Inelastic Deformation and Failure Analysis of Filament-Wound Composite Structures

Several fundamental problems associated with the mechanical behavior and failure of filament-wound composite structures are studied. Available experimental results on pressure testing of filament-wound composite tubes are analyzed to formulate the incremental constitutive relations of a filament layer under deformations with a large shear strain, and to correlate the intrinsic strain paths preceding the failure of the filament layer with the various failure modes of the structure. Implication of the results to the analysis of filament-wound structures is described. Micromechanical analyses using the boundary element method are conducted to determine the composite gross elastic moduli in terms of the constituent properties, and to study the fracture mechanics problems associated with fiber-matrix debonding and oblique matrix crack between adjacent fibers. Analytical models of delamination failure in filament-wound structures and composite laminates are proposed and the separation and postbuckling problems of helical and two-dimensional delaminations are extensively investigated. A variational method using stress functions is developed to obtain efficient and accurate solutions of free-edge interlaminar stresses in composite structures.