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Transverse Cracking of M40J/PMR-II-50 Composites under Thermal—Mechanical Loading

Part II — Experiment and Analytical Investigation

Department of Mechanical Engineering, Texas A&M University College Station, TX 77843-3123, USA, jaehyung{at}tamu.edu

Roger J. Morgan

Department of Mechanical Engineering, Texas A&M University College Station, TX 77843-3123, USA

Terry S. Creasy

Department of Mechanical Engineering, Texas A&M University College Station, TX 77843-3123, USA

E. Eugene Shin

NASA Glenn Research Center at Lewis Field, 21000 Brookpark Rd. Cleveland, OH 44135, USA

In this study, the effects of thermal cycling combined with mechanical loading on the microcracking of M40J/PMR-II-50 are investigated. Characterization of the failure mechanisms are conducted based on the critical parameters which cause composite microcracking, as presented in Part I. Based on the test results in Part I, the tests with intermediate in-plane lamina strain (0.175—0.350%) and an increased number of thermal cycles are added. Elevated temperature thermal cycling (23—250^°C) is also added to the original test plan to investigate the thermal cycling temperature amplitude effect on microcracking of the composites. Observations indicate that the elevated temperature exposure under mechanical loads causes an easy fiber/matrix debonding. Subsequent exposure to cryogenic temperatures results in fiber/matrix debonding due to the high thermal stresses associated with fiber/ matrix thermal expansion mismatch. Crack propagation under cryogenic exposures is shown to be dominant with an increasing number of thermal cycles, especially when combined with high temperature exposure associated with high amplitude of cyclic thermal stresses.

Key Words: M40J/PMR-II-50 (carbon fiber/polyimide composites) • thermal cycling • microcracks • interfacial failure • high temperature failure.

Journal of Composite Materials, Vol. 41, No. 9, 1067-1086 (2007)
DOI: 10.1177/0021998306067260


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