SU1619120A1 - Method of determining endurance limit of material - Google Patents

Abstract

The invention relates to the testing of materials, to methods for determining the fatigue limit. The purpose of the invention is to increase reliability by eliminating distortions associated with material damage during stresses above endurance limit. A sample of the material is cyclically loaded at a stepwise increase in the load level. At the first stage of each degree, the level of load is: ao of the previous load, and at the second level it is equal to the level of the first stage of the previous step. As a characteristic of the structural changes of the material by which the endurance limit is judged, the difference between the established temperatures of the second stage of the corresponding stage and the first stage of the previous one is determined. 2 Il.

Description

The invention relates to the field of material testing, to methods for determining the fatigue limit.

The purpose of the invention is to increase reliability by eliminating distortions associated with material damage during stresses above endurance limit.

FIG. 1 shows a staged loading program; in fig. 2 shows the dependences of the temperature increase 0 on the subsequent and previous loading steps on the loading level oa, obtained as a result of testing a sample of steel 45 (cp) for a pure circular bend.

A device for implementing the method is a test machine, which allows cyclically loading the sample and stepwise increasing the load level supplied by temperature sensors and the corresponding recording equipment.

The method is implemented as follows.

The sample is installed in a testing machine and cyclically load the sample, stepwise increasing the load level from a level below the fatigue limit (7XX). Each loading stage consists of two stages. The load level in the first stage 1 of each stage is higher than the previous one, and the load level in the second stage 2 of each stage is equal to the load level in stage 1 of the previous stage. Each stage consists of stages 1 and 2, and the load in stage 1 is higher than in stage 2. Stages 3, in which the load level is obviously below the fatigue limit, can consist of one stage 1.

At each stage of each step, the steady state heating temperature of the sample is determined, for example, as follows.

The duration of the loading section is predetermined with a constant

ABOUT

to about

Symemores speed, which determines at each stage the temperature at the end of the asc constant heating rate. Since the indicated temperature correlates with the established temperature, the latter can be judged from it. Measurement of the temperature increment in each gap is equivalent to a change in temperature, since the temperature of each stage is constant.

The method is based on the fact that the appearance of the difference in TO temperature different from zero at the second stage of the corresponding & stage and the first stage of the preceding stage is a preliminarily approximation of the control lines to the level of the limit of calculus-egsty, therefore it is possible to judge the occurrence of such difference reaching the endurance limit level and ensuring that the endurance limit has not been surpassed. In FIG. 1, points 4 correspond to the first and second, respectively, stages of the neighboring C upstairs at equal load levels, which are the corresponding temperatures of the beds, which corresponds to the failure to reach the endurance limit. Points 5 1 6 correspond to the first and second stages of the corresponding neighboring stages, at which at the stage of the last stage of the last pi the level of endurance is reached.

Example. The experiment was carried out on a sample from article G5 (n) of type VH1, which was subjected to rotation with rotation on the serial model of the MUI-6000 test. Heating of the working part of the orp sample with the use of a specially designed infrared pyrometer, chu; B-7epnev radiation in the range of sols of 1.8 -20 microns, Pyrometer indicator is degraded1 - by B degrees K, Chuvstachelgity 0.3, gd then at a time of 1 s.

Pre, g, zag, and at the level of loading 226 Svifla determined the optimal duration of the loading stage. She made 3 cycles (60 s). Step ng1ruda was conducted according to the program (Fig. 2} from 13) EDPA, with an interval between the steps of 12 MPa. After each stage, the sample was cooled to the initial temperature. At a loading level of 155 MPa, a temperature difference of 0.3 was recorded. K. Beginning with the feeding of nagruhsi, the test is not the previous test, and determined the I5men ° n1 | e increase

t-temperature L ©. JHO byps was fixed at a loading level of 238 MP, after a nz-rpv keny at a level of 250 MPa was 1 K. The last level was 250 MPa and was determined as the true limit of the endurance of the milled sample.

The above method tested 30 samples of the type VHi ci -1l.4k (ch.}. As a result of the statistical results, the mathematical expectation of the hardy limit for this batch was 245 MPa, which is consistent with the results of the direct fatigue tests, Forms with l and This is the way the limit was carried out by the engineer, which consists in loading the sample of the cyclides material from a level below the fatigue limit with step load of the sample unloading and cooling to UYZPNnoy temperature1 at the end each incandescent / at each stage, the value of the value of the newer tag of the peraturi paeogreech obozia, the structural change in the material, io KGm, is judged by the charmer; The fact that, with the method of govish-, postavernost1 | g, / those of the distorting, is connected with the damage of the material of the material: hiipx above the gd of the case and emostos, | implementing a gal;., from two days, that is, a sample of the dog is unloaded and loaded and used to increase the load of a new load. S first

At each successive stage, the joint stage at the second stage is carried out at the load level of the first stage of the previous stage, and the dryer is determined. flax on the second wave

for each stage / temperature of heating that has become, and for the quality of the xzrggeri; tikk structural changes determine the difference between the established temperatures of heating of the second stage of the corresponding stage

and the first one is the previous step.

/ 55 W South 226 250 174 ba, MPa Fi & .1

Claims (1)

Claim A method for determining the material endurance limit, namely, that the material sample is cyclically loaded from a level below the endurance limit with a stepwise increase in the load level with unloading and cooling of the sample to the initial temperature at the end of each stage and at each stage, the value of the steady-state sample heating temperature is determined, taking into account which determine the level of structural changes in the material, which is used to judge the endurance limit, distinguished by the fact that, in order to increase reliability by and elimination of distortions associated with material damage at voltages above the endurance limit, loading at each stage is carried out in two stages, between which the sample is additionally unloaded and cooled to the initial temperature, the load level is increased at the first stage of each subsequent stage, loading at the second stage of the corresponding stage carried out at a load level of the first stage of the previous stage and additionally determine at the second stage of each stage the steady-state heating temperature, and as a characteristic of structural changes, the difference in steady-state heating temperatures of the second stage of the corresponding stage and the first stage of the previous stage is determined. 1613120 I