Welcome to the thesis defence of Jonas Kjellstadli on December 17th

17 December: Jonas Tøgersen Kjellstadli – Faculty of Natural Sciences



Jonas Tøgersen Kjellstadli has submitted the following academic thesis as part of the doctoral work at the Norwegian University of Science and Technology (NTNU):

Local versus Equal Load Sharing in the Fiber Bundle Model

Assessment Committee

The Faculty of Natural Sciences has appointed the following Assessment Committee to assess the thesis:

  • Professor Hans J. Herrmann, ESPCI, France
  • Professor Ferenc Kun, Department of Theoretical Physics, University of Debrecen, Hungary
  • Professor Ingve Simonsen, Department of Physics, NTNU

Professor Simonsen has been appointed Administrator of the Committee. The Committee recommends that the thesis is worthy of being publicly defended for the PhD degree.


The doctoral work has been carried out at the Department of Physics, where Professor Alex Hansen has been the candidate’s supervisor. Professor Asle Sudbø has been the candidate’s co-supervisor.

Public trial lecture:

Time: 17 December at 10.15

Place: Disputasrommet, Main Building, NTNU Gløshaugen

Prescribed subject: “Failure processes

Public defence of the thesis:

Time: 17 December at 13:15

Place: Disputasrommet, Main Building, NTNU Gløshaugen

Summary of thesis:

Fracture is a huge field of research that includes physics, geology, materials science, and engineering. Most approaches are very specialized, but what if we instead want to focus on the big picture to look for general behavior and effects?

The fiber bundle model is a highly simplified model that can still describe many characteristic features of fracture phenomena, and is therefore very useful when investigating fracture processes generally. This thesis studies the equal load sharing (ELS) and local load sharing (LLS) variants of the fiber bundle model.

The holy grail of fracture research is to predict when catastrophic failure will occur. The first two articles develop two different approaches that can potentially be used to predict failure: energy considerations and the distribution of smaller fracture events.

The last two articles describe effects that occur in the LLS model, but are absent in the ELS model. The first is a statistical effect that can cause an apparent stability, where the model looks stable in a region where it is unstable. The second is a shielding effect that protects weak fibers at the expense of stronger ones. This effect can, surprisingly, make the LLS model – which contains local stress enhancement at the edges of cracks – more stable than the ELS model.