Indentation contact and penetration of ice by a semicircular indentor

Indentation contact and penetration of ice by a semicircular indentor is investigated computationally using the boundary element method (BEM). A series of BEM models is analyzed to show how the contact evolves from initial contact and penetration, up to the formation of macro cracks that result in ice splitting.NRC publication: Ye

Thickness-independent fracture in columnar freshwater ice:An experimental study

Experiments on columnar freshwater ice indicated that there is no detected effect of the ice thickness on the fracture behavior of columnar freshwater S2 ice. The influence of thickness was studied using large laboratory-grown samples. Two series of Mode I fracture tests were carried out using deeply edge-cracked 3-by-6-metre rectangular plates loaded monotonically at 1…100 μm/s. The ice was warm (above −0.5 °C), and the ice thickness varied in the range 10–40 cm. This paper analyzes the second series of tests and compares the results with the first series tests; the analysis of the latter was published in Gharamti et al. (2021) [2,3,4]. The viscoelastic fictitious crack model (VFCM) was applied to analyze the data and calculate the crack profile, fracture energy and the process zone size. The thickness affected only and linearly the values of the measured loads with no influence on the fracture properties: the apparent fracture toughness, fracture energy, crack opening displacements, notch sensitivity and process zone size.</p

Fracture energy of columnar freshwater ice

Funding Information: This work was funded though the Finland Distinguished Professor programme ”Scaling of Ice Strength: Measurements and Modeling”, and through the ARAJ research project, both funded by Business Finland and the industrial partners Aker Arctic Technology, Arctech Helsinki Shipyard, Arctia Shipping, ABB Marine, Finnish Transport Agency, Suomen Hyȵtytuuli Oy, and Ponvia Oy. This financial support is gratefully acknowledged. The second author (J.P.D.) thanks Business Finland for support by the FiDiPro Professorship from Aalto University, and the sabbatical support from Aalto University, which collectively supported an annual visit 2015–2016, and summer visits 2017–2019. Publisher Copyright: © 2021 The Author(s)This work investigates the influence of loading type, loading rate, and test size on the fracture energy of columnar freshwater S2 ice. The ice sheet in the Ice tank at Aalto University was very warm (above -0.5 ∘C) and thick (0.34<h<0.41 m). A program of nineteen mode I fracture tests using deeply cracked edge-cracked rectangular plates of various sizes (size range 1:39), loading types, and loading rates were carried out. Fourteen displacement-controlled tests (DC) were loaded monotonically to fracture, and five load-controlled tests (LC) were conducted with creep/cyclic-recovery and monotonic loading to fracture. Different methods for computing the fracture energy were applied and compared. The apparent fracture energy at crack growth initiation was obtained via Rice's J-integral expression (JQ) modified to be applicable to the special case of a deeply cracked edge-cracked plate as well as via a viscoelastic fictitious crack analysis (GVFCM). The work-of-fracture (Wf) was also evaluated. Both JQ and Wf weremeasured from the load-displacement record at the crack mouth. GVFCM was obtained from the back-calculated stress-separation (σ−δ) relation within the fracture process zone. A rather good agreement was obtained between GVFCM and JQ, especially for the large specimens. JQ and Wf exhibited interrelated size and rate effects. The Wf/JQ values for the DC tests were affected by rate and confined to a narrow range of 1 to 3. The creep-recovery loading did not affect the JQ values but led to an increase in the Wf and Wf/JQ values for most of the LC tests.Peer reviewe

Fracture of warm S2 columnar freshwater ice

Large scale laboratory experiments on size and rate effects on the fracture of warm columnar freshwater ice have been conducted with floating edge-cracked rectangular plates loaded at the crack mouth. The largest test plate size had dimensions of 19.5m x 36m. The overall crack-parallel dimension covered a size range of 1 : 39 , possibly the largest for ice tested under laboratory conditions. The loading rates applied led to test durations from fewer than 2 seconds to more than 1000 seconds, leading to an elastic response at the highest rates to a viscoelastic response at the lower rates. Methods for both the linear elastic fracture mechanics (LEFM) and a non-linear viscoelastic fictitious crack model (VFCM) were derived to analyze the data and calculate values for the apparent fracture toughness, crack opening displacement, stress-separation curve, fracture energy, and size of the process zone near a crack tip. Issues of notch sensitivity and minimum size requirements for polycrystalline homogeneity were addressed. Both size and rate effects were observed, as well as how these two factors are interrelated in the fracture of columnar freshwater ice. There was a size effect at low rates but no size effect at high rates. There was a rate effect for the larger test sizes but a weaker or no rate effect for the smallest test size. (c) 2020 Acta Materialia Inc. Published by Elsevier Ltd. This is an open access article under the CC BY-NC-ND license ( http://creativecommons.org/licenses/by-nc-nd/4.0/ )Peer reviewe

Ice internal friction: Standard theoretical perspectives on friction codified, adapted for the unusual rheology of ice, and unified

Sea ice contains flaws including frictional contacts. We aim to describe quantitatively the mechanics of those contacts, providing local physics for geophysical models. With a focus on the internal friction of ice, we review standard micro-mechanical models of friction. The solid's deformation under normal load may be ductile or elastic. The shear failure of the contact may be by ductile flow, brittle fracture, or melting and hydrodynamic lubrication. Combinations of these give a total of six rheological models. When the material under study is ice, several of the rheological parameters in the standard models are not constant, but depend on the temperature of the bulk, on the normal stress under which samples are pressed together, or on the sliding velocity and acceleration. This has the effect of making the shear stress required for sliding dependent on sliding velocity, acceleration, and temperature. In some cases, it also perturbs the exponent in the normal-stress dependence of that shear stress away from the value that applies to most materials. We unify the models by a principle of maximum displacement for normal deformation, and of minimum stress for shear failure, reducing the controversy over the mechanism of internal friction in ice to the choice of values of four parameters in a single model. The four parameters represent, for a typical asperity contact, the sliding distance required to expel melt-water, the sliding distance required to break contact, the normal strain in the asperity, and the thickness of any ductile shear zone