EXPERIMENTAL STUDY OF CAUSTICS OF MODE-I DYNAMIC CRACK RESPONSE IN ORTHOTROPIC COMPOSITES
High-speed Schardin photography and optical caustics method are introduced to study dynamic stress singularities of mode-I crack tip in orthotropic composites under impact. A series of dynamic caustic patterns stranding the crack tip of two kinds of laminated carbon fiber/epoxy resins composites under impact were re- corded. Variations of the caustic shape diameter due to the local stress singularity at the crack tip were examined. The characteristic size of caustics that is related to the mechanical parameter of local stress concentration was measured. The impact behaviors of two kinds of composites were compared. These results can help to evaluate strength and predict service life for composite structures.