The effects of high temperature on the tensile and fatigue properties of a 2124 Aluminum reinforced with 15 volume percent B4C particulate was studied experimentally. An increase in temperature gives rise to decreases in elastic modulus, yield strength, and ultimate strength. The room and high temperature fatigue properties were studied using the local stress/strain approach. At room temperature, crack initiation is observed as a shiny semi-circular surface occurring mostly at one corner of the rectangular shaped specimens. Under the SEM, the fracture surface consisted of a number of fractured particles and dimples.
Increasing the temperature to 300°C results in an appreciable decrease in the fatigue life of the composite. There was no observable crack initiation site and the fracture surface was covered entirely with dimples with few fractured particles. A relation between the fatigue life of a MMC and the stress amplitude normalized with respect to the yield strength and the temperature normalized with respect to the melting temperature of the matrix was developed. The effects of frequency upon the room and high temperature fatigue properties were also investigated. Furthermore, the effect of temperature sequence, i.e. high to room and room to high, upon the cumulative damage of metal matrix composites has also been analyzed.
The damage accumulation behavior of the materials was found to depend upon the loading sequence of the environment (temperature). Results show that for the sequence of room to high temperature the Palmgren-Miner damage accumulation relationship yields a good prediction. However, for sequences of high temperature to room temperature the damage accumulation is far less than one.