SU1409884A1 - Method of making fatigue crack of pre-set dimensions in specimens with nick - Google Patents

Abstract

This invention relates to the field of quality control of metals and alloys when tested for impact strength. The purpose of the invention is to improve the accuracy of cracking. The invention allows an accuracy of 0.2; Create a fatigue crack in notched specimens to determine impact strength. The stability of the acoustic contact with the ultrasonic transducer with the sample and its corresponding location on the end of the sample is provided by a magnetic holder. The required angle of incidence of the beam of ultrasonic vibrations from 4 to 5, the detuning from the signals — interference and notching, as well as the reception of the echo signal from the fatigue crack — are made by an ultrasonic transducer. Sounding is carried out at sensitivities (and of a flaw detector that corresponds to the detection of a calibrated fatigue crack in a test specimen. From the equality of echo signals from fatigue cracks in the test and test specimens, it is determined that the crack in the specimen penetrated to the required depth, 4 or 10 degrees (L

Description

The invention relates to the quality control of metals and alloys and can be used in any branch of mechanical engineering to create cracks of a certain size during tests for impact bending of samples with a notch.

The purpose of the invention is to improve the accuracy of cracking.

- In FIG. 1 shows a diagram of a pro-Q sounding sample with a notch; in fig. 2 is a diagram of the installation of an ultrasonic transducer with a piezoelectric element on a sample with a notch; Fig. 3 shows the oscillogram when adjusting the sensitivity; in fig. And - oscillogram of echo signals from a fatigue crack in the course of loading.

The installation diagram of the transducer and the sample (Fig. 1 and 2) shows 20 sample 1 with a notch, on the end of which an ultrasonic transducer 2 is mounted using a magnetic holder made in the form of a permanent magnet. 3 and the magnetic circuit 4. 5 The ultrasonic transducer is implemented in the form of a prism 5 and a piezoelectric element 6. The position 7 denotes a visor for pressing the transducer 2.- to it.

The essence of the method is, Q is as follows.

A sensitivity adjustment of a flaw detector (not shown) is carried out in advance to detect a calibrated fatigue crack in a reference sample and to receive an echo signal of a specified value from it. Then, the transducer 2 is clamped to the notched specimen by a magnetic holder, installed in a vibrator (not shown) and re-variable loading of the specimen by bending.

The design of the transducer 2 ensures the ultra35 beam to fall

sound vibrations at an angle of 4–5 to T6pijy HcnbrryeMoro of sample 1, as well as the height h from the front face of the piezoelectric element 6 to the surface of the test sample 1, which had an incision of 2.5–2.7 mm.

Using the same transducer 2, the echo signals from the fatigue crack growing in the process of loading in the test specimen 1 growing during the loading process are monitored and observed on the flaw detector screen. When the value of the echo signal becomes equal to the preset value of the training signal, which indicates that the depth of the trellis has reached

Q 5

0 5

Q

five

five

0

five

of this value, the loading of specimen 1 with a notch is terminated.

The method is carried out as follows.

The flaw detector is turned on, the contact medium (CIATIM-221 lubricant) is applied to the end of the test sample 1 (Fig. 2) and the transducer 2 is pressed against the end face with a magnetic holder. The corresponding movements of sample 1 with its pressing against the visor 7 of the magnetic core 4 receive the maximum signal from the crack on the flaw detector screen. This is the first signal A, after the probe signal (Fig. 3).

Use the Attenuator DB knob to set the amplitude of the signal A ,, equal to 30 mm, and the strobe pulse 1}) is positioned. Then, the sample to be tested is pressed to the transducer in the same way, and a maximum of the first false signal A is obtained on the oscillogram, which indicates that the transducer reaches the optimum acoustic contact with the sample surface.

Then, without disturbing the acoustic contact, the transducer with the sample is inserted into the vibrator to carry out repeated-variable bending loading. The vibrator is turned on and the voltage is brought to 100 V. Signal A, arises and grows. With a crack depth of 1 mm, a rapidly increasing signal Ap arises in the oscillogram (Fig. 4). When this signal reaches a height of 30 mm, the vibrator is turned off, the magnetic holder is removed with the test specimen, and the specimen with a fatigue crack in it is directed to the impact fracture.

From statistical data, it was found that when the alternating loads were removed from the specimen, when the above-mentioned signals were equal, the penetration depth of the fatigue cracks formed in the tested specimens was 1.5 ± 0.2 mm.

The applied magnetic holder measuring 40 x 11 x 9 mm (Fig. 2) consists of a permanent magnet 3 and a magnetic actuator 4.

Special transducer 2 is a 3 x 10 mm piezoelectric element 6, glued with epoxy resin to the end face of a prism 5 made of PCB of 13 X 10 X 5 mm. The end face of the prism 5 is horizontal.

The surface is a double face angle of 4 30 ± ± 30. The air wedge formed in relation to the horizontal surface is filled with a layer of epoxy resin. The current leads are soldered to the piezoelectric element 6 from the side of the smallest side surfaces.

The magnetic holder consists of two steel plates with a thickness of 1.5 mm, between which a permanent magnet measuring 24 x 11 x 5 mm is fixed with an adhesive. A brass 7 cap is attached to one plate to ensure the reproducibility of the introduction of ultrasonic vibrations into a strictly defined zone of the test specimens when they are replaced in the process of making fatigue cracks.

In addition, the magnetic holder ensures the stability of the acoustic contact of the transducer with the test specimen in the process of repeated-variable bending. A special transducer is connected to the magnet with epoxy resin.

Magnetic holder is applicable only when testing samples of size 10 X 11 X 55 mm. At the same time, in the above vibratote, the left side supporting cheek is displaced by 5 mm so that the protrusion end of the reinforced sample and the inner surface of the square hole are sealed with thin rubber to prevent the magnetic holder from attracting them to the test.

OS

When using a different vibrator

I

such changes in the dimensions of the specified magnetic holder are unavoidable, but the dihedral angle of ± 30 and the distance of 2.5 ± 2.7 mm from the front face of the piezoelement to the top surface of the test specimen on which the cut is made should remain unchanged.

Claims (1)

Invention Formula A method of creating a fatigue crack of a given size in notched specimens, consisting in re-treatment. alternating loading of the sample by bending and registering the growth of the size of the fatigue crack in the process of loading to obtaining a fatigue crack of a given size, characterized in that, in order to improve the accuracy of crack production, ultrasonic vibrations in the sample are angled - 5 to its end face of the piezoelectric element mounted on the end of the specimen so that the distance from the front of the piezoelectric element to the surface of the specimen on which the notch is made is 2.5 - 2.7 mm, take echo reflected from the fatigue crack The ultrasonic vibration signals measure the amplitude of the echo signals, and the sample is loaded until the amplitude of the echo signals corresponds to a crack of a given size. cpue.i / qyue.Z (rig. 3 pus.