TENSILE MECHANICAL PROPERTIES AND ITS EVALUATION OF ALUMINIUM ALLOY MATRIX GRADIENT COMPOSITESREINFORCED WITH SiC PARTICLES

The tensile mechanical properties are studied for the aluminium alloy matrix gradient composites reinforced with SiC particles. Gradient coefficient K_x, a new evaluating index of mechanical properties of materials, is put forward. The results of the basic research show that a tri-axial stress will be produced in the tensile specimens because of components property difference of the metal matrix gradient composites (MMGC). The results of the tensile test and fracture analysis show that the elastic modulus E and yield strengthσ_0.2 of the MMGC obey approximately the Role of Mixture (ROM) law. The tensile mechanical properties of the composites are remarkably influenced by the distribution of SiC particles. Fracture of the tensile specimen appears to have a toughness character and the composites can develop their potential in tensile properties when the matrix component is in outside and the component with high SiC volume fraction is in inside. Conversely, the fracture appears to have a brittleness character and mechanical properties of the composites will be decreased. The fracture way and the crack propagating orientation will be changed by the influence of many factors when the crack grows through the bonding interface. Interface cracking could be produced if there is a great difference of SiC volume fraction between two layers of the composites. The coefficients K_σb and K_δ can be used to identify gradient distribution and tensile properties level, but the coefficient K_E can be used to identify steadiness extent of the composites.