HEATING AND FLUCTUATIONS IN ELASTOPLASTIC SYSTEMS

Starting from the equations of motion of a simple system possessing th e properties of elastic and plastic bodies, we construct its Lagrangia n and Hamiltonian functions and also the Rayleigh dissipation function . This allows us to find the rate of heating of the system and to anal yze the fluctuations of basic observables. Introducing into the Hamilt on-Rayleigh equation of motion a random force producing on average the same effects as a dissipation function, we arrive first at the Langev in equations describing the fluctuations and then at a kinetic equatio n for the distribution function defined in the space of the collective variables. In this way a rather general scheme is established for sol ving dynamical problems in different and more complex elastoplastic sy stems, in nuclear physics and maybe even in physics of molecules and a tomic clusters. In a preliminary study, the model is applied to estima te the probability of the quasi-fission process coming from the therma l fluctuations of the nuclear shape. (C) 1998 Elsevier Science B.V.