RU1826022C - Method for testing material specimens for tensile strength - Google Patents

Abstract

Usage: in testing equipment, in strength tests. SUMMARY OF THE INVENTION: a reference sample is installed in a testing machine, it is heated, loaded to yield strength with a constant deformation rate, beyond the yield stress, loading is carried out with a stepwise increasing deformation rate. The strain rate is set equal to the strain rate and loading of the working sample is carried out at this rate. 4 ill.

Description

The invention relates to mechanical testing of samples of materials and relates in particular to tensile testing methods at high temperatures. The method can be used in the practice of scientific research organizations and factory laboratories in determining the characteristics of short-term strength and ductility of materials in a wide temperature range, as well as in assessing the stress-strain state of structural elements during loading.

The purpose of the invention is to increase the accuracy of determining the short-term characteristics of the strength and ductility of a material by isolating the rheological component of the strain rate and taking it into account in the process of setting the strain rate in the following tests.

A positive effect in the implementation of the proposed method is achieved by isolating the rheological component of the strain rate, reflecting the influence of the time factor, and obtaining the characteristics accordingly instantly. deformation independent of time.

The method is carried out as follows.

. A sample of the test material is secured in the grips of a short-term strength test machine, heated to a test temperature, and held at that temperature. The specimen is loaded with a fixed deformation rate selected from the range recommended by GOST 1497-84 and set by the speed of movement of the active capture. Beyond the yield strength. Using the dial gauge and stopwatch, the deformation rate ЈL is determined as the ratio of the active capture velocity dL / dt to the length of the working part of the sample from the ratio

SL

with

00

to

0

about

N) Yu

EL

det dL. j

dt

dt I

and strain rate Јо as the ratio of the recording speed of the elongation dS / dt on the diagram tape to the length of the working part of the sample I from the ratio

 deo dJ3 1 dt dt K7

ED

where K is the gain of the extension registration channel.

The values of the strain and strain rates measured during the test are compared and, if there is a mismatch, the strain rate is less than the strain rate, then a stepwise increase in the strain rate is achieved (Fig. 1). This operation is performed until the deformation rate of the sample, measured on its working part, reaches the value of the deformation rate measured between the active and fixed grips of the testing machine (Fig. 2). Thus, the value of the deformation rate of the material sample is established, which allows providing loading conditions for the entire Series of Yari samples at a fixed temperature, characterized by the absence of a time dependence of the deformation diagram. After that, a test of the working sample is carried out, the loading of which is carried out with the deformation rate set on the reference sample and from the results of which the mechanical characteristics of the material are determined at a given temperature.

Using the above method, tests were conducted on a batch of samples of the heat-resistant alloy EP718 in the temperature range of 20-1000 ° C and strain rates recommended by GOST 1497-84 and 49651-84 and amounting to 0.0025-0.00025. As the results of studies showed, the difference between the strain and strain rates is noted

at test temperatures above 800 ° C, it increases as it rises, as shown in FIG. 3, where curve 1 combines the values obtained for the range soon0

5 0 5 0 5

0 5

recommended by GOST, and curve 2 for speeds less than 0,00025.

In FIG. Figure 4 shows, by way of example, tensile diagrams of EP718 alloy specimens at strain rates recommended by GOST and corresponding to practically the upper value of its range. The margin of error in the estimation of tensile strength is 7%. With a decrease in the strain rate within the range specified by GOST, the error will increase accordingly.

The method of tensile testing of samples of materials allows, in addition to the known method, in addition to increasing the accuracy of determining the characteristics of short-term strength of the material, to evaluate the rheological component of plastic deformation under various temperature and speed test conditions and determine its effect on the strength properties of the material which is essential for assessing the life of structures when the component of the creep strain is commensurate with instantaneous strains.

Claims (1)

SUMMARY OF THE INVENTION A method for testing samples of materials for tensile strength, namely, that the reference sample is heated to the test temperature, loaded with a constant deformation rate to yield point, and the load and elongation of the sample are measured, characterized in that, with In order to increase accuracy by isolating the rheological component of the strain rate, loading of the reference sample beyond the yield strength is carried out with a stepwise increasing strain rate, measured at each stage scab its deformation and deformation rate is determined deforming speed coinciding with the deformation rate, is carried out heating the work piece, the work piece loading is carried out with the reference sample mounted on a deformation rate and determining the strength characteristics of the material.  i. 9igd. MO 700 800 900 1000 t, ° C 0 FIG. d FIG. 4