국내 최대 기계 및 로봇 연구정보

기술보고서

기술보고서 게시판 내용
타이틀	Evaluation of Delamination Growth Characterization Methods Under Mode I Fatigue Loading
저자	Murri, Gretchen B.
Keyword	CALIBRATING;; CANTILEVER BEAMS;; CRACK BRIDGING;; CYCLIC LOADS;; DATA REDUCTION;; DELAMINATING;; EXPONENTS;; FATIGUE (MATERIALS); FRACTURE STRENGTH;; GRAPHITE-EPOXY COMPOSITES;; LAMINATES;; MATHEMATICAL MODELS;; STRAIN ENERGY RELEASE RATE
URL	http://hdl.handle.net/2060/20120015491
보고서번호	NF1676L-14179
발행년도	2012
출처	NTRS (NASA Technical Report Server)
ABSTRACT	Reliable 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.