Compression and post-buckling damage growth and collapse analysis of flat composite stiffened panels

Abstract

Experimental and numerical investigations were conducted into the damage growth and collapse behaviour of composite blade-stiffened structures. Four panel types were tested, consisting of two secondary bonded skinstiffener designs in both undamaged and pre-damaged configurations. The pre-damaged configurations were manufactured by replacing the skin-stiffener adhesive with a centrally located, full-width Teflon strip. All panels were loaded in compression to collapse, which was characterised by complex postbuckling deformation patterns and ply damage, particularly in the stiffener. For the pre-damaged panels, significant crack growth was seen in the skin-stiffener interface prior to collapse, which caused a reduction in load-carrying capacity. In the numerical analysis of the undamaged panels, collapse was predicted using a ply failure degradation model, and a globallocal approach that monitored a strength-based criterion in the skin-stiffener interface. The pre-damaged models were analysed with ply degradation and a method for capturing interlaminar crack growth based on multi-point constraints controlled using the Virtual Crack Closure Technique. The numerical approach gave close correlation with experimental results, and allowed for an in-depth analysis of the damage growth and failure mechanisms contributing to panel collapse. The successful prediction of collapse under the combination of deep postbuckling deformations and several composite damage mechanisms has application for the next generation of composite aircraft designs.

Global behaviour of a composite stiffened panel in buckling. Part 1: Numerical modelling

“…However for a panel in compression it has been noticed that debonding of the stringer is not the source of the post-buckling failure for a prepreg co-cured stiffened panel [12], whereas it has been observed on a co-bonded stiffened panel at the element level [5] and it is combined with delaminations and fractures in the skin and the stringer flanges at the panel level [4,17]. As a distinct bonded interface is missing, panels manufactured by LRI from dry fabrics are intended to be a little different from those manufactured from co-bonded and co-cured structures made of prepregs.…”

“…These authors also explain how delamination occurs [5] and implement a global-local approach where the deformation field of a global shell model is incorporated at the boundary conditions of a three-dimensional model of a skinstiffener interface. The first step is to locate initiation of inter or intra laminar damage with a stress-based criterion.…”

A Global/Local Finite Element Approach for Predicting Interlaminar and Intralaminar Damage Evolution in Composite Stiffened Panels Under Compressive Load

“…[9,10] or by releasing not merged nodes laying in the same position (i.e. having the same coordinates) but belonging to two different fracture surfaces [5,11,12,16].…”

“…Usually global/local is accounted as synonymous of sub-structuring [16]: mainly a detailed local model receives as boundary conditions the deformation field obtained by a global model of the full structure thus defining a sequential global/local procedure which does not allow effects of the local model on the global one to be taken into account. An embedded global/local procedure is surely more suitable but requires the availability of interface elements or rather coupling elements able to take into account also large …”

Improvement and evaluation of polymer-matrix composite panels with hat stiffeners

“…For the study of hat-stiffened composite panels, a number of contributions in literatures [9][10][11][12][13][14] emphasized on the buckling or postbuckling behavior and failure mechanism particularly under external compression force or tensile load both theoretically and experimentally. Also some scholars [15][16][17] paid close attention to the pressure transfer mechanism and nondestructive examination of internal quality for the hat-stiffened panels.…”