Interphase growth characteristics and their significance in high temperature crack tip shielding
- Univ. of Rhode Island, Kingston, RI (United States)
An experimental study was carried out on two continuous fiber reinforced composites; SM 1240/Timetal-21 S and SCS-6/Timetal-21 S in order to identify the growth mechanisms of the fiber/matrix interphase and their influence on the high temperature bridging fatigue crack growth behavior. Specimens made of these two composites have been aged at temperatures ranging from 500-825{degrees}C for up to 600 hours in an air environment. In order to quantify the shear stress characteristics at the fiber/matrix interface, thin slices of these specimens have been subjected to fiber push-out, employing a displacement-controlled apparatus. The SCS-6 reinforced composite has shown an initial increase, followed by a decrease, with increasing aging time, in both the debond strength, {tau}{sub d}, and the frictional shear stress, {tau}{sub s}, indicating the presence of two possible competing mechanisms; growth of the interphase during aging and relaxation of the composite consolidation-induced radial residual stress. Timetal-21S/SM1240 has shown similar {tau}s behavior, and an initial decrease, followed by an increase, in {tau}d. This behavior has been attributed to interfacial growth and the matrix stress relaxation, with the initial drop in {tau}{sub s} resulting from the increasingly brittle nature of the TiB{sub 2} in the growing interfacial reaction zone. Repeated pushout/pushback testing has also been performed in order to identify the features of the steady state {tau}{sub s}, and the effects of wear on the sliding surfaces. Mechanisms responsible for the observed time and temperature variations have been investigated using finite element analysis. Finally, adopting the view that the Ti-MMC fatigue crack tip driving force is governed by the debonding rate of the interphase, the significance of the aging characteristics of the interphase in relation to the bridging fatigue crack growth mechanisms at elevated temperature was examined.
- OSTI ID:
- 175285
- Report Number(s):
- CONF-950686-; TRN: 95:006111-0242
- Resource Relation:
- Conference: Joint applied mechanics and materials summer meeting, Los Angeles, CA (United States), 28-30 Jun 1995; Other Information: PBD: 1995; Related Information: Is Part Of AMD - MD `95: Summer conference; PB: 520 p.
- Country of Publication:
- United States
- Language:
- English
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