Catálogo de publicaciones - libros

In this paper an approach for friction coefficient prognosis for the Groschwheel is presented. Since the solid rubber wheel (80 mm diameter) represents a simpli fied tyre model this contribution helps to investigate the rolling friction process and especially the feasibility and limitations of the automotive friction prognosis. The grip information is derived from influence parameters like road state, velocity, temperature etc. The methodical innovation of the approach proposed consists in the use of an artificial neural network as data based model that performs multi dimensional interpolation in the learning stage. The operating stage consists of common mathematical operations with low computational effort.

In Civil Engineering soils may be reinforced by different structures. Wires will interest us. Mixed sand and wire, known as , may be modelled as a continuous medium with classical behaviour laws [6] or with more sophisticated ones taking into account remote interactions [1].

A unified interface constitutive law for the description of contact and decohesion at bi-material interfaces is proposed. To this aim, a synthesis of the nonlinear models pertaining to Fracture and Contact Mechanics is presented. The issues pertinent to the implementation within the FE discretization framework are also discussed in detail. Finally, a numerical example of fatigue modeling at the mesoscopical level in a fiber-reinforced composite is provided.

The elasto-plastic normal contact of fractal surfaces is numerically investigated using a halfspace model. Artificial surface data are generated using the structure function, to study the influence of different surface parameters with respect to the load-area relationship and the load-gap relationship. The simulations show that for realistic surface parameters the deformation is always in the plastic range.

In this work a homogenization method presented by Bandeira et al [2,3,4] is enhanced in order to obtain by numerical simulation the interface law for the normal contact pressure based on statistical surface models. For this purpose elasticplastic behavior of the asperities is considered. Statistical evaluations of numerical simulations lead to a constitutive law for the contact pressure. The resulting law compared with other laws stemming from analytical investigations, like those presented by Greenwood Williamson [11] and Yovanovich [19, 32]. The non-penetration condition and the interface model for contact that takes into account the surface microstructure are investigated in detail.

Boundary layers are studied which are induced by micro-periodic boundary conditions as, for instance, in the case of contact of rough bodies. The adopted micromechanical framework is outlined briefly and two applications are provided. The finite element method is applied to study the normal contact compliance in the elasto-plastic regime, and the effect of macroscopic in-plane strain on contact response is analyzed. Secondly, a simple model for prediction of the effective heat transfer coefficient in steady-state conditions is presented.

A numerical model based on the solution of the normal contact between elastic half-spaces and subsequent post-processing according to the Mindlin and Deresiewicz solution for cyclic tangential loading is presented. Thanks to a recent extension of the Cattaneo-Mindlin analogy to the solution of tangential contact between non-convex domains, the proposed approach enables the study of cyclic micro-slip and energy dissipation between elastic bodies with general shapes in contact. In order to make the procedure straightforward and as general as possible, a non-dimensional formulation, based only on the normal contact load displacement curve, is proposed. The cyclic behaviour of the tangential contact of self-affine fractal surfaces, like those generated by fracture of concrete or rock, is described with several examples.

The stability of the equilibrium states of a simple mechanical system with unilateral contact and Coulomb friction is explored. When the external force is constant, the equilibrium states are completely determined by the mechanical properties of the system and the stability or instability of each of these states is proved. When the external force varies in time two stability results are given.

In this paper we discuss the stability of quasi-static paths of a single degree of freedom linearly elastic system with Coulomb friction and known normal force. A common and useful approximation for the equations that govern the slow evolution of many mechanical systems is to neglect inertia effects in the dynamic balance equations, and replace them by static equilibrium equations. Slow evolutions calculated with this approximation are called quasi-static evolutions. The relationship of this issue with the theory of singular perturbations has been established in [1], where the existence of fast (dynamic) and slow (quasi-static) time scales was recognized: a change of variables is performed that replaces the (fast) physical time by a (slow) loading parameter , whose rate of change with respect to time, = /, is decreased to zero. This change of variables leads to a system of dynamic differential equations or inclusions that defines a singular perturbation problem: the small parameter multiplies some of the highest order derivatives in the system. The concept of stability of quasi-static paths used here is essentially a continuity property relatively to the size of the initial perturbations (as in Lyapunov stability) and to the smallness of the rate of application of the external forces, (as in singular perturbation problems). This study applies for the first time to a nonsmooth context, the definition of stability of quasi-static paths, recently proposed by Martins et al. ([2], [3]).

Discomfort problems due to the noise emittence of braking systems in trains have suggested recently several mechanical analyses. This paper gives some of our results obtained from the numerical modelling of TGV brakes in relation with some experimental data. The numerical discussion is based upon the Coulomb’s law of contact with a constant coefficient of friction. A dynamic stability analysis enables us to show the loss of stability by flutter of the steady sliding response of the pad on the brake disks. We will present the numerical calculation of the unstable modes for the entire brake system which is a large structure. From an experimental point of view, the modal parameters have been measured for the brake system. We will present also the measures done at the train station giving the close-field acoustic. A comparison between these data and the numerical calculation help us to understand what happen during squeal.