Separation of crack extension modes in composite delamination problems

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

OSTI ID:175168

Beuth, J L ^[1]

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1. Carnegie Mellon Univ., Pittsburgh, PA (United States)

In order to predict composite delamination resistance, an applied stress intensity factor, K, or energy release rate, G, must be compared to a mode-dependent critical value of K or G from experiment. In the interfacial fracture analysis of most composite applications and some tests, the mode of crack extension is not uniquely defined. It is instead a function of distance from the crack tip due to the near-tip oscillatory singularity. The virtual crack closure technique (VCCT) is a method used to extract mode I and mode II energy release rate components from numerical (typically finite element) models. Crack extension modes extracted from oscillatory analyses using the VCCT are a function of the virtual crack extension length, {Delta}. In this work, a modified method is presented for using the VCCT to extract crack extension modes for the case of an interface crack between two in-plane orthotropic materials. The method does not attempt to alter the analysis to eliminate its oscillatory behavior (e.g. by changing material properties or by embedding the crack in a homogeneous interlayer). Instead, the argument is made that the oscillatory behavior is non-physical and that if its effects were separated from VCCT quantities, then consistent, {Delta}-independent modes of crack extension could be defined. Knowledge of near-tip fields is used to determine the explicit {Delta} dependence of VCCT parameters. Energy release rates are then defined with the oscillatory {Delta} dependence factored out. This modified VCCT method is applied to results from finite element analyses, showing that {Delta}-independent modes of crack extension result. The modified VCCT approach shows potential as a consistent method of extracting crack extension modes. The {Delta}-independent modes extracted using the modified approach can also serve as guides to test the convergence of finite element solutions.

• OSTI ID: 175168
• Report Number(s): CONF-950686--
• Country of Publication: United States
• Language: English

Related Subjects

36 MATERIALS SCIENCE
99 GENERAL AND MISCELLANEOUS
COMPOSITE MATERIALS
CRACK PROPAGATION
FINITE ELEMENT METHOD
INTERFACES
STRESS INTENSITY FACTORS
THERMODYNAMICS