Interaction of two parallel U-notches with tip cracks in PMMA plates under tension using digital image correlation

Stress intensity factors (SIFs) in a polymethyl methacrylate (PMMA) plate with two parallel cracks initiating from U-notch tips under the action of tensile loading were calculated using digital image correlation (DIC). The effect of notch and crack geometry, including crack length, notch depth, and distance between two notches were investigated experimentally. The displacement fields were determined by correlation between reference images and deformed images. The effect of rigid body motion and rotation was eliminated from displacement field, and SIFs were calculated using a least square algorithm. Also, the effect of subset size and number of terms in William's equation on SIFs was studied. The experimental results were compared with both analytical solution published in literature and Finite Element Method (FEM) simulation. A good agreement between results warrants the accuracy and effectiveness of the experiments. The results show that as the notch distance increases, the values of the mode I stress intensity factor (KI) for two adjacent U-notches approach the obtained KI value for a single notch specimen.