JPH0749944B2 - Simultaneous measurement of material thickness and sound velocity - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for simultaneously measuring material thickness and sound velocity, which is effective for production process control, nondestructive inspection, material test measurement and the like.

[0002]

2. Description of the Related Art In manufacturing processes such as rolling of metal and stretching of plastic sheets, it is necessary to keep the thickness of a product at a designed value, and therefore it is important to measure the thickness. Thickness measurement using ultrasonic waves is often used as a simple and highly accurate method. However, this measurement requires a value of sound velocity, and since the sound velocity value changes when the material changes, there is a problem that an error occurs in the measured value of thickness. vice versa,
For the quality control of the material, it is effective to measure the sound velocity, but generally it is necessary to measure the thickness accurately, and the thickness measurement error becomes the sound velocity measurement error.

To explain the above-mentioned point more concretely, when measuring the sound velocity of an object with ultrasonic waves, the thickness D of the object is measured separately with a micrometer, and this value and the round-trip propagation time of ultrasonic waves in the object are measured. It is common to calculate the speed of sound from the ratio of. That is, the time Δt during which the ultrasonic wave reciprocates in the plate thickness direction in the object is measured, and the sound velocity v is calculated by v = 2D / Δt. On the contrary, if the sound velocity in the object is known and the thickness of the object is desired to be obtained, a commercially available ultrasonic thickness gauge may be used. This ultrasonic thickness gauge calculates the thickness D by the formula D = vΔt / 2. That is, the sound velocity value v must be input in the ultrasonic thickness gauge. However,
In general, it is difficult to measure the thickness of an object, and the sound velocity may be unknown, and the thickness cannot be measured by the above method in such a case.

On the other hand, there are thickness gauges using fluorescent X-rays and eddy currents, but these also assume that the physical properties such as X-ray spectrum and electric conductivity are constant, and in this sense, they are super It has the same problems as the sonic thickness gauge. The most direct thickness measurement method is a method for obtaining the thickness from the displacement of a contact probe, such as a micrometer or a dial gauge.
However, this is the average value in the area of head thickness,
When the thickness differs depending on the location, it is difficult to obtain the thickness at the same location as the sound velocity measurement. Also, it is not easy to apply to a moving plate during production test or material testing. Further, as a non-contact thickness gauge, there is an optical probe such as a light section method, which is suitable for measuring a moving object. However, optical measurement is easily affected by dust and turbidity of liquid, and cannot be used in a harsh environment such as a production line.

[0005]

SUMMARY OF THE INVENTION The technical problem of the present invention is that it is possible to simultaneously measure the thickness and the sound velocity of the same portion of a material in a simple and highly accurate thickness measurement using ultrasonic waves. It is to provide a new method and significantly improve the accuracy and reliability of quality control.

[0006]

[Means for Solving the Problems] The method for simultaneously measuring the thickness and the sound velocity of the material of the present invention for solving the above problems is as follows.
A pair of ultrasonic transmitter and receiver are arranged so as to face each other in a liquid whose sound velocity v _C is known, and a plate-like material is inserted between them to transmit a direct transmitted wave V ₁ when ultrasonic waves are transmitted from the transmitter. , An interval Δt of arrival time of the round-trip wave V ₂ that has made one round trip in the material to the receiver, and an interval Δt of arrival time of the direct transmission wave V ₁ and the liquid transmission wave V ₃ when the material is not inserted. 'Is measured, and based on those time intervals, the sound velocity v of the ultrasonic wave in the material is obtained by v = v _C (1 + 2Δt' / Δt), and D = v _C (Δt / 2 + Δt ') It is characterized in that the thickness D is obtained.

More specifically, referring to the drawings,
In FIG. 1, it is assumed that the ultrasonic transmitter and the receiver have their relative positions fixed and are held in the ultrasonic wave propagating liquid at the sound velocity v _C. In a state where there is no plate-shaped material as a sample between the transmitter and the receiver, first, the ultrasonic pulse transmitted from the transmitter is detected and recorded by the receiver. This pulse is V ₃ in FIG.

Then, a sample made of a plate-shaped material is inserted between the transmitter and the receiver, and the same measurement is performed. The direct transmission wave from the transmitter is set to V ₁ in FIG. The round-trip wave that makes a round trip is the same V ₂ . At this time, if the sound velocity v in the sample is higher than the sound velocity v _C in the liquid, the arrival time of the direct transmitted wave V ₁ should be faster than that of the pulse V ₃ , and the time difference Δt ′ is Δt ′ = ( D / v _C −D / v). In addition, the round-trip wave V ₂ that has reflected back and forth once inside the sample twice has a time difference Δt = 2D / from the directly transmitted wave V _1.
It is easy to see that it is delayed by v.

Then, these equations yield two unknowns D and v.
Since both equations are solved for D and v, we obtain v = v _C (1 + 2Δt ′ / Δt) D = v _C (Δt / 2 + Δt ′). That is, the thickness of the sample and the sound velocity are simultaneously measured based on the difference in the ultrasonic wave propagation time when the sample is inserted between the transmitter and the receiver of the ultrasonic wave and when there is no sample and the round-trip propagation time in the sample. To be done.

On the other hand, FIG. 3 shows a case where the method of the present invention is applied to measurement in a material test. In this case, hold the sample on the material testing machine, apply a load, generate an ultrasonic pulse in the ultrasonic transmitter based on the output from the pulse generator, and pass it through the receiving ultrasonic lens. It is input and recorded in a digital oscilloscope, and the time intervals Δt and Δt ′ described above are measured to determine the change in the sound velocity of ultrasonic waves in the material and the thickness of the material.

In the material test, the thickness and material of the sample change momentarily due to deformation when a load is applied to the sample. The thickness varies depending on the place, and even if measured with a micrometer after the test, it is impossible to know the process of the change. Furthermore, the elastic modulus changes with the occurrence of strain, but it is very difficult to measure the change during the test. However, according to the method of the present invention described above, the change in thickness of the sample can be easily measured. Further, since the sound velocity in the sample changes with the change in elastic modulus, the method of the present invention that can measure the sound velocity at the same time is extremely useful for the measurement in this material test.

[0012]

EXAMPLE FIG. 4 shows a plate-shaped material of known thickness (measured by a micrometer) such as stainless steel or polyethylene, which is measured by the known thickness and the method of the present invention described with reference to FIG. The result of having compared thickness is shown. As can be seen from the figure, the results of the measurement according to the method of the present invention are accurately measured with respect to plates of various materials having a thickness of 0.3 mm to 15 mm, regardless of the difference in sound velocity. Further, in FIG. 5, the sound speeds measured for various materials by the method of the present invention are compared with the literature values of the sound speeds of those materials. Also in this case, the values of both are in good agreement. The above results show the usefulness of the present invention.

Further, the change in the sample thickness and the change in the sound velocity during tensile deformation at low temperature were simultaneously measured by the method as described with reference to FIG. The sample of SUS304 is shown in FIG.
FIG. 7 shows the thickness in the case of tensile deformation at 70 ° C., and FIG. 7 also shows the sound velocity and the echo amplitude ratio (V ₁ / V ₂ ).

In these measurements, the load was increased stepwise from 20 kg to 600 kg, the load was controlled to be constant at each step, and the measurement was performed after the elongation became constant. The sample thickness is
It decreased with increasing load, and the sound velocity also decreased. Furthermore, it was suggested that the echo ratio also decreased and the attenuation decreased. The thickness of these samples taken out after the test was measured at room temperature and the sound velocity attenuation was measured by a usual method, and it was confirmed that they were almost the same as the values at 600 kg. In particular, it can be seen that the attenuation is significantly reduced by the test at low temperature.
Confirmed from measurement at z. It was also confirmed from the change in magnetizability that this change was due to martensitic transformation.

[0015]

According to the method of the present invention detailed above,
The effects listed below can be expected. 1. According to the present invention, for a plate material or a thin film whose sound velocity and thickness are unknown, since the sound velocity and the thickness can be measured simultaneously and independently,
It is effective for quality control and non-destructive inspection of these materials.

2. According to the method of the present invention, a signal required for measurement can be obtained by transmitting and receiving one ultrasonic pulse at the same time, and at the same time, necessary calculation is extremely simple, so that measurement can be performed very quickly. This time can be less than 1 millisecond according to recent digital signal processing technology. Therefore, by using this feature, it becomes possible to measure the shape of the material at the moment of destruction and the change in sound velocity in association with each other.
It will be a powerful weapon for studying the fracture properties of materials.

3. The apparatus for realizing the method of the present invention can be reduced in cost because it only requires a transmission / reception circuit, a digital memory or a time interval measuring device, and a simple arithmetic unit used for a normal ultrasonic nondestructive inspection. Therefore, it can be easily used for inspection in a factory line and is useful for maintenance of production quality.

4. As described in detail above, a commercially available ultrasonic thickness meter requires input of sound velocity values, and thickness meters using fluorescent X-rays, eddy currents, etc. are also premised on input of physical property values unique to each device. However, the present invention does not require them. Further, in the contact type probe and the optical probe, the absolute thickness can be measured without setting the physical property values, but it is difficult to apply the method to a moving object or a non-clean environment. The method can be applied relatively easily to measurements in various environments.

[Brief description of drawings]

FIG. 1 is an explanatory diagram of a method of the present invention.

FIG. 2 is an explanatory diagram of signals obtained by the measuring method of the present invention.

FIG. 3 is an explanatory diagram of a case where the method of the present invention is applied to measurement in a material test.

FIG. 4 is a graph showing the results of comparison between the thickness of a sample having a known thickness and the thickness measured by the method of the present invention.

FIG. 5 is a graph comparing the sound velocity measured by the method of the present invention with the literature value of the sound velocity.

FIG. 6 is a graph showing the results of measuring the sample thickness during tensile deformation at low temperature in a material test.

FIG. 7 is a graph showing the results of measuring the sound velocity and the echo amplitude ratio.

Claims (1)

[Claims] 1. A direct transmitted wave when a pair of ultrasonic transmitters and receivers are arranged so as to face each other in a liquid whose sound velocity is known, and a plate-like material is inserted between them to transmit ultrasonic waves from the transmitters. When,
An interval Δt between arrival times at the receiver and a reciprocating wave traveling back and forth through the material, and an interval Δt ′ between arrival times between the direct transmission wave and the liquid transmission wave when the material is not inserted are measured. A method for simultaneous measurement of material thickness and sound velocity, characterized in that the sound velocity of ultrasonic waves in the material and the thickness of the material are obtained based on time intervals.