SU1254369A1 - Method of determining fatique damages in metallic articles - Google Patents

Abstract

The invention makes it possible to determine the stages of fatigue damage incoking before the formation of cracks. The product is subjected to cyclic loading, simultaneously exciting surface ultrasound waves in it and registering the reflected signal. In this case, the nature of the change in the energy of the echo pulse is recorded, the obtained curve is compared with the law of change of the cyclic load, and the degree of damage is judged by the deviation from it. 3 il. Mpu Yu SL th so about with

Description

This invention relates to a technique for controlling the quality of materials and can be used in ultrasonic inspection of products.

The purpose of the invention is to determine j c, the accumulation of fatigue, damage preceding the formation of trash; 5 n.

 At fmg, 1, the principle 10 is shown, the setup diagram for the re-apt method of the method; in fig. 2. - characteristic dependences of the energy of an echo pulse under cyclic loading at various stages of fatigue damage; FIG. 3 shows a graph of the change in the criterion for estimating the distortions of the energy curve of an echo pulse o. t, the law of cyclic loading at various stages of fatigue damage .20

The method is implemented as follows.

The test article or specially prepared sample 1 is installed. It is clamped, and the free end 25 undergoes repeated static bending with a frequency of 0, .3 Hz and a length corresponding to the change of stress, from O to. 0.8 dp at the maximum cross section of the sample, 30 where djj is the temporal resistance ,.

The excitation and reception of elastic capacitors, bans in specimen 1 (Fig. 1) is carried out using an ultrasonic transducer 2 of the combined type jj with a prism angle of 65 and an operating frequency of 5 MHz, and also a defectoscope 3 type DUK-66. Transducer 2 is preliminarily set (before loading) on the sample to the position at which the amplitude of the ultrasonic one: pulse reflected from the concentrator is maximum. The reverser is then shifted across the sample to a position corresponding to a 0.707 maximum value. amp.patt beats of the pulse and is fixed in such a field to enable the tracking of structural changes.

, in the metal at the top (edge) of the stress concentrator. Opt; kenny from the concentrator ul. Ultrasonic impulse

is taken by the transducer, amplified and selected by the defect circuit.: A toscope, and then fed to the input, integrator 4.0 of the integrator output

shot on type 5 recorder I338

. Dc current signal (signal).

45

50

j p

five

the value of k which is proportional to the energy of the echo pulse.

As can be seen from the record given in Fig. 2, as the sample is being used, the waveform changes. In the initial loading cycles, the nonlinear distortion of the signal is practically absent (Fig. Pro.). With a sample lifetime, nonlinear distortions of the signal appear (Fig. 26), the second are further changed (Fig. 2c, d) and disappear (2e).

To quantify the distortion, a coefficient K is introduced, which is the ratio of the amplitude of the non-linear distortion. L to the amplitude of the undistorted signal. The behavior of this coefficient (and hence the magnitude of nonlinear distortion) at various stages of fatigue damages is shown in FIG. 3.

At the first stage (incubation), there are practically no internal damages in the product (before accumulation of plastic deformations, estimated by the density of the shear lines), respectively, there are no distortions on the energy curve of the echo-pulse,; co.tora coincides with the law of cyclic load 1 (FIG. 2, a), respectively, the value of K O (FIG. 3). . With the production of the sample, distortions appear on the curve of the echo-impulse energy, which grows and reach a maximum value, respectively, the value of K (Fig. 3) increases from zero to maximum. This interval corresponds to stage II - destruction.

The maximum value of the coefficient K corresponds to the formation of. plastically deformed ripened metal zone of the p da is fragmented: -nrg: micro-cracks.

Further development leads to an increase in the degree of structural change, i accompanying an increase in the size and number of microcracks. At this stage (ill), the coefficient K decreases from the maximum value to zero, and at the fourth stage, the development of a microcrack, K equals zero.

Thus, in order to determine the degree of fatigue damage, it is necessary to subject the test article to an examination in accordance with the indicated method and evaluate the presence and behavior of nonlinear distortions. If they are missing, then fatigue

3 - 125 i

damage to the correspondents of the incubation stage, if it appeared and grow - pre-destruction stages; if present and diminished with a lifetime, the stages of the merging of scattered microcracks; if they are absent, the presence of trunk cracks can be detected by known methods, including visually.

Formula and goiter and

Method for determining fatigue damage in metal products

 W /; VU - J

Signal

694

by excitation in samples of pulses of surface ultrasonic waves under cyclic loading conditions} and recording the reflected signal, characterized in that, in order to determine the accumulation stage of fatigue damage preceding the formation of cracks, the change in the energy of the echo pulses per load is recorded and by the deviation of the curve corresponding to this i-fy change, from the law of cyclic loading, the degree of damage is judged.,

FIG. 7

fJ / Afp

ff

five

In FIG. 2

About OfB30 (u, 5S30jSl} fS4S, t J №г.

Editor V.Kovtun

Compiled by F. Samokhvalov, Tehred A. Kravchuk Proofreader S. Cherni

Order 4713/47 Circulation 773 Subscription

. VNIIPI USSR State Committee

for inventions and discoveries 113035, Moscow, Zh-35, Raushsk nab., 4/5

Production and printing company, Uzhgorod, Projecto st., 4

Claims (1)

10 Formulation by excitation of surface ultrasonic waves in pulses under cyclic loading and registration of the reflected signal, which, in order to determine the stage of accumulation of fatigue damage, preceding the formation of cracks, fix the change in the energy of the echo pulses per loading cycle and the deviation of the curve corresponding to this change from the law of the cyclic. The method for determining fatigue loading is judged on the degree of damage Editor V. Kovtun