Fracture propagation and prediction in heterogeneous materials
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School of Science |
Doctoral thesis (article-based)
| Defence date: 2013-09-04
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Authors
Date
2013
Major/Subject
Mcode
Degree programme
Language
en
Pages
67 + app. 93
Series
Aalto University publication series DOCTORAL DISSERTATIONS, 122/2013
Abstract
The topic of this thesis is fracture and damage. It is discussed with an experimental point of view in multiple geometries. In Publications I and II a 1D fracture line is driven through elastic medium that is paper. The fracture line propagates with jerky motion producing audible avalanches. These acoustic emission events obey Gutenberg-Richter statistics for energy and Omori law for waiting times. In Publications III and IV digital image correlation technique is used to measure local strains in paper creep experiments. The significance of local fluctuations increases during the experiment as the fluctuations decay slower than the average strain rate. The global strain rate is found to have a Monkman-Grant relation. In Publication V the global and local strains are used to predict the failure in the paper fatique experiment. The system is compared to a standard fiberbundle model with viscous components. Chapter 4 relates to unpublished work of two interacting cracks. Here, it is shown that curved cracks follow the local symmetry path where the shear stress intensity factor KII = 0.Väitöskirjan aihe on murtuminen ja vaurio. Tätä käsitellään kokeellisesta näkökulmasta useissa geometrioissa. Julkaisuissa I ja II yksiulotteinen murtorintama ajetaan läpi elastisen väliaineen, joka on paperi. Murtorintama etenee epätasaisesti tuottaen havaittavaa ääntä. Nämä akustiset tapahtumat noudattavat Gutenberg-Richter statistiikkaa energian suhteen ja Omorin lakia odotusakojen suhteen. Julkaisuissa III ja IV kuvakorrelaatiotekniikkaa on käytetty paikallisten venymien mittaamiseen paperin virumiskokeessa. Paikallisten venymien merkitys kasvaa kokeen kuluessa, koska venymänopeuden keskihajonta pienenee hitaammin kuin venymänopeuden keskiarvo. Kokonaisvenymänopeudesta löydetään Monkman-Grant suhde. Julkaisussa V paikallista ja kokonaisvenymää käytetään ennustamaan väsymiskokeen elinaika. Koetta verrataan viskoosiin kuitukimppumalliin. Kappale 4 liittyy julkaisemattomaan työhön kahden särön vuorovaikutuksesta. Säröt etenevät paikallisen symmetrian osoittamaa polkua. Tällä polulla leikkausvahvistuskerroin on KII = 0.Description
Supervising professor
Alava, Mikko, Prof., Aalto University, FinlandThesis advisor
Alava, Mikko, Prof., Aalto University, FinlandKeywords
fractures, materials, murtuminen, materiaalit
Other note
Parts
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[Publication 1]: Juha Koivisto, Jari Rosti, and Mikko Alava. Creep of a fracture line in paper peeling. Physical Review Letters 99, 145504, 4 pages (2007).
DOI: 10.1103/PhysRevLett.99.145504 View at publisher
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[Publication 2]: Jari Rosti, Juha Koivisto, Paola Traversa, Xavier Illa, Jean-Robert Grasso, and Mikko Alava. Line creep in paper peeling. International Journal of Fracture 151, 281, 17 pages (2008).
DOI: 10.1007/s10704-008-9258-7 View at publisher
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[Publication 3]: Jari Rosti, Juha Koivisto, Lasse Laurson, and Mikko Alava. Fluctuations and scaling in creep deformation. Physical Review Letters 105, 100601, 4 pages (2010).
DOI: 10.1103/PhysRevLett.105.100601 View at publisher
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[Publication 4]: Lasse Laurson, Jari Rosti, Juha Koivisto, Amandine Miksic, and Mikko Alava. Spatial fluctuations in transient creep deformation. Journal of Statistical Mechanics: Theory and Experiment P07002, 27 pages (2011).
DOI: 10.1088/1742-5468/2011/07/P07002 View at publisher
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[Publication 5]: Amandine Miksic, Juha Koivisto, and Mikko Alava. Statistical properties of low cycle fatigue in paper. Journal of Statistical Mechanics: Theory and Experiment P05002, 26 pages (2011).
DOI: 10.1088/1742-5468/2011/05/P05002 View at publisher