Flexural and low-cycle fatigue behavior of atmospheric ice

Abstract

Accretion of atmospheric ice on power transmission lines may have detrimental effects, sometimes with major socio-economical consequences. The mechanical behavior of this type of ice as an important aspect in the understanding of that issue is still unclear. In the present study, more than 70 tests were conducted using cantilever beams under gradually increasing cyclic load to measure the bending strength of various types of atmospheric ice. Atmospheric ice was accumulated in a closed-loop wind tunnel at −6, −10, and −20 °C, with a liquid water content of 2.5 g m−3. Ice samples accumulated at each temperature level were tested at the accumulation temperature, but the ice accumulated at −10 °C was also tested at −3 and −20 °C. Compared to the bending strength results for atmospheric ice under static load, the ice showed less resistance against fracture under cyclic load. It was also revealed that bending strength of atmospheric ice decreases with the test temperature. Another 60 samples of atmospheric ice were also tested under cyclic loads with constant amplitude. The tests revealed that the samples of atmospheric ice accumulated at −10 and −6 °C do not fail under stresses less than 1 MPa after 2000 cycles. At stress levels close to the bending strength of atmospheric ice, however, sometimes the specimen fails after a few hundred cycles. In comparison with the ice accumulated at −10 and −6 °C, atmospheric ice accumulated at −20 °C fails at stresses less than its bending strength. This can be attributed to the colder test temperature and the presence of cavities and cracks in this ice that reduce its bending strength during cyclic stresses.