Progressive failure analysis of composite structures

Abstract

This thesis presents the Progressive Failure Analysis (PFA) to enhance the design of the composite structure. A non-linear analysis is performed to establish equilibrium until a converged solution is obtained assuming no changes in the model. Once when the converged solution is obtained, the stresses within each lamina are determined. The obtained stresses are compared with the material allowable stresses and are used to determine the failure according to different failure criteria. If any lamina failure is detected by any of the failure criterion, the lamina properties are changed according to the particular degradation model. As the initial non-linear no longer correspond to an equilibrium state, the equilibrium has to be re-established by utilizing the modified lamina properties for the failed lamina by maintaining the current load level. This process is continued until no additional failures are detected. The load step is incremented until catastrophic failure of structure is detected. For experimental tests, an I-section specimen made of L-930 flame retardant carbon/epoxy composite is fabricated and tested for three point bending under two different support load conditions. From the load and displacement values obtained, the load-displacement graph is plotted for both support conditions and the basic stiffness equations are analysed. For numerical results, the I section specimen is modelled using Finite Element Modelling (FEM) in ANSYS 13.0 using ANSYS codes and simulated for obtaining displacement results and load-displacement graph is plotted and compared with the experimental results. From the load-displacement plot, the failed area is identified for both 400 mm and 500 mm support conditions. Failure criteria such as Tsai-Wu and Maximum stress theories are used for determining the mode of failure due to the applied load. Parametric analysis is also studied for the I-section specimens by varying the parameters and the corresponding graphs are plotted.