Analysis of thermally induced stress and strain in continuous fiber- reinforced composites
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INTRODUCTION
I T is well known that the difference between the coefficients of thermal expansion of composite phases combined with temperature change can produce plastic deformation in one or both phases. If thermally induced plastic deformation does take place in a composite, it may produce a number of potentially undesirable outcomes including: severely accelerated creep, t~,2j lowcycle fatigue of one phase or the entire composite, t3'4~ dimensional instability, 15'61or progressive sliding of one phase past the other. 17~Based on these observations; one would generally like to design metal-matrix composites for a service such that plastic deformation is not induced by in-service temperature changes. Furthermore, it may be useful to develop analytical and experimental procedures that can simply determine what temperature excursions will produce plastic deformation. This article presents an analysis of continuous fiberreinforced composites subjected to thermally induced internal strain mismatch. The analysis uses continuum elasticity and plasticity to determine the stress and deformation states in an axisymmetric model of a continuous fiber-reinforced composite as a function of temperature relative to a stress-free state, the reinforcement volume fraction, the elastic properties of the two phases, and axisymmetric applied loading. Arbitrary thermal histories as well as a temperature-dependent matrix flow stress may be adopted. The results of these simulations are usually presented in the form of axial strain vs temperature plots. This form is chosen because changes in slope for linear-elastic materials, or more HONGYAN ZHANG, formerly Postdoctoral Researcher with the Department of Materials Science and Engineering, Ohio State University, Columbus, OH, is now Postdoctoral Researcher with the Department of Materials Science and Engineering, University of Michigan, Ann Arbor, MI 48103. P.M. ANDERSON, Assistant Professor, and GLENN S. DAEHN, Associate Professor, are with the Department of Materials Science and Engineering, Ohio State University, Columbus, OH 43210. Manuscript submitted April 13, 1993.
METALLURGICAL AND MATERIALS TRANSACTIONS A
generally hysteresis in such curves on a complete temperature cycle, indicate that the matrix is flowing plastically. Such curves can be simply produced experimentally by traditional dilatometry experiments. This analysis can find application in a number of diverse areas. First, the prediction of accurate thermal expansion properties is important in precision equipment. Second, in order to develop composite materials that will avoid thermally induced plastic deformation in the range of application temperatures, both analysis and coupled diagnostic tests would be welcome. This analysis suggests that dilatometry can be useful in revealing the onset of thermally induced plasticity in composites. Third, it is often difficult to determine the in situ strength of the matrix phase in a composite because of the complications due to the constraint and load-shedding afforded by the
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