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

Abstract

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, lie = 20 m S-I, 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 smallscale 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.