ELEVATED-TEMPERATURE FRACTURE OF PARTICULATE-REINFORCED ALUMINUM .1. FRACTURE-TOUGHNESS

The plane-strain initiation and growth fracture toughnesses of powder- metallurgy-processed, SiC particulate-reinforced 2009 plate were measu red at temperatures from 25 degrees C to 316 degrees C. Initiation tou ghness from electrical potential monitoring (K-JICi) is 18 MPa root m at 25 degrees C, and is nearly constant to 220 degrees C before decrea sing sharply to 6 MPa root m at 316 degrees C. Growth toughness, given by the tearing modulus (T-R), is less than 3 from 25 degrees C to 125 degrees C, and increases dramatically above 200 degrees C. The magnit ude and temperature dependence of initiation toughness depend on detec tion of the critical fracture event. Standard measures of toughness K- IC and K-JIC exceed K-JICi and increase to a plateau with increasing t emperature. The fracture mode for the composite is microvoid nucleatio n, growth and coalescence at all temperatures. Void nucleation is asso ciated with SiC; such particles both crack and create stress and plast ic strain concentrations that rupture the interface or adjacent matrix , particularly at corners. Matrix plasticity and cavitation increase w ith increasing temperature. Void growth is regular at all temperatures , but limited by adjacent SiC particles. Both K-JICi and T-R are gover ned by the temperature-dependent crack-tip plastic stress and strain f ields, and the intrinsic damage resistance of the composite microstruc ture.