Development of Tools for Engineering Analysis and Design of High-Performance FRP-Composite Structural Elements

The objective of the present Ph.D. project has been to develop three analysis and design modules for implementation in the software program ESAComp. ESAComp is a software program for the analysis and design of composite laminates and laminated structures, which combines advanced analysis features with well-established design guidelines in an interactive computer envionment. The three modules developed for the program contain: Adhesive bonded joints including linear elastic and non-linear adhesive behaviour of adhesive bonded joints between composite laminates. The module includes facilities for the analysis of typically used standard joints as well as advanced joints. Layer drop-offs in sandwich panels and monolithic/solid laminates including exterior and embedded ply drops. Sandwich plates with Inserts including `through-the-thickness' and `fully-potted' inserts. The analyses of adhesive bonded joints are based on a new approach, where the adherends are modelled as beams or plates in cylindrical bending, and are considered as generally orthotropic laminates using classical lamination theory. Consequently, adherends made as asymmetric and unbalanced composite laminates are included in the analysis. The adhesive layers are modelled as continuously distributed linear tension/compression and shear springs. The possibility that the adhesive layers can display non-linear plastic eects is included in the analysis. In the modelling of the ply drop problems an interface/`resin-rich' layer between the plies is assumed, and the ply drop problems are therefore modelled in the same way as the adhesive bonded joints. In case the ply drops occur in the face sheets of a sandwich panel the core material is modelled using a `two-parameter' foundation model. For the analysis of sandwich plates with inserts a high-order sandwich plate theory, adopted especially for the purpose of studying sandwich plates with inserts and other `hard points', is used. The theory, which accounts for the transverse exibility of the core material, includes separate descriptions of the face sheets and the core materials as well as general specification of loads and boundary conditions. For all the structural problems addressed, the analyses are carried out following the same principal approach, which is based on an explicit formulation of the governing set of differential equations. The governing differential equations are formulated in terms of sets of coupled first-order ordinary differential equations, which are solved numerically using a direct integration-scheme known as the "multi-segment method of integration". For all the structural problems addressed solution procedures have been developed for the implementation in ESAComp. The solution procedures for the adhesive bonded joints have been used to conduct a parametric study, where the influence of using laminated adherends has been investigated. Based on this, a set of general design guidelines has been given in order to improve the structural performance and strength for joints with laminated adherends. The guidelines are also valid for the ply drop problems, since their mechanical behaviour are very similar. The results obtained for adhesive bonded joints, ply drops and insert problems have been compared with finite element analysis results. The results obtained for the insert problems has also been compared with interferometric measurements obtained using electronic speckle pattern interferometry (ESPI) on test specimens.