| The objective of this work was to study the bending and shear behavior of 3-D woven and woven/braided composites, and to explore means of improving them. A second-generation 3-D weaving machine was constructed at the College of Textile, North Carolina State University to produce the 3-D woven preforms. A layer of 2-dimensional braid with different braid angles and different braid yarn sizes had been added, using a conventional braiding machine, to the surface of some of the 3-D woven preforms to form woven/braided (combined) preforms.; All woven and combined preforms were consolidated into composites. Some 3-D woven and combined preforms were preheated and some were kept at room temperature before consolidation. During consolidation, two levels of consolidation pressures had been applied to study the effect of the consolidation pressure. Composite samples of the two structures have been tested for bending strength and modulus, interlaminar shear strength, and in plane shear strength and modulus.; All bending and shear properties increased for the 3-D woven and combined composites with increasing consolidation pressure and reasonably preheating the preforms to a certain degree. It is possible to increase bending and shear (transverse and in-plane) properties of 3-D orthogonal woven composites by adding a uniformly covered and thin layer of 2-D braid to the surface of the 3-D preform before consolidation. The highest in-plane shear properties for combined composites occurred at 45 degrees angle or close to that angle providing good braid layer for all braid tow sizes. More work is needed to optimize the braid angles, the braid tow size and the treatment conditions.; Statistical analysis and modeling have been conducted to study the resulting experimental values and determine quantitatively the effect of each factor affecting the mechanical and physical properties of the composites. Results showed great affiliation between mechanical properties and the treatment conditions.; Finite Element model was developed to predict the in-plane shear properties of the woven and combined composites. Results showed good agreement between the theoretical and actual values. |
