Chuanke Li

High Pressure Zones at Different Scales During Ice-Structure Indentation

In order to improve the estimation of the ice load during ice-structure interaction, this study aims to investigate the behaviour of high pressure zones at different scales. Small scale indentation tests of ice with four different sizes of indentors (10 mm, 20 mm, 40 mm and 100 mm in diameter) were conducted at Ocean Engineering Research Centre of Memorial University. The tests were conducted at −10 °C. The grain sizes were scaled up with the indentor sizes. The tests consist of three series with different orders of displacement rates. In this paper, Part of the field test data will be retrieved for the investigation. Microstructural changes of the ice after deformation in laboratory will be studied. A relationship between stress and nominal contact area is derived based on the data. Numerical simulations are conducted for the series with low displacement rates of laboratory tests. The simulation shows a good agreement with the tests.Copyright

Damage and Microstructural Changes in Ice in Compression during Interaction with Structures

A layer of damaged ice has been observed near the contact zone of ic -structure interactions in small scale, medium scale and full scale tes ts. Microcracking and recrystallization were observed in the layer. It is believed that pressure melting also occurs in the layer. The objective of the present work is to investigate the process of forma ti n of the layer. Triaxial confining tests were conducted at Memorial University of Newfoundl and with constant stress. The tests showed a pressure dependent process of damage. Microcracking and recrystallization were observed to be the main type of damage at low confining pressure l evels with possible melting at asperities in cracks. Recrystallization and melting were the main types of damage under high confinements. Damage was calibrated using a scalar parameter and the triaxial test data. Numerical simulations were conducted using finite element methods to simulate t he interaction process. The results are consistent with the observations from the medium scale tests. Introduction In arctic and sub-arctic water areas, sea ice and icebergs p rovide a challenge to shipping and to construction for industrial developments, particularly in the oil and g as sector. This has led to a focus on understanding of the mechanical behaviour of ice during its inter action with offshore structures at Memorial University of Newfoundland’s Ocean Engine er g Research Centre. The objective of the present research is to study the microstructral changes of ice during its interaction with offshore structures and implement mechanical model for numerical simulat ions. Ice is progressively damaged during its interaction with struc tu es. The two processes of importance are fracture and damage. These processes result in the formation of high pressure zones. The interaction area consists of a combination of high and low pressur e zones during crushing. The high pressure zones carry the majority of the interaction load (se e Fig. 1). In ship ramming trials on multiyear sea ice with the icebreaker C.C.G.S. Louis S. St. La urent in 1994, numerous local peaks in pressure were recorded on the hull during contact. Medium scale inde ntation tests on Hobson’s Choice Ice Island have shown peak pressures reaching as high as 70 MP a for a sensor of diameter 12.7 mm [1]. The areas of high pressure found locally are associated with a layer of damaged ice with fine grains and crushed ice. This layer was first observed by Kheisin and Kherepanov [2] and most recently in [3] through thin sections taken from field tests . In order to understand the high pressure zones and layer formation, triaxial small scale test s under compressive loading conditions were conducted [4,5]. Microstructural changes were investigated by t aking thin sections of the deformed specimens. Different types of damage were observed under different test conditions. In general, microcracking, dynamic recrystallization and pressur melting are dominant mechanisms. The damage mechanisms were found to be strongly pressure-dependent. Microcracking was observed to be the main damage form at low confinement and recrystal lization was the main mechanism of damage for ice under high confinement. Previous triax ial tests by Stone and others [6] have shown that damage can enhance the deformation of ice significantly. Data from triaxial tests were used to characterize damag e with a scalar parameter. A Key Engineering Materials Online: 2003-10-15 ISSN: 1662-9795, Vols. 251-252, pp 431-436 doi:10.4028/www.scientific.net/KEM.251-252.431