SU1562749A1 - Method of testing material for crack-resistance - Google Patents

Abstract

The invention relates to the testing of materials for crack resistance. The aim of the invention is to increase the reliability by providing the determination of both the characteristics of crack resistance and the effect on the characteristics of changes in the properties of the material in the zone of stress concentration. Two identical sample shapes are tested for crack resistance. In one sample, a fatigue crack is initially induced from the concentrator, after which the material is removed around the concentrator, absorbing the zone of damage to the material. In another specimen, the fatigue crack is pre-directed directly from the notch. With respect to the relevant characteristics of the crack resistance of the samples, the effect of the material damage on the crack resistance characteristics is judged. 5 il.

Description

This invention relates to methods for testing materials for crack resistance.

The purpose of the invention is to increase the reliability by providing the determination of both the characteristics of crack resistance and the influence on the characteristics of changes in the properties of the material in the stress concentration zone.

Figure 1 shows a sample for the implementation of the proposed method; Fig. 2 shows a planar specimen with an area intended to remove a part of the material (an additional specimen); FIG. 3 shows the dependence of the load P on the displacement of the banks of the notch o; Fig. 4 is a diagram of the change in load P from time t under shock loading in determining the dynamic viscosity.

destruction; FIG. 3 is a diagram of the change in load P when determining the growth rate of fatigue cracks over time t.

An installation for the implementation of the method is a test installation for loading specimens with a load corresponding to a determined crack resistance characteristic: impact, cyclic or static fracture toughness. The installation is equipped with means for measuring and recording loading parameters and cracking. The method is implemented as follows.

Two externally identical specimens are tested for appropriate crack resistance: sample 1 with a notch 2 of radius p, on the lateral surface.

Od

1C

3

WITH

and sample 3, however, the samples are prepared for testing differently. Sample 1 initially has a notch 2 concentrator with which a fatigue crack was induced, sample 3 initially had a concentrator 4 notch with which a fatigue crack was induced, after which the material around the concentrator was removed to form a material damage zone . In this case, h — the thickness of the removed part of the material in the direction of crack fracture is chosen from the ratios

Rn;

h 1 - 1

H

where R is the size of the zone of damage to the material, determined from formula 20

(1 +

 2Rn + p, 25

where 1n is the depth of the notch; 1 - crack length; P is the radius of the original concentrator;

p is the radius of the cut-out after the removal of 30 kg of a part of the material; - cyclic limit of proportionality; Kg - intensity factor

stress, 35

after which the samples are loaded until failure, and in relation to the characteristics of crack resistance, the degree of change in material properties in the stress concentration zone is judged: 40

Kcc Kic / K1C

vn / v,

rm

de K, K 1c - static viscosity

destruction of damaged and intact material; eg

Krs, K1) C - dynamic viscosity

destruction of damaged and intact material;

vn, v is the growth rate of fatigue -, - cracks, respectively, of damaged and intact material.

Q 5

0

five

0

five

0

five

g

,,

Example 1. Pre-made two series of samples with one-sided cuts of steel 15Kh2RFA (La2 584 MPa, 700 mtta), 10 pieces each: a series of flat samples 1 (Fig. 1) with a circular notch 2 of radius p, and a series of flat samples 3 (Fig .2) with a notch 4 wide K with an angle at the base oi and a radius of rounding p. Sample sizes: L 350 mm, b 45 mm, p, 25 mm, f O, 1 mm; To 3 mm, 1 p 8 mm, t 12.5 mm, about Ј 60 °.

Both series of specimens are sequentially placed in the grips of the testing machine and subjected to cyclic loading in order to initiate a fatigue crack with a length of 1 O, (1 28 mm). After that, in the Cv of samples 3 mechanically, a part of the metal in the vicinity of the concentrator 4 is removed on the EDM copying and polishing machine, as a result of which a sample with a lateral concentrator of radius / 2 is obtained, the mouth of which ends in a crack. The width of the removed part of the metal in the direction of the development of cracks h 2 mm.

Thus, a series of samples with a crack coming out of the concentrator is obtained, in which there are practically no tangible changes in properties in the stress concentration zone.

Example 2. Samples (lig.1 and 2) are alternately installed in the grippers of the testing machine Hydropulse 400 KN and statically loaded by stretching until complete destruction. At the same time, on a two-coordinate typewriter type 7004 (Hewlet Pakkard), a load diagram P is recorded - the movement of the notch banks (Fig. 3), which determine the critical PC corresponding to unstable destruction, and calculate the fracture viscosity. In relation to the viscosity of FJC, determined on sample 1, to the fracture toughness K1C, determined on sample 3, is judged by the degree of change in material properties in the concentration zone.

Example 3. Samples (Figures 1 and 2) are alternately mounted on the towers of a tandem copra and tested (according to the three-point bending pattern) for dynamic fracture toughness. At the same time on the oscilloscope record the load diagram P and time t

(FIG. 4), which determines the maximum load PJ} corresponding to the crack opening. Under load P, j and length 1 of the crack, the dynamic fracture toughness KSC for samples 1 and Kj is calculated, for samples 3 with respect to which changes in material properties in the zone of stress concentration.

Example 4. Samples (Figs. 1 and 2) are alternately mounted into the grippers of the Hydropulse 400 FH testing machine and cyclically loaded by stretching (Fig. 5) at a fixed load cycle asymmetry factor (R / pmax 0.1) and loading frequency 25 Hz. The magnitude of the magnitude of the load (DR RMO, KS-RMIN) is chosen so that the initial growth rate of the fatigue crack is not more than 5 "10 mm / cycle. The magnitude of the load is monitored using a digital voltmeter of the type MA313. The crack length is measured on the polished surface of the sample using an MBS-1 microscope with an accuracy not lower than 0.014 mm. To obtain a kinetic diagram of fatigue failure, the magnitude of the load is stepwise modified. By the ratio of the growth rate of fatigue cracks on samples 1 and 3 at the same magnitude of the magnitude of the stress intensity factor, the degree of change

material properties in the concentration zone

stress

Claims (1)

Invention Formula The method of testing the material for crack resistance is that a fatigue crack is induced as a notch on the lateral surface of a material sample with a concentrator, after which the sample is loaded until fracture and the crack resistance characteristics are determined in order to increase the reliability by to determine the effect on the characteristics of changes in the properties of the material in the stress concentration zone, the characteristics of the crack resistance of an additional specimen with a notch concentrator are determined and on the side surface, in which a fatigue crack is preliminarily widened, the length of which is equal to the length of the induced crack of the main sample, and the damaged material in the concentrator zone of the additional sample is removed before a cut is formed on its side surface, the radius is smaller than the crack length, The sample is made with a radius equal to the cutout radius, and the effect of a change in material properties in the concentrator zone is judged by the ratio of the corresponding characteristics of the crack resistance of the main and For more samples. 1 FIG. Z