JPS61207938A - Stress measuring method using sound elastic film - Google Patents

Abstract

PURPOSE:To execute a measurement having an excellent stress sensitivity by sticking a sound elastic film of a high polymer material to the surface of a testing member, and measuring a stress of the testing member from a difference of a sound pressure reflection factor by a variation of a Young's modulus of the film. CONSTITUTION:A high frequency electric signal which has been generated by an oscillator 4 is led to a piezoelectric transducer 3 through a circulator 6, and converted to an ultrasonic wave. Also, it is radiated to an ultrasonic propagation medium 7 and becomes an incident ultrasonic wave 8, and it is made incident vertically on the surface of a testing member 1. When the surface of the testing member 1 is covered by an adhesion, etc., with a sound elastic film 2 such as a high polymer material of a large attenuation, by which an intensity of a reflected wave of an interface to the testing member 1 becomes small, a variation of a Young's modulus caused by a difference of a distortion appears greatly as a difference of a sound pressure reflection factor, and in the film 2 and the propagation medium 7, a reflected ultrasonic wave 9 returns to the piezoelectric transducer 3 again, it is converted to an electric signal being proportional to the intensity of its reflected wave thereby, led to a receiver 5 through the circulator 6, and a reflected voltage is obtained. This reflected voltage becomes that which has reflected a distortion of the testing member 1.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a stress measuring method using an acoustoelastic coating, and more particularly to a stress measuring method using an acoustoelastic coating attached to the surface of a test member.

(Prior Art) Conventionally, stress measurement methods using photoelastic coatings have been widely known.

This known method uses the fact that the stress state on the surface of the test member is two-dimensional to determine the principal stress difference on the surface in the same way as in the case of two-dimensional photoelasticity.

That is, as shown in FIG.
, and is partially reflected by the semi-transparent mirror 24 to form an arrow 27
Incident light 27 traveling in the direction is made perpendicularly incident on the test member surface 21 via a polarizer (analyzer) 25 and a quarter-wave plate 26. The incident light 27 is applied to the glittering material coating 22.
It becomes reflected light 28 on the test member surface 21 , passes through the quarter-wave plate 26 and the polarizer 21 , passes through the semi-transparent mirror 24 , and then forms an image on the screen 29 . The stress applied to the surface of the test member is measured by the moiré fringes that appear on the image due to the two-dimensional strain on the surface of the test member.

(Problems to be Solved by the Invention) In the stress measurement method using the known photoelastic coating, it is essential that the photoelastic material used as the coating is optically transparent, and the light reflected on the surface of the test member In order to measure stress, the thickness of the photoelastic material coating can be considered to be equivalent to the characteristics of one twice as thick. This photoelastic sensitivity depends on the thickness of the photoelastic material in the coating, so the greater the thickness, the better.
In practice, the thickness cannot be increased very much, and the strain produced in the photoelastic material is extremely small, so it has the disadvantage of poor sensitivity. In addition, the coating needs to have a uniform thickness, and although the state of reflected light changes depending on the adhesion state of the photoelastic material coating to the test member surface, it is difficult to adhere well. Furthermore, there were problems in terms of actual accuracy, such as the need to polish the surface of the test member to a high degree of precision in order to obtain favorable reflected light.

Therefore, it has been practically difficult to apply the stress measurement method using such a photoelastic material coating to the stress measurement of actual structural members.

(Objective of the Invention) The present invention aims to solve the drawbacks of the above-mentioned technology using light and provide a method for measuring stress sensitivity that is excellent in stress sensitivity. The purpose is to provide a stress measurement method using

(Means for Solving the Problems) In order to achieve the above object, a stress measurement method according to the present invention uses a high frequency electric signal oscillator and receiver, a circulator, and a piezoelectric transducer, and The space between the deuser and the test member is filled with an ultrasonic propagation medium, and a sonoelastic film made of a polymeric material is pasted on the surface of the test member. Features (Function) characterized by measuring the stress of the test member from the difference in baroreflectance According to the stress measuring method of the present invention, the optical transparency and uniform thickness of the coating applied to the surface of the test member can be improved. It is almost independent of the characteristics, thickness limitations, polishing accuracy of the test member surface, etc.
By using a material whose acoustic impedance is relatively close to that of water as a coating (a coating may be used), it is possible to construct a measurement method with excellent stress sensitivity.

(Example) Hereinafter, a method for measuring stress using an anoelastic coating according to the present invention will be described in detail with reference to the drawings.

FIG. 1 shows a first embodiment of the invention. The sonoelastic coating 2 is attached to the surface of the test member 1 by adhesive or coating. The film 2 can be made of ordinary polymer films or paint films, but typical examples include bakelite celluloid, epoxy resin, polycarbonate, which is also used as a photoelastic film material, and optical materials such as Teflon resin. Transparent opaque materials can also be used. In this case, the thickness of the coating may be about 10 μm or more, and the thickness may have some non-uniformity. Furthermore, it is provided with an oscillator 4 and a receiver 5 for high-frequency electric signals, a piezoelectric transducer 3 that generates and receives ultrasonic waves, and a circulator 6. Fill with ultrasonic propagation medium 7. The ultrasonic propagation medium 7 has a function of suppressing the reflection attenuation at the interface and the attenuation in the propagation path of the ultrasonic wave, and usually water is used.

In the above configuration, the high frequency electric signal generated by the oscillator 4 is guided to the piezoelectric transducer 3 via the circulator 6 and converted into an ultrasonic wave.

The ultrasonic wave is further radiated to the ultrasonic propagation medium 7 to become an incident ultrasonic wave 8 which is perpendicularly incident on the surface of the test member 10 .

Since the stress (σ)-strain (ε) relationship of the acoustoelastic coating material has a nonlinear relationship as shown in Figure 3, the value of its longitudinal elastic function (δσ/aε) also depends on the strain (ε). However, it is non-linear.

Generally, the sound pressure reflectance (reflected wave intensity) at the interface between the acoustoelastic coating 2 and the ultrasonic propagation medium 7, which has the same strain as the surface of the test member 1, is high.

However, Z: Acoustic impedance of the propagation medium, Z2: Acoustic impedance of the acoustic elastic coating, δl: Density of the propagation medium, δ2: Density of the coating, C1: Longitudinal sound velocity of the propagation medium, B2 = Young's modulus of the coating. .

Therefore, a material with an impedance close to the acoustic impedance of the propagation medium 7 is selected, e.g.
If the surface of the test member 1 is coated with an acoustoelastic coating 2 such as a high-attenuation polymer material that reduces the intensity of the reflected wave at the interface, the change in Young's modulus due to the difference in strain will be as shown in Figure 3. As shown, this appears as a large difference in sound pressure reflectance.

At the interface between the coating 2 and the propagation medium 7, the ultrasonic wave 9 reflected by the above-mentioned sound pressure reflectance returns to the piezoelectric transducer 3 again, where it is converted into an electrical signal proportional to the intensity of the reflected wave, The signal is guided to the receiver 5 via the circulator 6, and a reflected voltage is obtained.

The reflected voltage reflects the distortion of the test member 1.

As mentioned above, if the ultrasonic waves 8 are perpendicularly incident on the test member l covered with the acoustoelastic coating 2, it is possible to obtain a sound pressure reflectance (reflected wave intensity) that depends on the strain of the test member 1. . This is because, as shown in Fig. 3, the strain amount of the acoustoelastic coating material and the Young's modulus are uniquely related, and the sound pressure reflectance at the interface between the acoustoelastic coating 2 and the ultrasonic propagation medium 7 is as shown above. Since it is expressed as follows, it is possible to relate the amount of distortion and the sound pressure reflectance via Young's modulus.

In this case, if water is used as the ultrasonic propagation medium 7 and a polymer material such as polycarbonate, which has low water absorption and has an acoustic impedance value similar to that of water, is used as the sonoelastic coating 2, stress can be reduced. This allows for highly sensitive measurements.

However, in this case, the reflected waves at the interface between the test member 1 and the sonoelastic coating 2 become noise. Therefore, a high-attenuation polymeric material is used as the coating so that the intensity of the reflected wave at the interface is significantly smaller than the intensity of the reflected wave at the interface between the propagation medium 7 and the acoustic elastic coating 2. It is necessary to select the thickness of the coating 2.

Conversely, when the thickness of the coating 2 is determined, the reflected wave at the interface between the propagation medium 7 and the acousto-elastic coating 2 and the reflected wave at the interface between the test member 1 and the acousto-elastic coating 2 are separated. It is necessary to use an oscillator 4 that is capable of generating an incident wave with such short pulses as possible.

Note that the piezoelectric transducer 3 normally used has a diameter of 1
Since the size is about 0 mm, the azimuth resolution in stress measurement is poor. Therefore, in order to improve the lateral resolution, an acoustic lens 10 is interposed between the piezoelectric transducer 3 and the ultrasonic propagation medium 7 to transmit the ultrasonic waves, as shown in another embodiment of FIG. to create a focused incident ultrasonic wave 11;
In addition, a positive focal point may be set on the surface of the acoustoelastic coating 2 so that the focused incident ultrasonic wave 11 is perpendicularly incident on the surface of the test member 1. This makes it possible to obtain resolution at the wavelength level of the ultrasonic waves used.

In the experiment, a polycarbonate film with a thickness of 0.3 mm was pasted on the surface of a test piece of iron-based material with a circular hole, and then the test piece was pulled and subjected to a reflection ultrasound microscope using ultrasonic waves with a frequency of 120 MHz. As a result, it was possible to obtain a strain distribution with a lateral resolution of about 12.5 μm.

(Effects of the Invention) Since the stress measurement method using an acoustoelastic coating according to the present invention has the above-described configuration, it is possible to measure optically opaque materials, which was impossible with the conventional photoelastic coating measurement method. can also be used as a coating, and in that case, the thickness of the coating that can be used only needs to be about 10 μm or more, and even if there is some non-uniformity in the thickness, the reflected waves at the interface with the test member is not a problem because it is attenuated or separated from the reflected wave at the interface with the propagation medium.

In addition, since the reflected waves from the interface with the test member are not used at all, the polishing accuracy of the test member surface is not so much of an issue. There is no problem.

Furthermore, the azimuth resolution can be improved by focusing the ultrasonic waves using an acoustic lens.

Therefore, the stress measuring method according to the present invention has the advantage that the scope of use is expanded, and that it can be used as is, for example, with existing corrosion-resistant coatings for metal materials and the like. It has many advantages over conventional known techniques.

[Brief explanation of drawings]

FIG. 1 is a schematic configuration diagram showing one embodiment of the present invention, FIG. 2 is a schematic configuration diagram showing another embodiment, and FIG. 3 is a stress-strain relationship curve diagram of the acoustoelastic coating material according to the present invention. , FIG. 4 is a schematic diagram of the structure of a conventional stress measurement method using a photoelastic coating. 1... Test member 2... Acoustic elastic coating 3...
Piezoelectric transducer 4... Oscillator 5... Receiver 6... Circulator 7... Ultrasonic propagation medium 8 - Incident ultrasound 9.12... Reflected ultrasound 10... Acoustic lens 1
1... Focused incident ultrasound Figure 1 Figure 2 Figure 3 - ε

Claims (1)

[Claims] 1. In a method for measuring stress on a test member, a high-frequency electric signal generated from a high-frequency electric signal oscillator is supplied to a piezoelectric transducer via a circulator and converted into an ultrasonic wave, and the piezoelectric transducer and the test member are The acoustic impedance of the surface of the test member is close to that of the ultrasonic propagation medium, and the intensity of the reflected wave at the interface with the test member is A sonoelastic coating such as a polymeric material with large attenuation is applied by coating, adhesive, etc., and the difference in sound pressure reflectance at the interface between the coating and the propagation medium due to the change in the Young's modulus of the coating is reflected by ultrasonic waves. is detected by the piezoelectric transducer, the electrical signal converted by this is directed to a receiver for high-frequency electrical signals by a circulator, and the receiver detects the difference in sound pressure reflectance due to the strain caused in the test member. A method for measuring stress using an acoustoelastic coating, characterized in that the stress in the test member is measured by detecting the stress in the test member. 2. In the method of measuring stress on a test member, a high-frequency electric signal generated from a high-frequency electric signal oscillator is supplied to a piezoelectric transducer via a circulator and converted into an ultrasonic wave, and a signal is filled between the piezoelectric transducer and the test member. The ultrasonic wave is directed to the test member through a certain ultrasonic propagation medium, and the surface of the test member has an acoustic impedance close to that of the ultrasonic propagation medium, and has a large attenuation that reduces the intensity of the reflected wave at the interface with the test member. In the piezoelectric transducer described above, an acoustoelastic coating such as a polymeric material is applied by coating, adhesive, etc., and the difference in sound pressure reflectance at the interface between the coating and the propagation medium due to a change in the Young's modulus of the coating is used as reflected ultrasound. The detected and converted electric signal is directed to a high-frequency electric signal receiver by a circulator, and the receiver detects the difference in sound pressure reflectance due to the strain generated in the test member, and performs the test. A stress measuring method using an acousto-elastic coating for measuring stress in a member, the acousto-elastic coating being characterized in that an acoustic lens is used between the piezoelectric transducer and the ultrasonic medium to focus the ultrasonic waves. Stress measurement method used.