In the last two decades a large amount of evidence have been collected by the research group of Professor Carpinteri about compositional changes and neutron emissions in solid bodies subjected to fracture tests. The cause of the compositional variations of medium-weight elements in the analysed specimens and of the revealed anomalous neutron radiations, which clearly indicated the nuclear nature of the phenomenon, was detected in the effect of nanoscale perturbations and mechanical instabilities in the solid matter. The development or the coalescence of the nanoscale instability was found to produce TeraHertz pressure waves (defined as “phonons”), that expand throughout the specimen crystal lattice and that are believed to be able to establish resonance with the Debye frequencies of the medium-weight elements, producing consequent fission reactions usually called LENR.