SU1731544A1 - Sample for cracking-resistance testing of welded joints and apparatus for testing the sample - Google Patents

Abstract

Use: to assess the resistance of welded joints and welds against cold cracks, cracks during heat treatment, and to assess the cyclic durability of welded joints in mechanical engineering. SUMMARY OF THE INVENTION: A sample is made of two identical plates fastened through an insert. The working part of the sample is made in the form of a beam of equal bending resistance. The device is equipped with an additional gauge of the relative movement of the racks. The loading mechanism of the device is in the form of a hinged screw-nut pair. The sample and device make it possible to increase the accuracy of measurement of the deformation of the sample and, therefore, to accurately calculate the stress in it. and produce tests not only in air, but also in an oven at elevated temperatures or in a cryochamber at reduced temperatures. 2 sp.f-ly. 5 il. sl C

Description

The invention relates to welding and can be used to assess the resistance of welded joints and welds against cold cracks, cracks during heat treatment, and to assess the cyclic durability of welded joints.

A known sample for tests for crack resistance, consisting of two plates connected to the Tavr weld, g, hub - the gap between the plates and the gripping areas - free rings of the plates.

The device for attaching this sample contains a frame, sample attachment points, and a lever device that transfers the load to the sample.

The disadvantage of the sample is the impossibility of its use for testing under cyclic alternating load and for testing for transverse cracks, which limits its scope.

A disadvantage of the device is the impossibility of its use for evaluating crack resistance at elevated temperatures due to the impossibility of placing the sample in a furnace with standard dimensions, which also limits the scope.

In addition, the reliability of the obtained data is low, since the used concentrator — the gap between the plates does not

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allows the correct calculation of the stress state.

Closest to the present invention is a crack test specimen made in the form of a prism. having a working area with a welded seam and a stress concentrator and gripping sections.

A device for testing this sample contains two loading rods, on one of which, in its central part, a sensor is installed to measure their mutual displacement, on the other, a load meter, made in the form of a beam, cantilever mounted to its center, is installed. the part at the free end of which there is a sensor for measuring the movement of the end of the beam and the thrust; a loading actuator in the form of a clamp mounted on the beam and the first joint, fixing a screw-nut pair mounted on the ends opposite to the gripping one, on which the test specimen is rigidly fixed,

The disadvantage of this sample is its limited scope due to the need to respect the ratio between the flexural rigidity of the specimen and the specimen in the range of 20-30, which is necessary to stabilize the stress state of the specimen during high-temperature tests. This ratio of stiffnesses can be achieved only with small sample sizes. This, in turn, does not allow welding the welds on the specimen, which fully comply with the tested technologies, due to the distortion of the thermal cycle.

A disadvantage of the known device is the low accuracy of measurement of forces and displacements and the laboriousness of operations during overloads (measurements of stresses in a sample by their size and sign).

The aim of the invention is to expand the technological capabilities and increase the accuracy and reliability of the tests.

This goal is achieved by the fact that the specimen for testing the crack resistance of welded joints, made in the form of a plate with a welded test joint and stress concentrate at the work site, is additionally provided with an insert and a second plate, in shape. dimensions and material are identical to the first, and the working part of the plates is made of variable width, while the insert is located between the plates from the wider part of them, rigidly fastened with them

and made a width equal to the greatest width of the working part of the plates,

A device for testing the crack resistance, containing two parallel racks, a gauge of their mutual movement, mounted in the central part of one of the racks, a load gauge mounted on a beam that is cantilever mounted on the other rack, and a loading mechanism with a nut and screw hinged on one of the racks, provided with an additional gauge of the mutual movement of the racks installed parallel to the first meter, the screw of the loading mechanism is fixed on the rack with the possibility rotation around its axis, and the nut is hinged to another strut.

The use of a sample of the proposed design allows two tests to be carried out simultaneously (on the first and second plates). The relatively large working part allows to reproduce the thermodeformation welding cycle with greater reliability, the sample design allows determining crack resistance to both transverse and longitudinal cracks, the presence of an insert between two identical plates with working parts allows determining the moment of crack occurrence in investigated welds on any of the plates, for example, by determining the coordinates of the source of acoustic emission (AE), installing sensors AE on racks and inset.

The proposed device makes it relatively easy to set (set) the required sign and magnitude of the voltage in the working part of the sample and makes an accurate calculation of them in the place of the occurrence of a crack both on the sample with the concentrator and without the concentrator.

In this case, the sample and the loading device form a single unit, i.e. are inextricably linked with each other, since only the proposed device allows the sample to create and accurately record the voltage of the required magnitude and sign with minimum dimensions and mass of the entire structure.

FIG. 1-3 presents the proposed sample; in fig. 4 - the proposed device; in fig. 5 - loading scheme.

The sample for crack resistance tests consists of two identical and parallel plates 1 and 2 with working and gripping parts and an insert 3. The working parts are made in the form of beams

equal bending resistance. The plates and the insert are rigidly fastened together.

The device for testing crack resistance consists of two racks 4 and 5, a loading mechanism, made in the form of a pair of screws 6 hinged to the ends of the racks, a screw 7, a nut 7, the screw being made running, a meter 8 of the load made in the form of a beam, cantilever mounted on one of the racks and equipped with a sensor 9, and two gauges 10 and 11 of the mutual movement of the racks.

The tests are carried out as follows.

Between the plates 1 and 2, on the side opposite to the gripping parts, outside the working part, insert 3 is installed and rigidly fastened to the plates, for example, by welding. The best results are achieved with the use of welding technology and welding materials that do not require heat treatment after welding.

The specimen is then mounted on a crack resistance test device. Racks 4 and 5 are set relative to each other at a distance equal to the height of the sample. The sample with its gripping parts is installed under the gripping sections of the racks. The racks and the sample are rigidly connected to each other in the gripping areas, for example, by welding with the same welding materials and using the same technology as in the welding of the sample.

The assembled (Fig. 4) sample and device are placed on the welding post and welds are made on the working part of the sample according to the technology being studied and the materials to be studied. After welding, stress concentrators (notch) are made on the specimen, if necessary, to determine the fracture toughness in a particular weld zone.

A sample with a loading device is moved into the furnace (when tested at elevated temperature) or into a cold chamber (when tested at reduced temperature) and creates the required voltages in the working section. The stresses in the working part of the sample are calculated by the following method (Fig. 5).

The deformations of the required level and sign in the working part of the plate are set with the help of a screw-nut loading pair. The level of the specified deformations is determined by the ratio

h (Ai-A2)

4 Li I

where Ј is the deformation of the surface of the sample to be bent;

h is the thickness of the working part of the sample;

Li is the sample length;

I is the distance between the indicators 10 and 11;

AI- movement measured by the indicator 10;

D2 - movement, measured by the indicator 11.

The bending stress is determined by the ratio

but

M TJ

where W is the moment of resistance to bending calculated by the size of the sample at the site of its destruction;

M - bending moment. In this case, the bending moment is determined by the deflection of the rack, measured by indicator 9, and is calculated from the ratio

 As (Li + L2),

where K is the stiffness of the rack (determined experimentally);

Dz - rack deflection;

L2 is the length of the stand from the point of attachment to the sample to the point of application of force,

when using samples with a concentrator made in the form of a Notch, the stress and strain at the bottom of the concentrator can be calculated by the ratios

Otah O. STNOM; Јmax (X Јnom,

where Otah, Јtah are the stresses and strains at the bottom of the concentrator;

Onom - Јnom - the same, outside the hub;

a is a theoretical coefficient of stress and strain concentration.

In order to achieve sufficient accuracy in estimating the deformation of the sample, the displacements AI and D must be measured with an accuracy of 0.01 mm, and when estimating the bending moment of measurement using the indicator Az, it must be performed with an accuracy of 0.001 mm.

The proposed sample and device allows us to quickly, with high reliability and with low labor costs and material costs, to assess the weldability of the metal with the selected welding technology.

Claims (2)

1. Sample for testing the crack resistance of welded joints, made in the form of a plate with welded The control seam and stress concentrator in the work area, characterized by 4to in order to expand technological capabilities and increase the accuracy and reliability of the tests, it is additionally equipped with an insert and a second plate in shape, size and material identical to the first, and the working part of the plates is made of variable width while the insert is located between the plates on the side of their wider part, rigidly fastened with them and made a width equal to the greatest width of the working part of the plates. 2. A device for testing the crack resistance of welded joints, containing two parallelly arranged racks, a relative displacement meter mounted in the central part of one of the uprights, a load meter attached to a beam which is cantilever mounted on the other upright, and a loading mechanism with a nut and screw hinged on one of the uprights, characterized in that In order to expand the technological capabilities and increase the accuracy and reliability of the tests, it is equipped with an additional gauge for the mutual movement of the racks installed parallel to the first gauge, the screw of the loading mechanism mounted on a rack so that it can rotate around its axis, and the nut is hinged to another rack. FIG. I yig 2 ZZSH J x / Figm Riga 5