  The fracture of materials is a catastrophic phenomenon of considerable
technological and scientific importance. Here, we analysed experiments designed
for industrial applications in order to test the concept that, in heterogeneous
materials such as fiber composites, rocks, concrete under compression and
materials with large distributed residual stresses, rupture is a genuine
critical point, i.e. the culmination of a self-organization of damage and
cracking characterized by power law signatures. Specifically, we analyse the
acoustic emissions recorded during the pressurisation of spherical tanks of
kevlar or carbon fibers pre-impregnated in a resin matrix wrapped up around a
thin metallic liner (steel or titanium) fabricated and instrumented by
A\'erospatiale-Matra Inc. These experiments are performed as part of a routine
industrial procedure which tests the quality of the tanks prior to shipment and
varies in nature. We find that the seven acoustic emission recordings of seven
pressure tanks which was brought to rupture exhibit clear acceleration in
agreement with a power law ``divergence'' expected from the critical point
theory. In addition, we find strong evidence of log-periodic corrections that
quantify the intermittent succession of accelerating bursts and quiescent
phases of the acoustic emissions on the approach to rupture. An improved model
accounting for the cross-over from the non-critical to the critical region
close to the rupture point exhibits interesting predictive potential.
