Orientation effects on the fracture of pond (S1) ice

The influence of structural anisotropy on the fracture toughness of S1 type freshwater ice was investigated by fabricating and testing three different fracture geometries from a single ice core. The ice was tested at −16°C using the Chevron Edge Notch Round Bar in Bending (CENRBB), a Chevron Notched Tension (CNT) specimen and the Semi-Circular Bend (SCB) specimen. By this procedure, a complete anisotropic apparent fracture toughness ( K Q) characterization is possible from one core. The specimens can be prepared with very little machining. This approach is therefore suitable for both field and, as in this work, laboratory studies. Three models are presented for computation of the stress-intensity-factor expressions for these specimens. There is a wide scatter in the K Q results and the apparent fracture toughness was higher for cracks perpendicular, than for cracks parallel, to the c-axis and the columnar grains. Possible explanations for this ambiguous behavior are discussed in terms of the microstructural influences and specimen size effects.