Damage Mechanism Of SiC_p/Al Composites Under Different Tensile Stress States

As a kind of structural material,SiC_p/Al composites are prone to deformation damage or even fracture under applied load.Therefore,in order to understand its deformation behavior under loading,the damage of SiC_p/Al composites under different loading states is studied in this paper.Firstly,the samples with different damage degrees were obtained by tensile test,and the microstructure of the composites in rolling direction,rolling normal direction and rolling transverse direction and the damage parameters of mechanical properties in rolling normal direction were characterized by microstructure analysis and nano-indentation test.in order to analyze and clarify the damage law of microscopic components and mechanical properties.Based on the test results,combined with the three-dimensional finite element model,the initiation and development of damage under different tensile stress states are simulated and analyzed,and the main factors affecting the damage of composites under different tensile stress states and the damage mechanism of composites are revealed.The results are as follows:The damage process of the material was observed by in-situ tensile test.it was found that the composite first produced microcracks near the particles,and the cracks extended mainly to the depth,and then to both sides.In the state of unidirectional tensile stress,the damage mechanism of the composites in three directions(rolling direction,rolling transverse direction and rolling normal direction)and different strain conditions is as follows:microcracks are preferentially formed at voids and weak interfaces,and under the action of tensile stress,large cracks are formed,which leads to the fracture of the composites.In this process,a small amount of reinforced particles fell off,and no particle fracture was found.Through the nano-indentation,it is found that the hardness and elastic modulus of the particles are higher than that of the interface,and the interface is higher than that of the matrix.In the process of unidirectional deformation,the hardness and elastic modulus of composites and their components decreased as a whole,and increased in the stage of plastic deformation.Under biaxial tensile stress,a small amount of microcracks appeared in the rolling direction of the composite at the initial deformation stage,accompanied by the shedding of fine SiC particles.With the increase of applied load,the matrix crack begins to propagate,more SiC particles fall off,and the shedding size of the particles increases gradually.In the process of deformation,the damage degree of the material in the rolling direction and transverse direction is higher than that in the rolling method,because the particles in the tensile direction are smaller and the number is large,which makes the material deformed more easily in the loading process.When the external force is close to the bearing capacity of the material,the material has serious deformation,a large number of particles fall off,and the cracks in the matrix continue to expand to form macroscopic cracks,which eventually lead to the failure of the composites.In the process of biaxial deformation,the hardness and elastic modulus of composites and their components decrease with the increase of strain.Compared with the unidirectional tensile stress,it is found that the damage degree of the composite is more serious under biaxial tension.The global and local tensile tests of the composites under different tensile stress states were simulated by finite element method,and the stress distribution,equivalent plastic strain distribution,stress triaxiality distribution and the effect of particles on the materials were analyzed.It is found that the stress and strain of SiC_p/Al composites under unidirectional tensile stress gradually concentrates from the overall uniform distribution to the center,and the stress and strain of biaxial tensile stress increases sharply along the diagonal direction.Under different tensile stress states,the stress triaxiality of the composites increases gradually in the whole deformation process,which tends to the tensile stress state,and the microcracks are easy to propagate,so the fracture surfaces of the composites show a large number of dimples.From the simulation results of the sub-model,it is found that the particle shedding or debonding of SiCp/Al composites during deformation is related to the high concentration of stress and strain at the nearby matrix,especially at the sharp corner of SiC particles.