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Uniaxial compression of saline columnar ice under variable strain rates - Ice-induced vibrations of offshore structures
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School of Engineering |
Master's thesis
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en
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53
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To investigate the mechanical response of sea ice under conditions representative of ice-induced vibrations (IIV) on offshore structures, uniaxial compression tests were performed on naturally formed saline columnar ice from Sveabukta, Svalbard. A sinusoidal advancing strain profile was designed to replicate the displacement and velocity characteristics associated with IIV events. Horizontal ice cores were subjected to constant, stepwise, and cyclic loading to evaluate the influence of variable strain rates on the mechanical response. Microstructure analysis under cross-polarized light was conducted on the ice samples using thin sections prepared with a CNC milling machine. Sections were produced both before testing, to document the ice texture, and after testing, to assess fracture development and failure patterns. The ice profile showed a granular upper layer, a columnar S2 middle layer with increasing grain size, and a lower layer transitioning towards skeletal S3 ice. Fracture analysis revealed grain boundary cracks typical of ductile failure, as well as V-shaped fractures and cracks cutting through grains, which are associated with brittle failure. All tests were conducted under confinedconditions using an acrylic cylinder to simulate in situ lateral pressure. The confinement promoted a more ductile response. A ductile-to-brittle transition strain rate of 1.0E-3 1/s was identified for the upper and middle ice layers, while the lower layer exhibited brittle failure at even lower strain rates. Under cyclic loading, only the upper layer showed increased peak stress compared to constant strain tests, while no significant strengthening was observed in the middle and lower layers. These findings provide new experimental data on the behavior of saline columnar ice under loading conditions relevant to offshore structures in ice-covered waters.