DESIGN OF A FIELD TEST FOR MEASURING THE FRACTURE TOUGHNESS OF SEA ICE

摘要

Fracture of sea ice plays an important role in determining the ice loads on offshore structures. The importance of incorporating fracture mechanics principles into ice load calculation has long been recognised. However, any method developed based on fracture mechanics demands the knowledge of this rather important parameter, i.e., the fracture toughness of sea ice. There have been controversies about the scale invariant fracture toughness K_(IC) of sea ice for over 25 years now, e.g., K_(IC) = 115 kPam~(1/2) was reported from laboratory measurement while K_(IC) = 250 kPam~(1/2) was reported from field scale. The size of the test specimen and the loading rate are the two major issues often raised when questioning the validity of a fracture toughness test. In view of such discrepancy in the reported values of fracture toughness, the Norwegian University of Science and Technology (NTNU) hosting the research-based innovation centre (SAMCoT), is making an effort to attack this long-existing problem. Two field tests in Svea at Spitsbergen are planned in the winters of 2015 and 2016. The rationale of the test is rather straightforward, i.e., we shall fracture a large enough ice floe with fast enough loading rate. The test in 2015 is a preparatory campaign for the main testing campaign in 2016. Based on existing fracture mechanics knowledge and precursors' experience with fracture toughness test, this paper describes the design process of the first test campaign with emphasis on the theoretical analysis. Interesting results regarding the size and loading rate requirement are obtained. By this paper, we hope to expose our work at this early stage to discussions, suggestions and criticism from worldwide experts in the field. Based on this test design, the first test campaign shall be carried out between March 20th-27th, 2015, after which we report the test results in a different paper separately.