The statistical properties and the localization of fracture precursors on heteregeneous materials
is studied by recording their acoustic emission as a function of the applied load. It's found that the
microcrack cluster together as the load increases and the instantaneous acoustic energy has an invariant
power law distribution. The integrated acoustic energy presents a critical divergency close to the failure load
for the sample. These result support the idea that fracture can be viewed as a critical phenomenon. Finally
a measure of the concentration of microcraks, which allows us to predict the failure load, is introduced.
These properties are studied also when a periodic load is applied to the sample. It's found that the Kaiser
e ect is not strictly satis ed in heteregeneous materials.