Scale effects on the fracture of ice

This dissertation presents experimental and theoretical work completed as part of ONR's Sea Ice Mechanics (SIMI) research program. The goals of the program are to acquire knowledge of sea ice over a broad range of scales (0.1m to 10km) and subsequently develop a physically based (function of temperature, brine channels, spacing of channels, porosity, salinity) constitutive model capable of predicting behavior over the wide range. An abundance of lab scale investigations have been completed on sea ice as well as investigations above the 1km scale. The laboratory scale testing is typically completed under isothermal conditions with sizes less than 0.5m. Very little fracture and constitutive data exists for the scales between 0.1m and 1km. To link the scales, in-situ fracture and tensile experiments were completed, successfully spanning the range of 0.5m to 80m. Six field trips to the Arctic were made with the latter five investigating the large scale behavior of sea ice. Forty-six fracture and flexure tests spanning the above mentioned size range provided both fracture and constitutive data necessary for achieving the goals of the program. As a result, two important discoveries were made and are discussed in detail in this dissertation.; First, analysis of the fracture results indicates that a scale effect on the nominal tensile strength of sea ice exists, consistent with results at both the lab and 1km scales. The strength decreases from a typical tensile strength of approximately 0.5 MPa at the lab scale to 50 kPa at the 80 meter size. The ability of two size effect laws developed for size effect behavior in concrete to predict this behavior is investigated.; Second, preliminary modelling efforts indicate that a linear viscoelastic model is not sufficient to predict the strain behavior of sea ice. A nonlinear stress dependence in the delayed elastic and viscous strain components was found to best fit the results. This nonlinear viscoelastic model is applied to the results of a fracture experiment completed as part of the SIMI program.