apparatus. In the indenter indentation test, a predetermined load is applied to the peening site of the object to be measured, and the displacement in the load direction of the indentation point in the object to be measured is measured. At this time, the predetermined load applied to the object to be measured is the same load as the additional load simulated by the elastic-plastic analysis.

  In step S12, a displacement-load curve as shown in FIG. 1 is obtained from the measurement result of indenter indentation test execution step S11.

In step S13, the displacement - indenter Maximum indentation depth from the load curve _{h max,} to obtain the residual displacement _{h r} and the elastic displacement _{h e.}

In step S14, the indenter maximum indentation displacement h _max , residual displacement h _r or elastic displacement h _e acquired in the displacement acquisition step S13 is added to the polynomial approximation expression acquired in the polynomial approximation expression acquisition step S4 in the analysis data acquisition process and converted into a database. By substituting each value, residual stress (σ _r ), which is a numerical value representing mechanical and physical characteristics, is identified.

Specifically, when obtaining the residual stress using the value of the acquired indenter Maximum indentation depth h _max, the polynomial approximate expression shown in the above-described Equation 1 or Equation 4], indenter Maximum indentation values of displacement h _max Is assigned. Also, when obtaining the residual stress using the value of the acquired residual displacement h _r, the polynomial approximate expression shown in the above-described Equation 2 or Equation 5, the value of the residual displacement h _r obtained in indenter indentation test substitute. When determining the residual stress using the value of the acquired acoustic displacement h _e is the polynomial approximate expression shown in the above-described [Expression 3] or [6], the value of the residual displacement h _r obtained in indenter indentation test substitute.

  The residual stress value is used for evaluating the soundness of the structure, so that a mechanical property evaluation method for the surface modified portion is performed.

  The process for identifying numerical values representing the mechanical and physical characteristics of the object to be measured is thus completed.

In addition, although the process which identifies a residual stress among mechanical and physical characteristics was demonstrated, it can obtain | require similarly about a yield stress and a longitudinal elastic modulus. Specifically, the indenter Maximum indentation depth _{h max} obtained by the displacement acquiring step S13, the value of the residual displacement _{h r} or elastic displacement _{h e,} by substituting each of [Expression 7] to [Expression 18], mechanical -Yield stress and longitudinal elastic modulus related to numerical values representing physical characteristics can be similarly identified.

  According to the mechanical property evaluation method for the surface modification part, the residual stress, yield stress and longitudinal elastic modulus are identified in consideration of the influence evaluation of the mechanical and physical properties due to the surface modification. Therefore, mechanical and physical characteristics can be evaluated more accurately.

  In addition to the change in residual stress due to the surface modification, other numerical values that affect the soundness evaluation such as yield stress and longitudinal elastic modulus can be obtained.

  In addition, evaluation of mechanical / physical characteristics, especially for structures inside nuclear reactors that are difficult to remove and evaluate mechanical / physical characteristics, such as internal structures in nuclear power plants, etc. It is effective in that it can be performed.

In the present embodiment, although a database to obtain the polynomial approximation from the analysis data, such as an indenter Maximum indentation depth residual stress h _max, the correlation between the residual displacement h _r and the elastic displacement h _e is one-to-one correspondence The attached data may be converted into a database as analysis data to identify residual stress and the like. For example, actual indenter indentation test indenter Maximum obtained by performing push displacement h _max relative to the object to be _measured, and the value of the residual displacement h _r or elastic displacement h _e, residual obtained by performing the elastoplastic analysis The analysis data, which is the value of each displacement associated with the stress one-to-one, is compared. Among the displacements in the analysis data, a displacement that matches the displacement acquired in the displacement acquisition step S13 is determined, and the value of the residual stress associated with the value is identified as the value of the residual stress of the object to be measured. If there is no matching displacement value, the closest displacement value in the analysis data is determined, and the residual stress value is identified by performing linear interpolation, for example.

  In addition, the object to be measured is not limited to the reactor internal structure, and various structures having a surface modification portion can be applied as the object to be measured.

  Further, the surface modifying means is not limited to water jet peening, and can be applied to the case where other surface modifying means such as, for example, forming a film on the surface of a structure is used.

[Second Embodiment]
Next, a second embodiment of the mechanical property evaluation method for the surface modified portion according to the present invention will be described.

  Of the various numerical values representing the mechanical and physical characteristics of the surface modified portion, not only one value changes independently, but each numerical value changes. For example, it is assumed that not only the value of the residual stress changes due to the effect of surface modification, but also influences and changes with the yield stress and the longitudinal elastic modulus. For this reason, not only functions for obtaining independent numerical values but also the residual stress, yield stress, and longitudinal elastic modulus values representing mechanical and physical properties are obtained in association with each other, thereby enabling more accurate mechanical property evaluation. It can be carried out. In the present embodiment, the polynomial approximate expression acquired in the first embodiment is used in order to acquire the residual stress, the yield stress, and the longitudinal elastic modulus representing the mechanical and physical characteristics in association with each other.

  A mechanical property evaluation method for the surface modified portion in the present embodiment will be described. FIG. 8 is a flowchart showing the process of analysis data acquisition processing.

  Since the analysis execution step S21 to the polynomial approximate expression acquisition step S23 are substantially the same as the analysis execution step S1 to the polynomial approximation expression acquisition step S4 of the analysis data acquisition process in the first embodiment, the description thereof is omitted.

In step S24, acquires indenter Maximum indentation depth _{h max,} the residual displacement _{h r} and the elastic displacement _{h e,} the residual stress (sigma _r), a function expressed as a function of yield stress (sigma _y) and the modulus of longitudinal elasticity (E) And create a database.

The indenter maximum indentation displacement h _max is an L−1 order polynomial approximate expression expressing the indenter maximum indentation displacement h _max as a function of residual stress [Equation 4], and an M−1 order polynomial expressed as a function of yield stress. By taking the sum of [Equation 10] which is an approximate expression and [Equation 16] which is an N-1 order polynomial approximate expression expressed as a function of the longitudinal elastic modulus, a function of residual stress, yield stress and longitudinal elastic modulus is obtained. Represented as:
[Equation 19]
h _max = (d _1r + d _2r σ _r + d _3r σ _r ² +... + d _Lr σ _r ^L-1 ) + (d _1y + d _2y σ _y + d _3y σ _y ² +... + d _My σ _y ^{M− _{1) + (d 1E + d}} 2E E + d 3E E 2 + ··· + d NE E N-1)
Further, the residual displacement h _r is a polynomial approximation L-1-order representation of the residual displacement h _r as a function of residual stress Equation 5], M-1 order polynomial approximation expressed as a function of yield stress [Equation 11] and [Numerical equation 17], which is an N−1 order polynomial approximation expressed as a function of the longitudinal elastic modulus, are obtained as a function of residual stress, yield stress and longitudinal elastic modulus. Is done.
[Equation 20]
h _r = (e _1r + e _2r σ _r + e _3r σ _r ² +... + e _Lr σ _r ^L-1 ) + (e _1y + e _2y σ _y + e _3y σ _y ² +... + e _My σ _y ^{M− 1} ) + (e _1E + e _2E E + e _3E E ² +... + E _NE E ^N-1 )
Further, the elastic displacement h _e is a polynomial approximation L-1-order representation of the elastic displacement h _e as a function of residual stress Equation 6], M-1 order polynomial approximation expressed as a function of yield stress [Equation 12] and [Numerical equation 18], which is an N-1 order polynomial approximate expression expressed as a function of the longitudinal elastic modulus, can be expressed as a function of residual stress, yield stress and longitudinal elastic modulus. Is done.
[Equation 21]
h _e = (f _1r + f _2r σ _r + f _3r σ _r ² +... + f _Lr σ _r ^L-1 ) + (f _1y + f _2y σ _y + f _3y σ _y ² +... + f _My σ _y ^{M− 1} ) + (f _1E + f _2E E + f _3E E ² +... + F _NE E ^N-1 )
The functions of the displacements represented by [Equation 19] to [Equation 21] are compiled into a database, and the analysis data acquisition process ends.

  Next, the process of identifying numerical values representing the mechanical and physical characteristics of the object to be measured will be described. FIG. 9 is a flowchart for explaining a process for identifying numerical values representing mechanical and physical characteristics.

  The indenter indentation test execution step S31 to the displacement acquisition step S33 are substantially the same as the indenter indentation test execution step S11 to the displacement acquisition step S13 in the step of identifying numerical values representing the mechanical and physical characteristics in the first embodiment. Description is omitted.

In step S34, the indenter maximum indentation displacement h _max and the residual displacement h acquired in the displacement acquisition step S33 are added to [Equation 19] to [Equation 21] which are functions of each displacement acquired in the function acquisition step S24 in the analysis data acquisition process. and _r or the value of the elastic displacement h _e assigns each to obtain simultaneous equations. By obtaining a solution of the simultaneous equations, the values of residual stress, yield stress and longitudinal elastic modulus are identified, and the mechanical property evaluation of the surface modified portion can be performed using these values. This completes the process of identifying numerical values representing mechanical and physical characteristics.

  According to the mechanical property evaluation method for this surface modification part, the higher-accuracy mechanical properties are identified by identifying the residual stress, yield stress and longitudinal elastic modulus values that represent the mechanical and physical properties. Evaluation can be made.

The figure which shows an example of the displacement-load curve which is a measurement result of the indenter indentation test with respect to a to-be-measured object. The flowchart explaining the analysis data acquisition process in 1st Embodiment. The graph which shows an example of the displacement-load curve acquired by performing the elastic-plastic analysis. The figure which shows an example of the analysis result of the correlation with a residual stress and each displacement. The figure which shows an example of the analysis result of the correlation with a yield stress and each displacement. The figure which shows an example of the analysis result of the correlation with a longitudinal elastic modulus and each displacement. The flowchart explaining the process of identifying the mechanical and physical characteristic in 1st Embodiment. The flowchart explaining the analysis data acquisition process in 2nd Embodiment. The flowchart explaining the process of identifying the mechanical and physical characteristic in 2nd Embodiment.

Claims (4)

Simulates the same conditions as the indentation test for an object having a surface modified portion whose surface characteristics have been modified by surface modification means, and numerical values representing the mechanical and physical characteristics of the object to be measured are used as parameters. An elasto-plastic analysis step of performing a plastic analysis, obtaining a correlation between the indenter maximum indentation displacement, residual displacement or elastic displacement and a numerical value representing the mechanical / physical characteristics and creating a database;
Performing an indenter indentation test on the object to be measured, and obtaining an indenter maximum indentation displacement, residual displacement or elastic displacement from a result of the indenter indentation test; and
The indenter maximum indentation displacement, residual displacement or elastic displacement obtained in the indentation test step is the correlation between the databased indenter maximum indentation displacement, residual displacement or elastic displacement and the numerical value representing the mechanical / physical characteristics. A mechanical property evaluation method for a surface modification portion, comprising: a mechanical / physical property identification step for comparing and identifying a numerical value representing the mechanical / physical property of the object to be measured. 2. The method for evaluating mechanical characteristics of a surface modified portion according to claim 1, wherein the numerical value representing the mechanical / physical characteristics is at least one of residual stress, yield stress and longitudinal elastic modulus. Correlation between the indenter maximum indentation displacement, residual displacement or elastic displacement acquired in the elastoplastic analysis step and the numerical value representing the mechanical / physical characteristics is expressed in a polynomial approximation formula to create a database,
In the mechanical / physical property identification step, a numerical value representing the mechanical / physical property is identified by substituting the indenter maximum indentation displacement, residual displacement, or elastic displacement acquired in the indentation test step into the polynomial approximation formula. The mechanical property evaluation method for a surface modified portion according to claim 1. The correlation between the indenter maximum indentation displacement, residual displacement or elastic displacement acquired in the elasto-plastic analysis step and the numerical value representing the mechanical / physical characteristics is as follows:
An expression representing the indenter maximum indentation displacement as a function of a numerical value representing the mechanical / physical characteristics; an expression representing the residual displacement as a function of a numerical value representing the mechanical / physical characteristics; Represented as a function of numerical values representing physical and physical characteristics and created as a database,
The mechanical / physical characteristic identification step includes: expressing the indenter maximum indentation displacement, residual displacement and elastic displacement as a function of a numerical value representing the mechanical and physical characteristics of the indenter maximum indentation displacement; To obtain a simultaneous equation by substituting the equation representing the mechanical and physical properties as a function of the numerical value and the equation representing the elastic displacement as a numerical function representing the mechanical and physical properties, respectively, 2. The method for evaluating mechanical properties of a surface modified portion according to claim 1, wherein numerical values representing the mechanical and physical properties are identified by solving simultaneous equations.

Images