IMPACT DAMAGE CHARACTERIZATION IN LAMINATED COMPOSITES (CRACK)
Abstract
Comprehensive studies of impact induced fracture in laminated composites are lacking, largely because of the complexity of the problem. The present research is an effort to provide a starting point for a simple working model for an impact induced fracture. An interactive study which uses a finite element numerical analysis together with experimental observations is done. A three layer cross ply graphite epoxy laminate is initially chosen for both experimental and numerical studies. The studies done on cross ply laminates are extended to quasi isotropic laminates. Experimental data for the three dimensional problem of impact of a flat strip by a spherical impactor are presented and interpreted qualitatively by comparison with a plane strain numerical analysis of an infinitely wide plate impacted by a cylindrical impactor. The role of transverse shear stress and flexural stress in damage initiation is established. A detailed presentation of damage is provided with exact delamination zones. Strain responses, using a plate finite element, are correlated with the experimental observations to provide a simple model for damage initiation in laminated composites. The results establish that the crack in the distal ply (opposite to the impact side) is produced when the transverse flexural strain in the ply reaches 9000 (mu)Strain in the impact zone.
Degree
Ph.D.
Subject Area
Aerospace materials
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