Semiempirical Formulae for Mechanical Properties Controlled by Strength and Ductility of Power-Law Hardening Metallic Ma
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JMEPEG https://doi.org/10.1007/s11665-018-3636-8
Semiempirical Formulae for Mechanical Properties Controlled by Strength and Ductility of Power-Law Hardening Metallic Materials Yandong Hu, Zhi-Zhong Hu, and Shu-Zhen Cao (Submitted October 9, 2016; in revised form June 12, 2018) Some subordinate mechanical properties, such as the strain hardening exponent (n) and the fracture true stress (rf ), are not available in general material property handbooks, although they are important in choosing materials. This paper investigated the relations between the subordinate mechanical properties to the basic ones for power-law hardening materials. Our semiempirical analysis shows that, in uniaxial tensile experiment, the strain hardening exponent is controlled by the ratio of the yield strength (rs ) and the ultimate tensile strength (rb ), and the value also equals to the maximum uniform strain. The absolute calculation errors of n on various metal materials are approximately within ± 0.03. Physically, n expresses the ability of the strength rising from the yield strength to the ultimate tensile strength during uniform deformation; it may also denote the maximum ability of uniform deformation before necking. The fracture strength is controlled directly by n, rb and the reduction in area (wK) in our concise expression. The relative errors of the fracture strength between the calculations and the measurements on metal materials are approximately within 20%. Results also indicate that the fracture true stress represents the increased stress during uniform deformation plus the concentrated stress caused by necking. Keywords
fracture true stress, plasticity, reduction in area, strain hardening exponent, strength
1. Introduction Under convention uniaxial tensile loads, the materialÕs mechanical properties controlling the behaviors can be divided into the basic mechanical properties and the subordinate mechanical properties. The basic mechanical properties are comprised of the elasticity, the strength and the ductility, etc. The strength includes the yield strength (rs ) and the ultimate tensile strength (rb ); the former is also called as the yield stress, and the latter is also called as the ultimate strength or the ultimate stress. The property of ductility includes the elongation and the reduction in area. The basic mechanical properties can be easily measured by standard tensile tests, and values can be found in common handbook of mechanical properties of material (Ref 1-3). Especially for those conventional metallic materials that appear power-law hardening behavior, the subordinate mechanical properties along with the basic ones are also essential to the choice of materials, such as the strain hardening exponent, the fracture strength and the maximum reduction in area during uniform deformation (Ref 3). However, these important subordinate mechanical properties are relatively difficult to Yandong Hu, State Key Laboratory of Ocean Engineering, Collaborative Innovation Center for Advanced Ship and Deep-Sea Exploration, School
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