Fracture propagation and prediction in heterogeneous materials

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 Chapter 4 relates to unpublished work of two interacting cracks.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.