Characterization of Damage and Fracture Processes in Short Fiber BMC Composites by Acoustic Emission

Acoustic emission (AE) and scanning electron microscope (SEM) techniques have been coupled with mechanical deformation to study the damage and fracture mechanisms in a short fiber BMC composite. During tensile deformation the initial damage process observed in the SEM was the formation of small cracks at filler particles and glass fibers. Damage due to this mechanism was identified with acoustic emission in the 40 dB ampli tude range. Onset of this damage mechanism occurred at very low strains and damage con tinued to accumulate until fracture. At higher strains the small cracks were observed in the SEM to coalesce to form large cracks spanned by pulled-out fibers. Formation of the large cracks was identified with a burst of AE in the 70 dB amplitude range just prior to fracture. Crack growth during stress relaxation fracture or in single loading tests occurred in a dis continuous manner due to the fiber reinforcement.