SiC/AZ91D复合材料中孔隙缺陷对裂纹萌生和扩展行为的影响

Effect of porosity defects on crack initiation and propagation behavior in SiC/AZ91D composites

采用内聚力模型及有限元分析方法,在含真实形貌SiC颗粒增强AZ91D镁基复合材料中引入孔隙缺陷,分析不同孔隙率及孔隙形状在单轴拉伸过程中对SiC/AZ91D复合材料力学行为的影响。结果表明:孔隙长径比为1时,孔隙率为0%、0.5%、1.0%、1.5%的复合材料的抗拉强度分别为351.214 MPa、339.452 MPa、325.735 MPa、306.791 MPa,抗拉强度随孔隙率的增加逐渐降低,复合材料中裂纹萌生和裂纹扩展时间均随孔隙率增加而提前。孔隙长径比越大,其尖端部位应力集中越严重,复合材料抗拉强度也越低。无孔隙缺陷的SiC/AZ91D复合材料裂纹萌生扩展机制是颗粒与基体交界处萌生微裂纹,微裂纹相互连接形成主裂纹绕开颗粒进行扩展致使材料断裂,含孔隙的SiC/AZ91D复合材料裂纹萌生扩展机制为微裂纹在孔隙周围萌生,与颗粒和基体交界处产生的微裂纹相互连接,汇集成主裂纹绕开颗粒扩展使材料断裂。

Using the finite element analysis method,this study introduced porosity defects into SiC/AZ91D magnesium matrix composites with realistic SiC particle morphology,and analyzed the influence of different porosity rates and shapes on the mechanical behavior of SiC/AZ91D composites during uniaxial tensile process.The results show that when the aspect ratio of the pore length to width is 1,the tensile strengths of the composites with void contents of 0%,0.5%,1.0%,and 1.5% are 351.214 MPa,339.452 MPa,325.735 MPa and 306.791 MPa,respectively.The tensile strength gradually decreases with the increase of porosity rate,and the initiation and propagation time of cracks in the composite material advances with the increase of porosity rate.As the aspect ratio of the pore length to width increases,the stress concentration at the tip of the pore becomes more severe,resulting in lower tensile strength of the composite material.The crack initiation and propagation mechanism in the SiC/AZ91D composite material without porosity defects involves the initiation of microcracks at the particle-matrix interface,followed by their interconnection to form a main crack,which propagates around the particles leading to material fracture.In the case of SiC/AZ91D composites with porosity,microcracks initiate around the pores and interconnect with microcracks generates at the particle-matrix interface,ultimately converging into a main crack that propagates around the particles,causing material fracture.