FATIGUE BEHAVIOR OF A CROSS-PLY METAL-MATRIX COMPOSITE AT ELEVATED-TEMPERATURE UNDER THE STRAIN CONTROLLED MODE

A study was conducted to investigate the fatigue behavior of a cross-p ly metal matrix composite subjected to fully-reversed, strain-controll ed fatigue cycling at elevated temperature. The stress-strain response , maximum and minimum stresses, and modulus during cycling were analyz ed to characterize the macro-mechanical behavior. Additionally, micros copy and fractography were conducted to identify damage mechanisms. Da mage always initiated in the 90 deg plies, but the governing factor in the fatigue life was damage in the 0 deg plies. The dominant failure mode was fracturing of fibers in the 0 deg plies when the maximum stra in was greater than 0.55 percent, but the dominant failure mode was ma trix cracking when the maximum strain was less than 0.55 percent. Comb ining the fatigue life data with the macro-mechanical and microscopic observations, a fatigue life diagram was developed and partitioned int o three regions. These regions showed relationships between the maximu m applied strain and the dominant damage mechanisms. Also, on a strain range basis, the fatigue lives of the specimens tested under the stra in-controlled mode in this study were compared with its counterpart un der the load-controlled mode of the previous study. It was found that the fatigue lives for these two conditions were the same within the ex perimental scatter.