SU1474462A1 - Method for determining internal stresses in an object made of polycrystal material - Google Patents

Abstract

The invention relates to non-destructive stress control methods and can be used for plastic polycrystalline metallic materials. The purpose of the invention is to improve the accuracy of determining internal stresses in objects made of materials with unknown parameters of a crystal lattice free from internal stresses. This is achieved by making an additional sample for mechanical testing from the object material, stepwise loading of this sample until plastic deformation occurs with simultaneous irradiation with an X-ray beam, recording the load and coordinates of characteristic points of the diffraction curve and calculating the stresses of the sample parameters on the sample. stress equal to yield strength. The yield strength is determined by the violation of proportionality between stresses and strains, or between stresses and lattice parameter.

Description

one

The invention relates to methods for non-destructive testing of internal stresses and can be used to determine the sum of principal stresses in crystalline materials with unknown parameters of a lattice free from internal stresses.

The purpose of the invention is to improve the accuracy of determining internal stresses in objects for which the lattice parameters in the absence of internal stresses are unknown, by making an additional sample for mechanical tests from the object material, stepwise loading of this sample until plastic deformations appear with simultaneous X-ray beam irradiation , registering the load and determining the lattice parameters and calculating the stresses taking into account the parameter value determined on the sample and the crystal lattice at a voltage equal to the yield strength.

The method is carried out as follows.

A sample for mechanical testing is made from the material of the object, for example, a thick-walled ring of small width. Ring cut

4 1

4b 4b

05

F

a wedge, used to create a load on the diametrically opposite part of the ring. Apply two marks on opposite sides of the slot on the adjacent to the slot sections of the end surface of the ring.

In the studied area of the cylindrical surface of the ring, a site is selected for an X-ray study of the structure of the crystal lattice, for example, using a diffractometer that allows recording the diffraction curve and finding the lattice parameters at large values of the Bragg diffraction angle and performing radiography. The distances between the marks are measured and the stresses in the ring are calculated using the known resistance formulas of the materials. Then stepwise increase the load by pushing the wedge into the slot, re-measuring the distance between the marks and determining the lattice parameter X-ray diffraction. The load is increased until the proportionality between the load and the lattice parameters is calculated, calculated on the basis of the experimental data obtained. From these data, the value of the sought lattice parameter for a stress equal to the yield strength is determined by the method of extrapolating the linear portion of the stress-period dependence of the lattice. The value of the lattice period corresponding to the absence in the lattice of internal stresses is determined by the formula

ao

one

..-.

period free from internal stresses of the crystal lattice; the period of the crystal lattice at a voltage equal to the yield strength; yield strength of the material, determined from the results of loading the sample; Poisson's ratio of material;

modulus of elasticity of the material. finding the lattice parameter, free from internal

voltages, the sum of the principal stresses in the studied area of the object is determined by the formula

E

Have

(ff, + (r,)

1 2- 1C

0

five

0

five

five

0

five

0

five

Where

(G, + G7

the sum of the principal stresses at a given point of the object; a - measured in this

the point of the period of the crystal lattice of the material.

Claims (1)

Using the proposed method for non-destructive testing of objects allows one to more accurately determine the internal stresses in the material, since the systematic errors in measuring the lattice parameters are mutually compensated, and the data used for the calculation (except for the elastic modulus and Poisson’s ratio) more accurately reflect the real properties the studied material. Invention Formula The method of determining the internal stresses in an object made of polycrystalline material, which consists in the fact that the studied surface area of the object is irradiated with an x-ray beam, the diffraction curve is recorded, the position of the selected diffraction pattern is determined maximum, and according to it, the lattice parameter of the material and from these data determine the sum of the principal stresses, characterized in that, in order to improve the accuracy of determining internal stresses in objects for which the lattice parameters are unknown in the absence of internal stresses, the material of the object is made a sample for mechanical testing, is subjected to a stepwise loading until plastic deformation occurs with simultaneous irradiation by an x-ray beam at each step, centration determination of the load and the lattice parameters are found m the lattice parameter at a voltage equal to the yield stress, and the obtained values of the lattice parameters used in determining the amount of the principal stresses on the test portion of the object surface.