RU2527671C2 - Testing method of sheet materials of tension - Google Patents

Abstract

FIELD: testing technology.

SUBSTANCE: invention relates to testing technology and can be used in the characterisation of the mechanical properties of sheet materials under conditions of uniaxial tension in the mechanical engineering, automotive industry, aircraft industry and other fields of industry. Essence: the sample of rectangular shape is loaded to destruction with flexible die in a rigid slit matrix with force perpendicular to the plane of the sample. During the test, a sample with a width of the working part exceeding three times its thickness is used. The cross sectional area of the sample working part in the place of destruction is determined, on the basis of which the volume of the limiting plasticity of its material is calculated.

EFFECT: possibility to determine with high accuracy and reliability the characteristics of the mechanical properties of sheet materials under uniaxial tension.

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Description

The invention relates to testing equipment and can be used to determine the characteristics of the mechanical properties of sheet materials under uniaxial tension in mechanical engineering, automotive, aircraft and other industries.

Closest to the proposed technical solution is a method of testing sheet materials in tension, presented in the patent [1].

In this method, a rectangular-shaped sample is loaded until it is destroyed by an elastic punch in a rigid slot matrix with a force perpendicular to the plane of the sample, which is applied through an elastic insert located in the central zone of the sample, having a length equal to 0.8 times the width of the working part of the sample and half its width lengths.

A disadvantage of the known technical solution is the low accuracy of tensile testing of sheet materials under uniaxial tension, due to localization of deformation (neck formation) on the working part of the sample, leading to distortion of the test conditions due to the transition from uniaxial to biaxial.

The claimed technical solution is aimed at improving the accuracy of the test by eliminating the localization of deformation (neck formation) on the working part of the specimen and ensuring uniaxial tension conditions until the specimen ruptures.

This is achieved by the fact that in the method of testing sheet materials for tension, according to the invention, to exclude localization of deformation (neck formation) on the working part of the sample, a sample is used with a width of the working part three times its thickness.

The drawing shows the test setup: to the left of the axis of symmetry the initial position of the sample before the test, to the right - the position of the sample after the test.

The method is as follows. A sample having a rectangular shape and attenuation on the working part, the width of which is three times the thickness of the sample, is made of the studied material. Before the test, measure the thickness t ₀ and the width b _{0 of the} working part of the sample. Then, the sample 1 is installed on the mirror of a rigid slotted matrix 2. In order to reduce the friction forces between the sample and the matrix, a 0.1 mm thick plastic film is placed. Between the elastic punch 3, placed in the container 4, and the sample 1 at both ends in the areas of the clamping and transitional parts are placed plates 5 of high-strength ductile metal, which block the deformation of the sample outside its working part. A press force is applied to the container 4 and the sample is loaded to failure.

Due to the use of an elastic medium as a punch material during testing, a high uniformity of pressure distribution on the working part of the sample is ensured, and thereby uniform uniaxial tension is realized within it up to the destruction of the sample. In this case, the sample is clamped to the matrix mirror along its entire contour, and the clamping force increases during deformation.

After the test, the sample 1 is removed from the matrix 2, the thickness t and the width b of the working part of the sample are measured at the fracture site, and the ultimate plasticity of the sample material ε _pr is calculated from the forum

ε _ol = ln (F ₀ / F),

where F ₀ = b ₀ · t ₀ is the initial cross-sectional area of the working part of the sample;

F = b · t is the cross-sectional area of the working part of the sample after the test.

Implementation of the proposed method will allow, in comparison with the known technical solution, to increase the accuracy and reliability of determining the characteristics of the mechanical properties of sheet materials under uniaxial tension.

An example of a specific implementation of the method

Testing of samples of sheet materials under uniaxial tension was carried out on a standard testing machine TsD-40. Three flat specimens made of D16AM aluminum alloy were tested. The working part of the samples was 40 mm long and 4.5 mm wide, which was three times the thickness equal to 1.5 mm. As an elastic medium for the punch in the test used technological rubber brand 3826.

Loading of the samples to failure was carried out according to the direct drawing scheme in an experimental stamp with a wide working part of the channel of a rigid slot matrix equal to 55 mm.

Failure of each of the three tested samples was not accompanied by localization of deformation (neck formation) and occurred in the center of the working part of the sample by the formation of a crack oriented normal to its longitudinal axis, which indicated that uniaxial tension conditions were realized during the test.

The ultimate plasticity of the material ε _pr is equal to the strain intensity ε _i accumulated at the time of fracture. In the case of uniaxial tension

where l ₀ , l - the estimated length of the sample, respectively, before and after the test.

In accordance with the condition of plastic incompressibility of the material

$$l_0{F}_0=lF.\left(\text{2}\right)$$

From a comparison of relations (1) and (2) it follows that the ultimate ductility

To establish the ultimate ductility for each of the tested specimens, the width b and thickness t of the working part of the specimen were measured at the fracture site and the cross-sectional area F was determined. The ultimate ductility averaged from the test results of the three specimens was found to be 0.34.

Thus, the presented experimental data allow us to conclude that it is possible to implement, with a sufficient degree of accuracy, the proposed method for tensile testing of sheet materials.

The proposed method allows to determine with high accuracy and reliability the characteristics of the mechanical properties of sheet materials under uniaxial tension. The proposed method can be used, in particular, to establish the ultimate ductility under uniaxial tension, necessary to build diagrams of the maximum formability of the material used in the design of technological processes for metal forming. Using the proposed test method will determine the necessary characteristics of the mechanical properties of sheet materials used in various industries, by conducting tests in the mechanical laboratories of industrial enterprises and research institutes.

Information sources

1. RF patent 2226682, cl. G01N 3/28. 04/10/2004, BI No. 10.

Claims (1)

A method of tensile testing of sheet materials, in which a rectangular-shaped sample is loaded until it is destroyed by an elastic punch in a rigid slot matrix with a force perpendicular to the plane of the sample, characterized in that a sample is used with a width of the working part three times its thickness, the cross-sectional area of the working part of the sample is determined in the place of destruction, on the basis of which the value of ultimate plasticity of its material is calculated.