Analysis and experimental characterization of out-of-plane properties of woven 3-D reinforced composites

Three-dimensional (3-D) reinforced textile composite materials have become an area of intense research due to superior delamination resistance and out-of-plane properties. Numerous investigators have successfully modeled and characterized the in-plane properties of this material class. Unfortunately, limitations in existing mechanical test methods have prevented characterization of the out-of-plane properties of 3-D reinforced composite materials. The lack of knowledge of the out-of-plane properties of 3-D textile composites has limited the application and optimization of this class of composite materials.; This dissertation presents work performed to develop mechanical test methods capable of measuring the out-of-plane tensile, compressive, shear and delamination properties of woven 3-D composites. The issues of stress field uniformity, load introduction, property measurement accuracy, strain gage versus unit-cell size, and specimen performance and repeatability are addressed for each specimen configuration. In addition to test method development, this work presents and analyses the observed out-of-plane mechanical properties and failure modes of several different 3-D woven composite materials.; Test methods were successfully developed to characterize the out-of-plane tensile, compression, shear and delamination resistance for 3-D woven materials. The test specimens were effectively used to determine the effects of resin and fiber properties, weave architecture and warp weaver tow distortion, due to RTM processing, on the out-of-plane properties of several 3-D woven composite materials. Tow distortions from RTM processing were shown to have a significant effect on out-of-plane elastic properties and failure modes. Warp weaver tow distortions were shown to significantly reduce the out-of-plane compression strength of 3-D weaves. Similarly, fiber/matrix interface properties were identified as a crucial area for future improvement of the shear and delamination resistance properties of 3-D weaves. In addition, several theoretical models were successfully developed to predict out-plane properties of 3-D woven materials. These models offer a starting point for improved design and optimization of 3-D weaves and 3-D weave hybrids with respect to elastic properties, out of plane compression strength and delamination resistance.