Evolution of Fiber Fragmentation in a Short-Fiber-Reinforced Metal-Matrix Model Composite during Tensile Creep Deformation

摘要

The objective of this work is to obtain deeper insight into the damage evolution occurring during creep in short-fiber-reinforced metal-matrix composites. Uniaxial tensile creep experiments were performed on a model composite with a lead (Pb) matrix. This system was chosen because it allowed the performance of all creep tests at room temperature, thus facilitating the detection of fiber fragmentation by acoustic emission measurements. By this experimental approach, for the first time, quantitative information about the spatial and temporal evolution of microfractures in creeping metal-matrix composite of this kind was obtained. The acoustic emission results show that fiber fragmentation sets in early in the creep life and continues to operate up to macroscopic failure, thus affecting the creep behavior in all stages including the steady-state regime. During the whole creep process, the fracture sites are homogeneously distributed in the specimen volume. These findings largely support the micromechanical damage model proposed by Dlouhy and co-workers, in which the creep process in short-fiber-reinforced metal-matrix composites is described as an interplay of work hardening and recovery in the matrix as well as fragmentation of the fibers.