This paper presents experimental measurements of the response of woven composite laminates to multiple low-velocity
impacts. Damage initiation and progression occur at multiple physical and temporal scales in heterogeneous materials,
including fiber breakage, matrix cracking, delamination and matrix relaxation. The sensor/interrogators were therefore
chosen specifically to provide insight into the order and progression of different failure modes. Measurements of the
contact force between the impactor and composite are measured throughout impact. Additionally, the dissipated energy
per impact event is also calculated from the impactor velocity. Surface mounted and embedded fiber Bragg grating
sensors are used for the measurement of the laminate response. Peak wavelength measurements are performed during
impact at 1 kHz, while full-spectral scanning is performed at 5 Hz during relaxation period of the laminate immediately
after impact and quasi-statically to measure post-impact residual strain states within the laminate. The results highlight
the depth of information embedded within the FBG full-spectral data sensors, as well as the added insight to be gained
from combined global-local measurements.
In this study, the development and optimization of embedded fiber Bragg grating (FBG) sensor networks within
composite materials was investigated. Various densities of optical fibers were embedded within composite laminates,
and low-velocity impact damage responses were evaluated to determine the effects on the mechanical behavior of the
laminates. The woven composites were subjected to multiple strikes at 2 m/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 for specimens with and without embedded optical fibers. Embedded fibers were
interrogated with light to determine the degree to which light could pass through them for each density and arrangement.
Cross sectional optical micrographs of the specimens were used to determine the local effects of the embedded fibers on
neighboring fibers and the surrounding matrix material, both before and after impact events. Currently FBG sensors are
being calibrated and prepared for embedment in specifically chosen configurations within the composite. They will be
serially multiplexed together to create a single fiber sensing network capable of monitoring damage over a large area.
Real time strain information will be gathered as future embedded laminates are subjected to impact events, and the
resulting data will be used to better monitor and predict damage in the composite system.
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