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Evaluation of Delamination Growth Characterization Methods Under Mode I Fatigue LoadingReliable delamination characterization data for laminated composites are needed for input to analytical models of structures to predict delamination. The double-cantilevered beam (DCB) specimen is used with laminated composites to measure fracture toughness, G(sub Ic), delamination onset strain energy release rate, and growth rate data under cyclic loading. In the current study, DCB specimens of IM7/8552 graphite/epoxy supplied by two different manufacturers were tested in static and fatigue to compare the measured characterization data from the two sources, and to evaluate a proposed ASTM standard for generating Paris Law equations. Static results were used to generate compliance calibration constants for the fatigue data, and a delamination resistance curve, G(sub IR), which was used to determine the effects of fiber-bridging on delamination growth. Specimens were tested in fatigue at a cyclic G(sub Imax) level equal to 50, 40 or 30% of G(sub Ic), to determine a delamination onset curve and delamination growth rate. The delamination onset curve equations had similar exponents and the same trends. Delamination growth rate was calculated by fitting a Paris Law to the da/dN versus G(sub Imax) data. Both a 2-point and a 7-point data reduction method were used and the Paris Law equations were compared. To determine the effects of fiber-bridging, growth rate results were normalized by the delamination resistance curve for each material and compared to the non-normalized results. Paris Law exponents were found to decrease by 31% to 37% due to normalizing the growth data. Normalizing the data also greatly reduced the amount of scatter between the different specimens. Visual data records from the fatigue testing were used to calculate individual compliance calibration constants from the fatigue data for some of the specimens. The resulting da/dN versus G(sub Imax) plots showed much improved repeatability between specimens. Gretchen
Document ID
20120015491
Acquisition Source
Langley Research Center
Document Type
Conference Paper
Authors
Murri, Gretchen B.
(NASA Langley Research Center Hampton, VA, United States)
Date Acquired
August 26, 2013
Publication Date
October 1, 2012
Subject Category
Composite Materials
Report/Patent Number
NF1676L-14179
Meeting Information
Meeting: 15th US-Japan Conference on Composite Materials
Location: Arlington, VA
Country: United States
Start Date: October 1, 2012
End Date: October 3, 2012
Funding Number(s)
WBS: WBS 877868.02.07.07.05.01.01
Distribution Limits
Public
Copyright
Work of the US Gov. Public Use Permitted.
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