SU1587400A1 - Method of determining fatigue range of material - Google Patents

Abstract

The invention relates to fatigue tests, and specifically to methods for determining the endurance limit of a material. The purpose of the invention is to improve accuracy by reducing the effect on the result of the conditions of attachment of the sample. The sample is fixed in the test setup and loaded cyclically in self-oscillation mode with a stepwise increase in the load level. At each step of loading, the relative energy of the scattering, referred to the energy of the oscillatory motion of the system, is determined, and the ratio of the relative energy of the fluid stage to the relative energy of the first stage is determined as the characteristic of the energy dissipation. The endurance limit is judged by the break point of the dependence of the energy dissipation characteristic on the load level. 1 il.

Description

The invention relates to fatigue tests, and specifically to methods for determining the endurance limit of a material.

The purpose of the invention is to improve accuracy by reducing the effect on the result of the conditions of attachment of the sample.

The drawing shows a typical dependence of the ratio Dg of the relative energy at the step / to the relative energy at the first step.

A device for implementing the method is a device for loading a sample in a self-oscillation mode, equipped with a cycle counter, a means of measuring frequency and amplitude.

The method is implemented as follows.

The sample is fixed in the grips of the test setup and cyclically loaded in self-oscillation mode at the resonant frequency, the frequency and amplitude of oscillations of the sample, the voltage, the electrical current and the duration of the electrical pulse in the feedback circuit are measured. The value of the relative energy dissipation i at each step of loading is determined according to

year

fiUjT AND; - a, where / is the serial number of the load step;

Ui is the voltage applied to the self-oscillating system at the i-fi stage;

f is the electric current in the feedback circuit;

7, is the duration of the electrical pulse in the feedback circuit;

a, - is the oscillation amplitude of the test sample;

0), - resonant circular oscillation frequency of the sample;

/ С - constant value, characteristic

for oscillating system, build

plot of ratios

relative dissipation of energy per caSP

00

four

approaching its value at the first (dullness from the amplitude of oscillations of sample 1, by the transition point of the direct dependence k of the curve, judge the magnitude of the material elongation limit. The amplitude of the oscillations is incrementally increased due to the increase in r | The parameters of the oscillatory process are measured: the frequency and amplitude of oscillations of the sample i | yeMoro of the sample, the voltage, the electrical JOK and the duration of the electric pulse in the feedback circuit, determine the value of the relative energy dissipation.

j The increase in the amplitude of oscillations and the associated increase in the amplitude of the stresses in the sample are carried out until the relative energy dissipation in the material begins to increase sharply. This is due to the fact that the cyclic stresses in the sample approached the endurance limit of the material. When testing a sample, energy dissipation occurs not only in the sample, but 1-: in the seals, in moving joints, d) rubbing against the air, etc. This is the TJepHbie characteristic of each oscillatory system | and a test device. The dissipation of energy in the material is proportional to the acting voltage. Therefore, in order to increase the accuracy of determining the endurance limit of a material, it is necessary to use the ratio of the values relative to the dissipation of energy, found on the rth loading stages, to the value found on the first stage.

); / l |)

5, and

and., un

SL-2

Compiled by N. Mezentsev

Tehred A. KravchukKorrektor O. Kravtsova

Editor O. Yurkovetska

Order 2415 Circulation 498 Subscription

NIIPI State Committee for Inventions and Discoveries at the State Committee on Science and Technology of the USSR

113035, Moscow, Zh-35, Raushsk iab., 4/5 Production and Publishing Combine Patent, Uzhgorod, ul. Gagarin, 101

This makes it possible to exclude from the process of determining the endurance limit of the material other sources of energy dissipation, besides the test sample, because the stresses in them do not reach the value of the fatigue limit.

According to the results obtained in the process of registering the parameters of the oscillatory process at each step of loading, the graph of the dependence of Ai on the amplitude of oscillations of the sample is plotted and the value of the endurance limit of the material is judged by the point of transition of the direct dependence to the curve.

Claims (1)

Invention Formula The method for determining the endurance limit of a material, which means that a sample of a material is cyclically loaded with a stepwise increase in the load level, starting from a level less than the endurance limit, and the characteristic of energy dissipation at each load step is determined, and the breaking point is determined energy dissipation characteristics from load, characterized in that, in order to increase the accuracy by reducing the effect on the result of the sample fixing conditions, loading at each stage is carried out in the self-oscillation mode at the resonant frequency, the relative value of the energy dissipation related to the sample is determined at each stage the energy of the steady-state oscillatory motion at a given stage, and the characteristic of the energy dissipation is the ratio of the relative energy of the corresponding stage to the relative energy of the first stage. and., un