Testing and measurement method for hardening curve of metal bar under large strain range

Abstract

The invention relates to a testing and measurement method for a hardening curve of a metal bar under a large strain range, and the method comprises the following steps of firstly carrying out round bar sample torsion test to determine an uniform torsion range, carrying out pre-torsion deformation of different levels on samples in the uniform torsion range, and calculating the corresponding pre-strain; subsequently carrying out round bar sample uniaxial tension test, carrying out uniaxial tension test respectively on torsion-free and torsion samples, determining an effective hardening curve before material necking according to the tension result of the torsion-free samples, determining a true stress and strain curve under different pre-strain levels of the samples by the torsion samples, and carrying out translation along a strain axis, wherein the amount of translation is the pre-strain cumulated by the corresponding pre-torsion deformation; finally extracting the true stress and totalplastic strain data corresponding to the maximum load point in the true stress and strain curves after each translation, fitting together with the pre-necking hardening curve determined by the samplewithout pre-torsion, and finally determining a hardening curve of the metal round bar samples under the large strain range.

Description

technical field [0001] The invention belongs to the technical field of testing the mechanical properties of metal materials, and in particular relates to a method for testing and measuring hardening curves of metal rods in a large strain range. Background technique [0002] Finite element simulation technology is widely used to simulate the metal plastic forming process, and its simulation accuracy depends on the input constitutive relationship, especially the hardening curve covering a large strain range. Uniaxial tensile test is a basic method to obtain the hardening curve of metal bars. Usually, it is assumed that the sample is uniformly deformed within the gauge length range, and the load-displacement curve is converted into a true stress-true strain curve. However, after the point of maximum load, the specimen deforms locally at the necked part, which is subjected to three-dimensional tensile stress. In fact, although the load decreases after the sample is necked, the ...

AI Technical Summary

Problems solved by technology

However, the actual measurement of the radius of curvature of the necking profile curve at the smallest section is very cumbersome, and the measurement cost is high and the efficiency is low

Moreover, the theoretical model method is derived based on the geometric approximation of the necking area. The research shows that the Bridgman method can obtain the hardening curve in a large strain range (about 1.0) under the premise of accurately obtaining the geometric parameters of the necking contour. Still have 3~10% error

The finite element iterative inversion method is carried out based on the optimization algorithm, but the iterative process usually requires hundreds of finite element calculations. Although more accurate results can be obtained, the calculation cost is too high

Therefore, the current methods for measuring the hardening of materials in a large strain range have more or less certain defects.

Images