Statistical properties of low cycle fatigue in paper

We consider fatigue fracture in the low-cycle limit. We use paper as the tested material and we study the failure and the deformation of individual samples, with a main emphasis on the possible predictability. The experimental procedure is to study fatigue in tension and follow the evolution of mechanical properties of paper samples. The primary quantity is the strain developing during load cycles and its evolution. Two concurrent methods are used to this end: vertical displacement measured by a laser interferometer sensor, and the digital image correlation technique (DIC). By the DIC, we obtain accurately at the same time displacement data and the spatial fields of strain and strain rate. The final rupture is signalled by a sharp final increase of different variables, like deformation, strain rate and their fluctuations. We find interestingly enough that looking at the evolution of these quantities during the first fatigue cycle only is already a good indicator about the lifetime of the sample. Crackling noise is also recorded during loading via acoustic emission (AE). AE is mostly accumulated during a short time interval before breakage. The results are compared with a fibre bundle model of fatigue in heterogeneous materials.