Test and calculation method for measuring equivalent plastic strain forming limit diagram

Abstract

The invention discloses a test and calculation method for measuring an equivalent plastic strain forming limit diagram. The method comprises the following steps: measuring real uniform strain and realbreaking strain of a material; calculating primary strain and secondary strain under different simple strain paths; and drawing and correcting an equivalent plastic strain forming limit diagram (EPS-FLD). Various defects in the prior art are overcome through theoretical innovation; a technical solution is provided for automobile steel under a new situation; meanwhile, the measurement of the uniform forming limit and the fracture forming limit of the material is integrated into a uniaxial tension DIC test; under the condition that no extra test is needed and a better technical target can be achieved, no extra test is needed, and precious manpower cost and equipment cost are saved, so that the method has important theoretical and engineering practice significance.

Description

technical field [0001] The invention relates to a method for determining the forming limit diagram, in particular to the test and calculation of the equivalent plastic strain forming limit diagram of metal materials and its correction method. Background technique [0002] Forming Limit Diagram (FLD for short) was jointly proposed by Keeler (SAE technical paper 650535) and Goodwin (SAE technical paper 680093) in the 1960s. Keeler proposed that the right half area is used for the analysis of the simple strain state area of ​​the double tension deformation of the sheet metal, and Goodwin extended the left half area for the analysis of the simple strain state area of ​​the sheet metal tension-compression deformation on the basis of Keeler. [0003] FLD depicts the extreme combination of primary strain (ordinate) and secondary strain (abscissa) near the localized necking state under different simple strain paths covering pure uniaxial tension to pure biaxial tension , the value ...

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Problems solved by technology

[0041] In view of the deficiencies in the prior art, the technical problem to be solved by the present invention is: in the uniaxial tensile test, the equivalent uniform strain of the measured material and equivalent fracture strain Based on the isotropic hardening model of the material, the equivalent plastic strain under the uniform forming limit and fracture forming limit of the material has nothing to do with the stress-strain state of the critical mesh circle, and according to the and The real principal strain ε in any simple strain state under the same deformation degree, such as uniform forming limit or fracture forming limit, can be calculated theoretically major and true secondary strain ε minor , thus, the equivalent plastic strain forming limit diagram (Equivalent Plastic Strain Forming Limit Diagram, referred to as "EPS-FLD") can be drawn without using the existing FLD measurement method, which directly avoids the shortcomings of the prior art

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