Compressive strength of atmospheric ice

Accumulation of atmospheric ice on power transmission lines is a source of tremendous damage to power networks. Despite the longstanding problem of atmospheric icing on network equipment, the mechanical properties and behavior of this type of ice under various loading conditions are still unclear. In the present study, more than 180 tests were carried out to measure the behavior of atmospheric ice under compression. For this purpose, ice was accumulated in the closed-loop wind tunnel of CIGELE (La Chaire industrielle sur le givrage atmosphérique des équipements des réseaux électriques) at three different temperatures (− 6, − 10 and − 20 °C) and liquid water content value of 2.5 g/m3. Each type of ice was tested at the same temperature at which it had been accumulated, and the ice accumulated at − 10 °C was also tested at − 3 and − 20 °C. Thin sections of the three types of atmospheric ice revealed that the average grain size for accumulated ice is 1.5 mm, 0.5 mm and 0.4 mm, for accumulation temperatures of − 6, − 10 and − 20 °C, respectively. For ice accumulated at − 20 °C the presence of cavities reduces ice strength at certain strain rates. The results of tests showed that the compressive strength of atmospheric ice increases when test temperature decreases. Moreover the dependency of strength on temperature is strongest in the mid range of the strain rates that were tested, i.e. at around 3 × 10− 3 s− 1. The tests also revealed that compressive strength of atmospheric ice at low strain rates increases as accumulation temperature decreases.