Damage progression in tailored laminated panels with a cutout and delamination growth in sandwich panels with tailored face sheets

This dissertation reports on studies of damage progression in laminated composites and sandwich structures. Both in-plane damage and delamination damage are addressed.; In the first part of this dissertation, a simple stiffness-tailoring concept has been applied to laminated flat plates and one quarter cylindrical shells with a cutout. Results show that the tailoring approach can increase ultimate loads up to 111% for the tensile loading and 165% for the compressive loading, increase initial buckling loads up to 175% and ultimate loads up to 240% for the flat plates. For the cylindrical shells, there is no distinct buckling until the ultimate load is reached. Relative improvements in ultimate loads up to 155% are shown to exist for these curved panels.; In the second part of this dissertation, an algorithm has been developed to trace moving delamination fronts of an arbitrary shape. Based on the algorithm, a delamination front can be defined by two vectors that pass through any point on the front. An important feature of this approach is that it does not require the use of meshes that are orthogonal to the delaminations front. Therefore, the approach avoids the adaptive re-meshing technique that may create a large computational burden in delamination growth analysis. An interfacial element that can trace the instantaneous delamination front, determine the local coordinate system, approximate strain energy release rate components and apply the fracture mechanics criteria has been developed and implemented into ABAQUS with UEL. Excellent agreements between the results from this new approach and those from analytical and experimental analyses by others validate the approach and the implementation. Finally, to study the delamination growth in a sandwich panel with its face sheets tailored, the interfacial element was applied to tie the undelaminated region between the top face sheet and the core material of the sandwich panel. Results show that the tailoring approach on face sheets can delay the onset of delamination growth and raise the ultimate loads up to 100%. If the unloaded edge is restrained in the out-of-plane direction, the tailoring approach can also improve the residual strength and stiffness of the sandwich panels.