Effects of mode I and mode II precracking on critical strain energy release rates

Conference · Sun Dec 31 04:00:00 EST 1995

OSTI ID:175130

Koudela, K L; Strauch, E C; Strait, L H ^[1]

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1. Applied Research Lab., State College, PA (United States)

Susceptibility to delamination is a major concern in many fiber reinforced composite structures. As such, a significant amount of research has been devoted to composite material damage growth characterization. Many of these studies have shown that damage growth is a function of whether or not the fracture test specimens are precracked and the types of precracks utilized. Therefore, to accurately characterize damage growth, effects of precracking must be quantified. In this study, mode I and mode II critical strain energy release rates were determined as a function of precrack type for unidirectional and quasi-isotropic double cantilever beam (DCB) and end-notched flexure (ENF) specimens. Analytical and compliance calibration data reduction techniques were used to calculate the mode I and mode H critical strain energy release rates from the experimental results. In addition, non-destructive and visual inspection techniques were used to determine initial (after precracking) and final (after fracture testing) delamination contour shapes. Determination of the pre- and post-test crack front shapes is important because the data reduction methods assume that delamination fronts are straight and crack extension is self-similar. Differences in the assumed delamination area and the true surface area created during crack extension can introduce errors into the energy release rate calculations. In this study, differences in crack front shape induced by mode I and mode II precracking techniques were shown to effect the mode I and mode II critical strain energy release rates. In particular, characterization of G{sub Ic} and G{sub IIc} using specimens precracked under a mode of loading different than the mode being characterized tended to produce crack growth that was not self-similar. Therefore, to provide the most accurate results, G{sub Ic} should be characterized using mode I precracked DCB specimens and G{sub IIc} should be characterized using mode H precracked ENF specimens.

• OSTI ID: 175130
• Report Number(s): CONF-950686--
• Country of Publication: United States
• Language: English

Related Subjects

36 MATERIALS SCIENCE
COMPOSITE MATERIALS
CRACK PROPAGATION
REINFORCED MATERIALS
STRAINS
SURFACE AREA