A contribution to the study of the compressive behavior of atmospheric ice

In the last decades, research on atmospheric icing of structures such as power transmission lines has attracted much interest. Accumulation and the shedding of atmospheric ice fromoverhead transmission lines and ground wires may cause their rupture and tower collapses, leading to power outages. The present work concerns a study of the compressive strength of atmospheric ice, under different experimental conditions such as strain rate, temperature, and porosity. For this reason, ice was accumulated in the closed loop wind tunnel at CIGELE (Industrial Chair on Atmospheric Icing of Power Network Equipment), under three temperatures (−20,−15 and −5 °C). The wind speed inside the tunnel was set at 20 m/s in order to obtain a mean volume droplet diameter (MVD) of 40 μm and a liquid water content (LWC) of 2.5 g/m3. Each type of ice was tested at the same temperature at which it had been accumulated. A tomographic analysis was carried out on a small specimen (cylinder of 1 cm diameter × 2 cm length) for each temperature in order to quantify the porosity and determine the grain size and their distribution. The obtained results show a strong dependence of the compressive strength on temperature, strain rate and porosity. The ductile–brittle transition was identified within a strain rate ranging between 10−4 s−1 and 10−3 s−1. It was found that compressive strength increases with decreasing temperature for deaerated ice. However, for atmospheric porous ice, compressive strength increases until −15 °C, then decreases for lower temperatures. Compressive strength of atmospheric ice is highly dependent on porosity, which is related to the amount, size and distribution of pores inside the ice