SU1552089A1 - Method of determining parameters of residual stresses in articles subjected to surface cold working - Google Patents

Abstract

This invention relates to acoustic methods of non-destructive testing. The purpose of the invention is to improve the accuracy of determining the parameters of residual stresses in products subjected to hardening of the surface by hardening, due to the sounding of the product by surface ultrasonic (US) vibrations of various frequencies and measuring the time of their propagation. As a result, layered information is provided. Surface ultrasonic vibrations emit in the product and receive the oscillations of the first frequency passed in the product given a base. Their propagation time is measured and the difference between this time and the time of passage of similar ultrasonic vibrations in the area of the product without stresses is determined. These operations are repeated at other frequencies in order of their decrease. According to the results of measurements at various frequencies, taking into account the depth of penetration of surface ultrasonic vibrations at these frequencies into the material of the product, the depth and the magnitude of the residual stresses are determined. 2 Il.

Description

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The invention relates to acoustic methods of non-destructive testing and can be used in determining parameters of residual stresses in products subjected to surface hardening, for example, in determining the magnitude and depth of surface stresses in parts after vibro-impact hardening.

The aim of the invention is to improve the accuracy of determining the parameters of residual stresses due to the stratification of information due to the sounding of the product by surface oscillations of various frequencies and measuring the time of their propagation.

FIG. a block diagram of a device implementing the method is presented; in fig. 2 is a plot of residual stresses in the product, determined as a result of the method implementation.

The method of determining the parameters of residual stresses in the products, flow fco

hardening by surface hardening is as follows. Surface ultrasonic vibrations at frequencies f ..., Ј. ... are successively excited in the product by observing the condition f j, f; f V1. Accept the vibrations of different frequencies that passed through the same test section of the product. The propagation time of the received ultrasonic vibrations is measured and the difference &T; the propagation time of the ultrasonic oscillations of the frequency fj in the tested and non-reinforced parts of the product. Find the product of the difference DT; and depths h; penetration of ultrasonic vibrations of frequency f into the material of the product. At each transition from the frequency f j, to the frequency f; compare the values of DT; b; ibt ;, h; ..,. Upon reaching the frequency fn, the measurement results on which satisfy the condition

Tts, bn, -l tn-bn. ABOUT,

complete the excitation of surface ultrasonic vibrations. The depth H of the bedding and the magnitude GJ of the residual stresses in the i-th layer are determined from the expressions

hn.,. E h;

g

HAIIhLlJL2LbjlAi

h; - h; H

40

de is the value of residual stresses in the layer located between depths h, JM and h; k - empirical coefficient

proportionality; UT; - time difference between the propagation of ultrasonic oscillations of the frequency f; on the investigated and non-reinforced areas of the product; h; - the depth of penetration of surface ultrasonic frequency oscillations into the material of the product;

H is the depth of the residual stresses;

i 1,2, ..., n is the sequence number of the frequency f; 55 oscillations excited when the frequencies are arranged in a series in decreasing order.

50

five

0

five

40

The method of determining the parameters of residual stresses in products subjected to surface hardening is carried out as follows.

On the controlled product 1, for example, the blade of a helicopter made of material AVT-1, strengthened by balls on a vibrating table by serial technology, in the measurement zone, inclined prismatic radiating 2 and receiving 3 transducers are installed. The generator 4, whose frequency is regulated by the modulator 5, excites the radiating transducer 2. The latter, in turn, excites surface ultrasonic oscillations in the product 1, which have traveled a predetermined distance over the surface of the product 1, are fed to the receiving transducer 3.

From the transducer 3 through the amplifier 6, the received signal is fed to the time interval meter 7, which measures the transit time of the surface ultrasonic oscillations of a given base (L 42 mm). Previously similar measurements are carried out on a separate piece of the product used for the manufacture of samples and freed by bleeding for 2 hours from all surface stresses, including preliminary process voltages. In product 1, ultrasonic oscillations of the following frequencies, MHz, are excited in series: f 18; Јg 11.5; f, 9.5; f 5; f5 3.6. For each frequency value, the difference DT of the time of passage of the base L by oscillations in the area under study and in the area free from all surface stresses is measured. In addition, for each frequency, the depth h of penetration of ultrasonic vibrations is determined. The measurement results are shown in the table.

-4,5

-8.1 -8.8 -8.1 -5.2

-4.5 -14.6-11.8-7.32 + 2.53

Since & Tsh5-0, the residual stresses are considered to lie at a depth of from 0.32 to 0.44 mm. Depth of residual for example

about

FIG. Z

Claims (1)

Formula r A method for determining the parameters of residual stresses in products subjected to hardening by surface hardening, which consists in exciting surface ultrasonic vibrations of a fixed frequency f in the product, receiving oscillations that have passed through the studied section of the product, measuring the propagation time of the received vibrations and determining the parameters of residual stresses based on a comparison of the measured time with the propagation time of surface vibrations of the same frequency on the unstrengthened section of the product, with the fact that, in order to increase the accuracy of determining the parameters of residual stresses, additionally excite surface ultrasonic vibrations of other frequencies f in the product; successively in decreasing order of frequencies, they take additional vibrations that have passed through the same section of the product, measure their propagation time, find the product of the difference ΔΤ; the propagation times of ultrasonic vibrations of frequency f (in the investigated and unstrengthened section of the product to a depth h 'of penetration of these vibrations into the product material, upon reaching the frequency f at which the negative product found is greater than the product & T _P. , · h _n . _t , consider the depth residual stresses lying between the values of h _n and h _n _ ,, and the value (Г; residual stresses in 15 layers located between the values of h; and h \ ₍ , is determined from the expression where J · is the value of the residual stresses in the ith layer; k is the empirical coefficient of proportionality; &h; - the difference in the propagation times of ultrasonic vibrations of frequency f; in the investigated and unstrengthened areas of the product; h; - the penetration depth of surface ultrasonic vibrations of frequency f 'in the product material; i = 1,2,3. ,,,, η, ... is the serial number of the frequency f, ’of the excited oscillations, when the frequencies are arranged in a row in descending order. Fig2