NOTCHED STRENGTH OF FABRIC LAMINATES .1. PREDICTION

A modified two-parameter model, based on the point stress criterion of the Whitney and Nuismer fracture model, is proposed for prediction of the notched tensile strength of laminated composites. An orthotropic finite width correction factor is used to find the notched tensile strength of infinite plates. A characteristic strength ratio is proposed that is constant for a given material system. A good correlation is found between the predicted notched tensile strengths of the finite width plates and the experimental values. The results are presented for the fabric laminates of eight different lay-ups. The proposed model is simple and more accurate

ELASTIC ANALYSIS OF WOVEN FABRIC LAMINATES .2. MIXED COMPOSITES

Mixed composites are formed by the combination of unidirectional tapes and woven fabrics. In this paper, a method is presented for predicting the elastic properties of mixed composites. The elastic properties of the mixed composites are compared with those of equivalent unidirectional composites. It was found that, along with impact and postimpact properties, mixed composites can also offer higher elastic properties than equivalent unidirectional composites

ELASTIC BEHAVIOR OF WOVEN FABRIC COMPOSITES .2. LAMINATE ANALYSIS

Two-dimensional models are presented for the elastic analysis of the plain weave fabric laminates. A methodology to generate the laminate configuration from the lamina configuration is given, The effect of lamina configuration and their relative positions with respect to each other on the in-plane elastic constants of the woven fabric laminates is studied. A laminate configuration with optimum shifts gives higher elastic properties compared to the other configurations. A comparison between in-plane elastic moduli of the unidirectionally laminated symmetric cross-ply laminates and plain weave fabric laminates is made. The in-plane elastic moduli of plain weave fabric laminates predicted by the models are found to he in good agreement with the experimental results

ELASTIC BEHAVIOR OF WOVEN FABRIC COMPOSITES .1. LAMINA ANALYSIS

Two-dimensional models are presented for the elastic analysis of a plain weave fabric lamina. These models take into account the actual fabric structure by considering the fiber undulation and continuity along both the warp and weft directions. possible presence of gap between adjacent yarns, actual cross-sectional geometry of the yarn and possible unbalanced nature of the plain weave fabric. Typical studies on the effect of fiber undulation and lamina thickness on the in-plane elastic constants are presented. A large discrepancy, similar to that reported in literature, is found between the predicted elastic moduli of plain weave fabric lamina by ID WF models and experimental results. On the other hand, the predictions of 2D WF models are fairly good since the two-dimensional extent of the fabric is considered in these models

ELASTIC ANALYSIS OF WOVEN FABRIC LAMINATES .1. OFF-AXIS LOADING

Two-dimensional woven fabric composite models are presented for the elastic analysis of orthogonal plain weave fabric lamina/laminate. Yarn continuity along both warp and fill directions and the actual yarn cross-sectional geometry and fabric geometry are considered in the analysis. Off-axis elastic properties are determined by coordinate transformation. Comparison is made between the off-axis elastic properties of plain weave fabric laminates and cross-ply laminates. It is found that the elastic properties of the plain weave fabric laminates are superior as compared to those of equivalent cross-ply laminates over a large range of off-axis angles

NOTCHED STRENGTH OF FABRIC LAMINATES .2. EFFECT OF STACKING-SEQUENCE

The effect of stacking sequence on the tensile strength of notched and unnotched woven fabric (WF) composite laminates has been experimentally investigated. Comparison is made with unidirectional (UD) tape laminate results that are available in the literature. The fabric structure is a governing parameter in the failure mechanisms of WF composites. The failure mechanisms of WF composites, therefore, differ from UD tape composites. The notch sensitivities of different lay-ups are compared by using the characteristic dimensions d0 and a0 of the Whitney and Nuismer fracture model. The ratio of predicted notched strength to unnotched strength, (sigma(N))PRE/sigma(0), is used to study the effect of stacking sequence and d/W ratio on the notch sensitivity of the WF composites. Results are presented for unbalanced plain weave E-glass/epoxy composites of eight different lay-ups. The criteria for choosing the optimum stacking sequence are discussed

FAILURE BEHAVIOR OF WOVEN FABRIC COMPOSITES

Woven fabrics are now considered important reinforcing materials for use as unidirectional (UD) tapes in composites technology. The understanding of the failure mechanisms in woven fabric composites, however, is not complete. The tensile behavior of on-axis and off-axis specimens of E-glass/epoxy and carbon/epoxy plain weave fabric composites with and without a hole is studied. The failure behavior of woven fabric composites differs from UD tape composites. Because of the interlaced nature of warp and weft fibers, their reorientation along the loading direction is possible in off-axis specimens. The reorientation of fibers may increase the notched strength over the unnotched strength. The failure modes in angle-ply laminates of UD tape are mostly matrix cracking, fiber pullout, delamination, and to some extent, fiber breakage, whereas in woven fabric composites, the ultimate failure is always due to fiber breakage which, in general, is a preferred failure mode