Improved Modeling of Iceberg Ice Constitutive Properties Using a Multi-scale Approach

ABSTRACT:

Iceberg ice is complex to model as properties tend to vary with a wide range of parameters (temperature, strain rate, bubbles, etc.) resulting in complex failure envelopes with low tensile strengths. This is compounded by the presence of size effects where larger areas typically have lower strengths. Furthermore, small-scale features (e.g., grains, bubbles, micro-cracks, planar flaws, veins) influence the overall behaviour, especially in tension. The existing approach relies on ice failure envelopes which overestimate the compressive and, to a much larger extent, the tensile strength of ice. These models typically have difficulty capturing failure initiating in the tensile regions and the associated microcracking and spalling.

As in many other heterogeneous materials, these microstructural details have substantial impact on the overall behaviour of ice structures, but considering them all in a single-scale finite element model is impractical, if not impossible. By using a multi-scale approach, small stress risers, such as bubbles, and subsequent microcracking can be captured at the microscale and allowed to influence the global response of the iceberg ice without compromising computational performance. This, in turn, can be used to refine current ice failure envelopes to better capture low strength tensile behaviour as well as scale effects. 

Validation studies based on comparison to four-point bending experiments show that the proposed approach is able to capture the influence of bubbles or other flaws on the overall flexural strength of iceberg ice and is an improvement over existing approaches to ice failure envelopes. Through improved understanding of ice strength, improved iceberg ice constitutive response can be incorporated into state-of-the-art finite element analysis of iceberg-structure interactions with the overarching goal of closer correlation with local stresses (hot-spot zones) and global response, especially for tensile loading scenarios. By improving upon the strength approach currently employed in modeling ice-structure interactions, Arctic designs can be developed and evaluated with more clarity on safety margins.

Sarzynski, M., Cordes, R., “Improved Modeling of Iceberg Ice Constitutive Properties Using a Multi-scale Approach”, Proceedings of ATC 2015, March 23-25, 2014, Copenhagen, DE.