3.1 INTRODUCTION

The general theory relating to dimensional stability of composite materials starts with the assumption of linearly elastic behavior. Elastic deformation is defined as "reversible alteration of the form or dimensions of a solid body under stress or strain" [1]. Elastic behavior hence implies the absence of permanent deformation, but in that case the material would be completely (mechanically) stable. It is doubtful if true elastic behavior exists, except perhaps in a quartz watch spring. In any case, deviations from elastic behavior are of eventual interest here, whether the loads are mechanical or non-mechanical (such as temperature). Inelastic behavior is commonly caused by plastic, viscoelastic or viscoplastic flow, microcracking, or solute absorption. Still, an elastic model is the most convenient starting point.

Analysis can be carried out at several levels of complexity, starting with the micromechanics and macromechanics models (such as classical laminate plate theory). Other broadly applicable analytical approaches include shear deformation theory, variational methods [2,3], and finite element methods [4]. Shear deformations play an important role in plate buckling and vibration determinations. Shear deformations are often underestimated when predicting deflections by classical plate theory. Interlaminar stresses, particularly important in compression and delamination predictions, are insufficiently evaluated in many models. The increased use of weaves and fabrics, three-dimensional reinforcements and flexible composites may lead to large non-linear deformations. Analytical methods are available to handle curved, continuous fibers in a ductile matrix, using step-wise incremental analysis [5]. Since composites are by nature heterogeneous and anisotropic, much of the science...