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Queen Mary University of LondonQueen Mary University of London
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School of Engineering and Materials Science
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PhD Thesis: Boundary element method for fracture mechanics analysis of thin-walled assembled structures undergoing large deflection

Author: DI PISA, C

Year: 2005

Supervisor(s): MH Aliabadi

In this thesis the boundary element method has been applied to multilayered aircraft structures. On the solid base of the already established boundary element formulation presented by Aliabadi, Dirgantara and Wen, new formulations have been developed in order to deal with the diverse problems encountered in advanced aircraft structures.

Reissner’s plate theory and 2D elasticity are adopted here to represent the behaviour of the plate. Multi-region formulation is used to simulate the assembled plate structures. Through cracks are introduced using the Dual Boundary Element Method (DBEM) and the Stress Intensity Factors (SIF) are evaluated using the Crack Opening Displacement (COD) technique and the J-integral. Crack growth processes are implemented using an incremental procedure.

Reinforcing element and different parts are bonded together so to build such structures. New formulations have been developed to simulate different type of bonding for assembled structures. Adhesive, Diffusion Bonding and Riveting have been considered and compared here. For such geometries, the de-bonding of the assembled parts is found to be of serious relevance. Such cases have been examined here, for different type of defects and several types of geometries have been examined. In order to evaluate the relevant fracture parameters a new formulation of the J-integral has been proposed and the results compared with the Energy Release Method (G).

The type of structures considered here undergoes large deflection under normal working load; therefore a large deflection formulation for assembled plate structures has been developed. Implementing an incremental load approach in a quasi-linear formulation the effects of large deflections are considered. This kind of approach limits the range to not to large deflection. The methods to evaluate the fracture parameters (such as COD, J-integral, G) have been extended to the large deflection analysis.