Dissimilarities and Similarities between Thermo-Mechanical and Isothermal Low Cycle Fatigues of a Titanium Alloy Matrix Composite, SP700/SCS-6
Masakazu OKAZAKI, Kazumi HIRANO and Yasuhiro YAMAZAKI
Abstract:Behavior of thermo-mechanical fatigue (TMF) failure of a new generation titanium alloy matrix composite, SP700/SCS-6, was studied, based on a series of investigations on; (I) mechanical properties under monotonic loading of the SP-700/SCS-6 composite and the matrix alloy; (ii) fiber push-out tests to represent the fiber/matrix interfacial strength at elevated temperatures; (iii) isothermal low cycle fatigue (ILCF) tests, (iv) interfacial reaction zone to characterize the microscopic damage evolution under the TMF test and the thermal cycle test without external load. A special focus was paid to understand both the mechanisms of TMF failure, and the dissimilarities and the similarities between the TMF and ILCF failures. From the results of these tests, it was shown that the differences of damage characteristics may be concerned with the degradation of the fiber/matrix interface by the crack propagation and reaction layer due to thermal cycles. These systematic investigations showed that the lives and the failure mechanisms of the TMF should be clearly distinguished from those of the isothermal ILCF, whereas there were a few similarities between them. It was also suggested the difference should be primarily originated from the cracking by the repeat of the thermal cycle and the resultant change in fiber/matrix adhesion strength. Key Words:Titanium alloy matrix composite, SP700/SCS-6, Thermo-mechanical fatigue (TMF), Isothermal low cycle fatigue (ILCF), Interfacial reaction zone, Fiber push-out tests, Fiber pull-out