Fracture energy of columnar freshwater ice: Influence of loading type, loading rate and size

I.E Gharamti,J.P Dempsey,A Polojärvi,J Tuhkuri

doi:10.1016/j.mtla.2021.101188

Abstract

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 were measured 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.

Highlights

The main goal of this thesis is to gain a better understanding of the fracture behavior of columnar freshwater ice under different loading scenarios
The current results are compared with the fracture results of monotonically loaded displacement control (DC) experiments of the same ice and same specimen size (3m x 6m, Chapter 3)
crack mouth where the loading is applied (CMOD) indicates the displacement rate at the crack mouth and is obtained by dividing CMOD by the failure time

Summary

Introduction

The main goal of this thesis is to gain a better understanding of the fracture behavior of columnar freshwater ice under different loading scenarios. Understanding the deformation and fracture processes of columnar freshwater ice is important in many engineering problems. Freshwater ice sheets fracture when in contact with ships, river ice fractures during interaction with bridge piers, and thermal cracks form in lakes and reservoirs. Climate change has led to a warmer, thinner, and broken ice. In addition, the applications like river ice breakup happen in late spring and the ice is very warm. The warming climate increases the importance of studying warm ice, and warming ice increases the importance of creep deformations. Historically cold ice has been studied typically

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