Elastic shielding during fatigue-crack growth of titanium matrix composites

摘要

The role of elastic shielding inreducing the local stress intensity factor(SIF)range during fatigue crack growth (FCG) has beeninvestigated using several single-ply compositeswith significantly different interfacial characteristics. The specimen geometrynecessitated the fatigue crack to initially growthrough a monolithic matrix region beforeimpinging on a set of longitudinally orientedfibers. This facilitated the assessment of thecrack shielding phenomenon from two regions: theregion where the crack interacted with the firstfiber, and at high stress levels when nonbridgingconditions prevailed in the fibrous region. Theextent of shielding was nearly identical in thetwo measurements for a given composite system.However, the shielding contribution was found todepend on the interface bond strength; theinterface with the highest bond strength providedthe largest degree of crack retardation in bothcases. A preliminary assessment of this dependencyhas been provided. The implications of using thecorrect shielding factor on both fiber strengthand life prediction are also discussed.