Filippo Cianetti

Random Loads Fatigue: The Use of Spectral Methods Within Multibody Simulation

The evaluation of the fatigue damage performed by using the Power Spectral Density function (PSD) of stress and strain state is proving to be extremely accurate for a family of random processes characterized by the property of being stationary. The present work’s original contribution is the definition of a methodology which extracts stress and strain PSD matrices from components modelled using a modal approach (starting from a finite element modelling and analysis) within mechanical systems modelled using multibody dynamic simulation and subject to a generic random load (i.e. multiple-input, with partially correlated inputs). This capability extends the actual stress evaluation scenario (principally characterised by the use of finite element analysis approach) to the multibody dynamic simulation environment, more powerful and useful to simulate complex mechanical systems (i.e. railway, automotive, aircraft and aerospace systems). As regards the fatigue damage evaluation, a synthesis approach to evaluate an equivalent stress state expressed in terms of the PSD function of Preumont’s “equivalent von Mises stress (EVMS)”, starting from the complete stress state representation expressed in terms of PSD stress matrix and easily usable in the consolidated spectral methods, is proposed. This approach allows and has allowed the use of the above methods such as the Dirlik formula as a damage evaluation method. An additional result is the conception and implementation of a frequency domain method for the component’s most probable state of stress, allowing quickly identification of the most stressed and damageble locations. The described methodologies were developed and embedded into commercial simulation codes and verified by using as a test case a simple reference multibody model with a simple flexible component.Copyright

A procedure for the virtual evaluation of the stress state of mechanical systems and components for the automotive industry: Development and experimental validation

This paper is part of the research activity led by the Machine Design Group of the University of Perugia, whose main objective was to set up and develop modelling criteria and methods for dynamic simulation of mechanical systems including flexible components. The activity was finalized to the design of systems using virtual prototyping, driving the modelling accuracy to simulate real functioning conditions of the system. It was therefore possible to extract realistic and directly usable information for fatigue component design using any fatigue damage evaluation criterion. In particular, the present work was developed with the cooperation of the research centre Elasis S.C.p.a. and concerns the set-up of methods and criteria for the development of the virtual prototype of an autovehicle, with the aim of simulating the conditions of sign-off tests. This aspect of virtual prototyping has a relevant importance. The sign-off tests of the vehicle, in fact, are standardized and the results obtained constitute one of the main sources of information for product development using physical prototypes. The industry is interested in reducing, as much as possible, the tests on prototypes by developing predictive virtual prototyping methods. The results obtained in this paper show an optimum correspondence between numerical and experimental simulations and demonstrate that time-domain stress/strain numerical recovery in critical points of the chassis is not only feasible but leads to quantitative information directly usable by fatigue damage evaluation methods.

The use of spectral method for fatigue life assessment for non-gaussian random loads

Abstract The well-known problem with the fatigue lifetime assessment of non-Gaussian loading signals with the use of spectral method has been presented in the paper. A correction factors that transform the non-Gaussian signal into an equivalent Gaussian signal proposed by Bracessi et al. (2009) has been used for the purpose of lifetime calculations together with Palmgren-Miner Hypothesis. The calculations have been performed for the 10HNAP steel under random non-Gaussian load with four dominating frequencies. The signal has been generated on the test stand SHM250 for random tension-compression tests. The results with zero and non-zero mean stresses have been used to calculate the fatigue life with the frequency domain method based on Dirlik’s model and with a time domain method with the use of the rainflow cycle counting algorithm. The obtained calculation results have been compared with experimental results.

Optimisation of the process of experimental sign off of a vehicle

This paper describes the designing process of durability sign off tests for new vehicles. The reliability tests must be based on experimental measures performed on physical prototype, subjected to tests on public roads. These data, translated into Rainflow domain, will be used to statistically define the target. Then the prototype is tested on test tracks so that a particular combination of them can be selected to define a sequence that can match the target. An IVECO vehicle will be presented as test-case. This activity is an outcome of the cooperation between the Industrial Engineering Department at the Perugia University and IVECO Testing Labs and Methodologies of Turin.

Motion sickness. Part II: experimental verification on the railways of a model for predicting motion sickness incidence

This is the second part of a two-part paper in which a new theoretical approach for predicting motion sickness is experimentally validated by field measurements. In this paper, an extended research activity aimed at the validation of a theoretical model (developed by the authors to evaluate the MSI index) is illustrated. The motion sickness incidence(MSI) index represents the percentage of people that vomit within a certain time interval and was defined to evaluate the passengers’ response to low frequency motions. The activity was aimed to a rail scenario and it was conducted together with a well-known company in the railway industry. The rail tests were performed in Slovenia during 2005 (European research project ‘FACT: Fast and Comfortable Trains’). In the paper, a comparison is made between the results, expressed in terms of MSI values and time histories, obtained from experimental results (subjective measures acquired using questionnaires) and by the authors’ theoretical model (starting from experimental objective measures acquired in the form of acceleration time histories).

Analytical Model, Multibody Simulation and Validation Tests for Dynamical Instability Reduction of a Grinding Machine With Dampers

The subject of the present paper is the dynamic instability (chatter) of machine tools. The chatter is a self-regenerative oscillatory phenomenon related to the tool-work piece interaction during the process; that leads to an incorrect surface finishing of work piece. In big machine tools passive damping components are often introduced in order to reduce the chatter. Those passive components have to be tuned to the natural frequency of chatter vibrations, measured experimentally or predicted theoretically. In this paper the reduction of chatter for a planar grinding machine is described. At first, a theoretical model for the prediction of the general chatter for planar milling will be described through two lumped parameters and a multi body numerical model. Moreover the correlation between the theoretical model and experimental measures in terms of receptance will be presented. Two different kinds of passive damper systems will be theoretically introduced. In the end, the experimental results for chatter reduction obtained with the passive dampers introduction will be shown.© 2011 ASME

A Methodology for Active Control of Multibody Test-Rig for Virtual Simulation of Vehicles Through Acceleration Inputs

Dynamic simulation through Multibody Systems is more and more used for the design of new industrial products to avoid long and expensive experimental tests on them. The research presented in this paper deals with the realization of an actively controlled virtual test-rig, functional for comfort and durability tests of entire vehicles. The virtual test rig, is capable to impose any experimental acceleration to the centers of the four vehicle wheels through four imposed displacements to the actuators. The active control is implemented with four independent degrees of freedom, one for every actuator. In the paper the active controller logic and its automatic setup will be fully explained. Moreover it will be also explained how to avoid the aliasing and the so called “random signal drift” problems. Finally the results of some virtual pave road experiments to an existing vehicle will be presented.Copyright

Boron Effect on Hardenability of High Thickness Forged Steel Materials

To fulfill the industrial demand of forged steels with high mechanical and microstructural requirements coupled with reduced cost, the possibility to decrease the content of Mo and other elements has been evaluated. In order to do that, the effect of boron addition (up to 30 ppm) on the steel hardenability has been investigated on two steels with different chemical composition at laboratory scale. In particular, the steel chemical composition has been designed in order to make effective the B addition in terms of hardenability. Two 80 kg ingots cast by a vacuum induction melting plant have been hot rolled by a pilot mill. The effect of B addition on hardenability has been evaluated and compared to that of steel for same application but without B. Results show an improvement of hardenability if 30 ppm B are added even if a Mo reduction is performed.

Numerical Modelling and Simulation of the Hot Rolling Mill Process

In the design of the rolling mill plants, it is fundamental to study the behaviour of the deformation process to assess the main process variables (such as torque and rolling force) in all operating conditions.In this paper, a finite element model is developed and the numerical simulations of the plastic deformation process, in the hot rolling mill of AISI 304 stainless steel, are shown. In the proposed model a Multilinear Isotropic Hardening behaviour of material has been assumed and true stress-true strain curves have been found, taking into account temperature and strain rate. Numerical results are compared with experimental measures regarding an existing hot rolling mill plant.

The use of the PCT index in railway motion sickness incidence evaluation

The aim of this paper is to define an evaluation method to quantify the index of motion sickness incidence (MSI) in railway motion conditions. This index is widely used in the literature to quantify illness symptoms that occur as a result of generic low-frequency motions (kinetosis). In fact, only one standard exists (ISO 2631) and it was defined for general motion and in particular for vertical acceleration motion conditions. No standards have been written that consider the conditions experienced in railway motion. This paper reports an evaluation approach that can be used to examine illness symptoms experienced during rail trips and involves indices and methods well-known in the rail industry. In particular the proposed approach involves the P ct index (EN 12299: Comfort index on curve transition) and some weighting curves for the filtering of accelerometer signals that are also specified in railway regulations (EN 12299, ISO 2631). The proposed method, that is consistent with a theoretical model that has been reported in the literature, allows the MSI index to be obtained as a function of travel time and/or track distance. The model is validated through a comparison with experimental data available in literature and with experimental data recorded for a tilting train during tests performed in Slovenia.