Showing papers by "Michael May published in 2019"
TL;DR: In this article, a beam theory-based analysis of the fracture toughness of fiber reinforced composites at high rates of loading is presented, which results in symmetric mode I opening of the crack and a robust analytical determination of fracture toughness without the need to measure the external forces acting on the specimen nor to visually estimate the crack length.
Abstract: The measurement of the fracture toughness of fiber reinforced composites at high rates of loading is still, despite years of research, not well established. This can be related to challenges in applying appropriate high rate loading on the specimen, accurately measuring the load, and in-situ determination of the crack length. In this work these challenges are addressed by using a direct wedge-on-specimen type loading of a double cantilever beam (DCB) specimen, high resolution optical deformation tracking, and a beam theory based analysis of the specimen deflection and crack length. This approach results in symmetric mode I opening of the crack and a robust analytical determination of the fracture toughness without the need to measure the external forces acting on the specimen nor to visually estimate the crack length. Tests carried out on carbon fiber reinforced epoxy composite at quasi-static and high rates (relative velocity up to 15 m/s) show the validity of the approach.
21 citations
TL;DR: In this paper, in-situ X-ray computed tomography and online stiffness monitoring were used to study damage initiation and propagation in multi-directional carbon fiber reinforced composite coupon subjected to tension-tension fatigue loading.
13 citations
TL;DR: In contrast to quasi-static experiments, in the high rate experiments the specimens showed notable residual load carrying capacity after the maximum stress, related to dynamic effects in fractured ice particles, which allowed the specimen to carry compressive load even in a highly damaged state.
Abstract: The initiation and propagation of damage in pure ice specimens under high rate compressive loading at the strain rate range of 100 s−1 to 600 s−1 was studied by means of Split Hopkinson Pressure Bar measurements with incorporated high-speed videography. The results indicate that local cracks in specimens can form and propagate before the macroscopic stress maximum is reached. The estimated crack velocity was in the range of 500 m/s to 1300 m/s, i.e., lower than, but in similar order of magnitude as the elastic wave speed within ice. This gives reason to suspect that already at this strain rate the specimen is not deforming under perfect force equilibrium when the first cracks initiate and propagate. In addition, in contrast to quasi-static experiments, in the high rate experiments the specimens showed notable residual load carrying capacity after the maximum stress. This was related to dynamic effects in fractured ice particles, which allowed the specimen to carry compressive load even in a highly damaged state.
11 citations