Fracture mechanics analyses for skin-stiffener debonding

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Abstract

Fracture mechanics analyses on two debond configurations are presented. The debond configurations analyzed were flange-skin strip and skin-stiffener configurations. Three-dimensional (3D) finite element analyses were performed using 20 noded isoparametric elements to model the debond configurations. Two methods that use the virtual crack closure technique (VCCT) were used to evaluate the strain energy release rate distributions across the debond front. In the first method the strain energy release rates (G-values) are calculated at the center of each element that are on the crack plane and along the crack front. In the second method the strain energy release rates are calculated at all the corner nodes of the elements that are on the crack plane and along the crack front. Both methods gave nearly identical G-distributions for the debond configurations studied. The 3D G-distributions obtained by these methods were compared to plane strain and shell analyses results from the literature for the flange-skin strip configuration. Good agreement was obtained; the plane strain results are ca 7% higher while the shell analysis results are ca 3% higher than the present 3D results. Analyses of the skin-stiffener configuration showed the G-distributions converged rapidly as the number of layers used to model the stiffener is increased. These convergence studies showed that there is a boundary layer effect near the ends of the debond and there is an elevation in the G-values in the region of the blade (web) of the stiffener. The analysis also showed that mode-II is the dominant mode for this debond configuration.

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