Panel stiffener debonding analysis using a shell/3D modeling technique

Abstract

A shear loaded, stringer reinforced composite panel is analyzed to evaluate the fidelity of computational fracture mechanics analyses of complex structures. Shear loading causes the panel to buckle. The resulting out -of-plane deformations initiate skin/stringer separation at the location of an embedded defect. The panel and surrounding load fixture were modeled with shell elements. A small section of the stringer foot, web and noodle as well as the panel skin near the delamination front were modeled with a local 3D solid model. Across the width of the stringer foo t, the mixed-mode strain energy release rates were calculated using the virtual crack closure technique. A failure index was calculated by correlating the results with a mixed-mode failure criterion of the graphite/epoxy material. The objective was to study the effect of the fidelity of the local 3D finite element model on the computed mixed-mode strain energy release rates and the failure index.

Multiple length/time-scale simulation of localized damage in composite structures using a Mesh Superposition Technique

“…The influence of the distance of the global/local transition from the delamination front was investigated by Krueger et al for the cases of delaminated test specimens [19,20] as well as skin/stringer debonding in an composite aircraft component [21,22]. Results, provided in terms of the mixed-mode strain energy release rates computed using the VCCT, demonstrate that, for an acceptable agreement with the reference solution, a minimum length of which the local subdomain needs to be extended, both ahead and in the wake of delamination front, can be identified.…”

Fracture Mechanics Analyses for Interface Crack Problems - A Review

“…The objective of the research was to study the effect of the fidelity of the local 3D finite element model on the computed mixed-mode strain energy release rates and the failure index [78]. This study also included the introduction and modeling of a resin layer at the delaminated interface between the top skin ply (-45° unidirectional tape) and the bottom of the flange (0° fabric layer).…”

“…Example of a stiffened shear panel with local three-dimensional modeling [78]. A square (1016 mm x 1016 mm) panel made of IM7/8552 carbon/epoxy tape was reinforced with three stiffeners made of IM7/8552 carbon/epoxy plain weave fabric.…”

Damage-Tolerant Design of Stiffener Run-Outs: A Finite Element Approach

“…Fracture initiation is expected when the GT exceeds the fracture toughness Gc for a given mixed-mode ratio GII / GT at each point along the crack tip. In other words, propagation at each point occurs when GT / Gc >1 [19,20]. The interlaminar fracture toughness Gc can be calculated by using the equation 2 [20] The value of Gc is normalised to the width-average value for the Tapered specimen.…”