Kuang Zhen-Bang

A new damage variable for low-cycle fatigue of metallic materials

Abstract Experimental results show that the inherent ductility in a material is deflected after cycle loading. Based on the concept of ductility deflection, a new fatigue damage variable D ψ for low-cycle fatigue is recommended in this paper. This new damage variable D ψ has definite physical meaning and can be measured with a simple experimental procedure. It can be connected directly with the usual mechanical properties of materials. D ψ increases slowly at the initial stage of cycle loading, but it increases rapidly after a definite cycle where the macroscale crack is formed. We define the turning point on the D ψ - N curve as the critical damage value D c ψ and its corresponding cycle number N is the fatigue life N f .

Mode I fracture in two dissimilar functional non-homogeneous planes

Abstract This study deals with the stress intensity factors (SIFs) in two dissimilar functional non-homogeneous materials containing cracks perpendicular to the interface. Assuming that the shear moduli of the materials vary exponentially with the spatial coordinates, the problem is reduced to the solution of a singular integral equation with a generalized Cauchy kernel. It is shown that the stresses possess the usual square-root singularity when the crack is fully embedded in one medium, but the singularity is dependent on m when an end of the crack is located at the interface. The singular index β decreases with increasing m , but is independent of α K .

Elastic-plastic fracture analysis of finite bodies—I. Description of the stress field

Abstract Stress and deformation were analyzed in detail by the large deformation plane strain finite element method for several specimens. An elastic-plastic stress field near a blunting crack tip in finite bodies was constructed; the stress field was composed of a dominant term with a different singularity from that of the Hutchinson-Rice-Rosengren (HRR) field, and a hydrostatic stress term. It was proved that the present stress field satisfies the equations of equilibrium of stresses and compatibility of strains in solid mechanics. The field was applied to describe the stresses near a blunting crack tip and the crack blunting for several specimens. Finally, the significance of crack tip blunting was discussed by extension of the damaged zone of the crack tip.

Elastic-plastic fracture analysis of finite bodies-II. Conditions of fracture initiation

Abstract The normal and triaxial stresses on uncracked ligament for different specimens were analyzed by large deformation plane strain finite element analysis (FEM) at their fracture loads, and the critical characteristic parameters (J, Q, k) of the stress field established in Part I [Fashang Ma and Zhen-Bang Kuang, Engng Fracture Mech. 48, 727–737 (1994)] were determined by fitting. Using several continuum damage mechanics (CDM) models and the present stress field, the conditions of the initiation of elastic-plastic fracture growth for different specimens were discussed in detail, and it was verified by experimental data that the critical conditions suggested in this paper are independent of specimen geometry and of the ratios of crack depth a to specimen width w when an appropriate microscopic model for fracture initiation is adopted. When characteristic parameters of the stress field k = 1 and Q = 0, the present conditions will reduce to the well-known elastic-plastic single parameter fracture criteria.

A finite element analysis for the temperature field produced by a moving heat source

Using moving mesh finite element method we discuss the temperature field produced by a moving heat source with the variable thermal conductivity and with the radioative and convective boundary conditions in a wide range of the velocity. The temperature-time relationships at various velocities in the static and moving coordinate systems are studied. The steady-state temperature distributions at various velocities in the moving coordinate systems are given. The temperature field produced by the plastic deformation at the process region (a region very near the crack tip) is also studied, and the results show that the highest temperature at the process region is lower than 1000°C or 1832°F.

The experimental and numerical studies on arrest process of a running crack

Abstract The arrest process of a running crack meeting a small hole or arrest cylinder was studied by means of experimental and numerical methods. The results showed that velocity of the running crack increased when the crack approached a hole, but the velocity decreased rapidly when the running crack approached the arrest cylinder. Whether the running crack passes through the hole or arrest cylinder depends on the dynamic stress intensity factor and the notch toughness of the hole or the dynamic fracture toughness of the arrest cylinder.

The analysis of crack propagation and arrest by moving element method

Abstract The moving element method is used for material containing an arrest plate and the propagating process of a running crack is analyzed. In particular the arrest process of a running crack in a structure with an arrest plate is studied in this paper for the first time.