A study on extrinsic cohesive elements for cohesive fracture modelling

• Main Author: Rytömaa, Samuli
• Other Authors: Polojärvi, Arttu, Insinööritieteiden korkeakoulu, Aalto-yliopisto, Aalto University
• Format: Master Thesis
• Language: English
• Published: 2016
• Subjects: cohesive element; cohesive fracture; sea ice; finite-element method; FEM; Ice Sheet; Sea ice
• Online Access: https://aaltodoc.aalto.fi/handle/123456789/22204

Fracture of quasi-brittle materials such as sea ice can be simulated using cohesive crack model. The model can be applied to finite-element method using cohesive elements, which can be divided into intrinsic and extrinsic types. Extrinsic type elements are better suited for simulations where the crack path is not known. One such application is ice-structure interaction simulation, where intact ice sheet breaks against an offshore structure. In this work the use of cohesive elements is studied, with focus in fracture of sea ice. A state-of-the-art review on cohesive fracture modelling and cohesive elements is conducted. As a computational part extrinsic cohesive fracture model for sea ice is developed for use in ice-structure interaction simulations. The model is based on earlier fracture model used in simulations of ice-structure interaction. This thesis also includes a study on cohesive fracture modelling using commercial finite-element software Abaqus as an alternative for in-house created codes. At the time Abaqus only includes intrinsic elements, but extrinsic element could be added as user-created element. Creating such elements is challenging and time-consuming, and the study results in Abaqus not being a feasible alternative for ice-structure interaction simulation. As a result of this work an improved version of the 2-D cohesive crack model is created. The model improves on the original model by in shear dominated cases. Wide variety of tests were conducted using MATLAB to compare the performance between the two models. The new model is found to be better compared to the original model in shear dominated cases, while performing equally well in tensile cases. Jään kaltaisten kvasihauraiden materiaalien murtumista voidaan mallintaa koheesiivista särömallia käyttäen. Malli voidaan liittää osaksi elementti-menetelmää käyttäen koheesiivisia elementtejä, jotka voidaan jakaa intrinsisiin ja ekstrinsisisiin malleihin. Ekstrinsinen malli soveltuu paremmin jään murtumisen kaltaisiin tapauksiin, jossa särön ...