Poor interfacial properties between reinforcement fibers and a Polymethylmethacrylate (PMMA) matrix may result in debonding between them, which is a major failure mechanism for fiber reinforced bone cement. Optimization of the shape of the fibers can improve load transfer between the fibers and PMMA matrix, thereby providing maximum overall strength performance. This paper presents a procedure for structural shape optimization of short reinforcement fibers using finite element analyses. The composite is modeled by a representative element composed of a single short fiber embedded in PMMA matrix. In contrast to most previous work on this subject, contact elements are employed between the fiber and the matrix to model a low strength interface. Most models assume a perfect bond. Residual stress, due to matrix cure shrinkage and/or thermal stresses, is also included in the model. The design objective is to improve the stiffness of the composite. The results presented show that a threaded end, short fiber results in mechanical interlock between the fibers and the PMMA matrix, which helps to bridge matrix cracks effectively and improve the stiffness of the composite.

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