Bill J. Lau

Date of Award


Document Type


Degree Name

Master of Science in Aeronautical Engineering


Department of Aeronautics and Astronautics

First Advisor

Anthony N. Palazotto, PhD


This study investigated the stress-strain response and failure modes of Graphite/Polyetheretherketone (Gr/PEEK) tension specimens containing a central elliptical hole. Both experiments and finite element numerical analyses were conducted. Test specimens included seven layups and three hole geometries; three of each combination were tested. The holes consisted of an ellipse with major axis aligned with the load axis, an ellipse with major axis transverse to the load axis, and a circle. Strain gages were located adjacent to the hole and midway between the hole and tab on all specimens. Strain data was used to plot stress-strain response. The analysis utilized a nonlinear finite element program, assuming plane stress. Linear stress-strain relationships are applied incrementally; piecewise cubic spline interpolation functions represent the material data provided to the program, accounting for the material nonlinearity. A strain energy failure criterion determines element failures. Analytical stress-strain results correlated well with experiment, with some divergence noted. Damage progression of the finite element models agreed with observed failure surfaces, except for unidirectional and crossply layups. These failed more suddenly, and the program is unable to capture this phenomenon. Interlaminar stresses developing in the actual tests and coarse regions of the finite element meshes were identified as probable sources of error.

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The author's Vita page is omitted.