Fatigue Crack Growth and Retardation Due to Overloads in Metal-matrix Composites Volume I. Fatigue Crack Growth In Boron-Aluminum Metal-Matrix Composites.

摘要

The fatigue crack growth in a Boron-Aluminum metal matrix composite is investigated. The material consists of II plies of diffusion bonded 5.6 mil boron fibers in a 6061 aluminum matrix. In this study, the composite is characterized as an orthotropic elastic-plastic material using uniaxial test specimens. The constraint effect of the plasticity encountered in specimens with stress gradients is characterized using a tapered specimen. The modeling is verified on a specimen with a centered circular hole and specimens with transverse and oblique fatigue cracks. A series of baseline fatigue tests are performed an transverse and oblique fatigue cracks. The baseline tests are run at room temperature using a 10 Hz sinusoidal loading with a minimum applied load near zero. An effective stress intensity factor is developed to correlate all the baseline fatigue data. Overload tests are carried out on transverse and oblique cracked specimens. The specimens are cycled as was done in the baseline tests, and a single tensile overload was performed. Cyclic loading to near failure followed. The post-overload crack growth behavior first accelerates, then decelerates. This crack growth eventually assumes its pre-overload state.