SU1516854A1 - Method of determining fatigue damage of material at high frequencies of loading - Google Patents

Abstract

The invention relates to the testing of materials, to methods for determining the fatigue damage of martensitic steels. The purpose of the invention is to improve the accuracy of determining the maximum damage to steels with martensitic structure. The sample with the concentrator is cyclically loaded at a high frequency and the temperature jump in the fracture zone is recorded at the moment of the occurrence of the fatigue crack, and the value of the specific volume of the fatigue crack as a characteristic of fatigue damage is determined from the temperature jump. 2 Il.

Description

The invention relates to the testing of materials, in particular, to methods for determining the fatigue damage of martensitic steels.

The purpose of the invention is to improve the accuracy of determining the maximum damage to steels with martensitic structure.

FIG. 1 shows an installation diagram for implementing the method; in fig. 2 - typical dependence of temperature on the number of cycles.

An installation for implementing the method includes connecting a magnetostrictive transducer 2, a hub 3 voltage, an ultrasonic generator 4, an antenna sensor 5, an electronic frequency meter 6, an induction sensor 7, a millivolt meter 8, a thermocouple 9, a potentiometer 10 to sample 1.

The method is carried out as follows.

A controlled sample 1 of martensitic steel is attached to a voltage concentrator 3, a magnetostrictive transducer 2 is connected to an ultrasonic generator 4, and high frequency cyclic oscillations are excited in the sample. The frequency of cyclic loading of the sample is measured by the antenna sensor 5 using a frequency meter 6. The amplitude of the vibrational strain along the sample is measured by an induction sensor 7 using a millivoltmeter 8.

The calibration of the sensor 7 amplitude of the vibrational strain is carried out using an optical microscope, measuring the amplitude of the displacement of the end of the sample. In this case, for a paluwave breakdown X

U1

The maximum amplitude value of the vibrational strain, which takes place in the center of the sample, is calculated from the ratio K to. In the center of the sample, where the sample is most likely to break, temperature and internal friction are measured. As a characteristic of the material damage at the moment of destruction, the value of the specific volume V of the fatigue crack from the ratio

where 1 is the width of the martensite plate

in the sample structure; E is Young's modulus; f is the loading frequency; X is thermal conductivity; Q - the quality factor of oscillatory

systems;

DT is the temperature jump at the moment of the formation of a crack, which is determined using a thermocouple 9, which is placed in the zone of the intended fracture. The moment of the appearance of a crack can be judged by the occurrence of the indicated temperature jump.

Example. The fatigue damage of samples of ZOHHS2A steel subjected to surface plastic hardening by dynamic work hardening, which, after quenching from temperatures of 870 ° C, were released in the temperature range of 220 - C20 s, was determined.

Cyclic loading of the sample is carried out by a high-frequency load with a frequency of 20 kHz. A half-wave sample with a diameter of 17 mm and a length of 130 mm is made for this. The sample is attached to a voltage concentrator of exponential form. The sample is loaded using a magnetostrictive transducer IIMC15A-18 and an ultrasonic generator UZG2-4M. To determine the working frequency of the oscillations of the sample, an electron-counted frequency factor of -35A is used. The emf induced in the induction sensor of the amplitude of the vibrational strain of the sample is measured using a B7-16 universal voltmeter. The inverse quality factor Q is used as a characteristic of internal friction.

To measure the temperature on the surface of the sample, a chromel-copel thermocouple is welded along the length of the center. The change in temperature during cyclic loading is recorded using a potentiometer KSP-4.

The sample is loaded so that the amplitude of the displacement at the end

about 20 TO m. In this case, the amplitude of the vibrational strain in the center of the sample 510. Internal friction at the point of probable fracture is determined by the temperature increase.

for 100 s cyclic loading of the sample. Then the cyclic loading of the specimen is carried out for the time necessary for the formation of fatigue trash; In this case, it is determined

temperature jump, which is accompanied by the formation of fatigue cracks (Fig. 2).

The results of determining the fatigue damage of the sample, taking into account the magnitude of the temperature jump and internal friction, are given in the table.

The results of determining the fatigue damage by the proposed method and the magnitude of local plastic deformation zones formed on the fracture are consistent.

Claims (1)

Invention Formula A method for determining fatigue damage to a material at high loading frequencies, comprising that in the process of loading the sample, the temperature is measured at the place of maximum self-heating and the largest amplitude of deformations of the sample, taking into account the quality factor oscillatory system and is judged on the fatigue damage of the material, which is characterized by the fact that, in order to increase the accuracy of determining the maximum damage to steels with the martensitic structure, the moment of formation of the fatigue crack is determined, at which the temperature jump is measured, and as a characteristic of the fatigue damage, the kgg value of the specific volume of the talastic crack is determined from the ratio e,   L -g 51516854  m is the maximum amplitude of deformations; 1 - plate width of martensite in the sample structure; 5 Е - Young's modulus; loading frequency; thermal conductivity; good quality; temperature jump in moment of education cracks. 1.4 3.2 4.0 3.5 3.7 1.7 10 15 25 FIG. /