The properties of slow crack growth in brittle materials are analyzed both
theoretically and experimentally. We propose a model based on a thermally
activated rupture process. Considering a 2D spring network submitted to an
external load and to thermal noise, we show that a preexisting crack in the
network may slowly grow because of stress fluctuations. An analytical solution
is found for the evolution of the crack length as a function of time, the time
to rupture and the statistics of the crack jumps. These theoretical predictions
are verified by studying experimentally the subcritical growth of a single
crack in thin sheets of paper. A good agreement between the theoretical
predictions and the experimental results is found. In particular, our model
suggests that the statistical stress fluctuations trigger rupture events at a
nanometric scale corresponding to the diameter of cellulose microfibrils.Comment: to be published in EPJ (European Physical Journal
