Fatigue damage of metal matrix composite laminates. Bimodal theory and damage optimization
Conference Paper
Overview
Additional Document Info
View All
Overview
abstract
Experiments suggest that two major modes of fatigue damage may develop in metal matrix composite laminates under cyclic loading which causes repeated plastic straining below the endurance limit. These consist of matrix cracks parallel to the fibers and matrix cracks transverse to the fibers. In this work the two modes of damage are related to the applied loads through a bimodal damage criterion, derived from the bimodal theory of plasticity for fibrous composites. Moreover, experiments suggest that a saturation damage state may result under certain loading conditions. This is identified here as a damage-induced shakedown state, and the low-cycle crack growth process associated with the cyclic plastic straining of the matrix is regarded as a shakedown mechanism in these MMC laminates. A model of the shakedown process is formulated as a nonlinear optimization problem where the total damage in the laminate is the objective function. This function is minimized under nonlinear constraints derived from the requirement that the prescribed loading program is contained within the yield surface of the damaged composite. The stiffness reductions predicted by the damage optimization solution are compared with experimental results on B/Al composite plates.
