Papers by Author: Chang Qing Sun

Abstract: The finite element method combined with the singular element was adopted to study the effects of thickness ratio of the coating-matrix, elastic modulus ratio of the coating-matrix, and the ratio of ensile stress and shear stress on the coating top on the stress intensity of the interface crack on the coating-matrix. Through calculations, results show that elastic modulus ratio of the coating-matrix has little effect on stress intensity factor of interface crack, while the thickness ratio and the tensile stress and shear stress ratio on the coating top have a great effect on it, which should be controlled in the coating-matrix structure design.

Abstract: Maximum normal stress criterion can be used to determine the cracking angle in the uniform and non-uniform zone. According to this theory, the propagating process of the crack in non-uniform composite material is simulated based on the finite element method. The results show that the crack advances wave-like and basically along the direction perpendicular to the maximum normal stress, which is of great guiding significance for the fracture resistance of such kind of structure.

Abstract: It is assumed that the physical parameters of functionally graded coating material accords with the variation of degree n polynomial, and based on this material model, the behavior of crack fracture on the interface of functionally graded coating is studied. The results show that when the functionally graded coating structure bears a tension load, stress intensity factors of mode I and mode II exist at the same time generally, and the intensity factor of mode I occupies a leading position all along. Besides, when the elastic modulus ratio of the base to the functionally graded coating top is 5 and the elastic modulus of functionally graded coating varies linearly, the stress intensity factor of interface crack is the smallest, and with the increasing of elastic modulus ratio, the optimal non-uniform parameter tends to be larger than 1.

Abstract: In this paper, aiming at three material parameter functions of functionally graded coating (FGC) which have different continuities, the influence of functionally gradient coating material continuity on the fracture behaviors of the crack on the interface between the base material and coating is studied. The results show that when the functionally graded coating structure is under a tension load, if the ratio of maximum elastic modulus of the FGC to the elastic modulus of the base is less than 10, the functionally graded layer which has C02 continuity can help to improve the fracture resistance of the interface crack, and if the ratio increases continuously, the functionally graded layer which has C13 continuity can help to improve the fracture resistance of the interface crack, which is of great guiding significance for practical engineering design.

Abstract: War-broken parts can be repaired quickly without electricity and gas in the wild by use of the thermit welding technology, so it is of great significance to study on welded quality of thermit welding parts for its military application. As the crack resistance of welded parts is an important target to estimate the welded performance, crack resistance test and microstructure analysis have been conducted on test specimens made of Q235 welded parts. Results showed that as the crack ratio was less than 20% in the Y-groove crack test, the crack propagation would not occur in the practical welding structure and that the crack resistance of welded joints could meet the welded demand.

Abstract: : According to the theory of liquid metal forging and liquid metal extrusion, a new kind of fabricating method for particles reinforced metallic matrix composite was put forward by author. In this paper, the extrusion process to semisolid thick liquid after the mixture was studied by means of the theoretical analysis and experimental methods. Mechanical characteristics of solidification during flowing and plastic deformation during solidification of the composite were found. So the base was built up for selecting technology parameters and for building a stabile process