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Effect of Data Reduction and Fiber-Bridging on Mode I Delamination Characterization of Unidirectional CompositesReliable delamination characterization data for laminated composites are needed for input in analytical models of structures to predict delamination onset and growth. The double-cantilevered beam (DCB) specimen is used to measure fracture toughness, GIc, and strain energy release rate, GImax, for delamination onset and growth in laminated composites under mode I loading. The current study was conducted as part of an ASTM Round Robin activity to evaluate a proposed testing standard for Mode I fatigue delamination propagation. Static and fatigue tests were conducted on specimens of IM7/977-3 and G40-800/5276-1 graphite/epoxies, and S2/5216 glass/epoxy DCB specimens to evaluate the draft standard "Standard Test Method for Mode I Fatigue Delamination Propagation of Unidirectional Fiber-Reinforced Polymer Matrix Composites." Static results were used to generate a delamination resistance curve, GIR, for each material, which was used to determine the effects of fiber-bridging on the delamination growth data. All three materials were tested in fatigue at a cyclic GImax level equal to 90% of the fracture toughness, GIc, to determine the delamination growth rate. Two different data reduction methods, a 2-point and a 7-point fit, were used and the resulting Paris Law equations were compared. Growth rate results were normalized by the delamination resistance curve for each material and compared to the nonnormalized results. Paris Law exponents were found to decrease by 5.4% to 46.2% due to normalizing the growth data. Additional specimens of the IM7/977-3 material were tested at 3 lower cyclic GImax levels to compare the effect of loading level on delamination growth rates. The IM7/977-3 tests were also used to determine the delamination threshold curve for that material. The results show that tests at a range of loading levels are necessary to describe the complete delamination behavior of this material.
Document ID
20110015832
Acquisition Source
Langley Research Center
Document Type
Conference Paper
Authors
Murri, Gretchen B.
(NASA Langley Research Center Hampton, VA, United States)
Date Acquired
August 25, 2013
Publication Date
September 26, 2011
Subject Category
Composite Materials
Report/Patent Number
NF1676L-12684
Meeting Information
Meeting: 26th ASC Annual Technical Conference
Location: Montreal, Quebec
Country: Canada
Start Date: September 26, 2011
End Date: September 28, 2011
Sponsors: American Society for Composites
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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