Small-scale laboratory experiments on the indentation failure of polycrystalline ice in compression: Main results and pressure distribution

Laboratory indentation tests were performed with the objective of studying processes of ice failure during indentation and the pressure distribution at the ice-indenter interface. The tests were performed using a 20-mm indenter on ice specimens with dimensions of 20 × 20 × 10 cm. Specimens were made of polycrystalline ice with a grain size of ~ 4 mm. The test setup included the use of a tactile pressure sensor to measure the local pressure distribution at the indentation site. This area was found to consist of isolated zones of very high pressure compared to the average pressures found during the tests. These peaks in pressure were often seen to vary in intensity throughout the test, analogous to the behavior seen during medium and full-scale interactions. The pressure distribution showed that the release of localized spalls are preceded by a build-up of pressure and followed by a decrease in total pressure as well as contact area. Isolated periods of cyclic-load crushing were accompanied by periodic load drops and regular decreases in contact area. In this case, the pressure distribution showed a centralized area of pressure that remained relatively constant throughout the crushing event, which supports the idea of dynamics associated with activity in the damaged layer.