On rate{independent hysteresis models Alexander Mielke Florian Theil Mathematisches Institut A Mathematics Institute UniversitÄat Stuttgart University of Warwick D{70569 Stuttgart Coventry CV4 7AL, U.K.
[email protected] [email protected] 5 April 2001 / revised 21 September 2001 1 Introduction This paper deals with a general approach to the modeling of rate{independent processes which may display hysteretic behavior. Such processes play an important role in many applications like plasticity and phase transformations in elastic solids, electromagnetism, dry friction on surfaces, or in pinning problems in superconductivity, cf. [Vis94, BrS96]. The evolution equations which govern those processes constitute the limit problems if the inuence of inertia and relaxation times vanishes, i.e. the system rests unless the external loading is varied. Only the stick{slip dynamics is present in the Cauchy prob- lem, this means that the evolution equations are necessarily non{autonomous. Although the solutions often exhibit quite singular behavior, the reduced framework o®ers great advantages. Firstly the amount of modelling can be reduced to its absolute minimum. More importantly, our approach is only based on energy principles. This allows us to treat the Cauchy problem by mainly using variational techniques. This robustness is necessary in order to study problems which come from continuum mechanics like plasticity, cf. [Mie00, CHM01, Mie01]. There the potential energy is invariant under the group of rigid body rotations SO(d) where d 1; 2; 3 is the dimension. This invariance implies that 2 f g convexity can almost never be expected and more advanced lower semicontinuity results (like polyconvexity) are required to assure the existence of solutions for a time discretized version of the problem.