Method for measuring uniaxial tension large-strain-range hardening curve of metal round bar specimen

Abstract

The invention discloses a method for measuring a uniaxial tension large-strain-range hardening curve of a metal round bar specimen, and belongs to the field of mechanical property testing of metal materials. The method only needs to perform the following steps of: measuring the radius of the cross section of a round bar tension specimen, calculating the stress strain value at the time of fracture,and fitting the stress strain values before necking and at the time of fracture by adopting a hardening model to determine an initial value of hardening model parameters; and then, generating a plurality of hardening parameter combinations by adopting an experimental design method, inputting hardening curves determined by the parameters into finite element software for tension simulation, outputting the corresponding simulated load displacement curves, calculating the sum of the absolute area differences between the simulated and experimental load displacement curves, constructing a responsesurface model by taking the value as the response and the hardening parameters as independent variables, taking the minimization of a response surface function as an optimization objective, optimizingan objective function by adopting a quadratic programming method, and determining that an optimal solution is a large-strain-range hardening curve of an experimental material. The scheme of the invention has the advantages of small calculation amount and high measurement accuracy.

Description

technical field [0001] The invention belongs to the technical field of mechanical property testing of metal materials, and in particular relates to a method for measuring hardening curves in large strain ranges of metal round bar samples in uniaxial tensile tests. Background technique [0002] The uniaxial tensile test is a basic method for testing the mechanical properties of metal materials. Usually, the load-displacement curve of the material is obtained by the uniaxial tensile test, and then the load-displacement curve is converted into 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 material is still hardening during the entire necking process, and the real stress should also be increasing. Therefore, the true stress-true strain curve directly converted from the load-displ...

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Problems solved by technology

[0008] The purpose of the present invention, in order to solve the problem of tedious measurement, large amount of calculation and large error when obtaining the hardening curve after necking by the current traditional method, a method for measuring the hardening curve of a metal round bar sample in uniaxial tension and large strain range is proposed , there is no need to measure the minimum section radius a i and the radius of curvature R of the necking outer contour i , without extensive finite element calculations

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