Title: Investigation of Skin/Stringer Interface Separation in Stiffened Composite Structures

Authors: Waruna Seneviratne, John Tomblin, Vishnu Saseendran, Mohamed Shafie

DOI: 10.33599/nasampe/s.21.0454

Abstract: Stiffened composite panels are widely used in aeronautical structures and experience complex deformation. In certification efforts, these structures must demonstrate the ability to sustain design limit load throughout service life. One of the critical failure modes in stiffened panels is skin-stringer separation. In the presence of inherent flaws or impact events, out of plane deformation can lead to separation of the skin. Hence, adequate design characterization of skin-stringer interface is a necessity. In certification approach where building-block analyses validated by test are used, standard test methods are not available beyond coupon or element level. In this study, a seven-point bend (7PB) based test methodology is employed to induce buckling based skin separation. Both co-bonded and secondary-bonded panels are considered. 7PB test method is used for demonstrating its capability of inducing considerable out of plane deformations, primarily caused by compressive loading or shear on stiffened structures. Furthermore, a cohesive zone model (CZM) is employed to predict damage initiation and progressive disbond growth at the skin-stringer interface. The simulated damage region is compared against ultrasonic (UT) scans taken at intermittent load intervals during quasi-static tests. Delamination growth primarily occurred at the skin-stringer interface and migrated to adjacent plies. The implemented zero-thickness cohesive zone model captured damage initiation and predicted the damage map. The 7PB test methodology is easy to install and robust for carrying out interface characterization in both adhesively-bonded and co-bonded composite structures.

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Conference: SAMPE NEXUS 2021

Publication Date: 2021/06/29

SKU: TP21-0000000454

Pages: 15

Price: FREE