Dynamic Crack Growth Past a Stiff Inclusion: Optical Investigation of Inclusion Eccentricity and Inclusion-matrix Adhesion Strength |
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Authors: | R Kitey H V Tippur |
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Institution: | (1) Department of Mechanical Engineering, Auburn University, Auburn, AL 36849, USA;(2) University of Illinois at Urbana-Champaign, Urbana, IL, USA |
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Abstract: | Interactions between a dynamically growing matrix crack and a stationary stiff cylindrical inclusion are studied optically.
Test specimens with two different bond strengths (weak and strong) and three crack-inclusion eccentricities (e = 0, d/2 and 3d/4, d being inclusion diameter) are studied using reflection mode Coherent Gradient Sensing (CGS) and high-speed photography. These
variants produce distinct dynamic crack trajectories and failure behaviors. A weaker inclusion-matrix interface attracts a
propagating crack while a stronger one deflects the crack away. The former results in a propagating crack lodging (‘key-hole’)
into the inclusion-matrix interface whereas in the latter the crack tends to circumvent the inclusion. When the inclusion
is in the prospective crack path, the maximum attained crack speed is much higher in the weakly bonded inclusion cases relative
to the strongly bonded counterparts. For a crack propagating towards a weakly bonded inclusion, the effective stress intensity
factor (K
e) value remains constant for each inclusion eccentricity considered. But these constant K
e values increase with increasing eccentricity. A distinct drop in K
e occurs when the crack is near the inclusion. In strongly bonded inclusion cases, on the other hand, monotonically increasing
K
e before the crack reaches the inclusion is observed. A drop in K
e is seen just before the crack reaches the inclusion. The mode-mixity estimates are of opposite signs for weakly and strongly
bonded inclusions in case of the largest eccentricity studied, confirming the observed crack attraction and deflection mechanisms.
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Keywords: | Dynamic fracture Crack-inclusion interaction Optical interferometry Filled polymers Toughening mechanisms |
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