Papers by Author: Huang Yuan

Abstract: Sintered powder metals have found wide applications in industry. However, the constitutive description under complex loading conditions is an open issue. In the present work, the inelastic deformation mechanisms of sintered iron are investigated using nano-indentation technique. With help of the finite element method, the material behaviour of powder particles can be identified from extensive nano-indentations. Furthermore, the micro-hardness of pre-strained specimens has been investigated as a function of the macro strains up to 14%. Nano-indentation measurements provide a linear correlation between the micro strains in power particles and macro deformation. Ca. 55% of total inelastic deformations are contributed from powder particles and the rest is caused by the void growth as well as micro crack propagation. In sintered metals the micro porosity plays an important role in inelastic deformations.

Abstract: Computational simulations of indentations in elastic-plastic materials showed overestimate in determining elastic modulus using the Oliver & Pharr’s method. Deviations significantly increase with decreasing material hardening. Based on extensive finite element computations the correlation between elastic-plastic material property and indentation has been carried out. A modified method was introduced for estimating elastic modulus from dimensional analysis associated with indentation data. Experimental verifications confirm that the new method produces more accurate prediction of elastic modulus than the Oliver & Pharr’s method.

Abstract: Creep damage is an important failure factor of high-temperature alloy. The fatigue crack growth under elevated temperature of the material is investigated for life prediction. In this paper, the numerical simulation of the crack propagation in nickel-based super alloy, IN718, was presented. A modified creep damage model was employed to accumulate the creep damage under cyclic loading conditions. The numerical results exhibit a reasonable agreement in the comparison with the experimental data. The cohesive zone approach, combining with the extended finite element method, has the ability to simulate the creep-fatigue crack propagation even for more complex loading conditions and specimen geometries.

Abstract: Extended finite element method is widely used to simulate the discontinuity problems, e.g. fatigue crack growth. This paper mainly analyzes the fatigue crack propagation under elevated temperature in nickel-based super alloy with extended finite element method. Cohesive zone model is used to describe the mechanical behavior around the crack tip. A modified creep damage model is introduced. Fatigue damage and creep damage are accumulated in a linear relationship. And the results produced by computational code are presented and draw a comparison with experimental observation.