Composites Science and Technology 44 (1992) 13-20 Notched strength of fabric laminates. II: Effect of stacking sequence P. S. Shembekar & N. K. Naik Aeronautical Engineering Department, Indian Institute of Technology, Powai, Bombay--400076, India (Received 9 August 1990; accepted 8 April 1991) 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 mechan- isms of WF composites, therefore, differ from UD tape composites. The notch sensitivities of different lay-ups are compared by using the characteristic dimensions do and ao of the Whitney and Nuismer fracture model. The ratio of predicted notched strength to unnotched strength, (ON)PRE/O0, 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. Keywords: notched strength, woven fabric, stacking sequence, unnotched strength, characteristic dimension, notch sensitivity NOTATION ao d do v, W or~ (ON)pRE (O )oT Oo Characteristic dimension (Whitney and Nuismer (WN) fracture model, average stress criterion) Hole diameter Characteristic dimension (WN fracture model, point stress criterion) Fibre volume fraction Width of specimen Notched tensile strength of a finite width plate---experimental Predicted notched tensile strength of a finite width plate Notched tensile strength of an infinite width plate, based on orthotropic finite width correction factor Unnotched strength INTRODUCTION The problem of the stress distribution around a circular hole in a composite plate and the Composites Science and Technology 0266-3538/92/$05-00 © 1992 Elsevier Science Publishers Ltd. 13 associated failure criteria have been the subject of extensive research. The fracture behaviour of composites depends on a number of intrinsic and extrinsic variables, which makes the problem complex. Although a considerable insight into the problem has been gained, a comprehensive evaluation of the effect of different variables on the fracture behaviour of composites is still lacking. The effect of some of the variables on the notched strength of composites has been discussed by Awerbuch and Madhukar.1 Because of their higher structural efficiency, unidirectional (UD) tape laminates are being widely studied. The use of woven fabric (WF) composites in structural applications is also increasing, but relatively few data and little work are available on woven fabric composites. They offer ad- vantages such as dimensional stability, deep draw shapeability, enhanced toughness and increased impact resistance. Because of the fabric structure, the failure mechanisms of WF composites differ from those of UD tape composites. The woven fabric consists of two sets of interlacing threads, the warp and the weft (fill), as shown in Fig. 1. The