| The fracture mechanism operative in Al-25Si-X composite was evaluated by FEM analysis. Two different types of Al-25Si-X composites were prepared for the investigation by varying matrix composition and heat treatment conditions; the hard/brittle sample revealed 0.8% elongation with 420 ㎫ U.T.S and the soft/ductile one revealed 16% elongation with only 165 ㎫ U.T.S. In the case of the hard/brittle sample, the crack was developed in Si particles under about 420 ㎫ by a stress concentration on it during elastic deformation. And then the sequential crack was developed in the Si particle in front of the cracked one, resulting in crack Propagation through matrix between both cracked Si particles. On the other hand, in the soft/ductile sample, the stress was also concentrated on the Si particles. However, cracks were not developed until the sample was deformed to about 7-9% elongation. Based on the calculations, a significant stress could be concentrated on the Si particles embedded in the matrix deformed up to 9% elongation, exceeding the fracture strength of Si particle even under low applied stress of 165 ㎫. |
|
