TRANSVERSE BEHAVIOR OF A UNIDIRECTIONAL COMPOSITE(GLASS FIBER-REINFORCED UNSATURATED POLYESTER) - PART-II - INFLUENCE OF SHRINKAGE STRAINS

A micromechanical investigation of the transverse creep behavior of un idirectionally reinforced glass fibre composites with an unsaturated p olyester matrix is presented. More specifically the influence of initi al strains induced by polymerization shrinkage of the unsaturated poly ester is studied. A previously established nonlinear viscoelastic mode l of the deformational behavior of the unsaturated polyester matrix is used in the numerical calculations. The matrix model includes effects of physical ageing of the resin and, in its general 3D-formulation, i s able to describe time-dependent lateral contraction (Zhang, Ernst an d Brouwer, 1997. Mech. Mater. 26, 141-166, 167-195). It has been shown that this uniaxially characterized 3D model can be used to describe t hree-dimensional loading situations successfully. In another paper (Zh ang, Ernst and Brouwer, 1998. Mech. Mater. 27 (1998) 13-36), the theor y has been further applied to model the transverse creep of the compos ites. New fibre packing geometries have thereto been presented. These packing geometries overcome the shortcomings of the traditional rectan gular and hexagonal geometries, as in some sense they take into accoun t the inhomogeneous fibre distribution in the transverse plane. In thi s paper, the initial strains induced by curing shrinkage of the unsatu rated polyester during the manufacturing process of the composite are introduced. The model calculations show that the stresses caused by th e initial strains gradually relax in the composite even without extern al loading. Complete relaxation of these stresses however takes a very long time and may never be realized in practice. It is further shown that, although the global creep behavior is relatively insensitive to the presence of initial strains, the local stress distribution is comp letely distorted. This result suggests that polymerization shrinkage s ignificantly influences the onset of crack initiation in composites. ( C) 1998 Elsevier Science Ltd.