Date of Award
Doctor of Philosophy (PhD)
Edge delamination in composite laminates with adjacent layers oriented at different fiber angles is a major failure mode because of the existence of high interlaminar stresses and poor interlaminar properties. Mitigation of edge stresses poses a challenge even to date. This research provides a detailed analysis and a potential approach to solve this problem in a carbon/epoxy composite laminate. Two extreme laminates of stacking sequence (0n/90n)s and (+45n/-45n)s subjected to separately applied tensile and thermal loading were considered. These problems have been treated in the literature as a mathematical or bare interface model, wherein the material properties jumped between the adjacent layers of different fiber orientations. A microscopic analysis of laminate cross section showed that the interface was not really bare but there was a thin resin layer of thickness of about 5.0% of the ply thickness. This realization completely changed the modeling and potential modification of the interphase. The region between the plies was represented by a resin layer interphase. A three-dimensional composite finite element (FE) analysis was performed using ANSYS version 12 code. The FE modeling and analysis were verified with the literature for both (0/90)s and (+45/- 45)s laminates for axial tensile loading as well as temperature change. The resin interphase layer with thicknesses of 2.5%, 5.0% and 7.5% of the ply thickness were modeled using three different material properties representing: elastic (brittle epoxy), elastic-plastic (toughened epoxy) and non-linear (interleaved polymer nanofiber composite). As the layer thickness became zero, the bare interface results were recovered. Then, for non-linear resin layer the edge stresses reduced indicating that the interleaving of interphase region had a potential to mitigate edge stresses and thus the edge delamination failure.
Ghantae, Srikanth Sundaresh, "Analysis And Mitigation Of Edge Stresses In Multi-Directional Fiber Reinforced Composite Laminates" (2012). Dissertations. 15.