FRACTURE MECHANICS ANALYSES OF COMPOSITE SKIN-STIFFENER DEBOND CONFIGURATIONS WITH SHELL ELEMENTS

摘要

Fracture mechanics analyses of skin-stiffener debond configurations using shell elements are presented. Two types of debond configurations are studied: a flange-skin strip and a skin-stiffener debond configuration. The flange-skin strip configuration examines debond growth perpendicular to the stiffener while the skin-stiffener debond configuration examines debond growth parallel to the stiffener. Unidirectional and quasi-isotropic laminates are considered for the flange and skin in the flange-skin strip debond configuration. Only unidirectional laminates are considered for the stiffener, flange, and skin in the skin-stiffener debond configuration. Four-node and 9-node shell elements are used to model both debond configurations. The stiffener flange and skin are modeled as two different layers of elements and, in the bonded portion, the translational degrees-of-freedom of the corresponding flange and skin nodes are constrained to be identical. Strain energy release rate (G ― values) formulae are presented for both 4-node and 9-node element models based on the virtual crack closure technique (VCCT). Average values of the strain energy release rates are calculated using a gradient method. The VCCT formulae and the gradient method are used to study the individual mode and the total strain energy release rates for both debond configurations. The G ― values predicted by these methods are compared with those predicted by plane-strain and 3D finite element analyses. Excellent correlation is obtained among all the analysis results, thus validating the VCCT formulae derived for the 4- and 9-node shell elements.