| Summary: | Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Aeronautics and Astronautics, 2011. === Cataloged from PDF version of thesis. === Includes bibliographical references (p. 303-305). === The response of grooved composite laminates to out-of-plane contact loading is examined using numerical modeling through the consideration of contact pressure and stresses within the laminate, with particular focus on the area local to the groove. Finite element analysis is employed via ABAQUS, a commercial finite element modeling software. The indentor is modeled as a rigid body, and the validity of this approximation is assessed through comparison with a deformable, linear elastic indentor. The influence of ply angle is investigated through consideration of a family of [+/-[theta]/0]13s laminates for values of [theta] of 15°, 30°, 45°, and 60°, along with a quasiisotropic [+/-45/0/90]10s and a crossply [0/90]20s configuration, all using T700/2510 graphite/epoxy. The linearity of the response is investigated, and two loading configurations are studied and compared: a two-dimensional, cylinder-loaded configuration, and a three-dimensional, sphere-loaded configuration. Results show that the Hertzian contact model for isotropic bodies cannot be used to determine contact pressure due to an inability of that model to analytically determine the appropriate contact length. The basic form of the contact pressure curve is similar to the Hertzian model, but with significant local variations superposed due to stiffness variation, particularly in the longitudinal direction, due to ply orientation angle. Thus, if the contact length is supplied, the Hertzian model can be a valid overall approximation. Total vertical load magnitude is determined to be a primary factor in the response, as it determines contact length, and thus the distribution of contact pressure and the form of the stress field. The response is found to vary with significant nonlinearity with respect to applied load due to the relationship with contact length. The rigid body approximation of the steel indentor is deemed sufficiently accurate to capture the overall behavior, due to the high difference in stiffness between the steel indentor and the through-thickness stiffness of the composite. There is significant variation between the two-dimensional models and the three-dimensional models, particularly in determining the magnitude of the response. However, the two-dimensional model is sufficient to observe trends, and could be of use in preliminary design and analysis, although the full three-dimensional model is required to accurately determine the response in the final analysis, largely due to important issues of variation along the groove. In general, stress behavior is dependent on the laminate and the particular stress, with stress fields between laminates showing some similar trends, but also high variability depending on the composition of the laminate. === by Jaffar S. Iqbal. === S.M.
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