SU1516852A1 - Method of determining endurance with the given mean stress of cycle - Google Patents

Abstract

The invention relates to fatigue tests, namely to methods for determining the limit of endurance. The purpose of the invention is to improve the accuracy by reducing the errors associated with the choice of the amplitude step in determining durability therefrom. Samples of the material are cyclically loaded until failure at different amplitudes and cyclical changes in the average stress, which changes to a predetermined value. The endurance limit is determined by the point of fracture, the dependence of durability on amplitude. 2 Il.

Description

The invention relates to fatigue tests, namely to methods for determining the limit of endurance.

The purpose of the invention is to improve accuracy by reducing errors, associated with the choice of the step on the amplitude in determining the dependence on it of durability.

FIG. Figure 1 shows the dependence of voltage on time; in fig. 2 - the dependence of durability on the loading amplitude.

A device for the implementation of the method can be a testing machine, which allows loading samples at a two-part change in load with time.

The method is implemented as follows.

The sample is loaded in a two-part mode, with high-frequency loading, which is cyclic loading with a given amplitude (JQ superimposed on a low-frequency loading with medium voltage C, and an amplitude GO that determines the change in average voltage, load cycle . Low-frequency loading changes the average stress from a value below the endurance limit to a predetermined one at which the endurance limit is determined.

Changing the amplitude G g with the same law of change of the average

stress, the dependence of durability on amplitude is obtained, the fracture point of which is G (fi is the limit of material endurance at average stress C}.

gpg

-6, + Go i

since it is at this average stress that damage accumulates in the material.

Dp bring the fatigue limit at the experimental value of the asymmetry coefficient G to the fatigue limit under symmetric loading (S, use the equation

b -, (G „% V0“ ,, - bGc ,,).

where (f - coefficient of sensitivity to load asymmetry;

b. ,

01

 ° | P2max is the maximum value of the average high-frequency loading voltage. In the case when the magnitude of the coefficient of sensitivity to the asymmetry of loading is unknown, the tests are carried out at a constant average and two values of the amplitude are low

frequency loading (5d ,, ib

a 17

The tests are carried out by the proposed method with obtaining two values of the amplitude of the high-frequency loading Gfl corresponding to two

the values of the fatigue limit at two values of the asymmetry coefficient of loading. From this equation follows the dependence for determining the magnitude of the coefficient of sensitivity to asymmetry of loading

YYG- ,, Jaai-Oaii

° - (f- ai

 a42

15

20

25

thirty

Claims (1)

Invention Formula The method of determining the endurance limit for a given average stress cycle, which consists in that the samples are cyclically loaded to failure at different amplitudes, asymmetric cycles and determine the dependence of durability on amplitude, which, according to the break point, determines the endurance limit characterized by In order to increase accuracy by reducing the errors associated with the choice of the amplitude step in determining the durability dependence on it, the average voltage is cyclically changed from a value below the right Stamina case with a symmetrical cycle to a predetermined value with a period exceeding the period of the cyclic loading. .J atf ffffo . at. - Editor S. Pekar Order 6380/42 VNIIPI State Committee for Inventions and Discoveries at the State Committee on Science and Technology of the USSR 113035, Moscow, Zh-35, Raushsk nab. 4/5 Z-W FIG. 3-W Compiled by D. Pospelov Tehred L. Oliykh Corrector M. Pojo Circulation 789 Subscription