DAMAGE AND FRACTURE OF NOTCHED NONWOVEN AND WOVEN COMPOSITE LAMINATES

The monotonic uniaxial tensile notched strengths of two non-woven laminates (T300/914) and three woven laminates (E-glass/E51) were measured, and have also been predicated from the point- and average-stress criteria (PSC and ASC), the two-parameter criterion (TPC), the point- and maximum-strength models (PSM and MSM). The damage mechanism has been investigated. These criteria and models have to assume empirical parameters which must be determined with experimental information. Although the TPC can in appearance give the best fit results and can quantitatively describe notch sensitivity, it needs much experimental information to determine the parameters. It is therefore not as convenient to use as the PSC and ASC. The PSM and MSM not only can give good predicted results, but also make it possible to analyze the damage ply by ply in notched laminates. For the non-woven laminates, the notched strength of the laminate not favoring delamination can be more precisely predicted than that of the other one; the MSM can give the best predicted results; the principal damage steps predicted can be verified by the unusual experimental techniques such as radiography because they undergo cracking in the 90 degrees plies, +/-45 degrees plies and 0 degrees plies, and final fracture. For the woven laminates, the notched strength of the quasi-isotropic laminate can be more precisely predicted than those of the others; the ASC can give the best predicted results; although principal damage steps can also be predicted, they still cannot be verified by experiments such as radiography because neither visible cracks (even in the 90 degrees plies) nor delamination (even for the stacking sequences favoring delamination) can be experimentally observed before final fracture. The means of assessing the damage mechanism experimentally and predicting it with models in the woven case are problems which remain to be solved.