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Testing and Analysis of Composite Skin/Stringer Debonding under Multi-Axial LoadingA consistent step-wise approach is presented to investigate the damage mechanism in composite bonded skin/stringer constructions under uniaxial and biaxial (in-plane/out-of-plane) loading conditions. The approach uses experiments to detect the failure mechanism, computational stress analysis to determine the location of first matrix cracking and computational fracture mechanics to investigate the potential for delamination growth. In a first step, tests were performed on specimens, which consisted of a tapered composite flange, representing a stringer or frame, bonded onto a composite skin. Tests were performed under monotonic loading conditions in tension, three-point bending, and combined tension/bending to evaluate the debonding mechanisms between the skin and the bonded stringer. For combined tension/bending testing, a unique servohydraulic load frame was used that was capable of applying both in-plane tension and out-of-plane bending loads simultaneously. Specimen edges were examined on the microscope to document the damage occurrence and to identify typical damage patterns. For all three load cases, observed failure initiated in the flange, near the flange tip, causing the flange to almost fully debond from the skin. In a second step, a two-dimensional plane-strain finite element model was developed to analyze the different test cases using a geometrically nonlinear solution. For all three loading conditions, computed principal stresses exceeded the transverse strength of the material in those areas of the flange where the matrix cracks had developed during the tests. In a third step, delaminations of various lengths were simulated in two locations where delaminations were observed during the tests. The analyses showed that at the loads corresponding to matrix ply crack initiation computed strain energy release rates exceeded the values obtained from a mixed mode failure criterion in one location. Hence, unstable delamination propagation is likely to occur as observed in the experiments.
Document ID
20050042016
Acquisition Source
Langley Research Center
Document Type
Reprint (Version printed in journal)
Authors
Krueger, Ronald
(National Academy of Sciences - National Research Council Hampton, VA, United States)
Cvitkovich, Michael
(National Academy of Sciences - National Research Council Hampton, VA, United States)
OBrien, Kevin
(Army Research Lab. Hampton, VA, United States)
Minguet, Pierre J.
(Boeing Co. Philadelphia, PA, United States)
Date Acquired
August 22, 2013
Publication Date
January 1, 2000
Publication Information
Publication: Journal of Composite Materials
Volume: 34
Issue: 15
Subject Category
Composite Materials
Distribution Limits
Public
Copyright
Public Use Permitted.
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