Mechanical characterization of woven fabric composite materials

The mechanical behavior of woven fabric composites is presented in this study through modeling of the elastic properties and experimental studies on the failure behavior and fracture analysis. A two-dimensional laminate theory based elastic model for the prediction of the elastic constants of satin weave fabric composites is developed. The predicted elastic constants are compared with results from other models and correlated with the experimental data. An experimental study is presented on mechanical response in tension, compression and shear and on damage development in tension of two woven fabric composite systems viz. carbon/epoxy and glass/epoxy. Damage inspection of the carbon/epoxy composite under tension revealed that the initial failure was cracking of pure matrix regions followed by transverse bundle cracking. Fill/warp debonding and longitudinal splits of the fill bundles occurred close to ultimate failure of the composite. The glass/epoxy composite displayed damage in the form of fill/warp debonding and longitudinal splits, but no transverse yarn cracking. Interlaminar fracture behavior of a five-harness satin orthogonal woven fabric carbon/epoxy composite laminate loaded in mode I, mode II and mixed mode has been investigated. Special emphasis was put on microscopic details of crack growth, and their relation to the fracture resistance. For all fracture mode combinations it was found that crack growth occurred in a nonplanar region of topology determined by the weave pattern and relative positioning of the plies adjacent to the crack plane. The woven fabric structure constrains fiber bridging, but partial debonding of transversely oriented fiber bundles led to occasional crack branching, stick-slip behavior leading to variations in the mode I fracture resistance. Slow stable crack growth occurred in the mode I and mode II fracture specimens prior to unstable fracture and resulted in nonlinear load-displacement response.