Hyperbolic back-stepping measuring method of uniaxial tension stress and train of metal round bar specimen

Abstract

The invention discloses a hyperbolic back-stepping measuring method of uniaxial tension stress and strain of a metal round bar specimen, and belongs to the technical field of mechanical property testing of metal materials. The method is based on a hyperbolic rotating body model of step-by-step expansion of uniaxial tension instability necking of the metal round bar specimen, and the standard distance elongation in the tensile process of the round bar specimen only needs to be measured, and coordinate information of the curve of the outer contour of the round bar specimen after breaking is extracted, a necking hyperbolic equation and a necking minimum section radius at each moment are calculated through back-stepping, thus the curvature radius of the minimum section at the necking positionat this moment can be obtained through a curvature radius formula, and finally, real stress and real strain at this moment can be calculated by a Bridgman method. According to the hyperbolic back-stepping measuring method, a testing and measuring link of the necking minimum section radius and the curvature radius of the outer contour in an existing method is omitted, the measurement accuracy of the stress and strain curve in a large strain range is improved, and the hyperbolic back-stepping measuring method has important significance for mechanical property testing of the metal materials.

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 stress-strain curves in large strain ranges in uniaxial tensile tests of metal round bar samples. Background technique [0002] The uniaxial tensile test is a basic method for testing the mechanical properties of metal materials. Usually, the load-gauge length elongation curve of the material is obtained by the uniaxial tensile test, and then the load- The gauge elongation curve is converted to a stress-strain curve. However, the sample begins to shrink after the maximum load point, and the sample deforms unevenly within the gauge length range. Therefore, it is inaccurate to directly convert the load-instantaneous gauge length curve to the stress-strain curve after tensile instability, and the specimen gradually changes from the uniaxial stress state to the triaxial stress state after necking. Since the c...

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Problems solved by technology

[0003] The purpose of the present invention, in order to solve the difficult problem that the radius of curvature measurement of minimum section radius of necking and necking outer contour curve at the minimum section place is loaded down with trivial details and error is big in Chen Chi method at present, propose a kind of metal round bar sample uniaxial tensile test large The strain range stress-strain curve measurement method does not need to directly measure the radius of curvature of the minimum section radius of the necking and the necking outer contour curve at the smallest section, but reverses it by extracting the necking outer contour curve of the broken test rod

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