JP3159143B2 - Non-destructive inspection method of internal organization - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION The present invention relates to an internal structure of a workpiece subjected to a surface hardening treatment by quenching or the like.
A method for grasping nondestructively.

[0002]

2. Description of the Related Art Heretofore, there has been used a method of transmitting an ultrasonic wave that can penetrate a work which has been subjected to a surface hardening treatment by quenching or the like to non-destructively grasp the state of an internal structure. FIG. 9 shows a state of the internal structure of the quenched work 1. At a certain depth from the surface 2 of the work 1, a hardened layer 3 transformed into a desired hardened layer is formed. Then, as the depth increases, the influence of the heat treatment is gradually weakened, whereby the degree of alteration is gradually reduced to the base layer 5 which is not affected by the heat treatment via the boundary layer 4. In practice, it is rare that the boundaries between the above-mentioned layers are clearly present, and the state of the organization changes gradually. However, here, for the sake of convenience of explanation, it is assumed that the above-mentioned three layers are used. I do.

[0003] In order to grasp the state of the internal structure of the work 1, an inspection method using ultrasonic waves is used. In this case, an ultrasonic pulse of a specific frequency is used. An ultrasonic pulse can penetrate inside tissue if its wavelength λ is greater than the roughness of the internal tissue. When the propagation velocity v is constant (the sound velocity in the work is constant), the frequency f and the wavelength λ have an inverse relationship (f = v / λ). Thus, the frequency that can be transmitted can be specified.

The size of the internal structure of the work 1 is such that the quenched layer 3 has the finest structure, the boundary layer 4 has a coarser structure, and the base layer 5 has the finest structure. Therefore, when grasping the depth of the quenched layer 3, an ultrasonic pulse having a frequency that can be transmitted through the quenched layer 3 but cannot be transmitted through the base layer 5 is used as the specific frequency. When the ultrasonic pulse of this specific frequency is transmitted to the surface 2 of the work 1, a reflected ultrasonic wave as shown in the graph of FIG. 10 is measured. The vertical axis of the graph indicates the intensity I of the reflected wave, and the horizontal axis indicates the propagation time T from transmission of the ultrasonic wave to measurement of the reflected wave. The reflected wave S is a surface reflected wave on the surface 2 of the work 1, and the reflected wave R is a boundary reflected wave on the boundary layer 4. Then, since the propagation speed v at which the ultrasonic wave propagates in the work 1 is constant,
The depth D of the quenched layer 3 can be obtained from the propagation time T ₂ until the reflected wave R is measured (D = (v × T)
/ 2). Thus, the conventional method determines the propagation time T ₂ from the waveform of the reflected wave. That is, the state of the internal tissue is grasped from the waveform of the measured reflected wave. As the above-mentioned conventional example, the inventors disclose the details in JP-A-7-229705.

[0005]

However, the above-mentioned conventional example has the following problems. In the conventional example, the ultrasonic wave is transmitted to the work 1 and the propagation time (depth of the quenched layer 3) is obtained from the waveform of the reflected wave. Therefore, the actually measured reflected wave R is a very small level. . Therefore, in order to more clearly detect the waveform of the reflected wave R, it is necessary to increase the output of the ultrasonic wave. Therefore, the energy of the ultrasonic wave is increased at a certain point by squeezing the ultrasonic wave and forming a focal point. Then, a technique of obtaining a clear reflected wave R by focusing this focus on the boundary layer 4 is adopted.

When the ultrasonic wave is focused on the quenched layer 3, the transmitted ultrasonic wave does not generate a reflected wave, and the ultrasonic wave that has reached the boundary layer 4 is already diffused. Therefore, a clear reflected wave R cannot be obtained. Further, when the focus is on the base layer 5, since the ultrasonic waves are not concentrated yet at the boundary layer 4, a clear reflected wave R cannot be obtained, and the ultrasonic waves are not reflected on the boundary layer 4. Cannot be transmitted, the waveform of the reflected wave at the focal position is disturbed, and it becomes impossible to measure the propagation time. That is, unless the ultrasonic waves are accurately focused, the reflected wave R cannot be clearly measured.

Therefore, there is a contradiction that the depth of the boundary layer 4 must be grasped in advance in order to grasp the internal structure of the work. Conventionally, a technique has been adopted in which ultrasonic waves are experimentally transmitted while changing the focal position variously, and the boundary layer 4 is estimated from the waveform of the reflected waves obtained here.
The inventors disclose the details of this method in Japanese Patent Application Laid-Open No. H8-220077. However, in this method, the waveform of the reflected wave to be measured changes depending on the state of the surface 2 of the work and the state of the internal structure, and it has been difficult to quantitatively measure various works. Therefore,
The value of the measured reflected wave R tends to vary, and highly reliable measurement data can be obtained only by skilled workers.

SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned problems, and an object of the present invention is to make it possible to grasp the state of the internal structure of a work accurately, easily and nondestructively, and to improve the quality of the work. It is to further improve the reliability of products and reduce costs by performing checks more reliably.

[0009]

Means for solving the above-mentioned problems according to the present invention is to transmit an ultrasonic pulse of a specific frequency focused on a predetermined depth of a work, and an ultrasonic wave reflected from the work. After counting the number of peak signals of the pulse, the process of changing the predetermined depth is repeated, and the internal tissue is inspected from the counted number, wherein a threshold value is provided for the level of the ultrasonic pulse reflected from the workpiece. And counting the number of peak signals separately inside and outside the threshold value.

In the present invention, a peak signal of an ultrasonic pulse reflected (hereinafter, referred to as a reflected wave) while moving the focal point of the ultrasonic wave of a specific frequency from the surface of the work to a desired depth. Count the number. By the way, when inclusions such as cracks and impurities exist in the range where the focal point of the ultrasonic wave is moved, the ultrasonic pulse reflected by the inclusions is much larger than the boundary reflected wave. Therefore, a threshold value is provided for the level of the ultrasonic pulse reflected from the work, and the number of peak signals is counted separately inside and outside the threshold value. Then, the position of the inclusion is grasped from the peak signal outside the threshold. Further, the number of peak signals inside the threshold value is compared with a predetermined value corresponding to the quenched layer to be obtained, and the reflection at the focal depth of the ultrasonic wave when these values satisfy a certain relationship. The propagation time of the wave is obtained, and the state of the internal tissue is grasped from the propagation time.

According to another aspect of the present invention, there is provided a method for transmitting an ultrasonic pulse of a specific frequency to a predetermined depth of a work by focusing the ultrasonic pulse on a predetermined depth of the work. the threshold is provided, in and out of the threshold, respectively after counting the number of peak signal for each unit time, the predetermined depth repeated strokes to change, aggregate the peak number of signals counted per unit time Then, the distribution pattern is obtained, and the internal tissue is inspected from the distribution pattern.

According to the above configuration, while moving the focal point of the ultrasonic wave of the specific frequency from the surface of the work to the desired depth, the number of peak signals of the reflected ultrasonic pulse is calculated as
Count and record every unit time. By the way, when inclusions such as cracks and impurities exist in the range where the focal point of the ultrasonic wave is moved, the ultrasonic pulse reflected by the inclusions is much larger than the boundary reflected wave. Therefore, a threshold value is provided for the level of the ultrasonic pulse reflected from the work, and the number of peak signals is counted separately inside and outside the threshold value. Further, the number of peak signals inside and outside the threshold value counted for each unit time is totaled, and from the distribution pattern, the peak signal is generated at a given depth of the work, and at which depth the reflected signal is reflected. The characteristics of the distribution pattern, such as whether the wave is increasing, are obtained. From this distribution pattern, the state of the internal organization is grasped.

In the present invention, a distribution pattern obtained by summing up the number of peak signals of reflected waves having a level not exceeding the threshold value can be used for an internal tissue inspection. The set threshold value separates the reflected wave caused by the inclusion from the reflected wave caused by a change in the state of the internal tissue. Therefore, the state of the internal tissue is grasped without being affected by the reflected wave due to the inclusion by counting the peak signal number of the reflected wave of the level not exceeding the threshold value.

Further, in the present invention, a distribution pattern obtained by summing up the number of peak signals of reflected waves having a level exceeding the threshold value can be used for specifying the position of the inclusion in the internal tissue. . The reflected wave having a level exceeding the set threshold value is a reflected wave generated by the inclusion. Therefore, the position of the inclusion in the internal tissue is specified from the distribution pattern of the peak signal number of the reflected wave, and the state of the internal tissue is grasped.

[0015]

Embodiments of the present invention will be described below with reference to the accompanying drawings. Here, the same or corresponding portions as in the conventional example are denoted by the same reference numerals, and detailed description thereof will be omitted.

FIG. 1 schematically shows an inspection apparatus for performing a nondestructive inspection method for an internal tissue according to a first embodiment of the present invention. The inspection device 6 places the work 1 in a water tank 7 filled with water, and supports the work 1 with a scanning device 9 so that an ultrasonic sensor 8 which is a means for transmitting an ultrasonic pulse can move in the water. Scanning device 9 is three-dimensional
The ultrasonic sensor 8 can be moved to the next position. The ultrasonic sensor 8 has a function of focusing an ultrasonic pulse to be transmitted. The ultrasonic measurement device 10 includes an ultrasonic transmission / reception circuit therein and is connected to the ultrasonic sensor 8.
To transmit an ultrasonic wave of a specific frequency to the ultrasonic sensor 8
To receive the reflected wave received at. Then, a peak signal level of a reflected wave and a peak signal propagation time, which will be described later, are sent to the data analyzer 11. The scanning device 9 is connected to a control device 12, and the operation of the scanning device 9 is controlled by the control device 12. Also,
The control device 12 is connected to the data analysis device 11 and sends the position data of the scanning device 9 to the data analysis device 11. In the data analyzer 11 (a personal computer or the like can be used),
Based on the received data, the scattering probability distribution of the reflected wave is calculated as described later, and the internal structure of the work 1 is inspected.

Here, the procedure of the method for inspecting an internal tissue according to the first embodiment of the present invention will be described. 2 to 4
Shows the inspection process in order. In each figure, (a) shows the focal position inside the work 1, (b) shows the measured waveform of the reflected wave, (c) shows the propagation time of the reflected wave, and counts the peak signal of a predetermined level or more. The relationships with numbers are shown respectively.

First, an ultrasonic pulse of a specific frequency is transmitted from the ultrasonic sensor 8 to the workpiece 1 with its focal position fixed. As the specific frequency, as in the conventional example, when the depth of the quenched layer 3 is grasped, the quenched layer 3 can be transmitted, but the boundary layer 4 is hardly transmitted (the base layer 5 is Value that cannot be transmitted). The ultrasonic sensor 8 is moved by the scanning device 9 shown in FIG. 1 to gradually reduce the distance between the ultrasonic sensor 8 and the work 1 (generally, this is referred to as a water distance) while gradually reducing the ultrasonic pulse. Is gradually moved from the surface 2 of the work 1 toward the base layer 5 (FIG. 2). In addition, the ultrasonic sensor 8 repeats the movement and the temporary stop, and emits an ultrasonic pulse at each temporary stop.
By the way, when the transmission interval of the ultrasonic pulse is set to 1 kHz, 1000 peak signals can be counted in one second. Only the pick-up is picked up and its count is recorded in correspondence with the passage of the propagation time.

FIG. 2 shows an initial stage of the inspection process. As shown in FIG. 2A, the focal point F of the ultrasonic pulse at this time is on the hardened layer 3 of the work 1. The waveform of the reflected wave obtained here is shown in FIG. At this time, a reflected wave S (a surface reflected wave on the surface 2 of the work 1) is detected, but a reflected wave R (a boundary reflected wave in the boundary layer 4) having a predetermined level or more, that is, a peak signal cannot be detected. Also, as shown in the figure, inclusions
When 13 exists, the reflected wave U by the inclusion 13 is detected. The reflected wave U due to the inclusion 13 is much larger than the reflected wave R detected in a later inspection process. (The difference between the amplification factor of the amplifier required to detect the reflected wave R and the amplification factor required to detect the reflected wave U is 1
0 dB or more. Therefore, when the amplification factor of the amplifier is set so that the reflected wave R can be detected, the detection signal of the reflected wave U is detected as a saturation level.

Therefore, a threshold value is set for the level of the ultrasonic pulse reflected from the work. As shown in FIG. 2B, the inside of the threshold value is defined as a region A and the outside of the threshold value is defined as a region B, and the count of the peak signal is separately performed inside and outside the threshold value. As described above, since the reflected wave U is detected as the saturation level, it is easy to distinguish the reflected wave R from the reflected wave U. FIG. 2C shows the transition of the count number of the peak signal related to the reflected wave R by a solid line. The transition of the count number of the peak signal related to the reflected wave U is indicated by a dotted line. In this inspection process, the count number N of the peak signal related to the reflected wave R does not increase as the propagation time T elapses. However, the count number of the peak signal related to the reflected wave U rapidly increases and decreases within a certain range of the propagation time T.

FIG. 3 shows an intermediate stage of the inspection process. As shown in FIG. 3A, the focal point F of the ultrasonic pulse transmitted from the ultrasonic sensor 8 moves to the boundary layer 4 of the work 1 by shortening the water distance as compared with that in FIG. . FIG. 3B shows the waveform of the reflected wave obtained here. In this inspection process, a peak signal (reflected wave R) having a level equal to or higher than a predetermined level is clearly detected after a certain time has elapsed since the detection of the reflected wave S. Also, as in the case of FIG. 2B, the peak signal related to the reflected wave U is clearly detected. Therefore, as shown in FIG. 3C, the count number N of the peak signal in the area A increases with the lapse of the propagation time T, and when the propagation time T corresponds to the intermediate layer 4,
The count number N becomes the maximum. Then, as the propagation time T further elapses, the count number N decreases.
The count number of the reflected wave U in the area B is shown in FIG.
It sharply increases and decreases in the same range as (c).

FIG. 4 shows the final stage of the inspection process. As shown in FIG. 4A, at this time, the water distance is further reduced, and the focal point F of the ultrasonic pulse transmitted from the ultrasonic sensor 8 reaches the base layer 5 of the work 1. FIG. 4B shows the waveform of the reflected wave obtained here. At this time, after a certain time has passed since the detection of the reflected wave S,
A peak signal (reflected wave R) of a predetermined level or more is detected. The peak signal related to the reflected wave U is shown in FIG.
It is clearly detected as in FIG. Therefore, as shown in FIG. 4C, the count number N of the peak signal in the area A increases or decreases as the radio wave time T elapses. The count number of the reflected wave U in the area B is shown in FIG.
(C), rapidly increases and decreases in the substantially same range as FIG. 3 (c).

When the above measurement is completed for each measurement object, the data analyzer 11 (FIG. 1)
As shown in FIGS. 3 (c) and 4 (c), a large number of data (each having a different focal depth) recording the count number N of the peak signal for each unit time and separately inside and outside the threshold value.
Tally. Then, as shown in FIG. 5, a pattern of how the number of peak signals counted per unit time is distributed with respect to the propagation time is separately obtained for each of the region A and the region B. From this distribution pattern, characteristics of the distribution pattern of the peak signal generation depth, such as when the peak signal is generated, that is, at what depth, and at what depth the peak signal is increasing, are read.

From the aggregated data relating to the area A, for example, the time when the count number N has reached a value smaller by a predetermined ratio from the propagation time when the number of peak signals is the maximum is determined.
Is determined as the formed depth. This criterion is an example, and the difference in the material of the work and the set value of the specific frequency, etc.
Various settings can be made according to the conditions at the time of measurement. Therefore, the propagation time when the number of peak signals is maximum is used as a criterion, or the time when an intermediate value between the minimum value and the maximum value of the number of peak signals is achieved is used as a criterion,
The discontinuity of the distribution pattern (such as a change in the rate of increase of the peak signal) can be used as a criterion. Also, from the aggregated data relating to the region B, it is possible to grasp the position (depth) of the inclusion, for example, based on the time point when the number of peak signals becomes maximum.

The operation and effect obtained from the embodiment of the present invention having the above configuration are as follows. In the present embodiment, while the focal point F of the ultrasonic pulse having the specific frequency is gradually moved from the surface 2 of the work 1 to the base layer 5,
The reflected wave of the ultrasonic pulse is measured for each position of the focal point F. In addition, a threshold value is provided for the level of the ultrasonic pulse in the reflected wave, a region A is inside the threshold value, and a region B is outside the threshold value. Do. In the area A, only a peak signal (reflected wave R) exceeding a predetermined level is picked up and its count is recorded in correspondence with the elapse of the propagation time. Similarly, the peak signal (reflected wave U) in the area B is recorded in correspondence with the elapse of the propagation time. Then, the data recorded at the end of the measurement is totaled for each of the areas A and B, and a pattern of how the number of peak signals counted per unit time is distributed with respect to the propagation time is obtained. . The characteristic of this distribution pattern is read, and the depth at which the quenched layer 3 is formed is determined from the distribution pattern of the region A. The position of the inclusion is grasped from the distribution pattern of the region B.

The point to be noted here is that the number of peak signals obtained from the point of focus F to the surface of the workpiece 1 to the base layer 5 is totaled, and the distribution pattern of the number of peak signals obtained here is obtained. The purpose is to determine the depth of the quenched layer 3 and to grasp the position of the inclusion. That is, unlike the related art, the ultrasonic wave is focused on a certain point and the depth of the quenched layer 3 is not determined from only the data (waveform of the reflected wave) obtained therefrom. In a range,
By statistically processing a plurality of measurement data (the number of peak signals) that can be easily measured, the quenched layer 3 is reliably distinguished from the inclusions, and the depth of the quenched layer 3 and the position of the inclusions are determined. Can be detected more accurately.

Further, since the focal point F is moved from the surface 2 of the work 1 to the base layer 5,
There is no need for a skilled worker to previously adjust the focus F to a specific position (such as the boundary layer 4), and the entire inspection process can be automated. Moreover, the waveform of the measured reflected wave is directly converted into the quenched layer 3.
It does not use it as a basis for determining the depth of an object or the position of an inclusion, but also statistically processes a plurality of measurement data. Therefore, factors that adversely affect the waveform of the reflected wave, such as the positioning accuracy of the scanning device 9 and the degree of attenuation of the ultrasonic wave due to a change in the water distance, do not affect the quality of the inspection result. It also facilitates the management of the accuracy required for From the above, anyone can grasp the state of the internal organization of the work accurately, easily and nondestructively.

FIG. 6 shows an application example of this embodiment.
Let us consider a case where the work 1 to be inspected has a cylindrical shape such as a rotating shaft as shown in FIG. In this case, the inspection device 6
(FIG. 1) includes a work driver (not shown) that rotatably supports a work and is capable of freely controlling a rotation angle, and a control device (not shown) for the work driver. A device that can send the rotation angle data of the work to the device 11 (FIG. 1) is used.

When measuring the frequency of occurrence of the peak signal of the scattered wave (reflected wave), the rotation angle W of the work 1
For example, 1/1000 of one rotation is defined as one rotation angle, and when the counting of the peak signal for one rotation is completed, the ultrasonic sensor 8
The operation of reducing the water distance Z by a predetermined distance is repeated. Then, the data obtained for each rotation angle W is totaled, and the same processing as in FIGS. 2 to 5 is performed, and the depth of the quenched layer 3 and the position of the inclusion are grasped for each rotation angle W. Then, from the distribution pattern of the region A, a sectional view showing a change in the state of the internal tissue is created as shown in FIG.
Output to Further, from the distribution pattern of the region B, FIG.
As shown in (1), a cross-sectional view showing the position of the inclusion is created and output to the display device.

Also in this application example, a threshold value is provided for the level of the reflected wave to be detected, and the number of peak signals of the reflected wave is counted separately inside and outside the threshold value, so that the change in the state of the internal tissue can be prevented. It is possible to visualize separately from the position of the inclusion. Therefore, the internal organization can be grasped more accurately. Also, although the description is omitted, the state change of the internal structure is similarly applied to a work having a flat surface,
It is possible to visualize separately from the position of the inclusion.

[0031]

As described above, the present invention has the following effects. First, according to the method according to claim 1 of the present invention, a threshold value is provided for the level of the ultrasonic pulse reflected from the work, and the count of the number of peak signals is performed separately inside and outside the threshold value. Even without a skilled worker, it is possible to accurately grasp the change in the tissue and the position of the inclusion without destruction. Therefore, the work quality can be more reliably checked, and the reliability of the product can be improved and the cost can be further reduced.

According to the method of claim 2 of the present invention, the count of the number of peak signals is divided inside and outside of the threshold value, and is counted for each unit time, so that the inside of the threshold value is counted. From the distribution pattern, it is possible to determine the characteristics of the distribution pattern, such as at which depth of the workpiece the peak signal is generated and at which depth the reflected wave is increasing. Then, from the distribution pattern, it is possible to accurately grasp the state of the internal structure nondestructively without depending on a skilled worker.

Further, according to the method according to the third aspect of the present invention, the distribution pattern obtained by summing the number of peak signals of the reflected wave having a level not exceeding the threshold value has an effect on the reflected wave due to the inclusion. It is possible to accurately grasp the internal organization without receiving it.

In addition, according to the method of the fourth aspect of the present invention, the position of the inclusion in the internal tissue can be determined from the distribution pattern obtained by totalizing the number of peak signals of the reflected wave having a level exceeding the threshold value. Accurate identification becomes possible, and diversification of information obtained from non-destructive inspection of internal tissues can be achieved.

[Brief description of the drawings]

FIG. 1 is a schematic view showing an apparatus for performing a nondestructive inspection method for an internal tissue according to an embodiment of the present invention.

FIGS. 2A and 2B show an initial stage of an inspection process according to an embodiment of the present invention, in which FIG. 2A shows a focal position inside a workpiece 1, FIG. 2B shows a waveform of a measured reflected wave, and FIG. FIG. 4 is a diagram showing the relationship between the propagation time of a reflected wave and the count number of a peak signal having a predetermined level or more, divided into a region A and a region B in FIG.

3A and 3B show an intermediate stage of an inspection process according to the embodiment of the present invention, in which FIG. 3A shows a focal position inside the work 1, FIG. 3B shows a measured reflected wave waveform, and FIG. FIG. 4 is a diagram showing the relationship between the propagation time of a reflected wave and the count number of a peak signal of a predetermined level or more, divided into a region A and a region B in FIG.

4A and 4B show the final stage of the inspection process according to the embodiment of the present invention, in which FIG. 4A shows the focal position inside the work 1, FIG. 4B shows the waveform of the measured reflected wave, and FIG. FIG. 4 is a diagram showing the relationship between the propagation time of a reflected wave and the count number of a peak signal having a predetermined level or more, divided into a region A and a region B in FIG.

FIG. 5 is a diagram showing a distribution pattern of peak signals in which the count numbers of peak signals recorded for each unit time are totaled in an area A and an area B in the embodiment of the present invention.

FIG. 6 is a schematic diagram showing a configuration of a main part of an apparatus for performing a nondestructive inspection method of an internal tissue according to an application example of an embodiment of the present invention.

FIG. 7 is obtained by an application example of the embodiment of the present invention;
It is sectional drawing showing the state change of an internal structure.

FIG. 8 is obtained by an application example of the embodiment of the present invention;
It is sectional drawing showing the position of an inclusion.

FIG. 9 is a cross-sectional view showing a state of an internal structure of a quenched work.

FIG. 10 is a schematic diagram showing a reflected wave of an ultrasonic pulse obtained by a conventional nondestructive inspection method for an internal tissue.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Work 2 Surface 3 Quenching layer 4 Boundary layer 5 Base layer A Area inside threshold B Area outside threshold F F Focus of ultrasonic pulse N Count of peak signal R Reflected wave S Reflected wave T Propagation Time W Workpiece rotation angle

Claims (4)

(57) [Claims] 1. A process of transmitting an ultrasonic pulse of a specific frequency focused on a predetermined depth of a work, counting the number of peak signals of the ultrasonic pulse reflected from the work, and changing the predetermined depth. Is a method of examining internal tissue from the count number, wherein a threshold value is provided for the level of the ultrasonic pulse reflected from the work, and inside and outside the threshold value, the count of the peak signal number is divided. A nondestructive inspection method for an internal tissue, which is performed. 2. An ultrasonic pulse of a specific frequency is transmitted while being focused on a predetermined depth of a work, and a threshold value is provided for a level of the ultrasonic pulse reflected from the work. after counting the number of peak signal for each unit time, the predetermined depth repeated strokes to change, the distribution pattern determined by aggregating the peak number of signals counted per unit time, the internal tissue from the distribution pattern A non-destructive inspection method for an internal tissue, comprising: 3. The method according to claim 2, wherein a distribution pattern obtained by summing up the number of peak signals of reflected waves having a level not exceeding the threshold value is used for an internal tissue inspection. Destructive inspection method. 4. A distribution pattern obtained by summing the number of peak signals of reflected waves having a level exceeding the threshold value is used for specifying the position of an inclusion in an internal tissue. Non-destructive inspection method for internal tissues as described.