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Creep Behavior of the Interface Region in Continuous Fiber Reinforced Metal-Matrix Composites
NAVAL POSTGRADUATE SCHOOL MONTEREY CA DEPT OF MECHANICAL ENGINEERING
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The accurate incorporation of interface effects on creep in metal matrix composites is contingent on the direct experimental determination of the deformation kinetics. The goal is accomplished by isolating the composite interface and precisely measuring the creep characteristics of the interface, by utilizing a fiber pushout apparatus to apply a constant force on the fiber of a model single fiber composite SFC, so that the interface can creep under the applied shear stress. Two different model fibermatrix systems one with no mutual solubility and the other with limited mutual solubility were investigated. In both systems, the interface displayed Bingham flow diffusional flow with a threshold stress. The Finite Element Method FEM was utilized to check the conceptual validity of the test approach for one of the model systems, and to provide insight into the design of the sample and test apparatus. FEM was also utilized to estimate the residual radial stresses present in the model composite system following cooling from an elevated to ambient temperature. Based on the experimental results and the FEM analysis, an analytical model is advanced to incorporate the effect of radial residual stresses on the creep of the fibermatrix interface. The model yields an explicit constitutive law which describes the stress, temperature, and matrix property dependence of interfacial creep. The model also indicates that the experimentally observed threshold stress is directly attributable to the radial stress acting on the fibermatrix interface.
APPROVED FOR PUBLIC RELEASE