JPS60203854A - Measuring method of crack propagation speed of material - Google Patents

Abstract

PURPOSE:To improve the accuracy of measurement by arranging plural groups of probes consisting of transmitters and receivers so that an ultrasonic beam crosses a crack expected line, detecting the reduction of a receiving level as arrival at the crack and measuring the crack propagation speed on the basis of the interval of the probes and a crack arrival time interval. CONSTITUTION:When it is supposed that a crack line CL exists on a material M such as a steel plate, transmitters 1A-1X and receivers 2A-2X are arranged on one surface US and the other surface BS respectively as groups with intervals in the crack propagation direction. Plural frequency signals are outputted from a signal generator and transmitted/received by respective frequency levels different in respective adjacent groups. In addition, a reception amplifier, a waveform storage device, a synchroscope and an analyzer are arranged to detect the reduction time of the receiving level as the arrival at a crack and detect the crack propagation state.

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field of the Invention] The present invention relates to a method for measuring the crack growth rate of a material, which is applied to grasping the dynamic behavior of brittle fracture propagation and stoppage of a steel plate.

[Technical background of the invention and its problems]

This type of measurement is extremely important for the safety evaluation and improvement of materials, and several research reports have been published. For example, 334-34 of the Transactions of the Japan Society of Naval Architects, No. 144.
There is a ``Study on the dynamic aspects of high-speed cracks (3rd report)'' on page 2.

Including this miscellaneous article, when measuring the crack propagation rate in the past, a strain gauge is pasted as a crack detection gauge on the steel plate, and the rupture time of this gauge is detected, or the strain change is detected, and each The measurement was based on the difference in time to failure of the cage or the time difference in strain change, and the position where the gauge was attached.

However, since this conventional method detects the breakage of a gauge attached to the surface of a steel plate, if a crack develops only inside the steel plate, the gauge will not break and measurement itself will not be possible. Even if a strain change is detected, since the strain change is detected on the surface of the steel plate, the measurement is indirect and has poor accuracy. Furthermore, if only the gauge is cut before the steel plate breaks, the resulting speed is unreliable.

[Purpose of the invention]

SUMMARY OF THE INVENTION An object of the present invention is to solve the problems of the conventional method and to relate to a method for measuring the rate of crack growth in a material, which can accurately and accurately detect crack growth regardless of the state of crack growth.

[Summary of the invention]

In order to achieve this objective, the method of the present invention uses a plurality of sets of ultrasonic transmitter and receiver probes, so that the ultrasonic beam crosses the predicted crack line where a crack is expected to occur. They are arranged at intervals in the direction of propagation, and the transmitter emits a continuous wave of ultrasonic waves, which is received by the receiver, and a decrease in the level of the received signal is recognized as reaching the crack, and the probe is placed between the probes. This method is characterized in that the crack growth rate is measured based on the interval between cracks and the crack arrival time interval.

The first main point of the present invention is to basically utilize ultrasonic waves and utilize the fact that the received signal level decreases as the crack reaches the crack, and conversely to try to know when the crack is reached. Second, the probe is placed so that the ultrasonic beam crosses the expected crack line. As a result, it is possible to directly detect the progress of cracks in the steel plate, and there is an advantage that even cracks only inside the steel plate can be detected. Thirdly, in order to know when the ultrasonic wave has arrived at the crack, it is designed to emit continuous waves, unlike the Glucian waves used in flaw detection.

[Specific examples of the invention]

The present invention will be explained below using a concrete example using a steel plate shown in the drawings. M is a material such as a steel plate, and when it is expected that the probe will enter the material along the crack half-line, according to the present invention, a transmission type ultrasonic probe is used as the ultrasonic probe, and the Transmitter elements IA, IB, .

2B, . . . form a set, and are arranged at intervals in the crack propagation direction (in the illustrated example, the width direction of the steel plate).

3 is a signal generator, and the continuous wave generated from this is amplified to a maximum of 40 watts by output amplifiers 4A, 4B, . . . and then given to each transmitter IA, IB, . From there, the transmitted signals are transmitted into the material M, and the transmitted signals are received by the receivers 2A, 2B, . . . , and amplified by the reception amplifiers 5A, 5B, . High-speed waveform storage devices 6a and 6b using data recorders as
...input each set independently and store them along the time axis. A synchronoscope 7 and an analysis device 8 are also attached.

Here, as shown in Fig. 3, the signal generator 3 outputs continuous waves of multiple types of frequencies, for example, two types of frequencies, 5 MHz and 10 MHz, and transmits and receives waves with different frequencies for each adjacent pair. is desirable for signal discrimination.

Incidentally, the narrower the spacing between the probes, the more accurately the crack velocity can be measured, but if the spacing is too narrow, there is a risk of picking up adjacent signals.For this reason, in the above example, the frequencies of the adjacent probes are changed to reduce noise. This is to pick up the signal only at that position while removing it.

Thus, if the crack that has just developed reaches between the transmitter and the receiver and blocks the ultrasound beam, the received signal level will drop to the fourth level.
It decreases as shown in the figure. If the time at which the signal level begins to decrease is determined for each measurement set, the crack velocity V can be determined as Δt/Δt from the time difference Δt and the measurement position interval Δt.

Note that the reception amplifier is not necessarily necessary if the output is large, the resolution of the waveform storage device is high, or the recording speed is fast.

〔Effect of the invention〕

In summary, according to the present invention, the crack growth rate can be measured without being influenced by the form of the crack or its progress.

[Brief explanation of the drawing]

Fig. 1 is a front view of an embodiment of the method of the present invention, Fig. 2 is a plan view thereof, Fig. 3 is a flow diagram of the signal processing system, and Fig. 4 is a correlation diagram showing an example of signal level reduction due to reaching a crack. be. IA-IX...Sender, 2A-2X...Receiver, 3
...Signal generator, 6a-61...Waveform storage device, M
... Compensation fee.

Claims (1)

[Claims] (1) Multiple pairs of ultrasonic transmitters and receivers are arranged at intervals in the direction of crack propagation so that the ultrasonic beam crosses the predicted crack line where cracks are expected to occur. , a continuous wave of ultrasonic waves is transmitted from the transmitter and received by the receiver, and a decrease in the level of the received signal is recognized as reaching the crack, and is based on the interval between the probes and the time interval of reaching the crack. A method for measuring a crack growth rate of a material, the method comprising: measuring the crack growth rate of a material.