Finite element analysis of the stress distributions near damaged Si particle clusters in cast Al-Si alloys

The finite element method is used to study the effects of particle cluster morphology on the fracture and debonding of silicon particles embedded in an Al-1%Si matrix subjected to tensile-compressive cyclic loading conditions. Representative of an actual cast A-Si alloy, clusters of silicon inclusions (4-8 particles) are considered rather than a single isolated inclusion or an infinite periodic array of inclusions. The silicon particles are modeled with a linear-elastic constitutive relationship and the matrix material is modeled using an internal state variable cyclic plasticity model fitted to experimental data on matrix material. A total of seven parameters are varied to create 16 idealized microstructures: relative particle size, shape, spacing, configuration, alignment, grouping and matrix microporosity. A two-level design of experiment (DOE) methodology is used to screen the relative importance of the seven parameters on the fracture and debonding of the silicon particles. The results of the study demonstrate that particle shape and alignment are undoubtedly the most dominant parameters influencing initial particle fracture and debonding. Particle debonding results in a local intensification of stresses in the Al-1%Si matrix that is significantly larger than that due to particle fracture. The local stress fields after particle fracture are primarily concentrated within the broken particle halves. After the fracture of several particles within a cluster, the spacing between adjacent particles enters as a second-order effect. When several particles within a cluster debond, the spacing between adjacent particles enters as a dominant effect due to the large local stress intensification in the surrounding Al-1%Si matrix. (C) 2000 Elsevier Science Ltd. All rights reserved.