Dipartimento di Meccanica

ABSTRACT Weight reduction becomes increasingly important in design of engine components, but in the same time designers have to improve engine efficiency increasing in-cylinder pressure and temperature. The paper presents a description of literature damage models and life assessment methods for thermo-mechanical fatigue. The aim is to investigate the life prediction results in the case of a specific load history such as thermal and mechanical loading conditions upon an exhaust manifold.

Abstract In the present paper some different monitoring techniques are investigated. By means of an experimental test rig, different methodologies are evaluated in order to suggest a useful monitoring technique for bearing defects. This analysis points out that Crest Factor, RMS and Peak Value methods are similar and provide limited information. The Cepstrum is able to identify problems in machinery components, but it does not provide advantages in rolling bearing defects detection.

ABSTRACT The paper presents the design of a new strain gauge transducer together with the analysis based on experimental signals carried out on a section of B category Italian railway line. The transducer is installed in a 29 mm hole made in rail web; it measures vertical and lateral forces that vehicles exchange with rail. The most important innovation of the transducer is the capability to separate vertical contribution from lateral one in a no invasive way.

Abstract In this paper a multiscale numerical simulator is described. The simulator has been developed with the aim of giving to surgeons and cardiologists a tool to evaluate the effect on the whole cardiovascular system before a surgical or pharmaceutic intervention. The system has morphological patient data as input and gives pressure and flow time dependent data as output. It is also possible to introduce finite element models interfacing with the lumped parameter simulator with the aim of obtaining the local contour of flow.

Abstract Theory of curve crossing and curve veering phenomena is well known in structural dynamics, but only few papers have used test bench to demonstrate and validate this eigenvalues behaviour. The aim of this paper is to present a theoretical and experimental analysis on a nonsymmetric experimental structure with eigenvalues curve veering and crossing phenomena.

The tribology of cam-roller follower conjunction is highly dependent on the engine type and working conditions. The interface experiences transient conditions due to variations in contact geometry and kinematics, as well as loading. These lead to instantaneous and capricious behavior of the lubricant through the contact, which determines the regime of lubrication. The resulting frictional characteristics are affected by the shear of the lubricant film and the interaction of rough surfaces themselves. Thus, specific analysis is required for any intended new engine configuration. Therefore, a tribo-dynamic model, combining valve train dynamics, contact kinematics and tribological analysis is required. An important issue is to develop a simple yet reliable and representative model to address the above mentioned pertinent issues. This would make for rapid scenario-building simulations which are critical in industrial design time-scales. The current model has been developed in response to the above mentioned requirements. A multi-body dynamic model for the valve train system based on the key design parameters is developed and integrated with an EHL tribological model for the cam-follower contact. To keep the model simple and easy to use and to avoid time-consuming computations, the analytical EHL model makes use of Grubin's oil film thickness equation. Viscous and boundary contributions to friction are obtained as these account for the losses which adversely affect the engine fuel efficiency.

In the paper the Cell Method, a discrete method for solving partial differential equations, is applied to a time dependent thermo-mechanical problem. The basic equations are developed with a multiphysics approach and results, both in two-dimensional and tree- dimensional models, are presented. By means of the comparison with finite element approach, some advantages of the proposed methodology are highlighted, in particular quick model construction, capability to separate thermal strain from the mechanical one and, as a consequence, the capability to model the strain and stress evolution in a time dependent problem, considering possible mutual effects between thermal and mechanical fields.

The growing necessity of accuracy in analyzing engineering problems requires more detailed and sophisticated models. Those models can include mul- tiphysics interactions, that, sometimes, are highly nonlinear and the application of the superposition principle is then not possible. The cell method can be suitably used to study nonlinear multiphysics problems, because its theoretical framework for the physical laws is intrinsically multiphysics. In this way it is possible to take into account the mutual effects between different physics. Within the cell method framework, the coupling terms can be directly formulated in terms of the global variables used for the solution of the elementary problems. In this way it is possible to solve the coupled problem in a single solver run. In this paper a nonlinear pro- cedure for elastostatic analysis with cell method is developed and the Fixed Point technique is applied to a 1D two-node cell and to a 3D four-node tetrahedral cell. The procedure is numerically and experimentally validated. After the theoretical part, a nonlinear thermo-mechanical analysis of an exhaust manifold is presented as case-study.

Nonlinear rotors are often considered as potential sources of chaotic vibrations. The aim of the present paper is that of studying in detail the behaviour of a nonlinear isotropic Jeffcott rotor, representing the simplest nonlinear rotor. The restoring and damping forces have been expanded in Taylor series obtaining a 'Duffing-type'equation. The isotropic nature of the system allows circular whirling to be a solution at all rotational speeds. However there are ranges of rotational speed in which this solution is unstable and other, ...