Instrumentation of mode I and mode II tests for crack tip strain profile study under static and cyclic loading

Results are reported from an experimental investigation of the damage mechanisms of mode I and mode II delamination on static and fatigue loadings. DCB specimens of unidirectional fiber glass-epoxy laminates were exposed either to the static loading or bending fatigue conditions while being monitored for acoustic emissions to track the initiation and propagation of cracks. A damage mechanism was observed at the crack tip and was associated with interlaminar fracture. The data indicated that damage occurs in three steps: elastic behavior, initiation and damage growth, and crack propagation. Crack tip damage was amenable to study in terms of data on strain parallel and perpendicular to the crack plane, reflecting mode II and mode I delamination, respectively.