Discrete numerical investigation of the ratcheting phenomenon in granular materials

Several relevant geotechnical works, such as railway and road embankments, offshore foundations and vibrating machine foundations, are affected by the progressive accumulation of irreversible settlements. These latter represent the macroscopic evidence of the progressive rearrangement of particles under cycling loading, which is commonly referred to, in the literature, as ratcheting. This phenomenon is well known, but it is quite difficult to describe it by means of an appropriate constitutive model. As a consequence, the evaluation of durability of the aforementioned structures remains an open problem. In this article, the phenomenon will be approached by employing a Distinct Element model capable of describing the evolution of the microstructure induced by cyclic mechanical perturbations. Several analyses are performed in order to stress the influence of both the stress level and loading history on the mechanical response of a numerical model of a sand specimen. The numerical analyses are intended to provide an experimental background for conceiving a simplified macro approach based on generalised plasticity theory. In particular by means of probe test the plastic potential and the hardening parameters will be defined as a function of the current stress state and loading history.     

Springback compensation in deep drawing applications

This work deals with the problem of springback compensation in sheet metal forming. Satisfactory results can be achieved by performing “die compensation”: the die is modified pretending to obtain a different configuration at the end of the punch stroke, but in order that the final piece coincides with the desired one after the deformation due to springback. Empirical die compensation has nowadays been replaced by numerical simulation, but the inverse problem that needs to be solved is non-trivial since the transformation from the modified geometry of the die and the final piece obtained from it implies a very complex FEM simulation. In this work we set the whole process of springback compensation on solid physical and mathematical grounds. An optimization algorithm based on the Gauss-Newton method is proposed to deliver automatic die compensation and its performance is investigated on some test cases.     

Viscoelastic Solids of Exponential Type. II. Free Energies,Stability and Attractors

The asymptotic behavior for solutions of the semilinear motion equation of a linear viscoelastic solid of exponential type (VSET) is studied and the existence of a global attractor is proved. These results are obtained by means of a suitable class of quadratic free energies defined on the minimal state space and making use of semigroup techniques. This is the second part of a plan which was started in a previous paper [6] by the study of state-space representation, minimality and controllability for VSET.     

Periodic Solutions of Symmetric Perturbations of Gravitational Potentials

It is shown that for certain symmetric perturbations of gravitational potentials in the space, which admit two first integrals of motion, a circular solution of the unperturbed system with inclination different from 0 and π gives rise to a periodic solution of the reduced dynamics which is defined in the quotient space of the action by the subgroup that fixes the symmetry axis. In the planar case, if we assume that the system admits a first integral of motion which is also symmetric with respect to the origin, then it is shown that each circular solution of the unperturbed problem gives rise to a periodic solution of the perturbed system.     

Large deviation approach to non equilibrium processes in stochastic lattice gases

We present a review of recent work on the statistical mechanics of non equilibrium processes based on the analysis of large deviations properties of microscopic systems. Stochastic lattice gases are non trivial models of such phenomena and can be studied rigorously providing a source of challenging mathematical problems. In this way, some principles of wide validity have been obtained leading to interesting physical consequences.     

Fast deprotection of phenoxy benzyl ethers in transfer hydrogenation assisted by microwave

Phenoxy benzyl ethers are easily and quickly deprotected in the presence of ammonium formate and microencapsulated Pd(0)EnCat with the assistance of microwave irradiation. This procedure can be applied in the presence of other functional groups as well. The described protocol is particularly convenient for the preparation in a parallel and automatic fashion of libraries of compounds possessing a phenol type moiety.     

Classification of all irreducible unitary representations of the stabilizer of the horicycles of a tree

In this paper we describe all irreducible unitary representations of the stabilizer of the horicycles associated with an end of a homogeneous tree. This work is partially supported by G.N.A.F.A. of the C.N.R., Italy.