  We present statistical analysis of acoustic emission (AE) data from tensile
experiments on paper sheets, loading mode I, with samples broken under strain
control. The results are based on 100 experiments on unnotched samples and 70
samples with a long initial edge notch. First, AE energy release and AE event
rates are considered for both cases, to test for the presence of "critical
points" in fracture. For AE energy, no clear signatures are found, whereas the
main finding is that the event rate diverges 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. We also discuss the dependence of the AE
energy and event interval distributions on average event rates.
