A novel method to determine full-range hardening curve for metal bar using hyperbolic shaped compression specimen

In the determination of full-range hardening curve with compression test, the influence of friction and the corresponding stress correction have always been an enormous challenge. In this study, a hyperbolic shaped specimen is designed to conduct compression test for the determination of hardening curve in large range of strains without the effect of friction. The associated stress correction method is firstly derived by performing a series of finite element simulations of compression tests using the proposed specimen with the hardening curves composed with different combinations of initial yield stresses and strain hardening exponents. Finally, the hardening curves of mild steel Q420 obtained from the compression test using the proposed specimen are implemented in the simulation and verified with experimental data. The results show that the hyperbolic shaped compression specimen can not only remove the undesirable effect of friction but also determine the hardening curve in large range of strains. The established stress correction method for the hyperbolic shaped compression specimen is solely dependent on the strain hardening exponent, which can provide accurate hardening curve merely based on the experimental measurement of load vs. displacement curve and radius of middle cross section. Moreover, the hyperbolic shaped compression specimen provides a feasible approach to determine the strain hardening exponent of material.