The Strength and Ductility of Ice Under Tension

Tensile experiments have been performed on aggregates of equiaxed and randomly oriented ice I_h 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 σ_f = σ_o + kd^−1/2 where σ_o = 0.51 MPa and k = 0.03 MPa m^1/2. At the lower rate the ice is ductile over the same range of grain size and its strength is given by the relationship σ_f = Kd^−1/2 where K = 0.050 MPa m^1/2. These effects are explained quantitatively in terms of the nucleation and propagation of cracks.