The Strength and Ductility of Ice Under Tension

Tensile experiments have been performed on aggregates of equiaxed and randomly oriented ice Ih of varying grain size (1.4 to 7.9 mm) at −10°C at two strain rates, 10−3 s−1 and 10−7 s−1. At both rates, which were held constant using “feed-back” control, the tensile strength decreased with increasing grain size. This result confirms earlier work on grain size effects in which the rate randomly varied (from 0.6 × 10−6 s−1 to 3 × 10−6 s−1) from test to test. At the higher rate the ice is brittle over the complete range of grain size and its strength is given by the relationship σf = σo + kd−1/2 where σo = 0.51 MPa and k = 0.03 MPa m1/2. At the lower rate the ice is ductile over the same range of grain size and its strength is given by the relationship σf = Kd−1/2 where K = 0.050 MPa m1/2. These effects are explained quantitatively in terms of the nucleation and propagation of cracks.