Evaluation of the stress-strain relationship in the high strain region of high strength materials by using the shear stretch test

Abstract

Stress-strain relationships are used in FEM analysis. After uniform deformation, they are simply extended values expected from ones measured without experiment. The purpose of this research was to understand the stress-strain relationship in the high strain region after uniform deformation. We investigated a method for understanding this relationship in high strength materials using a simple shear test. The relationship in this region was calculated by determining a constant parameter κ as the coefficient between equivalent stresses and shear stresses. Using this constant, the relationship after uniform deformation was extended from the result of a stretching test. This method is called the κ method. In the case of high-strength materials, it is difficult to avoid rotating the specimen under a high testing load. Because of this problem, we designed the shape of the specimen so that it had two symmetrical deformation areas. The notch shapes for the deformation areas on the specimen were designed to reduce the load and provide a strong gripping force. In terms of shortening the deformation region, it is difficult to ignore a non-uniform deformation. To reduce the influence of non-uniform deformations, the effect of the R shape on the notch end was evaluated. The uniformity of two specimens with R1.5 mm and R7.0 mm on the notch end was examined by FEM. The values of κ, which were determined from the shear stress and shear strains based on the results of FEM, depended on the equivalent strain. In the case of R7.0 mm, the κ results were almost constant, and this was a suitable result for applying the κ method. The change in κ was affected by the non-proportional stress ratio, the stress error of the observed shear stress, and the strain error of observed shear strain. In the case of R7.0 mm, it was found that there was an advantage for the constant stress error in the higher strain region. Using R7.0 mm and R1.5 mm specimen shapes, we applied a shear test with two kinds of high-tensile steels and aluminum materials. From experimental results, the values for κ on R7.0 mm were also more constant than on R1.5 mm in the higher strain region. A high stress-strain relationship after uniform deformation was obtained in high-tensile steels and aluminum materials. This research could therefore be used to understand the stress-strain relationship in the high strain region of high strength materials.