Buckling and debond growth of partial debonds in adhesively bonded composite flanges
Abstract
The strains at which buckling and debond growth occur in adhesively bonded composite flanges containing an initial debond were experimentally measured using sandwich panel and coupon type specimens. Test parameters investigated were: initial debond geometry, the adhesive critical strain energy release rate (Gc), flange material stiffness, and layup sequence. Buckling strains were found to be dependent on initial debond length, flange stiffness and layup sequence. Flanges with a longer initial debond length showed lower buckling strains. Buckling strains increased as the twisting to bending stiffness ratio (D66/D11) increased due to changes in flange layup sequence. Debond growth was found to be strongly dependent on initial debond length but, weakly dependent on flange width. Flanges having higher bending stiffness exhibited a significantly lower debonding strain. Ultrasonic C-scans revealed that debond growth occurred along a curved front, as dictated by the post-buckling deformation of the flanges. Finally, changes in twisting to bending stiffness ratio (D66/D11) due to different flange layup sequences resulted in a variation of post-buckled flange out-of-plane (u3) deformation shape. This was found to affect the debond front shapes as the debond grew. Finite Element Analysis (FEA) based Virtual Crack Closure Technique (VCCT) fracture analysis was conducted. Critical strain energy release rates measured from Double Cantilever Beam (DCB) and Mixed-Mode Fracture (MMF) tests were used as input values and the FEA predictions were shown to be capable of accurately simulating the buckling and debonding behaviors. The FEA study included all the testing parameters investigated in the experiments and also revealed the mode-I, II and III strain energy release rate profiles at the debond front. From the strain energy release rate profiles, fracture mode content and the major fracture mode in each specimen type were clearly understood. The FEA methodology developed within the current study has been shown to be capable of predicting the buckling and debonding tests very well. Being FEA based, this methodology can be applied to the analysis of other facture problems which due to their complexity would otherwise require expensive experimental investigation.
Degree
Ph.D.
Advisors
Kim, Purdue University.
Subject Area
Aerospace materials|Mechanical engineering
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