Experimental investigation of fatigue behavior of curved composite laminates
Tutor / director / evaluatorMateo García, Antonio Manuel
Document typeMaster thesis
Rights accessOpen Access
In the aerospace and wind turbine industries, high demand for light weight structures with high strength extend the use of composite laminates in a wide variety of geometries as load carrying elements. However, more complex geometries as curved composite laminates experience delamination and matrix cracking due to high interlaminar stresses induced in the curved region. Moreover, under cyclic loading failure on these components initiates under lower stress states so that fatigue behavior of curved composite laminates are critical. This thesis discusses the experimental investigation of fatigue behavior of curved composite laminates under bending moment. Bending moment is obtained at the curved region by applying axial load from both tips of the curved composite laminates. A special loading fixture is designed in order to apply axial load to curved specimens in universal testing machine. Two different lay-up configurations are investigated; 15s unidirectional as fiber dominated and [03/903/03/903/03]s cross-plied laminates as matrix dominated. Static loading experiments are conducted in order to obtain average ultimate strength of materials to use in fatigue loading experiments and compare the damage pattern with the fatigue failure. The load-displacement curves are recorded for both static and fatigue loading cases. The failure is observed using high speed camera under static loading. DSLR camera images and micrographs are taken for both static and fatigue experiments. Under static loading, two load drop is observed for  UD laminates until failure. Under fatigue loading,  UD laminates experience one sharp load drop, then stiffness degrades gradually until failure. The failure pattern of  UD laminates under static and fatigue loading is completely different. Cross-plied laminates show similar behavior on load-displacement curves and failure mechanisms under static and fatigue loading. Under static and fatigue loading, unexpected failure mechanisms are observed for cross-plied laminates which are found to be sensitive to the manufacturing defects.