Rearrangement of local stress and strain fields due to damage initiation in a model composite system

Damage initiation in ductile matrix reinforced composite systems occurs primarily by cracking of reinforcements or by decohesion at the reinforcement-matrix interface. The damage event causes a redistribution of the local stress/strain fields, and may lead to accelerated failure of the composite sample. The present work examines the mechanics of stress redistribution in a model two-phase composite material, characterized by a uniform, square reinforcement arrangement. The constitutive models defining damage initiation by particle cracking and interfacial decohesion were developed and incorporated into finite element models. Damage was initiated in the central reinforcement, and its effect on the neighbourhood stress/strain fields was assessed. The models predicted that, for both modes of damage initiation, the stress in the reinforcements above and below the damaged reinforcement was lowered, while that in the reinforcements at the side or on the diagonal were enhanced. If the failure stresses for all the reinforcements in the composite were similar, this could lead to a catastrophic failure process. These observations for the model composite system can significantly help determine effective design criteria for more complicated composites such as metal matrix composites.