Strain Field Measurement in Fracture Process Zone

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Abstract
Center‐notched mortar plate specimens are loaded in tension. A multiple sensitivity vector holographic setup is developed to record several deformation stages during the stable crack propagation range. The three‐sensitivity vector setup enables the calculation of both crack opening displacements and strain fields around the crack trajectories. An image analysis system is used to isolate the interferometric effect from the sandwich holograms, resulting in fringe patterns with perfect contrast. Image analysis is also used as a faster, more accurate, and more consistent method for fringe count. After evaluation of the holograms, the existence of tensile forces transmitted through the crack faces is associated with the presence of tensile strain behind the crack tip. A definition of the fracture process zone (FPZ) is proposed based on the difference between experimentally observed and linear elastic fracture mechanics (LEFM) strain fields. Deviations from the linear elastic solution show a relatively small zone of nonlinearity in front of the crack tip and a wake fracture process zone (WFPZ) behind the crack tip. A cohesive crack type of model with a bilinear closing process zone is used to predict the experimental observations.