Numerical Fracture Mechanics Analysis of Cracked Fibre-Metal Laminates with Cut-Outs

B.E. Cudzilo, C.L. Tan


The boundary element method (BEM) for two-dimensional numerical stress analysis is employed to investigate crack-face bridging of cracked fibre-metal laminates (FML) with cut-outs in this study. The fracture mechanics prediction of crack growth in these perforated laminates involves the interaction of the geometry and crack size, the delamination between the pre-peg and metal layers, and the extent of fibre-bridging of the crack flanks with the stress field caused by the cut-out. The present work investigates the effects of a stress concentration on the fibre-bridging stress and the stress intensity factor of a bridged crack in fibre-metal laminates. A number of cracked configurations are analyzed and the FML, ARALL2, is considered. The bridging stresses on the crack flanks are modeled in the 2-D analysis using power-law expressions and with the mechanical properties of the laminate homogenized through the thickness. An iterative scheme is employed to solve for the bridging stresses as they are not known a priori. Three dimensional finite element method (FEM) analyses are also carried out to confirm the validity of the 2-D BEM models. FML's with circular cut-outs will contain high bridging stresses near the cut-out resulting in fibre failure there, causing a reduction of the extent of fibre bridging of the crack. Results of the study show a likelihood of fibre failure near the edge of the cut-out and this could lead to a reduction of the bridging length. Comparison of the BEM with the FEM stress intensity factors for the range of problems analyzed reveals that the percentage difference is generally less than about 6%, except for a few cases when the power-law index of 0.5 is assumed. The BEM results indicate an increasing bridging stress and stress intensity factor with decreasing bridging length and the benefits of the fibre bridging of the crack are clearly demonstrated. This numerical study confirms that the 2-D BEM models employed can indeed be used to provide a quick and reasonable estimate of the stress intensity factor for a bridged crack in a FML with a circular cut-out.

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