The Deformation Response of 3D Woven Composites Subjected to High Rates of Loading.

Abstract

The use of polymer matrix composites is widespread, with development in automotive, aerospace and recreational equipment. These applications have produced loading scenarios which are unfamiliar and not well understood. Several applications involve impact loading, which produces large strain rates and delamination failure. New manufacturing methods have led to 3D weave geometries that provide composites with damage protection. This is accomplished through elimination of delamination, and localizing the extent of damage.

The present work is a combined experimental and computational study aimed at developing a mechanism based deformation response model for 3D woven composites, including the prediction of failure strengths at high loading rates. Three unique experimental configurations have been developed; along with finite element based simulations to predict the material response and failure mechanisms that are experimentally observed.

End Notch Flexure (ENF) tests were used to determine the effectiveness of the Z-fiber at resisting crack propagation. The crack propagation was found to have rate dependent properties, with architecture based parameters required to predict the strength and resistance. The computational results reinforced the experimental observations. A new FE implementation captured the effectiveness of the Z-fiber reinforcement bridging the crack.

Shock impact testing was performed to simulate the effects of blast loading on the material. New experimental methods were utilized to record the deformations and strains which led to observations of matrix micro-cracking, the first failure mode. Computational models were developed to predict the material behavior subjected to shock loading, including matrix micro-cracking, which was predicted accurately.

Finally, split Hopkinson pressure bar (SHPB) testing was done to understand the high strain rate behavior of the material in compression in all three directions. The warp and weft directions showed an increase in strength of 100% at elevated rates and a transition in failure mode, from kink band formation to delamination. Through-the-thickness testing revealed a small increase in load from rate effects and a transition in failure mode from delamination to shear band formation. Computational models focused on analyzing a representative unit cell of the 3D architecture. Simulations of the SHPB tests, led to predictions of the moduli, failure loads and failure modes accurately.