AN EXPERIMENTAL AND THEORETICAL-STUDY OF CREEP OF A GRAPHITE EPOXY WOVEN COMPOSITE/

The creep behavior of woven fiber polymer composites has been investig ated through both an experimental study and analytical modeling. In th e modeling, the matrix is assumed to be a 4-parameter model (a Maxwell -Voigt combination) and the fibers to be elastic. The fiber undulation model developed by Ishikawa and Chou for elastic behavior of woven fi ber composites has been extended to the viscoelastic system by the cor respondence principle. This considers the longitudinal and transverse fibers separately. The weave geometry and dimensions are accounted for , thus bringing the model closer to the actual composite. While this m odel has been used previously to predict the composites elastic behavi or, this is the first time it is considered as a viscoelastic solid, w hich helps determine its time dependent behavior. The resultant model takes into account the different parameters associated with the weave (the density of the fibers in the weave, the radius of the fibers and the profile of the fill and warp fibers), volume concentration of the fiber and matrix in the composite, and the elastic moduli of the fill and warp fibers and the viscoelastic properties of the polymer matrix. We have conducted creep tests on graphite fiber/epoxy composites to e valuate our model. Experiments have been conducted from room temperatu re (22 degrees C) to 200 degrees F (93 degrees C). The results from ex periments have been analyzed and an inverse simulation has been perfor med to obtain the unknown parameters of the matrix and fibers in the c omposite. The model is then used to predict the creep behavior of the woven fiber composite under other loading conditions and temperature l evels, showing satisfactory agreement with the data.