The strength reduction of a graphite-epoxy laminate due to dropping plies is investigated experimentally and analytically. Laminates were tested under uniaxial tension and compression. All the laminates were flat on one side with the plies dropped from the middle of a [( ± 45/0/90)<sub>s</sub> (N<sub>d</sub>) ( ± 45/0/90)<sub>s</sub>]<sub>T</sub> laminate, where N<sub>d</sub> denotes the number of dropped-plies and their orientations. A total of 54 specimens were tested consisting of eight dropped-ply configurations, or values of N<sub>d</sub>. This geometry creates an eccentric load path which causes local bending moments in the region of the ply drop-off. The strength of a laminate with dropped-plies is less than the strength of its thin section, and the compression specimens exhibited a lower strength than a tension specimen of the same configuration and width. For the laminates in this study, the reduction in strength is directly related to the axial stiffness change between the thick and thin sections of the laminate. The three-dimensional state of stress in the laminate was evaluated by the finite element method. The magnitude of the interlaminar stresses at the ply drop-off for N<sub>d</sub> = [0₄]<sub>T</sub> are greater than for N<sub>d</sub> = [90₄]<sub>T</sub> . The initial failure event for N<sub>d</sub> = [0₄]<sub>T</sub> was a delamination between the dropped plies and upper sublaminate at the drop-off. The tensile interlaminar failure criterion predicts this as the critical location in the finite element model as well. However, the tensile interlaminar criterion underestimates the failure initiation load. The cause for this may be due to the inaccuracies in the modeling of the ply drop-off geometry in the finite element analysis. The magnitude of the stresses at the ply drop-off are sensitive to changes in the finite element mesh geometry. The N<sub>d</sub> = [90₄]<sub>T</sub> laminates were stronger than the N<sub>d</sub> = [0₄]<sub>T</sub> laminates and the N<sub>d</sub> = [90₄]<sub>T</sub> laminates failed in the thin section away from the drop-off. / M.S.
| Identifer | oai:union.ndltd.org:VTETD/oai:vtechworks.lib.vt.edu:10919/106087 |
| Date | January 1986 |
| Creators | Curry, James M. |
| Contributors | Aerospace Engineering |
| Publisher | Virginia Polytechnic Institute and State University |
| Source Sets | Virginia Tech Theses and Dissertation |
| Language | English |
| Detected Language | English |
| Type | Thesis, Text |
| Format | ix, 104 leaves, application/pdf, application/pdf |
| Rights | In Copyright, http://rightsstatements.org/vocab/InC/1.0/ |
| Relation | OCLC# 15170446 |
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