FLC (forming limit curve) testing method based on variation of strain rate

Abstract

The invention relates to an FLC (full-load current) testing method based on the variation of a strain rate. The method comprises the following steps: acquiring a surface strain distribution cloud chart of a test sample; exporting epsilon(t) of each location point; calculating a strain rate of the point-in-time on each location point epsilon(t) to form (described in the specification), calculating a first derivative value of the strain rate of each point-in-time on (described in the specification), and recording the point-in-time corresponding to the moment when a negative value or a maximum value first appears in the first derivative value as t1; repeating the steps to obtain t2 to tn; comparing the values of t1 to tn, adopting the point-in-time with the value being most repeated as a moment t0 when the test sample begins to be necked, finding out an epsilon major and a corresponding epsilon minor in the test sample necking area on the surface strain distribution cloud chart at the moment t-1, wherein the epsilon major and the corresponding epsilon minor are used as a limiting strain point of the material; repeating the steps to obtain 5 to 8 limiting strain points; marking the limiting strain points on a main / secondary strain plane, and connecting the limit strain points to obtain the FLC. By adopting the method, the influence caused by a cross-section strain distribution pattern can be effectively avoided, and the accurate and reliable FLC can be acquired.

Description

technical field [0001] The invention relates to an FLC test method, in particular to an FLC test method based on strain rate changes. Background technique [0002] The forming limit of a material refers to the ultimate deformation degree that can be achieved when the material begins to shrink, and the ultimate strain data points obtained under different linear strain paths (ε major ,ε minor ) constitutes the forming limit curve (FLC) of the material on the primary and secondary strain planes, which is a core indicator of the formability of sheet metal. The national standard GB / T24171.2-2009 discloses a method of measuring the ultimate strain through cross-sectional strain distribution shape fitting calculation (position correlation analysis method). This method selects the primary and secondary strain data on both sides of the crack (filter part of the strain data in the constriction area), using inverse parabola fitting to calculate the ultimate strain, the ultimate strai...

AI Technical Summary

Problems solved by technology

However, the shape of the cross-sectional strain distribution is closely related to the material, the geometric shape of the sample, and the test conditions. The above problems are difficult to avoid, which is an inherent deficiency of the position correlation analysis method.

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