The main objective of this work was to investigate and predict the behavior of damaged structural elements (skin-stringer panels). The study combined characterization through testing with fractographic analysis, and analysis of delamination using the finite-element method. The experimental studies entailed investigation of damage growth from embedded skin defects in panels under compressive load, and the subsequent structural failure. Parameters such as defect size, location with respect to substructure and through-thickness position were studied. Local delamination and global panel buckling were modeled, and the resulting delamination growth was simulated using a moving mesh technique. The results illustrated the importance of the location of the 90° plies to the damage evolution, and the criticality of global buckling and stringer detachment in the structural failure. The understanding gained from both the experimental investigations and numerical simulations has led to guidelines for realistic modeling and rules for designing damage tolerant structures.
Analysis of fracture growth, and in particular at interfaces, is pertinent not only to load-carrying members in composite structures but also as regards, e.g., adhesive joints, thin films, and coatings. Ordinarily linear fracture mechanics then constitutes the common tool to solve two-dimensional problems occasionally based on beam theory. In the present more general effort, an analysis is first carried out for determination of the energy release rate at general loading of multilayered plates with local crack advance either at interfaces or parallel to such. The procedure is accomplished for arbitrary hyperelastic material properties within von Karman plate theory and the results are expressed by aid of an Eshelby energy momentum tensor. By a feasible superposition it is then shown that the original nonlinear plate problem may be reduced to that of an equivalent beam in case of linear material properties. As a consequence of the so-established principle, the magnitude of mode-dependent singular stress amplitude factors is then directly determinable from earlier two-dimensional linear beam solutions for isotropic and anisotropic bimaterials and relevant at determination of cohesive and adhesive fracture. The procedure is illustrated by an analysis of combined buckling and crack growth of a delaminated plate having a nontrivial crack contour.
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