The evolution of notch-tip damage during static loading in center-notched unidirectional boron/aluminum and silicon carbide/titanium composites was characterized through a two-prong investigation involving experiments and analysis. The effects of heat treatment on the failure process in boron/aluminum were addressed. In the experimental phase, the notch-tip damage initiation and progression was monitored and recorded in real time through a high-magnification (× 150) closed-circuit television system, acoustic emission, and load-deformation responses. Fracture surface morphologies were examined via a scanning electron microscope in order to identify the microfailure mechanisms.
In the analytical phase, a numerical technique was employed to predict the failure process in the materials studied without specifying the crack path a priori. The predictions elucidated the failure mechanisms and their interaction in the evolution of damage ahead of an existing crack. Correlations were made with experimental results in terms of the observed failure process and load-deformation responses. Good agreement was obtained between the observed failure process and predictions. The computational predictions captured the salient features in the observed failure processes.
Notch-tip damage progression was quite different in the various materials studied. A complex state of damage developed in the vicinity of the notch-tip consisting of several dominant failure mechanisms. The various failure mechanisms were identified, and the development of the notch-tip damage zones was determined.