Bridging Stress Distributions During Fatigue Crack Growth in Continuously Reinforced [0] Metal Matrix Composites

An optimization procedure was developed to deduce the fiber bridging stresses from crack opening displacements measured in situ during crack growth. This procedure was used to determine the bridging stress distribution during fatigue crack growth in a unidirectionally reinforced metal matrix composite (SCS-6/TIMETAL®21S). The bridging stress is non-zero at the crack tip contrary to predictions from conventionally used shear lag models. The bridging stress at the crack tip is proportional to the applied far-field stress. The deduced bridging law is similar to the new shear lag models with non-zero bridging stresses at the crack tip. Any bridging model can be used to predict the crack growth behavior by choosing appropriate values of the frictional shear stress (τ). Consequently, the magnitude of the stresses in the fibers bridging the crack will depend on the fiber bridging model. Hence, the fiber tensile strength required to predict the onset of fiber failure will also depend on the fiber bridging model.