Papers by Author: Zhao Xi Wang

Abstract: Damage of metals due to the influence of hydrogen is quite frequent and leads to dangerous failures. The characteristics of the hydrogen embrittlemnt of the 65Mn steel were evaluated with small punch test. With the increment of the amount of the hydrogen absorbed into the alloy at room temperature, the strength and the toughness of the material reduce. From the small punch experimental results, it is found the total impact energy, the fracture strain and the fracture stress decrease with the increment of the cathodic hydrogen charging time. The fracture surfaces change from the typical ductile fracture with big voids to the typical intergranular brittle fracture mode after hydrogen absorbed in the specimens with higher charging current density.

Abstract: At the present time, as the steam conditions and capability of the supercritical power unit increasing, the unit reliability is an important factor for the unit efficiency. High temperature, thick walled pipes are widely used in power plants and chemical plants. In this paper, life of the welded joint was predicted by the methods of skeletal point (SP) rupture stress rupture stress, which was calculated by finite element method (FEM). For the life prediction of welded component, the continuum damage mechanics was employed too. The life prediction of the welded joint by SP rupture stress was compared with the life prediction by the method of continuum damage mechanics (CDM). The research results showed that the two predicted methods were consistent. So, it can be concluded that the SP rupture stress can be used for predicting life of the high temperature welded component. The SP rupture stress method was used conveniently for the structure of power plant or other high temperature components.

Abstract: The purpose of this paper is to evaluate the vibration of the small bore pipe in nuclear piping under the fatigue loading due to flow fluctuation. The vibration speeds of the pipe-lines were measured to get the effective velocity which is found larger than the allowable value calculated from EDF evaluation method. To perform the piping vibration assessment and construction, the natural shape and the vibration stress at the socket weld position was evaluated by finite element analysis with ABAQUS. From the linear cumulative damage theory, the fatigue life is predicted with the results that lower than the designation level. According to the position of the maximum vibration speed calculated from FEA simulations, the valve is fixed by the rigid support. The natural frequency and the corresponding mode shape are discussed with much lower vibration velocity and vibration stress.

Abstract: Experiments of fracture toughness with non-standard SENB specimens of five different thicknesses were performed to investigate the size effect on the ductile and brittle fracture for different temperatures. From the experimental results it is found that size effects both brittle and ductile fracture with the same trend but for different mechanical reasons. The ductile fracture toughness increases firstly with increased plastic deformation zone size and plastic fracture strain under general yielding conditions, and then drops down due to the plastic deformation zone size not changing much which is less than the residual ligament width and the increase of the proportion of the high stress triaxiality zone to the whole specimen. The fracture toughness of the lower shelf increases with increasing thickness of the plastic deformation zone size under small scale yielding conditions, and then drops down due to the increase of the high out-of-plane constraint.

Abstract: Detailed experiments of fracture toughness in which SENB specimens of five different thicknesses were included were carried out to investigate the size effect in the ductile to brittle transition temperature region. It is found that the fracture toughness of the upper shelf increases with the thickness of the specimens with the similar geometry. While the fracture toughness of the lower shelf decreases with the thickness in the range of 4mm to 12mm and then drops up from 12mm to 16mm with the appearance of shear lips which present the shearing fracture under the plane stress state. The tearing modulus dJ/da which determines the resistance to stable crack growth increases with the increment of thickness and the reduction of the temperature. The results of the stress triaxiality increasing with the reduction of the thickness explain well the experimental results.