The Size Effect in Tensile Test of Steels

Efforts to characterize small-scale tensile properties are driven by the need to reliably predict the performance of engineering parts during service. It has been clearly demonstrated that tensile properties depend on test specimen size. Smaller test specimens of railway wheel steel R7T exhibit shorter elongation to failure. Both uniform elongation and post-necking elongation increase with decreasing gauge length of specimens with the same cross-sectional area. A nonlocal damage model based on a strain gradient-dependent constitutive plasticity theory reproduces experimental findings. Detailed computations predict that the elongation to failure increases proportional to the square of the ratio of the steel characteristic length to the diameter of the circular cross-section of the specimen. Heterogeneous damage nucleation is taken into account to explain the effect of specimen size on the ductility of the investigated steel. The evolution of porosity due to nucleation of voids is a decisive factor affecting the dependence of ductility on specimen size; void growth plays a secondary role.