Failure behavior of composite laminates under out-of-plane loads
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Date
2012.
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Thesis (M.S.) - Bogazici University. Institute for Graduate Studies in Science and Engineering, 2012.
Abstract
In this study, failure behavior of fiber-reinforced composites under out-of-plane loads is investigated by means of four – point bending tests. Firstly, four – point bending tests are modeled analytically using the classical lamination theory (CLT). Considering unidirectional [θ6]s as well as balanced symmetric [θ3/-θ3]s composite laminates , the maximum allowable moment resultants as a function of fiber orientation angle, θ, are obtained using Tsai-Wu, maximum stress, maximum strain, Hashin, Tsai-Hill, Hoffman, quadric surfaces, modified quadric surfaces and Norris failure criteria. Secondly, the same tests are simulated using the finite element method (FEM) in ANSYS with layered 3-D solid elements. In order to apply the failure criteria like Tsai-Hill and obtain the maximum allowable moment resultants as a function of fiber orientation angle, θ, according to these failure criteria, ANSYS Parametric Design Language is used Convergence analysis is carried out to find a balance between computational cost and accuracy of results. Another analysis is conducted for optimal positioning of the loads so as to ensure that static failure modes dominate delamination failure mode. For this purpose, the failure index results of a delamination criterion are compared with the results of Tsai-Wu and maximum stress failure criteria for different loading positions. A test setup is then constructed according to the predicted optimal support positioning and experiments are conducted for both unidirectional and symmetric balanced laminates having fiber orientation angles ranging from 0° to 90° with 15° increments. The differences between the model predictions and experimental results are discussed.