SU974213A1 - Specimen for investigating sheet material crack resistance in cyclic loading - Google Patents

Description

The invention relates to testing equipment for the study of materials, in particular, samples 1M for studying the crack resistance of sheet material under cyclic loading.

A known sample for investigating the crack resistance of sheet material under cyclic loading, made in the form of a plate with two-sided side cuts perpendicular to the direction of loading.

The known sample contains two pairs of bilateral side cuts of the same length tlj.

The disadvantage of the known sample is the low productivity of the study, since for the study of the growth of cracks of various initial lengths it is necessary to carry out tests of various samples.

The purpose of the invention is to increase research productivity.

This goal is achieved by the fact that in a sample for investigating the crack resistance of a folded material with cyclic loading of a plate filled with double-sided side cuts perpendicular to the loading direction, at least three pairs of double-sided side cuts of different length, but identical for each pair, were made.

The drawing shows a sample with incisions of different lengths.

The sample is made of a plate of the sheet material under investigation and contains gripping parts 1 and 2, transition parts 3 and 4 and working part 5, on which at least three pairs of symmetrical double-sided side cuts 6, perpendicular to the direction of stretch, coinciding with

15 axis of symmetry of the sample. Neurez are located at a distance m from each other, satisfying the condition

I

ttets11, where - the length of the greatest 20

This cut. The incisions are made by making a mechanical elec- The minimum notch length for determining the 25 value of the coefficient K, the intensity of stresses is chosen equal to the sample thickness. The minimum length of the notch for measuring the crack growth rate is equal to

30 le5a1-10, where is the base

increment of crack length due to measurement accuracy. The maximum length of the Gpat notch is chosen equal to eta 3.5-4 ,. The cuts are located on the specimen in order of increasing their length: t., ..

The width of the 2W sample is chosen equal to

2W, P + 2A,

where 2 (L 2, + 2p,

p is the notch radius, 2h 100 mm,

rndx f Vmin - maximum and minimum crack growth rate to be measured accordingly when a crack develops from cuts with length

tna% and ETTPL

The study of the crack resistance of the sample material is carried out as follows.

The sample is placed in the grips on the loading device and is loaded cyclically. Under cyclic loading, cracks develop from the tips of the cuts. At the first stage, at the top of the cuts, a crack crack with a length of 3cri2j is grown. While in the notch of the minimum length the length of the fatigue crack will be equal to the minimum required value of E from 2j7, for the notch of the maximum length the length of the fatigue crack in the wave of the notch will be equal to 2j3V x / Vmin. Value is chosen in the interval Yu

CYCLE

-4 MM

- 5-10

and from the tops of the cracks.

cycle

where the initial length is shorter, cracks develop at lower rates.

During the test, the observation first of all leads to the growth of a crack propagating from a notch of maximum length. When the length of this crack reaches utsei 0f

The rate of growth of this crack is determined as the ratio, where .dN is the number of load cycles corresponding to crack growth, and the value of the stress intensity factor K. Further, an observation is made. cracking behind a crack of smaller length and thus constructing a diagram of crack propagation in the velocity range,. The use of a sample with double-sided cuts of various lengths makes it possible to increase the productivity of the tests and to obtain the fracture growth diagram - coefficient 2Q stress intensity K. By testing only one sample.

Claims (1)

Invention Formula Sample for investigating the crack resistance of sheet material at. cyclic loading, made in the form of a plate with double-sided side cuts, perpendicular to the direction of loading, about l and. due to the fact that, with the whole increase in research productivity, at least three pairs of 35 bilateral side cuts of different length, but the same for each pair. Sources of information taken into account in the examination d0 1. Proceedings of coordination meetings on hydraulic engineering. Issue 103. L., Energie, 1975, p. 162-167 (prototype).