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Abstract
Compression testing of large, thin, stiffened composite panels is complex due to the susceptibility of such panels to premature buckling and failure. Such failures are due to the artefacts of testing, such as, offset at load introduction edges, non-uniform distribution of loads, nature of lateral supports, crushing of panel edges etc. In this paper, a novel approach for compression loading of thin stiffened composite panels is proposed and validated from finite element analysis supported by tests. Compression loading of such panels (less than 2mm thick) is challenging since the edges are susceptible to local crushing. To avoid this, loading edges of the panel were encased in mild steel casing blocks filled with finely grounded aluminium powder mixed with epoxy resin. Coupon level tests were conducted to measure mechanical properties of the interface between composite and casting mixture. Digital Image Correlation (DIC) technique was used in these tests to measure the full field strains and to validate numerical simulations. Further, finite element analysis of the actual composite test panel with end casting mixture was performed which indicated that interface shear stresses and compression stresses at maximum expected load are much lower than allowables obtained from specimen tests. Hence, the Aluminium-Epoxy cast mixture proposed in this study can be used safely to cast edges of large stiffened panels for axial compression tests.
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References
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- Degenhardt, R., Rolfes, R., Zimmermann, R. and Rohwer, K., "COCOMAT - Improved Material Exploitation of Composite Airframe Structures by Accurate Simulation of Post-buckling and Collapse", Composite Structures, Vol.73, Issue 2, May, 2006, pp.175-178.
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References
Composites Materials Handbook, Vol.3, "Polymer Matrix Composites: Materials Usage, Design and Analysis", MIL-HDBK-17-3F, June 2002.
Degenhardt, R., Rolfes, R., Zimmermann, R. and Rohwer, K., "COCOMAT - Improved Material Exploitation of Composite Airframe Structures by Accurate Simulation of Post-buckling and Collapse", Composite Structures, Vol.73, Issue 2, May, 2006, pp.175-178.
Zimmermann, R., Klein, H. and Kling, A., "Buckling and Post-buckling of Stringer Stiffened Fiber Composite Curved Panels - Tests and Computations", Composite Structures, Vol.73, Issue 2, May, 2006, pp.150-161.
Zimmermann, R. and Rolfes, R., "POSICOSS - Improved Post-buckling Simulation for Design of Fiber Composite Stiffened Fuselage Structures", Composite Structures, Vol.73, Issue 2, May, 2006, pp.171- 174.
Abramovich H, et al., "Experiments on Axial Compression Post-buckling Behaviour of Stiffened Cylindrical Composite Panels", 44th AIAA/ASME/ASCE/AHS Structures, Structural Dynamics, and Materials Conference, 7-10 April, 2003, Norfolk, Virginia.
Degenhardt, R., Kling, A. and Klein, H., "Experiments on Buckling and Postbuckling of Thin-walled CFRP Structures Using Advanced Measurement Systems", International Journal of Structural Stability and Dynamics, Vol.7, No.2, 2007, pp.337-358.
Sutton, M. A., Orteu, J. J. and Schreier, H.W., "Image Correlation for Shape, Motion and Deformation Measurements: Basic Concepts, Theory and Applications", Springer, 2009.
ABAQUS Version 6.10 Documentation, Rhode Island, USA , 2010.