ELEVATED-TEMPERATURE FRACTURE OF PARTICULATE-REINFORCED ALUMINUM .2. MICROMECHANICAL MODELING

Micromechanical fracture-toughness models are applied to experimental results for a metal-matrix composite (2009/SiC/20p-T6) to understand t he temperature dependencies of toughness and fracture mechanisms, as w ell as to test quantitatively a continuum fracture-mechanics approach. Models which couple the crack-tip strain held, characteristic fractur e-process distance and measured intrinsic microvoid-fracture resistanc e predict the temperature dependencies of fracture-initiation (K-JICi) and crack-growth (T-R) toughnesses from 25 degrees C to 316 degrees C . The temperature dependencies of K-JICi and T-R result from the inter play between the fracture resistance and the crack-tip strain held, ea ch being temperature-dependent. Strain-based models are equally valid for void nucleation- or growth-controlled fracture. A scenario for fra cture is nucleation-controlled damage within SiC-particle clusters, co rresponding to K-JICi, followed by cluster-damage growth to coalescenc e under increasing stress intensity. Void growth is stabilized increas ingly at elevated temperatures.