Fracture toughness and crack growth of brackish ice using chevron-notched specimens

Abstract

Field-test equipment called FIFT (a Field Instrument for Fracture toughness Tests on ice) was used in both field and laboratory fracture-toughness tests on brackish sea ice from the Gulf of Bothnia. An experimental calibration was performed and a compliance expression was then derived for the Short Rod Chevron Notched (SRCN) specimen. Using the SRCN configuration, for which the initial crack growth is shown to be stable, and measured load-point displacements, preliminary crack-growth velocities are found. The obtained estimated crack velocity is, on average,ȧe= 20 ms−1, albeit with a large standard deviation. The results indicate that critical crack (crack-jumping) growth occurs. The apparent fracture toughness,KQ, was found to have a pronounced dependency on porosity in the form of brine volume. The results obtained are derived from a linearly elastic fracture mechanics (LEFM) theory. Consequently, the tests were designed to satisfy small-scale yielding requirements in terms of notch sensitivity and brittleness. The linearity of the load vs crack-opening displacement curves together with a size-effect study, showing that the specimen is notch-sensitive for grain-sizes ranging from 1.6 to nearly 100 mm, indicate that LEFM could be applicable.