Naomi Hamada

Relationship Between Rockwell C Hardness and Inelastic Material Constants

This paper describes the relationship between Rockwell C hardness and elastic-plastic material constants by using finite element analyses. Finite element Rockwell C hardness analyses were carried out to study the effects of friction coefficient and elastic-plastic material constants on the hardness. The friction coefficient and Youngs modulus had no influence on the hardness but the inelastic materials constants, yield stress, and strain hardening coefficient and exponent, had a significant influence on the hardness. A new equation for predicting the hardness was proposed as a function of yield stress and strain hardening coefficient and exponent. The equation evaluated the hardness within a ±5% difference for all the finite element and experimental results. The critical thickness of specimen and critical distance from specimen edge in the hardness testing was also discussed in connection with JIS and ISO standards.

Universal J-Integral to Assess Multiaxial Low Cycle Fatigue

This paper proposes the universal J-integral for correlating multiaxial low cycle fatigue lives, utilizing the crack opening displacement approach. The universal J-integral is a function of Young’s modulus, yield stress, strain biaxiality and specimen geometry, so that it is not necessary to conduct multiaxial low cycle fatigue tests to determine the universal J-integral. To derive the universal J-integral, J-integral for a biaxially loaded Mode I crack was equated with the equivalent strain based on crack opening displacement (COD strain). The COD strain is a parameter to express the strain intensity ahead of a Mode I crack subjected to biaxial strains, normal and parallel to the crack. The J-integral was shown to be a suitable parameter for correlating crack propagation rates in the biaxial straining conditions. The J-integral was extended to a parameter, named the universal J-integral, to correlate multiaxial low cycle fatigue lives, taking account of the material dependency. The universal J-integral successfully correlated the multiaxial low cycle fatigue lives of type 304 stainless steel, Cr-Mo-V steel, Inconel 738 LC nickel base superalloy and Sn-37Pb eutectic solder universally within a factor of three scatter band independent on the material.Copyright