JP6529853B2 - Residual stress evaluation method - Google Patents

Description

  The present invention evaluates the residual stress present in the surface layer of a test sample having a convex shape formed of a metal material or the like based on the speed of sound (propagation time) of ultrasonic waves propagating through the surface layer of the test sample. Residual stress evaluation method.

Measurement of non-destructive residual stress of machine parts and structures is extremely important in diagnosing deterioration of these parts and structures. Conventionally, X-ray diffraction has been mainly used for nondestructive residual stress measurement (evaluation). However, in X-ray diffraction, an extremely shallow region of the surface layer of the sample to be measured is used. There is a restriction that only (several μm) can be evaluated.
Therefore, as a residual stress evaluation means (acoustic elasticity method) using ultrasonic waves capable of eliminating these limitations and concerns, ultrasonic stress measurement devices and ultrasonic stress measurement methods disclosed in Patent Documents 1 and 2 are proposed. It is done.

  The ultrasonic stress measurement device disclosed in Patent Document 1 is an ultrasonic data obtained when a longitudinal ultrasonic wave and two transverse ultrasonic waves whose vibration directions are orthogonal to each other propagate through the inside of a stress measurement target material. An ultrasonic stress measuring device for analyzing the residual stress of the material to be stress measured using the following equation, and is disposed around a longitudinal wave probe P0 for transmitting and receiving the longitudinal wave ultrasonic waves, and the longitudinal waves First and second horizontal shear wave probes P1 and P2 for transmitting and receiving shear wave ultrasonic waves having a horizontal vibration direction are disposed on both sides in the horizontal direction of the probe P0, and the longitudinal wave probe P0 A probe assembly comprising first and second vertical shear wave probes P3 and P4 for transmitting and receiving shear wave ultrasonic waves whose vibration directions are vertical directions on both sides of the probe; and the probe An ultrasonic transmission / reception control unit for performing transmission / reception control of ultrasonic waves to each probe of the assembly And a measurement data analysis unit for inputting ultrasonic data of each of the probes from the ultrasonic transmission / reception control unit, obtaining sound velocity data of each ultrasonic wave, and analyzing residual stress of the material to be subjected to stress measurement. It is characterized by

  The ultrasonic stress measurement device disclosed in Patent Document 2 includes a longitudinal ultrasonic probe and a shear ultrasonic ultrasonic probe that can be disposed on the surface of a stress measurement target material, and the above-mentioned two types of probes. A probe drive mechanism capable of moving or rotating along the surface of the material, and an operation of transmitting / receiving ultrasonic waves to a measurement target portion of the material to one of the two probes. After that, by controlling the movement of the probe drive mechanism, the arrangement of one probe and the other probe is switched, and the other probe transmits ultrasonic waves to the same measurement target region. The reception operation is performed, and for the shear wave ultrasonic probe, N rotations per rotation angle of 180 ° / N (N: integer of 2 or more) are performed, and transmission and reception operations at each rotation position Probe control means for performing the operation, and the transmission and reception operations of the two probes. A measurement data analysis means for obtaining a constant of surface texture acoustic anisotropy from sound velocity data of surface acoustic waves obtained, and calculating a residual stress of a stress measurement object material based on the obtained constant; It features.

JP, 2010-236892, A JP, 2008-76387, A

The techniques disclosed in Patent Literatures 1 and 2 are based on the acoustoelastic effect that the speed of sound of propagation ultrasonic waves propagating through a specimen (the measurement material) changes according to residual stress, and the above-mentioned X-ray exposure The problem can be avoided. However, since the stress dependency (acoustic elastic coefficient) of sound velocity in metal materials is generally small, the sound velocity of the propagation ultrasonic wave propagating through the sample of the object can be stabilized with high accuracy in order to improve the accuracy of evaluation of residual stress. There is a problem that it is necessary to measure.

  Therefore, Patent Documents 1 and 2 both measure the speed of sound of these propagation ultrasonic waves using longitudinal ultrasonic waves and shear wave ultrasonic waves, and evaluate the residual stress in the sample of the object based on the measured values of the speed of sound. The purpose is to The patent documents 1 and 2 attempt to improve the measurement accuracy of the speed of sound (residual stress) by reducing the error factor caused by the uncertainty of the propagation distance of the propagation ultrasonic wave by using the longitudinal wave and the transverse wave together. ing.

However, since Patent Literatures 1 and 2 are techniques for evaluating residual stress in the depth direction in a flat-plate analyte sample, it is impossible to assess residual stress present in the surface layer of an analyte sample having a curved surface shape. .
The reason is that the inventors of the present invention conducted intensive studies and, as a result, evaluate the residual stress present in the surface layer of the subject sample having a curved surface shape, in particular a convex shape (small radius of the curved surface). This is because it has been found that there is a problem that a measurement error occurs in the propagation time of the propagation ultrasonic wave propagating in the surface layer.

  More specifically, when the propagation ultrasonic wave propagating on the surface layer of the object sample having the curved surface shape is a surface SH wave, in addition to the component propagating on the surface layer along the curved surface shape, it does not follow the curved surface shape of the object sample. There is a component (shortcut component of surface SH wave) propagating linearly inside (see the lower broken line in FIG. 2). When the surface SH waves propagated through these two different paths overlap, a measurement error is included in the propagation signal.

  As shown in FIG. 5, a short-cut component is included in the propagation time (gray color in the figure) of the surface SH wave propagating on the surface layer of the measurement sample having a convex shape (short-circuit component is superimposed) Therefore, as can be seen from comparison with the propagation time of the surface SH wave propagating in the surface layer of the flat plate (black in the same figure), it can be confirmed that the waveform is greatly affected by the shortcut component. That is, it can be seen that a measurement error occurs in the propagation time of the surface SH wave in the convex-shaped measurement sample.

Since the propagation time of the surface SH wave becomes uncertain due to the measurement error described above, it becomes difficult to evaluate the residual stress present in the surface layer of the convexly-shaped object sample with high accuracy.
Therefore, when evaluating the residual stress which exists in the surface layer of the subject sample which has curved surface shape, patent documents 1 and 2 can not be adopted.
Therefore, in view of the above problems, the present invention corrects the measurement error of the propagation time caused by the inclusion of the shortcut component of the propagation ultrasonic wave in the object sample having a curved surface shape, and corrects the propagation time of the corrected propagation ultrasonic wave The present invention provides a residual stress evaluation method capable of evaluating the residual stress present in the surface layer of a subject sample with high accuracy.

In order to achieve the above-mentioned object, the following technical measures are taken in the present invention.
The residual stress evaluation method according to the present invention is a residual stress evaluation method for evaluating residual stress present in the surface layer of a convexly shaped object sample based on the propagation time of ultrasonic waves propagating in the surface layer of the object sample. Transmitting the ultrasonic wave to the surface layer of the subject sample, receiving the ultrasonic wave transmitted through the surface layer of the subject sample, and transmitting the ultrasonic wave received in the receiving step Calculating a correction time for correcting the propagation time of the ultrasonic wave calculated in the propagation time calculation step, and correcting the propagation time of the ultrasonic wave with the calculated correction amount If, on the basis of the correction the ultrasonic correction propagation time corrected in step, have a, and evaluation step of evaluating the residual stresses present in the surface layer of the test sample, wherein the ultrasound table And the correction step calculates a correction amount for correcting the propagation time of the surface SH wave calculated in the propagation time calculation step, and calculates the correction amount of the surface SH wave using the calculated correction amount. The propagation time is to be corrected, and the evaluation step is performed on the surface layer of the subject sample based on the correction propagation time of the surface SH wave corrected in the correction step and the propagation time of the Rayleigh wave. It is characterized in that the residual stress present is to be evaluated .

  Preferably, a flat plate test piece made of the same material and flat as the subject sample in advance, and a plurality of convex test pieces having the same material as the subject sample and having a convex shape of different radius In the correction step, while making the propagation distances of the surface SH wave and the Rayleigh wave constant, the propagation time of the surface SH wave in the flat plate test piece is calculated to be a reference propagation time. The propagation time of the surface SH wave in the plurality of convex test pieces is calculated and stored as the convex propagation time for each radius, and the convex propagation time corresponding to the radius of the convex shape in the sample, and the reference propagation The correction amount may be calculated as a difference from time.

  Preferably, a flat plate test piece made of the same material and flat as the subject sample in advance, and a plurality of convex test pieces having the same material as the subject sample and having a convex shape of different radius In the correction step, the propagation distance of the surface SH wave in the flat plate test piece is set for each propagation distance after the propagation distances of the surface SH wave and the Rayleigh wave are made to be plural. The propagation time of the surface SH wave in the plurality of convex test pieces is calculated and set as the convex propagation time for each radius based on the propagation time of the Rayleigh wave in the sample. Calculating the actual propagation distance, and estimating the radius of the convex shape of the sample from the convex propagation time corresponding to the calculated actual propagation distance and the propagation time of the surface SH wave in the sample And, the may calculate the correction amount as the difference between the convex propagation time of the surface SH wave in the test sample, and the reference propagation time corresponding to the radius of the estimated said convex.

  According to the present invention, in an object sample having a curved surface shape, the measurement error of the propagation time caused by the inclusion of the shortcut component of the propagation ultrasonic wave is corrected, and the object is measured based on the corrected propagation time of the propagation ultrasonic wave. The residual stress present on the surface layer of the sample can be evaluated with high accuracy.

It is a figure which shows schematic structure of the residual-stress evaluation apparatus by embodiment of this invention. It is a figure which expands and shows schematic structure of the transmission probe of the residual-stress evaluation apparatus by this embodiment, and a receiving probe. FIG. 7 is a diagram schematically showing a method of measuring the propagation time T _S of the surface SH wave of the flat plate test piece and the convex test piece in the first embodiment. In the first embodiment, a graph summarizing the measurement results of the propagation time T _S of the surface SH wave flat test piece and the convex test piece, and the propagation time T _S of the surface SH wave in the test sample convex FIG. 6 is a diagram showing a method of calculating a correction amount ΔT _S to be corrected. In the second embodiment is a view showing an outline of a measuring method of the propagation time T _S of the surface SH wave flat test piece and the convex test piece. In the second embodiment, a graph summarizing the measurement results of the propagation time T _S of the surface SH wave flat test piece and the convex test piece, and the propagation time T _S of the surface SH wave in the test sample convex FIG. 6 is a diagram showing a method of calculating a correction amount ΔT _S to be corrected. A propagation time T _S of the surface SH wave propagating surface of the flat plate is a diagram showing by comparing the propagation time T _S of the surface SH wave propagating surface of the test sample that is a convex shape.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.
First, the basic configuration of the residual stress evaluation apparatus 1 used in the embodiment of the present invention will be described with reference to FIGS. 1 and 2.
The present invention is, for example, a metallic material such as a steel material, and is formed on a test sample (measurement sample) W formed in a convex shape (curved surface shape) or a mechanical component or structure including a plurality of members. The convex-shaped portion (sample W) to be evaluated is to be evaluated.

The residual stress evaluation apparatus 1 propagates an ultrasonic wave to the surface layer after the convex-shaped measurement sample W (hereinafter referred to as a convex-shaped measurement sample) to measure the propagation time of the propagated ultrasonic wave, and It is an evaluation (measurement) device based on the propagation time, the residual stress present in the surface layer of the convex measurement sample W.
Here, the surface layer is a region of a predetermined depth range below the surface (subsurface) of the convex measurement sample W, and is, for example, a region shallower than several mm in depth.

As shown in FIG. 1, the residual stress evaluation device 1 includes a transmission probe 2, a reception probe 3, a pulse generator 4, and a waveform sampling device 7.
As shown in FIG. 2, the transmission probe 2 is an ultrasonic probe in which, for example, a flat plate-like piezoelectric element 20 is installed inside the ultrasonic wave propagation medium 21, and is disposed on the surface of the convex measurement sample W Ru. When a pulse voltage of a predetermined voltage is applied to the piezoelectric element 20 from the pulse generator 4, the transmission probe 2 outputs an ultrasonic wave of a predetermined frequency and sends the ultrasonic wave to the surface of the convex measurement sample W.

The transmission probe 2 outputs an SH wave, which is a horizontal component of a transverse wave, as an ultrasonic wave, and outputs an SV wave, which is a vertical component of a transverse wave oscillating in a direction perpendicular to the vibration direction of the SH wave. The output SH waves and SV waves excite a plurality of types of ultrasonic waves having different vibration forms, ie, surface SH waves and Rayleigh waves, on the surface layer of the convex measurement sample W.
On the other hand, the receiving probe 3 is an ultrasonic probe in which, for example, a flat plate-like piezoelectric element 30 is installed inside the ultrasonic wave propagation medium 31, and differs from the transmitting probe 2 on the surface of the convex measurement sample W Placed in position. The receiving probe 3 receives the surface SH wave and the Rayleigh wave (propagating ultrasonic wave) incident on the piezoelectric element 30 as a plurality of types of propagating ultrasonic waves having different vibration forms, and generates the voltage generated by the reception as the Rayleigh wave and the surface. It is output to the outside as a detection signal (propagation signal) of the SH wave.

The waveform sampling device 7 receives the detection signals of the surface SH wave and the Rayleigh wave output from the amplifiers 5 and 6 and extracts the waveform of the detection signal, and the reception signal of the trigger signal to the detection signal of the Rayleigh wave is used. calculates the propagation time T _R for by measuring the time until receiving Rayleigh waves, calculates the propagation time T _S of measuring the time until reception surface SH wave surface SH wave detection signal from the reception of the trigger signal Do.

Now, the propagation distance L 'of the surface SH wave and the Rayleigh wave is the distance L between the transmission probe 2 and the reception probe 3 and the propagation distance in the transmission probe 2 and the propagation distance in the reception probe 3 In addition, it is also a propagation path of surface SH waves and Rayleigh waves.
A residual stress evaluation method using the above-described residual stress evaluation apparatus 1 will be described based on the drawings.
First, the basic concept for evaluating the residual stress present in the surface layer of a flat plate (steel material) will be described, and thereafter, the method of evaluating the residual stress present in the surface layer of the convex measurement sample W in the present embodiment. Explain.

The residual stress σ present in the surface layer of the flat plate can be expressed using a function of the propagation time T _S of the surface SH wave and the propagation time T _R of the Rayleigh wave, as exemplified in the equation (1) below.

In evaluating the residual stress σ present in the surface layer of the flat plate, the propagation time T _S of the surface SH wave and the propagation time T _R of the Rayleigh wave are acquired from the waveform sampling device 7, and the above equation (1) or the like is used. , Evaluate (measure) residual stress σ present in the surface layer of a flat plate.
However, when the residual stress σ ′ present in the surface layer of the convex measurement sample W is evaluated using the above equation (1), the presence of the residual stress σ ′ can not be accurately evaluated.

As shown in FIG. 2, in addition to the surface SH wave propagating along the convex shape (upper broken line in the same figure), the surface SH wave propagating along the surface layer of the convex measurement sample W has a convex shape There is a short-cut component of the surface SH wave (lower broken line in the figure) linearly propagating inside the convex measurement sample W, not along the surface. The propagation time T _S includes a shortcut component of the surface SH wave, which causes a measurement error. That is, the calculated propagation time T _S (measured value) becomes indeterminate.

Therefore, in the present invention, the propagation time T _S including the short-cut component of the surface SH wave as a measurement error is corrected, and the corrected propagation time T ′ _{S of} the surface SH wave and the propagation time T _{R of the} Rayleigh wave are corrected. The residual stress σ ′ present in the surface layer of the convex measurement sample W is evaluated on the basis of
Note that the Rayleigh wave, the sample to be measured even in the convex (curved) shape, there is little change in the propagation time T _R of Rayleigh wave propagating surface of the convex.
First Embodiment
A first embodiment of the residual stress evaluation method in the present invention will be described.

The residual stress evaluation method according to the present embodiment includes a sending step, a receiving step, a propagation time calculating step, a correcting step, and an evaluating step.
The above-mentioned residual stress evaluation method will be described in detail based on each step.
In the sending step, the SH probe and the SV wave are sent from the transmission probe 2 to the surface of the convex measurement sample W. The SH wave sent out to the surface of the convex measurement sample W excites the surface SH wave shown by the broken line in FIG. 2, and the SV wave excites the Rayleigh wave shown by the solid line in FIG.

In the receiving step, the receiving probe 3 receives the surface SH wave and the Rayleigh wave propagated through the surface layer of the convex measurement sample W. At this time, the voltage generated by the reception is output as a detection signal of the Rayleigh wave and the surface SH wave. The output detection signal is amplified by the amplifiers 5 and 6, and the amplified detection signal is output to the waveform sampling device 7.
In the propagation time calculation step, the waveform sampling device 7 samples the waveforms of the detection signals of the surface SH wave and the Rayleigh wave, and receives the trigger signal output from the pulse generator 4. Then, to calculate the propagation time T _S of the surface SH wave by measuring the time until the reception of surface SH wave detection signal from the reception of the trigger signal, the time from the reception of the trigger signal and receiving a Rayleigh wave detection signal the measures to calculate the propagation time T _R of Rayleigh wave.

In the correction step, a correction amount ΔT _S for correcting the propagation time T _S (measured value) of the surface SH wave is calculated in the propagation time calculation step with a reference propagation time T _S0 of the surface SH wave previously calculated. Calculated from the propagation time T _S of the surface SH wave, the propagation time T _S of the surface SH wave is corrected with the calculated correction amount ΔT _S to obtain a corrected propagation time T ′ _{S of} the surface SH wave.
In the evaluation step, the evaluation device 8, based correction propagation time T _'S correction surface SH wave calculated in the correction step, to the propagation time T _R of Rayleigh wave and calculated by the propagation time calculating step, the lower The residual stress σ ′ present in the surface layer of the convex measurement sample W is evaluated using the equation (2) of

Subsequently, a characteristic of this embodiment, the step of correcting the propagation time T _S of the surface SH wave, will be described in detail.
A plurality of convex test pieces Ta having the same material as the convex measurement sample W in advance and having the same material as the convex test sample W and having the same material as the convex measurement sample W An arbitrary number of convex test pieces Tb are prepared.

As shown in FIG. 3A, first, the propagation time T _S0 of the surface SH wave in the flat plate test piece Ta and the propagation time T _R0 of the Rayleigh wave are calculated. Here, let propagation time TS0 of the surface SH wave in flat plate test piece Ta be the reference propagation time of the surface SH wave used at a correction _| amendment step.
Next, the propagation time T _SX of the surface SH wave in the convex test piece Tb and the propagation time T _RX (X: arbitrary number) of the Rayleigh wave are calculated for each radius r (r _{1 to} r _X ).

For example, the radius of the convex shape when the convex test piece Tb of r _1, the propagation time T _S1 of the surface SH wave, the propagation time T _R1 of Rayleigh waves are calculated.
As shown to FIG. 3B, propagation time _TSX of surface SH wave corresponding to every radius r of convex shape is put together on the graph etc. FIG. Specifically, the radius r of the convex shape on the horizontal axis, vertical axis and as the propagation time T _SX surface SH wave, the propagation time of the surface SH wave T _SX calculation result, i.e., the propagation of surface SH wave in each test piece Plot the time T _S0 -T _S3 . The graph in which the propagation times T _{S0 to} T _S3 are plotted is stored later as a correction graph used when calculating the correction amount ΔT _S in the correction step.

Note that the summary of the propagation time T _S0 through T _S3 of surface SH wave in each test piece, or may be stored as a correction table. That is, keep the propagation time _T S0 _{through T S3} of surface SH wave in each test piece as correction data.
In the correction step, a correction graph (correction data) in which the propagation times T _{S0 to} T _{S3 and the} like of the surface SH wave in each test piece shown in FIG. 3B are stored, and based on this correction graph A correction amount ΔT _S of the propagation time T _S of the surface SH wave in W is calculated.

For example, in the actual measurement (measurement of the sample W), the radius of the convex shape is r ₂ and the propagation time T _S2 of the surface SH wave in the convex measurement sample W is calculated as shown in FIG. Referring to the correction graph, it can be understood that it corresponds to the plot point C. And a plot point A indicating a reference propagation time T _S0 of the plotted point C and the surface SH wave, the propagation time T _S of the surface SH wave in convex sample W, there is a measurement error due to shortcuts component of the surface SH wave You can see that

Therefore, taking the difference between the plot points A and plot point C, as the correction amount [Delta] T _S of the propagation time T _S of the surface SH waves the difference in convex measurement sample W, is calculated.
The corrected propagation time T ′ _S is calculated by adding the calculated correction amount ΔT _S to the propagation time T _S of the surface SH wave in the measured convex-shaped measurement sample W as in the following equation (3).

As described above, in advance, to calculate the propagation time T _SX surface SH wave in the test piece, by preparing as correction data together the propagation time T _SX, convex to be evaluated It becomes possible to easily and accurately calculate the correction amount ΔT _S for correcting the propagation time T _S of the surface SH wave propagating in the surface layer of the measurement sample W.
Second Embodiment
A second embodiment of the residual stress evaluation method in the present invention will be described.

The residual stress evaluation method according to the present embodiment is characterized in the correction step, and will be described in detail focusing on only this correction step. The sending step, the receiving step, the propagation time calculating step, and the evaluating step in the present embodiment are the same as the procedure described in the first embodiment, and thus the description thereof will be omitted.
By the way, in the present embodiment, the evaluation object is different from the first embodiment, and for example, a convex shape such as a joint (welded portion) where a mechanical component is joined to a structure etc. The measurement sample W is an evaluation target of the residual stress σ ′.

Therefore, in the present embodiment, the correction step of calculating the correction amount ΔT _S for correcting the propagation time T _S of the surface SH wave is different from the procedure of the first embodiment.
A plurality of convex test pieces Ta having the same material as the convex measurement sample W in advance and having the same material as the convex test sample W and having the same material as the convex measurement sample W An arbitrary number of convex test pieces Tb are prepared.

In the present embodiment, as shown in FIG. 4A, the arrangement of the transmission probe 2 and the reception probe 3 such that the propagation distance L ′ of the surface SH wave and the Rayleigh wave is different in each test piece. do. For example, the propagation distance L 'is set to three types of 50 mm, 100 mm, and 200 mm, and for each propagation distance L', the propagation time T _SX of the surface SH wave in each test piece and the propagation time T _RX of the Rayleigh wave calculate.

Specifically, a flat plate test piece Ta is prepared, and the propagation distance L 'is set to 50 mm. Then, the propagation time T _S0 (50) of the surface SH wave of the flat plate test piece Ta and the propagation time T _R0 (50) of the Rayleigh wave at the propagation distance L ′ = 50 mm are calculated. Here, the calculated propagation time T _S0 (50) of the surface SH wave of the flat plate test piece Ta is taken as the reference propagation time of the surface SH wave at the propagation distance L ′ = 50 mm.

Subsequently, a convex test piece Tb having a convex shape with a radius of r ₁ is prepared, and the propagation distance L ′ is set to 50 mm. The propagation time T _S1 (50) of the surface SH wave of the convex test piece Tb in which the radius of the convex shape at the propagation distance L ′ = 50 mm is r ₁ and the propagation time T _R1 (50) of the Rayleigh wave are calculated. Thus, the propagation distance L '= on set to 50 mm, the convex test piece Tb radius of the convex shape is r _2, the convex test piece Tb radius of the convex shape is r _3, each surface SH Wave propagation times T _S2 (50), T _S3 (50) and Rayleigh wave propagation times T _R2 (50), T _R2 (50) are calculated.

Furthermore, the propagation time of the surface SH wave and the propagation time of the Rayleigh wave are set using the flat plate test piece Ta and the convex test piece Tb after setting each propagation distance L ′ (L ′ = 100 mm, 200 mm). Ask. That is, T _S0 (100) to T _S3 (100) and T _R0 (100) to T _R3 (100), and T _S0 (200) to T _S3 (200) and T _R0 (200) to T _R3 (200) Ask for

Furthermore, as shown in FIG. 4B, the propagation time of the surface SH wave corresponding to each propagation distance L ′ (L ′ = 50 mm to 200 mm) and for each convex shape radius r (r _{0 to} r ₃ ) T _SX and the propagation time T _RX of the Rayleigh wave are put together in a graph or the like and stored as a correction graph (correction data). In FIG. 4B, the case of L '= 50 mm is represented by a graph of X, the case of L' = 100 mm is represented by a graph of Δ, and the case of L '= 200 mm is represented by a graph of □. There is.

Based on the correction chart shown in FIG. 4B, it calculates the correction amount [Delta] T _S of the propagation time T _S of the surface SH wave in convex measurement sample W.
Specifically, in the actual measurement (measurement of the convex measurement specimen W), and the propagation time T _S of the surface SH wave in convex sample W, the propagation time T _R of Rayleigh wave is calculated.
First, when the propagation time T _S of the surface SH wave is applied to the correction graph of FIG. 4B and referred to, it corresponds to two points of the plot point E (graph of Δ mark) and plot point F (graph of □ mark) I understand.

Next, when the calculated propagation time T _R of the Rayleigh wave is applied to the correction graph of FIG. 4B and referred to, it can be understood that the graph of Δ corresponds. Since this graph has a propagation distance L 'of 100 mm, it is estimated that L' = 100 mm in the measurement of the convex measurement sample W.
Thus, referring to the correction graph of FIG. 4B, even if there are a plurality of propagation distances L with the same propagation time T _S in the surface SH wave, the propagation distance L from the value of the propagation time T _R of the Rayleigh wave Is uniquely determined. That is, it can be said that the propagation distance L can be uniquely narrowed down by using the correction graph of FIG. 4B.

Thereafter, in the correction graph of FIG. 4B, attention is paid to the graph of Δ.
The radius of the convex shape in the convex measurement sample W is estimated to be r ′ ₂ (plot point E) by applying and referring to the calculated propagation time T _S of the surface SH wave with respect to the graph of Δ marks. Do.
A plot point E indicating the propagation time T _S (100) of the surface SH wave with the estimated radius r ′ ₂ and a reference propagation time T _{S 0} (1) of the surface SH wave at propagation distance L ′ = 100 mm
This difference is calculated as the correction amount ΔT _S of the propagation time T _S (100) of the surface SH wave in the convex measurement sample W by taking the difference from the plot point G indicating 00).

The corrected propagation time T ' _S (100) is calculated by adding the calculated correction amount ΔT _S to the propagation time T _S (100) of the surface SH wave in the measured convex-shaped measurement sample W as in equation (3). calculate.
As described above, the propagation time T _SX of the surface SH wave of each test piece and the propagation time T _RX of the Rayleigh wave are calculated in advance for each propagation distance L ′, and the respective propagation times T _SX , After T _RX is prepared as correction data collectively, the propagation time T _S of the surface SH wave, which changes depending on the size of the radius r of the convex shape, and the change almost regardless of the size of the radius r of the convex shape Correction amount for correcting the propagation time T _S of the surface SH wave propagating on the surface of the convex measurement sample W whose value of the radius r of the convex shape is unknown by using the propagation time T _{R of the} Rayleigh wave which does not It becomes possible to calculate ΔT _S easily and with high accuracy.

It should be understood that the embodiments disclosed herein are illustrative and non-restrictive in every respect. In particular, in each embodiment disclosed this time, matters not explicitly disclosed, for example, operating conditions and conditions, various parameters, dimensions of components, weights, volumes, etc. Without deviating from this, those skilled in the art will employ values that can easily be envisioned.

DESCRIPTION OF SYMBOLS 1 Residual stress evaluation device 2 Transmission probe 3 Reception probe 4 Pulse generator 5, 6 Amplifier 7 Waveform sampling device 8 Evaluation device 20, 30 Piezoelectric element 21, 31 Ultrasonic wave propagation medium W Convex measurement sample (convex shape Subject sample)
Ta flat plate test piece Tb convex test piece

Claims (3)

A residual stress evaluation method for evaluating residual stress present in the surface layer of a convexly-shaped object sample based on the propagation time of ultrasonic waves propagating in the surface layer of the object sample,
A sending step of exciting an ultrasonic wave on the surface layer of the subject sample;
A receiving step of receiving an ultrasonic wave propagated through the surface layer of the subject sample;
A propagation time calculating step of calculating a propagation time of the ultrasonic wave received in the receiving step;
A correction step of calculating a correction amount for correcting the propagation time of the ultrasonic wave calculated in the propagation time calculation step, and correcting the propagation time of the ultrasonic wave with the calculated correction amount;
Evaluating the residual stress present in the surface layer of the subject sample based on the corrected propagation time of the ultrasonic wave corrected in the correcting step;
I have a,
The ultrasonic waves are surface SH waves and Rayleigh waves,
The correction step calculates a correction amount for correcting the propagation time of the surface SH wave calculated in the propagation time calculation step, and corrects the propagation time of the surface SH wave with the calculated correction amount.
In the evaluation step, residual stress present in the surface layer of the subject sample is evaluated based on the correction propagation time of the surface SH wave corrected in the correction step and the propagation time of the Rayleigh wave. The residual stress evaluation method characterized by being . In advance, a flat plate test piece made of the same material and flat as the subject sample, and a plurality of convex test pieces made of the same material as the subject sample and having different radii are provided. Leave,
In the correction step,
Assuming that the propagation distance of the surface SH wave and the Rayleigh wave is constant, the propagation time of the surface SH wave in the flat plate test piece is calculated to be the reference propagation time, and the propagation of the surface SH wave in the plurality of convex test pieces Calculate the time and set it as the convex propagation time for each radius,
The residual stress evaluation method according to claim 1 , wherein the correction amount is calculated as a difference between a convex propagation time corresponding to a radius of a convex shape in the subject sample and the reference propagation time. In advance, a flat plate test piece made of the same material and flat as the subject sample, and a plurality of convex test pieces made of the same material as the subject sample and having different radii are provided. Leave,
In the correction step,
The propagation time of the surface SH wave in the flat plate test piece is calculated for each propagation distance after making the propagation distance of the surface SH wave and the Rayleigh wave plural, and the propagation time of the surface SH wave is taken as a reference propagation time. Calculate the propagation time of the surface SH wave in the test piece and store it as the convex propagation time for each radius,
An actual propagation distance is calculated based on the propagation time of the Rayleigh wave in the subject sample,
From the convex propagation time corresponding to the calculated actual propagation distance and the propagation time of the surface SH wave in the subject sample, the radius of the convex shape of the subject sample is estimated;
Claim 1, characterized in that to calculate the correction amount said as the difference between the convex propagation time of the surface SH wave in the test sample, and the reference propagation time corresponding to the radius of the estimated said convex Residual stress evaluation method.