JPH07229798A - Residual stress measuring method and its device - Google Patents

Abstract

PURPOSE:To provide a measuring method to measure the residual stress of a material relatively simply and securely by utilizing supersonic wave, and its measuring device. CONSTITUTION:One side surface of an about semi-spherical wave guide body 1 is placed adhering to a material to be measured 2. A supersonic wave is oscillated from an oscillator 9 which can slide on the about semi-sphrical surface 4 of the wave guide body 1, and its reflected wave is received by a receiver 10. The position where the received reflected wave has the maximum value is sought, and the directions of the main stresses 61 and 62 are specified together with their orthogonal directions. As to those directions, the sound velocities V3 and V2 at the oscillation angle theta of the primary input reflected wave of the supersonic wave, and the sound velocities V1' and V2' at the oscillation angle theta' of the secondary input reflected wave depending on a double refraction phenomenon when the oscillation angle is changed at the same position are measured. The residual stress (sigma1-sigma2) is calculated from the sound velocity difference (V1-V2) and (V1'-V2').

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method of measuring residual stress of various materials using ultrasonic waves and a measuring apparatus therefor, and particularly to measuring residual stress inside the surface layer of a material relatively easily and accurately.

[0002]

2. Description of the Related Art Conventionally, various physical methods have been used as a method for qualitatively knowing the residual stress of various materials. Also,
Mechanical methods and X-ray methods are used as quantitative methods. Among them, the X-ray method is the X-ray method on the surface of the material to be measured.
The displacement of the crystal lattice of the material is measured from the diffraction image of the scattered X-ray generated by projecting a line, and the stress value is calculated from the result, which has the advantage that the material can be measured nondestructively.

[0003]

However, the above-mentioned X
The line method cannot avoid the influence of material anisotropy caused by, for example, the manufacturing history of the material. Further, the measurement depth is limited to 300 Å at most, which is very close to the surface, and it is hard to say that this is the residual stress of the material.

[0004]

In view of the above problems, the present inventor has conducted research based on an idea that is completely different from the conventional technique, and uses ultrasonic waves to measure the residual stress of a material. I succeeded in doing so.

The ultrasonic wave used is shear horizontal shear wave (S
H wave), and is preferably a pulse wave having a frequency of 0.5 to 20 MHz.

First, this ultrasonic wave is oscillated by an oscillator toward the inside of the material to be measured through a waveguide placed in close contact with one surface of the material to be measured. Then, while the reflected wave from the measured material is being received by the geophone, the oscillation position of the ultrasonic wave is slid little by little, and the direction in which the received reflected wave takes the maximum value is measured to obtain the measured material. The direction of the maximum principal stress σ ₁ of is specified, and two principal stress directions are specified together with the direction of the principal stress σ ₂ orthogonal to this direction.

Next, with respect to the direction of the maximum principal stress σ _{1 and} the direction of the principal stress σ ₂ orthogonal thereto, the sound velocity V at the oscillation angle θ of the primary incident reflected wave of the ultrasonic wave.
₁ , V ₂ and the oscillating angle at the same position to change the sound velocity V ₁ ′ at the oscillating angle θ ′ of the secondary incident reflected wave based on the birefringence phenomenon,
V ₂ 'were measured and, acoustic velocity difference (V ₁ -V ₂₎ and (V _1' -
The residual stress is calculated from V ₂ ′).

The material of the shoe which constitutes a part of the ultrasonic oscillator and the geophone is acrylic, metal, quartz or Si.
C, graphite, zirconia, TiC-based cermet, WC-based cemented carbide or the like is used. Further, the shoe is capable of adjusting an incident / reflection angle of an incident / reflected wave.

On the other hand, it is assumed that the waveguide has a shape formed by one surface having a shape in close contact with one surface shape of the material to be measured and a substantially hemispherical surface.

[0010]

The reason why the type of ultrasonic wave used in the present invention is preferably shear horizontal shear wave (SH wave) is that the shear wave has a characteristic of propagating at right angles. This is because the horizontal wave has high stability without causing a phenomenon such as mode conversion from a transverse wave to a longitudinal wave when reflected on the bottom surface of the material.

The reason why the frequency of the ultrasonic wave is preferably in the range of 0.5 to 20 MHz is that if the frequency is too small, the wavelength becomes too long and the measurement accuracy decreases, and conversely if the frequency is too large. This is because the wavelength becomes too short and is likely to be attenuated. The frequency range is a range that ensures good accuracy and is suitable for preventing excessive attenuation.

The reason why the waveform of the ultrasonic wave is preferably the pulse wave is that the pulse wave has an effect of preventing the ultrasonic waves from interfering with each other in a complicated manner at the time of reflection on the bottom surface of the material.

The material of the shoe forming part of the ultrasonic oscillator and the geophone has an appropriate acoustic impedance difference from the material to be measured, is transparent, and is made to come into contact with the waveguide. While sliding, a material with good wear resistance is selected.

One surface of the waveguide has a shape capable of closely adhering to one surface shape of the material to be measured. For example,
If the material surface is flat, one surface of the waveguide is processed to be flat, and if the outer peripheral surface of a cylindrical material, one surface of the waveguide is processed to be a concave surface with the same curvature, so that ultrasonic waves can smoothly propagate. .

The surface of the waveguide other than the contact surface is formed into a substantially hemispherical shape, and the ultrasonic oscillator and the geophone are brought into contact with the substantially hemispherical surface so that the contact position can be freely moved. By aligning the directions of the oscillator and the geophone with the center of the ball, it is possible to always arrange the fixed point regardless of the contact position.

Under the above-mentioned conditions, the measurement range of the residual stress of the material to be measured finally obtained by the measurement means of the present invention is the measurement range of the residual stress of the ultrasonic oscillator and the geophone in the width direction. Is the range in contact with, and the range from the material surface to the reflection point of the ultrasonic wave in the depth direction. Then, the obtained measured value is an average value in the range,
Compared with the conventional measuring method, the residual stress value of the measured material is more reliable.

[0017]

EXAMPLE An example of the residual stress measuring method of the present invention and the measuring apparatus therefor will be described with reference to the drawings.

In FIG. 1, a waveguide 1 is a solid material having a shape formed by a flat surface 3 that is in close contact with one flat surface of a material 2 to be measured in a flat plate shape and a substantially hemispherical surface 4.
If the contact surface with the material to be measured 2 is a curved surface, the portion corresponding to the flat surface 3 needs to be a curved surface following the curved surface.

A groove 5 is provided on the substantially hemispherical periphery of the waveguide 1, and the projection 5 provided on the base of the arm 6 having a substantially semi-circular shape is fitted with the groove 5. The arm 6 can swivel about the axis of symmetry of the waveguide 1.

The arm 6 is provided with a groove 8 in its longitudinal direction, and an ultrasonic oscillator 9 and a geophone 10 are inserted in the groove 8. The oscillator 9 and the geophone 10 are movable in the groove 8 and, in combination with the swing of the arm 6,
Any position can be set on the substantially hemispherical surface 4.

FIG. 2 is a schematic view showing an embodiment of the oscillator 9 (or the geophone 10), and is a vertical cross section in a state of being fixed to the arm 6. A screw 12 is cut at one end of a case 11 of the oscillator 9 and fixed to the arm 6 by tightening a nut 13. The shoe 14 incorporated in the tip of the oscillator 9 refracts the ultrasonic beam and makes it enter the waveguide 1. Since the end face slides while contacting the waveguide 1, an appropriate acoustic impedance difference is obtained. Acrylic, metal, quartz, SiC, graphite, zirconia, TiC-based cermet, WC-based cemented carbide and the like, which are transparent and have wear resistance, are suitable.

3 and 4 are schematic diagrams for explaining the principle of the present invention.

More specifically, the substantially hemispherical shape of the waveguide 1 means a shape whose spherical center coincides with the bottom surface of the measured material 2. In other words, it is a shape obtained by subtracting the thickness of the measured material 2 from the hemisphere.

Now, an ultrasonic wave is oscillated from the oscillator 9 toward the spherical center, and a reflected wave from the bottom surface of the material 2 to be measured is received by the geophone 10.
While sliding on the approximately hemispherical surface 4,
It is assumed that the reflected wave has the maximum value when it reaches the position shown in (a). At this time, the maximum principal stress σ ₁ inside the material to be measured 2 and another principal stress σ ₂ orthogonal thereto are as shown in FIG.

FIG. 3B is a lower side view of FIG. 3A, where the oscillation angle is θ and the sound velocity is V ₁ in the above state. Then changing the oscillation angle, and geophone secondary reflected waves based on the birefringence phenomenon repeatedly reflected in the order of bottom-top-bottom surface of the measured material 2, the oscillation angle of the lever theta ', the acoustic velocity V _1' and To do.

After that, the arm 6 is turned by 90 degrees to bring the arm 6 into the state of FIG. 4 (a), and the same measurement as above is repeated. FIG. 4B is a right side view of FIG. 4A. The sound velocity at the oscillation angle θ is V ₂ and the sound velocity at the oscillation angle θ ′ is V ₂ ′.

In the above measurement, the oscillating ultrasonic wave is
Shear horizontal wave (SH) of transverse wave with frequency of 0.5 to 20 MHz
Wave) and a pulse wave. Since the oscillator 9 and the geophone 10 are symmetric with respect to the symmetry axis of the waveguide body 1, operability is improved by engraving the angle scale on the arm 6. Further, it is preferable to engrave angular scales along the groove 5 of the waveguide 1 also in the turning direction of the arm 6.

The residual stress is calculated from the following equations 1 and 2. The sonic velocities V ₀ are the sonic velocities V ₁ and V ₂ when measuring the sample in the natural state (non-loaded state) of the measured material _2.
Is the average speed of. Similarly, the speed of sound V ₀ ′ is the average speed of the speeds of sound V ₁ ′ and V ₂ ′ of the sample. Further, C _ik is the elastic modulus of the material crystal, and S _ik is the elastic coefficient, which is a constant separately obtained from experiments or calculations.

[0029]

[Equation 1]

[0030]

[Equation 2] However,

[0031]

[Equation 3]

[0032]

[Equation 4] Calculated from the simultaneous equations of Equations 1 and 2 (σ ₁ −σ ₂ )
Is the required residual stress.

FIG. 5 shows an example of the system of the residual stress measuring device of the present invention, which is constructed by connecting an ultrasonic pulse oscillating and vibration receiving device, a sound velocity measuring device and a computer. The ultrasonic pulse oscillating and vibration receiving device is configured by functions such as synchronous pulse oscillating, ultrasonic pulse oscillating, amplifying, and zero-cross time detection.

[0034]

INDUSTRIAL APPLICABILITY As described above, the residual stress measuring method and the measuring apparatus thereof according to the present invention provide an unprecedented method of measuring residual stress of various materials using ultrasonic waves. It has a feature that it can measure even inside the surface layer, and can be measured relatively easily and accurately.

[Brief description of drawings]

FIG. 1 is a diagram showing an embodiment of a residual stress measuring device of the present invention, and is a perspective view of a waveguide 1 portion.

FIG. 2 is a vertical sectional view of an oscillator 9 fixed to an arm 6 shown in FIG.

FIG. 3 is a schematic diagram for explaining the principle of the present invention,
(A) is a plan view and (b) is a lower side view thereof.

FIG. 4 is a schematic diagram for explaining the principle of the present invention,
(A) is a plan view and (b) is a right side view thereof.

FIG. 5 is a system diagram showing an embodiment of the overall configuration of the residual stress measuring device of the present invention.

[Explanation of symbols]

 1 Waveguide 2 Material to be measured 6 Arm 9 Oscillator 10 Geophone 14 Shoe

Claims (8)

[Claims] 1. An oscillator 9 oscillates an ultrasonic wave toward the inside of the material to be measured 2 through a waveguide 1 placed in close contact with one surface of the material to be measured 2 to measure the material 2 to be measured. While the reflected wave from the sample is received by the geophone 10, the oscillation position of the ultrasonic wave is slid little by little, and the direction in which the received reflected wave takes the maximum value is measured to obtain the maximum value of the measured material 2. The direction of the principal stress σ ₁ is specified, and two principal stress directions are specified together with the direction of the principal stress σ ₂ orthogonal to this direction, and the direction of the maximum principal stress σ ₁ and the principal stress σ orthogonal to the direction. Oscillation of the secondary incident reflected wave based on the birefringence phenomenon by changing the oscillation angle at the same position as the sound speeds V ₁ and V ₂ at the oscillation angle θ of the primary incident reflected wave of the ultrasonic wave in each of the _two directions. angle theta 'acoustic velocity V ₁ in the' measured and V ₂ ', acoustic velocity difference (V ₁ -V ₂₎ Contact Beauty (V ₁ '-V _2') from the residual stress (σ ₁ -σ ₂₎ Residual stress measurement method to calculate the. 2. The type of ultrasonic wave is shear horizontal wave (S
The residual stress measuring method according to claim 1, wherein the residual stress is H waves). 3. The frequency of ultrasonic waves is 0.5 to 20 MHz.
The residual stress measuring method according to claim 1 or 2, wherein 4. The residual stress measuring method according to claim 1, wherein the waveform of the ultrasonic wave is a pulse wave. 5. The material of the shoe 14 constituting a part of the ultrasonic oscillator 9 and the geophone 10 is acrylic, metal, quartz, SiC, graphite, zirconia, TiC-based cermet, WC-based cemented carbide or the like. The residual stress measuring method according to claim 1, wherein the residual stress measuring method is used. 6. The shoe 14 of the ultrasonic oscillator 9 and the geophone 10 according to claim 5 is a shoe 14 capable of adjusting the oscillation / received angle of an incident / reflected wave. The residual stress measuring method according to claim 5. 7. The shape of the waveguide 1 is formed by one surface 3 having a shape in close contact with one surface shape of the measured material 2 and a substantially hemispherical surface 4. The residual stress measuring method according to claim 1. 8. A substantially semi-circular arc-shaped arm 6 capable of turning around a symmetry axis is provided on a substantially hemispherical surface 4 of a waveguide 1, and an ultrasonic oscillator 9 and an ultrasonic oscillator 9 are provided on the arm 6. A residual stress measuring device in which a geophone 10 is incorporated so as to be movable in the longitudinal direction of the arm 6.