Critical phenomena in creep and damage

The deformation and the damage evolution are studied in creep and fracture experiments using paper samples. Experimental methods utilized are the digital image correlation and the acoustic emission. Statistical models of the deformation and fracture are tested. In the tensile geometry, the Andrade creep phase characterized by a power law decay of the strain rate, and the increase of the relative strength of strain rate fluctuations. The integrated deformation follows a data collapse appropriate for an absorbing state phase transition. The fluctuation scaling is confirmed to exist in the logarithmic primary creep regime, but not in the creep recovery. In the peel-in-nip geometry, under a constant force, advancing front exhibits creep-depinning phase transition. Numerical models suggest that it corresponds the motion of an elastic line with a long-range elastic interaction. The probability distributions of the event energies, waiting times between events and the correlated dynamics of the intermittent crackling noise are studied in the fracture phenomena, in various different loading modes and loading geometries. Analogies to the tectonic seismicity is discussed. The concept of criticality is studied in the tensile experiment and a strain imposed loading. The idea of criticality implies the presence of a divergences in the acoustic emission time series. The event rate is found to diverge, when a sample-dependent "critical time" of the maximum event rate is approached. This takes place after the maximum stress is reached. The results are compared with statistical fracture models of heterogenous materials.