JPS61286750A - Method for flaw detection by standing wave of ultrasonic wave - Google Patents

Abstract

PURPOSE:To make it possible to easily detect the presence of an internal flaw, by transmitting ultrasonic waves to an object to be inspected comprising a wooden material from a plurality of probes and measuring the phase of a received standing wave. CONSTITUTION:For example, a probe 3 transmitting an ultrasonic wave and probes 1, 2 receiving a standing wave are arranged to the flaw detection surface A of an object 4 to be inspected comprising a lauan board material. Next, the cut groove 5' corresponding to an internal flaw is formed to the predetermined position of the object 4 and an ultrasonic waves having a sine wave form of 1-10kHz are transmitted at every 0.2kHz from a signal generator 6 through the probe 3 and the generated standing waves are received by the probes 1, 2 and, when the phase difference is compared with the phase difference characteristics preliminarily measured at the time of no flaw, the presence of the cut groove 5' can be detected because there is phase difference exceeding the threshold value of the phase difference set corresponding to the object 4. By this method, the presence of the internal flaw can be detected certainly and easily.

Description

[Detailed Description of the Invention] (Industrial Application Field) The present invention detects internal defects in a flaw detection target such as a wood-based material or a composite material by naturally interfering with ultrasonic waves transmitted inside the flaw detection target. waves (hereinafter referred to as standing waves in the present invention).

) is used in the field of flaw detection.

(Prior Art) In the woodworking industry to which the present invention is applicable, defects inside logs have conventionally been estimated by visual inspection based on intuition gained from many years of experience. Very recently, ultrasonic flaw detection methods, which have been used for non-destructive testing of metal materials, have been attempted to detect internal defects in wood. In this method, is there a transmission method in which ultrasonic waves are transmitted from one end of the wood to the other end, or is the ultrasonic wave emitted from the end of the wood reflected back by internal defects? There are reflection methods for measuring, but these have the following problems, and it is currently difficult to use them to detect internal defects in materials.

In other words, in a heterogeneous material such as wood, where annual rings and xylem coexist, it is necessary to use low-frequency ultrasonic waves to propagate through the material with as little attenuation as possible. There is a limit to the ability to distinguish differences based on speed variations. Furthermore, when measuring the arrival time of the received wave, there is a human judgment error in determining the rise time (more precisely, the time at the moment of arrival) of the received waveform, and if the end of this judgment is low, it is difficult to detect defects. Furthermore, in the reflection method using low frequencies, interference occurs between the transmitted wave and the reflected wave, making it difficult to extract the reflected wave.

(Problems to be Solved by the Invention) The present invention replaces the conventional method of determining the presence or absence of an internal defect based on the time difference between received waves by determining the presence or absence of an internal defect based on the phase difference in the shape of the received waves. This is an attempt to solve this problem through a method.

(Means for Solving the Problems) The present invention measures the phase of standing waves generated on the inner and outer surfaces of a wood-based material by ultrasonic waves emitted from one or more locations inside an object to be detected. achieve that purpose.

The principle of the present invention will now be explained based on FIG. 1, which qualitatively describes that the phase of a standing wave shifts due to the presence of a defect. In the figure, 1 and 2 are probes that receive standing waves, 3 is a probe that emits ultrasonic waves, and 4 is a probe that transmits ultrasonic waves.
denotes the object to be inspected, 5 denotes an internal defect, and a and b denote the spacing between the probe 6 and the probes 1 and 2. Transmission probe 6
When a continuous wave of ultrasonic waves is transmitted, the waves propagate in various directions indicated by arrows, and the surface waves, reflected waves, and transmitted waves interfere with each other to form a standing wave. Here, if the flaw detection target 4 is symmetrical in material and color with respect to the transmitting probe 6, the standing wave obtained from the probes 1 and 2, which are equally spaced from the probe 3, is The waveforms have the same phase. However, if a defect 5 as shown in the figure exists in the object 4, the ultrasonic waves are refracted and reflected at the defect, resulting in disturbance in the standing waves on the side of the defect. Comparing the respective waveforms received by receiving probes 1 and 2 under this condition, they are out of phase with each other. In this way, the presence or absence of internal defects can be investigated from the difference in the phase of the standing waves. The present invention utilizes the above principle.

(According to the present invention, the degree of the above-mentioned phase shift varies depending on the size, position, type, etc. of the defect, but when a knot defect existing inside an Akita cedar log is detected, The existence of a node defect can be determined quantitatively based on a threshold value of a phase shift of about 90 degrees or more.In addition, the measurement points of the standing waves mentioned above can be measured at two locations. Alternatively, defects can also be detected by measuring and memorizing the phase of each location, and then comparing the difference between the two phases.Furthermore, in the present invention, the frequency of the ultrasonic waves used is It can be selected arbitrarily depending on the properties of the object to be detected and the defects to be detected.When targeting wood-based materials, a frequency of about 1 to i Q Kl (Z is appropriate.This also means that the object to be detected is uniform It is possible to detect even minute internal defects by using ultrasonic waves with a higher frequency range as the material becomes more sensitive. By using a means of transmitting ultrasonic waves through pins protruding from the bottom of the probe, it improves the poor workability of conventional methods such as adding a contact medium, applying adhesive, or mechanical adhesion, and improves the precision of positioning the probe. can be increased.

(Example) An example of the present invention will be explained in detail based on the drawings. First, an example of internal defect detection of a lauan plate material, which is said to have a relatively thin key annual ring layer, is shown in Fig. 2. This is an explanatory diagram of a standing wave flaw detection device for a lauan plate material, which is a target object 4, in which a signal generator 6 transmits signals from 1 KHz to i every 0.2xaz via a probe 3 that is brought into close contact with the center of the flaw detection surface A of the lauan plate material. QK
Sine wave ultrasound up to Hz? Send. The generated standing waves are received by probes 1 and 2, which are arranged at equal intervals of 60 g from probe 3. When examining the phase difference of the standing waves depending on the presence or absence of internal defects in this embodiment, Fig. 3 shows that the standing waves of the lauan plate are stable in a state where the notched grooves 5' are not inserted instead of the internal defects 5. This is a graph showing the phase difference of existing waves, and the SN4 diagram is the same graph with a notch 115' added, but in Figure 3, the frequency is 2JKHz.
A standing wave with a phase difference of about 110 degrees when transmitted and 60 degrees at input KHz indicates a standing wave. Next, in Figure 2,
The phase difference of the standing wave when a notch 5' with a depth of 4 is made at a point 6 cWA to the right along the bottom from the point drawn from the perpendicular line from the position of the probe 3 to the bottom surface B is As is clear from Figure 4, the phase difference is about 180 degrees at frequency 2, f3 KHzg, and about 110 degrees at 7.2 KHz, and the phase difference is about 50 degrees high at both frequencies due to the presence of the groove. It has become. In this way, the phase difference characteristics when there are no defects can be ascertained in advance, and if a phase difference that exceeds a phase difference threshold set according to the object to be detected is observed, the presence of an internal defect can be estimated. .

As a second example, an example of detecting internal defects in a silvicultural cedar log with bark will be shown. FIG. 5 is an explanatory diagram of a standing wave flaw detection device for log materials. In the figure, the probe 6 is probed at regular intervals along the contour (circumferential line) of a surface perpendicular to the longitudinal direction (generating line) of the log material (parallel to the end surface of the log material), which is the object 4 to be tested for flaws. Place children 1 and 2. In this example as well, the phase difference of the standing waves obtained from the flaw detection object varies depending on the annual ring distribution of the log, the circularity of the cross section of the log, the size and shape of the internal defect, etc. Further, when the circumference of the ultrasonic wave transmitted from the probe 6 and the position of the ultrasonic wave 2 have a certain relative relationship, the phase difference of the standing wave changes greatly. That is, as the relative relationship approaches, the phase difference initially increases greatly and then rapidly decreases. On the other hand, as the distance from this relationship increases, the phase difference increases again, exhibiting a so-called valley phenomenon. Figure 7 shows standing waves on the cross section of a log material with known internal defects. The phase difference is shown in a circular coordinate diagram, and it has been confirmed that internal defects exist near circle IN scales 11 and 32, which will be described later. In the figure, the value in the radial direction is the magnitude of the phase difference P, and the phase difference in the radius corresponding to the outer circumference line is 108 degrees.The scale on the outer circumference line indicates the position of the probe B during flaw detection. . Probes 1 and 2 are each placed at equal intervals of two scales from probe 3. In FIG. 7, the area where the threshold value exhibits a valley phenomenon with a phase difference of 90 degrees or more is at circumferential scale 11.
and 32, which approximately correspond to the positions of internal defects measured in advance.

(Effects of the Invention) As explained above, the present invention measures the phase difference of standing waves, which is a new principle completely different from conventional ultrasonic flaw detection methods, to improve It has the effect of detecting internal defects regardless of the skill level of the person.

[Brief explanation of the drawing]

Is the drawing an implementation of the present invention? Fig. 1 is an explanatory diagram of the ultrasonic standing wave flaw detection method of the present invention, Fig. 2 is an explanatory diagram of the first embodiment of the present invention applied to plate materials, Fig. 1, and Fig. 6S4 are the first embodiment. Graph 1 of the phase difference showing the flaw detection effect of Fig. 5 is an explanatory diagram of the flaw detection device applied to log materials as a second embodiment, Fig. 6 is a cross-sectional view taken along line A-A' in Fig. 5, and Fig. 7 is a log It is a graph showing the effect of positioning of defects inside the material. In the figure, 1 and 2 are receiving probes, 3 is a transmitting probe,
4 is an object to be inspected, 5 is an internal defect, 6 is an ultrasonic signal generator, and 7 is an oscilloscope.

Claims (3)

[Claims] (1) A method of non-destructively detecting internal defects using ultrasonic waves, which involves measuring the phase of a standing wave caused by ultrasonic waves emitted from one or more probes into a wood-based material. , a standing wave flaw detection method characterized by determining the presence or absence of internal defects. (2) Ultrasonic standing wave flaw detection according to claim (1), characterized in that a protruding pin is provided on the bottom of the probe, or the probe is in close contact with the probe via the pin. Method. (3) In a method of non-destructively detecting internal defects using ultrasonic waves, the phase of a standing wave generated by ultrasonic waves emitted from one or more probes to a wood-based material is measured multiple times. Ultrasonic waves that are characterized by measuring and comparing the phase differences simultaneously or separately at different locations, and using the obtained phase difference to determine the presence or absence of internal defects using a threshold value corresponding to the object to be detected as a reference. standing wave flaw detection method.