| 講演要旨： |
The development of fiber reinforced MMCs for structural applications necessitates a comprehensive understanding of fatigue properties at elevated temperatures. Although the thicker composites could be fabricated successfully, the characterization of strain controlled fatigue behavior remain as a challenging task. Total axial strain LCF tests have been performed at 700K on SiC/Ti-15V-3Cr-3Al-3Sn composite. The 32 plies thick plate material enabled fully reversed tension-compression tests to be run without buckling. The cyclic stress and strain response and fatigue life of the composite have been characterized in terms of applied strain range and compared with the data obtained concurrently on un-reinforced Ti-15-3 alloy. Mechanisms of fatigue damage initiation, propagation and fracture were evaluated. Transmission electron microscopy revealed phase changes that occurred during fatigue testing in the Ti-alloy matrix, fiber-matrix interface and ply interfaces. The deformation substructure and precipitation behavior of in-situ matrix have been found to vary from point to point. The modulus changes of the composite during cyclic deformation have been found useful in predicting the onset of secondary alpha precipitation in the in-situ matrix. The effects of testing mode and specimen geometry on fatigue life of the composite are also highlighted. |
