Finite Element Analysis of Post-buckled Composite Structures

Abstract

During high-speed flight, an aircraft may experience high stress gradients as a result of high-frequency aerodynamic interactions. Exterior composite panels on an aircraft are also susceptible to buckling due to thermally-induced axial loads. These exterior post-buckled panels are prone to snap-though behaviours resulting in large deformation responses coupled with high internal stresses. This phenomenon may lead to reduced structural integrity, resulting in a reduced life-cycle. Previous work investigated snap-through of a laminated composite plate specimen. A composite plate was mechanically buckled and subjected to dynamic loading via a shaker system. The post-buckled plate's snap-through displacement responses were analyzed. Later, numerical models of the plate specimen were created using in-house finite element codes to analyze the stress fields. The models concluded that post-buckled plates experiencing snap-through may result in larger amplitude stresses and reduced fatigue life. This thesis serves to advance this previous work and the understanding of post-buckled plate snap-through behavior using commercial finite element software. Finite element models generated in Abaqus/CAE are used to study these structural components. As preliminary work, an Abaqus plate model of the experimental composite plate specimen from previous work is created. The Abaqus model is subjected to dynamic loading resulting in snap-through behaviors. The snap-through results are compared with previous experimental and numerical results mentioned above. The Abaqus finite element models matched the expected results of the previous experimental and numerical work very closely, validating the Abaqus model. The relationship between static and dynamic analysis of snap-through responses is then explored within this work to further develop an understanding of the effect of snap-through on fatigue life. An important, previously unexplored, aspect of this work is the comparison of dynamic stresses to the stresses in the static equilibrium configurations. Within this thesis laminated composite plates undergoing snap-through are modeled using Abaqus both statically and dynamically. The stress results are compared between static and dynamic simulations to determine the efficacy of utilizing static analyses, which are computationally efficient, to predict dynamic stresses. Finally, fatigue methods are analyzed for the applications of composite plates undergoing snap-through responses. As composite panels experience periodic snap-through stresses may increase significantly. Plate life will be evaluated using a method involving constant fatigue life diagrams to characterize fatigue life of plates along the entire plate surface.