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The mode-II dynamic fracture behavior of poly(methyl methacrylate) (PMMA) was experimentally and numerically studied using ultra high-speed photography combined with digital image correlation and meshfree numerical simulations. Experiments were performed by launching a projectile from a gas gun onto pre-notched rectangular PMMA specimens. Two sample geometries were used, double edge notch specimens and single edge notch specimens. Additionally, two variations of the single edge notch specimen experiments were performed, in the first experiment the projectile directly hit the sample and in the second one a buffer was placed between the sample and projectile to ensure uniform loading. Finally, the effect of the notch sharpness was explored. The impact location was below the notch to ensure mode-II loading, which would then transition into mode-I loading once the crack starts to grow. Mode-II critical stress intensity factors were extracted and it was found that notch sharpness and loading conditions can have an effect on the path the crack follows upon fracture. All of these results were compared to numerical simulations of the crack propagation processes using a meshfree method. The numerical model successfully predicted the fracture toughness and the crack-path angle within 4% and 7% of experimental values, respectively. In addition, crack-tip speeds greater than 300 m/s were observed experimentally and numerically.

An experimental investigation of the mode-II dynamic fracture behavior of carbon fiber/epoxy composites when exposed to moisture intake in excess of 1 wt% was conducted. In particular, one goal was to investigate if the different moisture intake methods result in different dynamic fracture responses. Experiments were performed by launching a projectile from a gas gun onto pre-notched unidirectional carbon fiber/epoxy rectangular specimens manufactured in-house. Additionally, the material was characterized in-house to account for material property degradation due to water intake. Two different aging techniques were used to obtain the desired moisture contents. First, hygrothermal aging was used to obtain 1.5 wt% moisture uptake by having samples submerged in water at $$65\,^\circ$$ C. Second, submersion in water at room temperature was used to obtain the same effect, resulting in longer soaking times. Ultra high-speed photography combined with digital image correlation were used to extract stress intensity factors from each experiment. The experiment successfully obtained dominant mode-II loading of the crack. It was found that carbon fiber/epoxy samples with no significant moisture content had a a higher mode-II critical stress intensity factor compared to samples that were aged. Additionally, no significant differences were found between the different types of aging techniques.