Samuel J. DeFranco

Crack propagation and fracture resistance in saline ice

Crack propa gation in saline ice (a model sea ice) is investigated in this study in an atte mpt to under stand the processes of crack growth at one loading rate and two temperatu res. As has been previou sly observed in cold sea ice and warm or cold fresh -water ice, crack growth occurs in initiat ion /arrest incr ement s. The energetic stabil ity cri teria of crack growth are exa mined in saline ice and growth is charact erized in terms of the fractu re-resistance param eter KR. This paper offers the development of a new fractu re geom etry capable of sustained stable crack growth and the prese ntation of fractu re-resis tance curves for saline ice at -25° and -15°C. The important findi ngs of this paper are that: (i) in warm sal ine ice, ext ensive local crack -tip dama ge is acco mpanied by a limited amount of slow, stable crack extension; (ii) fracture in cold saline ice is characte rized by locally negative KR behavior; and (iii) fracture in cold or warm saline ice is cha racterized by glob ally posit ive KR curve behavior.

Fracture analysis of base-edge-cracked reverse-tapered plates

This paper presents a fracture mechanics analysis of the base-edge-cracked reverse-tapered (RT) fracture geometry. Motivation for this study was the use of this test geometry in Phase 1 of a recently completed joint-industry-agency project entitled ‘Large-Scale Ice Fracture Experiments’. Underlying the choice of the RT fracture geometry for Phase 1 was the desirability of achieving crack propagation in a controlled and stable manner; such control would allow a number of observations to be made on one testpiece. Reverse tapering greatly improves not only crack growth stability but also crack path stability. The weight function method was used to provide accurate wide-ranging stress intensity factor (SIF), crack face displacement (COD) and crack opening area (COA) expressions for the RT subject to any loading. The required weight function was obtained through a finite element analysis of this geometry subject to a reference load case which determined the associated stress intensity factor and crack opening displacements. The Wu and Carlsson procedure was followed. A key modification to the latter procedure facilitated the attainment of the reference CMOD for all crack lengths, including the zero ligament limit; this was achieved by considering an additional reference solution. This modification is general in nature and could be pursued whenever the reference CMOD is not known analytically. An analytical solution for the crack opening area (COA) was also achieved for the special case of concentrated loading at the crack mouth. This solution can be applied to any geometry where the reference CMOD expression is known.

Fracture resistance determination of freshwater ice using a chevron notched tension specimen

Crack growth resistance (R-curve behavior) measurements on large grained S1 type freshwater ice were conducted in the Ice Mechanics Research Laboratory at Clarkson University. To overcome previous difficulties in obtaining stable cracking in freshwater ice, a new crack geometry was developed. The short rod Chevron Notched Tension (CNT) specimen was found to be extremely favorable in the sense of promoting stable,stick-slip, crack growth over a large portion of the uncracked ligament. A negative fracture resistanceKR-curve was evaluated for this ice at -16°C.

Crack Growth Stability in Saline Ice

Crack initiation and propagation in saline ice were investigated in this study in an attempt to understand the processes of crack growth under low loading rates and variable temperatures. As has been previously observed in sea ice and freshwater ice, crack growth occurred in initiation/arrest increments. The energetic stability criterion of crack growth are examined and crack growth is characterized in terms of the fracture resistance-stress intensity factor K R . Salient features of this study are the development of a new fracture geometry capable of sustained crack growth over longer crack lengths and the presentation of a fracture resistance curve for saline ice.

Orientation effects on the fracture of pond (S1) ice

Abstract The influence of structural anisotropy on the fracture toughness of S1 type freshwater ice was investigated by fabricating and testing three different fracture geometries from a single ice core. The ice was tested at −16°C using the Chevron Edge Notch Round Bar in Bending (CENRBB), a Chevron Notched Tension (CNT) specimen and the Semi-Circular Bend (SCB) specimen. By this procedure, a complete anisotropic apparent fracture toughness ( K Q ) characterization is possible from one core. The specimens can be prepared with very little machining. This approach is therefore suitable for both field and, as in this work, laboratory studies. Three models are presented for computation of the stress-intensity-factor expressions for these specimens. There is a wide scatter in the K Q results and the apparent fracture toughness was higher for cracks perpendicular, than for cracks parallel, to the c -axis and the columnar grains. Possible explanations for this ambiguous behavior are discussed in terms of the microstructural influences and specimen size effects.

The fracture of sea ice

This paper describes investigations directed towards the identification of an appropriate fracture parameter for sea ice. It is concluded that for laboratory sized specimens, LEFM is not suitable for characterizing the fracture of warm sea ice. A cohesive crack approach is used to model the nonlinear load vs displacement behavior observed experimentally. The fracture of sea ice is characterized by the fracture resistance curve K R .

A joint industry field expedition to study ice conditions in Pechora Sea, 1993

This paper describes the arrangements of an international joint industry field study on the ice conditions in the Pechora Sea in 1993. In the near future the Pechora Sea will attract the petroleum industry, and the areas developed then will be offshore structures like pipelines, production structures, a tanker terminal, and ice breaking vessels including tankers and icebreakers. The ice field work in the area started in winter 1992 when a Russian-Finnish expedition (by the Finnish-Russian Offshore Technology Working Group) was made. The main companies involved in the commissioning of the expedition were the Kvœrner Masa-Yards Arctic Research Centre (MARC), the Arctic Offshore Research Centre of Helsinki University of Technology (AORC), and the Arctic Marine Geological expedition (AMIGE). During the winter of 1993 the same group and, in addition, the Polar Research Institute of Fishing and Oceanography (PINRO) arranged the second expedition to the Pechora Sea funded by five petroleum companies: AMOCO, EXXON, NESTE, NORSK HYDRO, and TEXACO.