Public Defense in Mechanical Engineering, M.Sc. Waqas Ahmad

First-ever quantitative measurement of the process zone size in ice using Digital Image Correlation

Growing interest in the offshore wind energy in the Arctic region demands a better understanding of how ice fractures. This will not only help us design safer offshore structures but also improve current models used to study the fracture of ice. This thesis focuses on the development of a full-field measurement method, Digital Image Correlation (DIC), to study tensile mode-I fracture of both saline and freshwater ice. Compared to the conventional methods of measuring ice deformation using LVDTs and lasers, DIC enabled the study of crack growth and the coupling of the deformation fields with the microstructure of ice. Using DIC data and thin section analysis, the thesis establishes that the crack growth process in ice is dependent on the orientation of its grains. The categorization of fracture results based on crack growth nature also influenced the potential interpretation of rate and scale effects commonly discussed in ice mechanics. The findings of this thesis also include the first quantitative measurement of the upper bound of the nonlinear fracture process zone in ice. The comparison of the measured results with the viscoelastic fictitious crack model (VFCM), conventionally used to numerically calculate the process zone (PZ) size, showed that the results from the model were dependent on the nature of the crack growth. Moreover, the accuracy of the VFCM improved when higher spatial resolution crack opening displacement data from DIC was used in the numerical calculation of PZ. These findings highlight the importance of the use of full-field measurement techniques to understand the complex nature of ice. Additionally, they also emphasize further development of fracture models used in ice to design safer offshore structures in the Arctic. 

Doctoral Student: Waqas Ahmad

First Opponent: Associate Professor in Climate Engineering Wenjun Lu, NTNU, Trondheim, Norway

Second Opponent: PhD Mark Iadicola, NIST, USA

Custos:Professor Jukka Tuhkuri, Aalto University School of Engineering, Department of Mechanical Engineering

The public defense will be organized as a hybrid event - on campus in Lecture Hall 213a, Otakaari 4 and on Zoom.

Thesis is publicly displayed 10 days prior to the defense in the publication archive Aaltodoc of Aalto University. 

Contact information of the doctoral student: Waqas Ahmad, [email protected], +358504771636

Doctoral theses in the School of Engineering: https://aaltodoc.aalto.fi/handle/123456789/49