NUCLEATION OF FEATHER CRACKS IN COLUMNAR FRESH-WATER ICE - EXPERIMENTAL-OBSERVATIONS

Biaxial compression experiments were carried out to investigate the me chanism of feather crack nucleation in columnar freshwater ice. The te sts were performed with a strain rate of 10(-3) s(-l) at -10 degrees C . It is shown that the nucleation of feather cracks corresponds to a t ransition when the last of the remaining ligaments bonding the two gra ins fractures and the grain boundary transforms into a traction-transm itting frictional crack. This is in contrast to the nucleation of wing cracks, proposed earlier, where the nucleation was due to the onset o f viscous sliding of grains. In addition to the mechanism, the nucleat ion stress for feather cracks was measured for different confinement r atios. A fracture-mechanics-based model for the nucleation process is presented by V. Gupta and R. C. Picu [Nucleation of feather cracks in columnar freshwater ice: Theoretical modeling, manuscript in preparati on.]