Elastic shielding during fatigue-crack growth of titanium matrix composites

The role of elastic shielding in reducing the local stress intensity factor (SIF) range during fatigue crack growth (FCG) has been investigated using several single-ply composites with significantly different interfacial char acteristics. The specimen geometry necessitated the fatigue crack to initia lly grow through a monolithic matrix region before impinging on a set of lo ngitudinally oriented fibers. This facilitated the assessment of the crack shielding phenomenon from two regions: the region where the crack interacte d with the first fiber, and at high stress levels when nonbridging conditio ns prevailed in the fibrous region. The extent of shielding was nearly iden tical in the two measurements for a given composite system. However, the sh ielding contribution was found to depend on the interface bond strength; th e interface with the highest bond strength provided the largest degree of c rack retardation in both cases. A preliminary assessment of this dependency has been provided. The implications of using the correct shielding factor on both fiber strength and life prediction are also discussed.