Experimental Determination of Fatigue Crack Growth Behavior and Surface Strain Distribution of ‘Faint-Waist Pure Shear’ Specimens with Different Crack Tip Radii

Abstract

Abstract The influence of the initial crack-tip radius on the fatigue behavior and the strain distribution in the vicinity of the blunted crack tip was determined experimentally using a servo-hydraulic testing machine and an optical full-field strain analysis method. Two different elastomer grades (SBR, EPDM) were selected for the experimental work. The strain analysis method used, based on the image correlation technique, was found to be an effective tool to determine strains, strain distributions and gradients near the crack tip for elastomeric materials. Different material behavior was observed in the two rubber types investigated. While the crack tip was regularly blunted (half circle shape) for EPDM and the strain gradient was low (less steep), the crack tip was sharp (less blunted) with a higher strain gradient for SBR. Furthermore the crack tip radius was found to be an important influencing factor on the initiation of crack growth, but not on the crack growth behavior after initiation. Based on the experimental results a phenomenological, first-order, crack-growth initiation law was proposed, dependent on the crack tip radius, the tearing energy at crack growth initiation for a sharp crack and a parameter representing the influence of the crack tip radius.