Isothermal and Thermomechanical Fatigue of Cross-Ply SCS-6/TIMETAL®21S

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The response of a [0/90]2S, SCS-6/TIMETAL®21S metal matrix composite under isothermal and thermo mechanical fatigue (TMF) environments was investigated. Four sets of tests were conducted involving in-phase and out-of-phase TMF from 150° to 650°C along with isothermal fatigue at both 150°C and 650°C. Experimental results indicated in-phase loading produced shorter fatigue lives than those under out-of-phase loading at high applied stress levels. Conversely, out-of-phase loading produced shorter fatigue lives at lower stress levels. Isothermal fatigue lives at 650°C were longer than those under in-phase conditions by approximately the same factor for all applied maximum stresses. 150°C isothermal loading conditions produced fatigue lives greater than those obtained in the other three cases. Fracture surface examination to determine the dominant failure mechanisms showed that the 150°C and 650°C isothermal fatigue and the out-of-phase TMF all exhibited evidence of matrix cracking, the worst case being the out-of-phase TMF. There was no indication of matrix cracking for the in-phase TMF tests indicating fiber dominant fatigue failure. Examination of strain history and modulus history as well as observations of the very different trends in the fatigue-life curves suggest that different failure mechanisms dominate the out-of-phase TMF behavior in contrast to in-phase and isothermal fatigue behavior. Analysis, using a linear life fraction model, further suggests that the fatigue lives under the four conditions examined here are controlled by these separate mechanisms.


This is an Open Access article published by De Gruyter and distributed under the terms of the Creative Commons Attribution-NonCommercial-NoDerivatives License, which permits non-commercial re-use, distribution, and reproduction in any medium, provided the original work is properly cited, and is not altered, transformed, or built upon in any way. CC BY-NC-ND 4.0



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Science and Engineering of Composite Materials