In-Situ Failure Identification in Woven Composites Throughout Impact

In this study, measurements form low-impact velocity experiments including embedded and surface mounted optical fiber Bragg grating (FBG) sensors were used to obtain detailed information pertaining to damage progression in two-dimensional laminate woven composites. The woven composites were subjected to multiple strikes at 2m/s until perforation occurred, and the impactor position and acceleration were monitored throughout each event. From these measurements, we obtained dissipated energies and contact forces. The FBG sensors were embedded and surface mounted at different critical locations near penetration-induced damaged regions. These FBG sensors were used to obtain initial residual strains and axial and transverse strains that correspond to matrix cracking and delamination. The transmission and reflection spectra were continuously monitored throughout the loading cycles. They were used, in combination with the peak contact forces, to delineate repeatable sensor responses corresponding to material failure. From the FBG spectra, fiber and matrix damage were separated by an analysis based on signal intensity and the behavior of individual Bragg peaks as a function of evolving and repeated impact loads. This provided independent feedback on the integrity of the Bragg gratings which can serve to eliminate errors in the strain data such as due to sensor debonding or fracture. The critical indicators present in the sensor spectra for the mapping of these sensor failure modes are derived.