On Characteristics of Ferritic Steel Determined during the Uniaxial Tensile Test

Tensile uniaxial test is typically used to determine the strength and plasticity of a material. Nominal (engineering) stress-strain relationship is suitable for determining properties when elastic strain dominates (e.g., yield strength, Young’s modulus). For loading conditions where plastic deformation is significant (in front of a crack tip or in a neck), the use of true stress and strain values and the relationship between them are required. Under these conditions, the dependence between the true values of stresses and strains should be treated as a characteristic—a constitutive relationship of the material. This article presents several methodologies to develop a constitutive relationship for S355 steel from tensile test data. The constitutive relationship developed was incorporated into a finite element analysis of the tension test and verified with the measured tensile test data. The method of the constitutive relationship defining takes into account the impact of high plastic strain, the triaxiality stress factor, Lode coefficient, and material weakness due to the formation of microvoids, which leads to obtained correctly results by FEM (finite elements method) calculation. The different variants of constitutive relationships were applied to the FEM loading simulation of the three-point bending SENB (single edge notched bend) specimen to evaluate their applicability to the calculation of mechanical fields in the presence of a crack.