JPH0431350B2 - - Google Patents

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. It is used in the field of flaw detection using waves created by standing waves (hereinafter referred to as standing waves in the present invention).

(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. This method uses a transmission method in which ultrasonic waves are transmitted from one end of the wood to the other, or a reflection method in which the ultrasound waves emitted from one end are reflected back by internal defects and are measured. These methods have the following problems, and it is currently difficult to use them for detecting internal defects in materials.

In other words, in a heterogeneous material such as wood, where tree 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 are limits to distinguishing between differences based on speed differences. Furthermore, when measuring the arrival time of the received wave, the rise time of the received waveform (more precisely, the time at the moment of arrival)
This judgment is accompanied by human judgment errors, and if the accuracy of this judgment is low, it becomes impossible 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 solves the drawbacks of the conventional method of determining the presence or absence of internal defects based on the time difference of received waves.
This problem is attempted to be solved by a method that similarly determines the presence or absence of the wave based on the phase difference in the shape of the received wave.

(Means for Solving the Problems) The present invention provides a method for non-destructively detecting internal defects using ultrasonic waves, in which a single ultrasonic beam is transmitted at a required measurement point of a wooden flaw detection object. A standing wave of ultrasonic waves emitted from a probe is received by a standing wave reception probe at equally spaced detection positions on the object across the probe, and Input the waves into a measuring means, measure the phase difference between the two standing waves with the measuring means, and use the phase difference characteristic value of an intact and intact wood-based flaw detection object under the same measurement conditions as a threshold;
The presence or absence of an internal defect is determined by comparing the phase difference with the threshold value as a reference.

Here, the principle of the present invention will be explained based on FIG. 1. FIG. 1 qualitatively describes that the phase of a standing wave shifts due to the presence of an internal defect 5. In the figure, 1 and 2 are standing wave receiving probes (hereinafter simply referred to as probes) that receive standing waves;
3 is an ultrasonic transmitting probe that emits ultrasonic waves (hereinafter simply referred to as a probe); 4 is an object to be inspected; 5 is an internal defect; a and b are probe 3 and probe 1. The placement accuracy with and 2 is shown. When a continuous ultrasonic wave is emitted from the probe 3, the wave propagates 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 object 4 is the same in material and shape with the probe 3 at the center, the waveform of the standing wave obtained from the probes 1 and 2 that are equally spaced from the probe 3 are waveforms with the same phase. However, if an internal defect 5 as shown in the figure exists unilaterally inside the inspection target 4, the ultrasonic waves are refracted and reflected at the defect, and as a result, the standing waves on the defect side are disturbed. occurs. Comparing the respective waveforms received by probes 1 and 2 under this condition, they are out of phase with each other. The presence or absence of internal defects can be investigated from the phase difference of such standing waves. The present invention utilizes the above principle.

(Function) According to the present invention, the degree of the phase difference changes depending on the size, position, type, etc. of the defect, but when a knot defect existing inside an Akita cedar log is detected, A phase difference of approximately 90 degrees is set as a threshold value, and the presence of a node defect can be quantitatively determined based on the degree of phase difference greater than this value. Furthermore, even if the standing waves are not measured at two locations at the same time, defects can also be detected by measuring and storing the waveform at one location at a time, and then measuring the phase difference between the two locations. can. Furthermore, in the present invention, the frequency of the ultrasonic waves used can be arbitrarily selected 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 10 KHz is appropriate. Furthermore, the more uniform the material of the object to be inspected, the more minute internal defects can be detected by using ultrasonic waves of a higher frequency range. Furthermore, in the present invention, as a method for bringing the probe into close contact with the object to be detected, a means for transmitting ultrasonic waves through a pin protruding from the bottom of the probe is used, and conventional methods such as adding a contact medium, applying an adhesive, or In addition to improving workability such as mechanical adhesion, it is possible to improve the positioning accuracy of the probe.

(Example) An example of the present invention will be explained based on the drawings. Fig. 2 shows an example of internal defect detection of a lauan plate material, which is said to have a relatively thin annual ring layer. This is an explanatory diagram of a standing wave flaw detection device for lauan plate material. This is an explanatory diagram of a standing wave flaw detection device for lauan plate material. Emit sinusoidal ultrasound waves. The generated standing waves are received by probes 1 and 2, which are closely arranged with pins inserted at equal intervals of 6 cm from the probe 3 to the left and right. In this embodiment, when examining the phase difference of the standing waves depending on the presence or absence of internal defects, Fig. 3 shows the position of the standing waves in a state where the cut grooves 5' in place of the internal defects 5 are not made in the lauan plate material. This is a graph showing the phase difference, and shows a standing wave with a phase difference of about 110 degrees when transmitting at a frequency of 2.8KHz and about 60 degrees at 7.2KHz. Figure 4 is the second
As shown in the figure, this is the same graph with a cut groove 5' with a depth of 4 cm made at a point 6 mm 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. , the phase difference of the standing wave in this case is
As is clear from Figure 4, the phase difference is approximately 180 degrees at a frequency of 2.8 KHz and approximately 110 degrees at 7.2 KHz, and at both frequencies, the presence of the groove 5' increases the phase difference by approximately 50 degrees. ing. In this way, the phase difference characteristics when there are no defects can be ascertained in advance, and if a phase difference exceeding the phase difference threshold set according to the object to be detected is observed, the presence of an internal defect 5 can be estimated. be.

As a second example, an example of detecting internal defects 5 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 3 is placed along the contour (periphery line) of a surface perpendicular to the longitudinal direction (generating line) of the log that is the object 4 to be detected (parallel to the end surface of the log), and at regular intervals. Place probes 1 and 2. In this example as well, the phase difference of the standing waves obtained from the object to be tested is based on the annual ring distribution of the log,
It varies depending on the roundness of the log cross section, the size and shape of the internal defect 5, etc. Further, the phase difference also changes depending on the frequency of the ultrasonic waves emitted from the probe 3. Furthermore, internal defects 5 such as knots, probe 3, probe 1
When the positions of and 2 have a certain relative relationship, the phase difference of the standing waves changes significantly.
That is, as the relative relationship approaches, the phase difference increases greatly at first, and then decreases rapidly.
On the contrary, as the distance from this relationship increases, the phase difference increases again, a so-called valley phenomenon.

Figure 7 is a circular coordinate diagram showing the phase difference of standing waves on the cross section of the material when a log material with internal defects 5 is known in advance is detected.
It is confirmed that these exist near circumferential scales 11 and 32, which will be described later. In the figure, the value in the radial direction represents the magnitude of the phase difference, and in this case, the phase difference indicated by the radius represents 108 degrees. The scale on the outer circumference line indicates the position of the probe 3 during flaw detection, and in this example, measurements were taken at 65 dividing points around the entire circumference of the log. Therefore, if the diameter is larger than this, the number of measurement points will increase, and if the diameter is smaller than this, the number of measurement points will decrease, so choose the dividing scale in the circular coordinate diagram appropriately. It is determined. Probes 1 and 2 are each placed at equal intervals of two scales from probe 3. If the measurement results of the phase difference are expressed as a circular coordinate diagram shown in Fig. 7 according to the measurement positions determined in Fig. 6, the threshold value is
Areas exhibiting a valley phenomenon with a phase difference of 90 degrees or more (this state is illustrated for convenience, but if you tilt the figure to the right, it will match exactly with Fig. 6) are marked on the circumferential scales 11 and 32. They exist at two central locations, which approximately correspond to the locations of internal defects that have been confirmed in advance.

(Effects of the Invention) As explained above, the present invention provides phase difference characteristics in a defect-free state that corresponds to the target conditions such as the type, size, and shape of each object to be tested and the measurement conditions such as the transmission frequency of the ultrasonic waves. This is because the presence or absence of internal defects is determined by comparing the phase difference of the detected object measured under the same conditions with the determined phase difference.
It has the effect of allowing flaw detection regardless of the proficiency level of the flaw detection technique.

[Brief explanation of drawings]

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 a plate material, and Fig. 3 is a defect-free state in the first embodiment. Fig. 4 is a graph showing the phase difference of the standing waves in the state in which notches are made in the first embodiment, and Fig. 5 is a graph showing the phase difference of the standing waves in the state where the cut grooves are made in the first embodiment. Fig. 6 is a sectional view taken along A-A' in Fig. 5, and Fig. 7 shows the phase difference in the circumferential measurement position of the log in the second embodiment in the radial direction. It is a circular coordinate diagram. In the figure, 1 and 2 are probes for receiving standing waves, 3 is a probe for transmitting ultrasonic waves, 4 is an object to be detected, 5 is an internal defect, 6 is an ultrasonic signal generator, and 7 is an oscilloscope.

Claims (1)

[Claims] 1. In a method for non-destructively detecting internal defects using ultrasonic waves, ultrasonic waves emitted from a single ultrasonic emitting probe are used at required measurement points of a wood-based flaw detection target. A standing wave due to a sound wave is received by a standing wave receiving probe at equally spaced detection positions of the object across the probe, and the standing wave is inputted from both probes to a measuring means. , the phase difference between the two standing waves is measured by the measuring means, the phase difference characteristic value of the intact and healthy wood-based flaw detection object under the same measurement conditions is taken as a threshold value, and the An ultrasonic standing wave flaw detection method characterized by comparing the phase difference to determine the presence or absence of internal defects. 2. The ultrasonic standing wave flaw detection method according to claim 1, wherein a protruding pin is provided at the bottom of the probe, and the probe is brought into close contact with the object to be detected via the pin.