Damage characterization of surface and sub-surface defects in stitch-bonded biaxial carbon/epoxy composites

The scope of this work is to study the effects of manufacturing and installation defects on mechanical performance of polymer matrix composites appearing in civil infrastructure and aerospace applications. The objective of this study is to create a link between defects detected through nondestructive testing (NDT) and the mechanical performance of the composite structures using strain mapping technique. Monotonic tensile samples of polymer matrix stitch-bonded biaxial composite laminates [90,0]s are tested. Flash Thermography, a conventional NDT technique, is used to predict detectable pre-existing surface and sub-surface irregularities and defects. Attention is drawn to the homogenized mechanical behavior and to damage initiation and propagation. Damage onset and propagation are studied using time-dependent nonlinear regression of the strain field. Effects of the manufacturing and installation irregularities on damage initiation, propagation, and failure are monitored as the structure is subjected to load or studied at the end of the loading process.