1,721,086 research outputs found
Valutazione del danno in gruppi di taglio ad impatto
No full textmanutenzione predittiva nelle macchine automatiche.
una applicazione di analisi del segnale proveniente da gruppi di taglio cart
A model for diffusive and displacive phase transitions: Thermo-chemo-mechanical coupling effects
No full textA diffuse interface phase field model is proposed for the unified analysis of diffusive and displacive phase transitions under nonisothermal conditions. Two order parameters are used for the description of the phenomena: one is related to the solute mass fraction and the other to the strain. The model governing equations come from the balance of linear momentum, the solute mass balance (which will lead to the Cahn-Hilliard equation) and the balance of internal energy. Thermodynamic restrictions allow to define constitutive relations for the thermodynamic forces and for
the mechanical and chemical dissipations.
Numerical tests carried out at different values of the initial temperature show that the model is able to describe the main features of both the displacive and the diffusive phase transitions,
as well as their effect on the temperature
Laser processing of thin films for industrial packaging
No full textSingle layer thin-film materials such as aluminum, polyethylene, polypropylene, and their multi-layer combinations such as aluminum-paper have been exposed to different laser radiation. A wide number of samples have been processed with 10 - 12.5 ns IR and Green, and 500 - 800 ps IR laser radiation at different translating speeds ranging from 50 mm/s to 1 m/s. High quality incisions have been obtained for all tested materials within the experimental conditions. The presented results provide the necessary parameters for an efficient cut and processing of the tested materials, for the employment of pulsed laser sources in the packaging industry, allowing the laser to prevail in lieu of more costly and energy intensive methods. © 2014 SPIE
Automated Structural Composites Components Production for Taping
No full textQuesta dissertazione tratterà l’argomento dello studio di metodi di progettazione e processi tecnologici innovativi per l’industrializzazione in medio-grande serie di componenti strutturali in materiale composito.
L’interesse della ricerca verso questo ambito è suscitato dai notevoli vantaggi che l’utilizzo di materiali dall’alto rapporto prestazioni meccaniche/peso danno nella ricerca di elevate prestazioni in applicazioni sportive e diminuzione dei consumi ed emissioni inquinanti in mezzi di trasporto di grande serie.
Lo studio di componenti in materiale composito è caratterizzato dalla peculiarità di non poter disgiungere la progettazione della geometria della parte da quella del materiale e del processo, ed in questo senso nella figura del progettista si vanno a riassumere sinergicamente competenze riguardanti i tre ambiti.
Lo scopo di questo lavoro è la proposizione di una metodologia di progettazione e produzione di componenti strutturali che permetta l’utilizzazione ottimale della natura fibrosa del materiale composito sia dal punto di vista del trasferimento dei
carichi tra diversi componenti, sia dal punto di vista del processo di laminazione che avviene per nastratura automatizzata. Lo studio è volto a mostrare in quali termini tale tecnologia sia potenzialmente in grado di superare i vincoli di forma ed i limiti di efficienza meccanica delle giunzioni tra le parti e di garantire maggiore produttività e costi inferiori rispetti ai diversi metodi di produzione che rappresentano oggi lo stato dell’arte dell’industrializzazione in medio-grande serie.
Particolare attenzione verrà posta sull’utilizzo della tecnologia oggetto di studio per la produzione di telai automobilistici.This dissertation will address the topic of the study of methods of design and technological innovation for the industrialization processes in medium to large number of structural components made of composite materials.
The focus of research into this area is caused by the considerable advantages that the use of materials from mechanical performance ratio / weight loss in the search for high performance sports applications and reduce fuel consumption and pollutant emissions in transports.
The study of composite materials is characterized by the peculiarity of not being able to separate the design of the part geometry from that of the material and process, and in this sense in the figure of the designer is going to summarize synergistically skills on the three areas.
The purpose of this work is the proposition of a methodology of design and production of structural components which allows optimum utilization of the fibrous nature of the composite material both from the point of view of the transfer of loads between different components, both from the point of view of the rolling process which takes place by taping automated. The study is intended to show in what way this technology has the potential to overcome the constraints of the form and the limits of mechanical efficiency of the junctions between the parties and to ensure higher productivity and lower costs to comply with different production methods, which have become the state of industrialization in medium to large series.
Particular attention will be placed on the use of the technology being studied for the production of automotive frames
The Dynamics of Passive Torsional Fatigue Test Rigs: Innovative Applications of Universal Joints
No full textThe dynamics of a passive back-to-back test rig have been characterised, leading to a multi-coordinate approach for the analysis of arbitrary test configurations. Universal joints have been introduced into a typical pre-loaded back-to-back system in order to produce an oscillating torsional moment in a test specimen. Two different arrangements have been investigated using a frequency-based sub-structuring approach: the receptance method. A numerical model has been developed in accordance with this theory, allowing interconnection of systems with two-coordinates and closed multi-loop schemes. The model calculates the receptance functions and modal and deflected shapes of a general system. Closed form expressions of the following individual elements have been developed: a servomotor, damped continuous shaft and a universal joint. Numerical results for specific cases have been compared with published data in literature and experimental measurements undertaken in the present work. Due to the complexity of the universal joint and its oscillating dynamic effects, a more detailed analysis of this component has been developed. Two models have been presented. The first represents the joint as two inertias connected by a massless cross-piece. The second, derived by the dynamic analysis of a spherical four-link mechanism, considers the contribution of the floating element and its gyroscopic effects. An investigation into non-linear behaviour has led to a time domain model that utilises the Runge-Kutta fourth order method for resolution of the dynamic equations. It has been demonstrated that the torsional receptances of a universal joint, derived using the simple model, result in representation of the joint as an equivalent variable inertia. In order to verify the model, a test rig has been built and experimental validation undertaken. The variable inertia of a universal joint has lead to a novel application of the component as a passive device for the balancing of inertia variations in slider-crank mechanisms
A model for diffusive and displacive phase transitions in steels
No full textHeat treatment of steels is a process of fundamental importance in tailoring the properties of a material to the desired application; developing a model able to describe such process would allow to predict the microstructure obtained from the treatment and the consequent mechanical properties of the material.
A steel, during a heat treatment, can undergo two different kinds of phase transitions [p.t.]: diffusive (second order p.t.) and displacive (first order p.t.); in this thesis, an attempt to describe both in a thermodynamically consistent framework is made; a phase field, diffuse interface model accounting for the coupling between thermal, chemical and mechanical effects is developed, and a way to overcome the difficulties arising from the treatment of the non-local
effects (gradient terms) is proposed.
The governing equations are the balance of linear momentum equation, the Cahn-Hilliard equation and the balance of internal energy equation. The model is completed with a suitable description of the free energy, from which constitutive relations are drawn.
The equations are then cast in a variational form and different numerical techniques are used to deal with the principal features of the model: time-dependency, non-linearity and presence of high order spatial derivatives.
Simulations are performed using DOLFIN, a C++ library for the automated solution of partial differential equations by means of the finite element method; results are shown for different test-cases. The analysis is reduced to a two dimensional setting, which is simpler than a three dimensional one, but still meaningful
Sulla ricerca del minimo dei consumi per vetture sportive
No full textLa ricerca oggetto di questa tesi, come si evince dal titolo stesso, è volta alla riduzione dei consumi per vetture a forte carattere sportivo ed elevate prestazioni specifiche. In particolare, tutte le attività descritte fanno riferimento ad un ben definito modello di vettura, ovvero la Maserati Quattroporte.
Lo scenario all’interno del quale questo lavoro si inquadra, è quello di una forte spinta alla riduzione dei cosiddetti gas serra, ossia dell’anidride carbonica, in linea con quelle che sono le disposizioni dettate dal protocollo di Kyoto. La necessità di ridurre l’immissione in atmosfera di CO2 sta condizionando tutti i settori della società: dal riscaldamento degli edifici privati a quello degli stabilimenti industriali, dalla generazione di energia ai processi produttivi in senso lato. Nell’ambito di questo panorama, chiaramente, sono chiamati ad uno sforzo considerevole i costruttori di automobili, alle quali è imputata una percentuale considerevole dell’anidride carbonica prodotta ogni giorno e riversata nell’atmosfera.
Al delicato problema inquinamento ne va aggiunto uno forse ancor più contingente e diretto, legato a ragioni di carattere economico. I combustibili fossili, come tutti sanno, sono una fonte di energia non rinnovabile, la cui disponibilità è legata a giacimenti situati in opportune zone del pianeta e non inesauribili. Per di più, la situazione socio politica che il medio oriente sta affrontando, unita alla crescente domanda da parte di quei paesi in cui il processo di industrializzazione è partito da poco a ritmi vertiginosi, hanno letteralmente fatto lievitare il prezzo del petrolio. A causa di ciò, avere una vettura efficiente in senso lato e, quindi, a ridotti consumi, è a tutti gli effetti un contenuto di prodotto apprezzato dal punto di vista del marketing, anche per i segmenti vettura più alti.
Nell’ambito di questa ricerca il problema dei consumi è stato affrontato come una conseguenza del comportamento globale della vettura in termini di efficienza, valutando il miglior compromesso fra le diverse aree funzionali costituenti il veicolo.
Una parte consistente del lavoro è stata dedicata alla messa a punto di un modello di calcolo, attraverso il quale eseguire una serie di analisi di sensibilità sull’influenza dei diversi parametri vettura sul consumo complessivo di carburante.
Sulla base di tali indicazioni, è stata proposta una modifica dei rapporti del cambio elettro-attuato con lo scopo di ottimizzare il compromesso tra consumi e prestazioni, senza inficiare considerevolmente queste ultime. La soluzione proposta è stata effettivamente realizzata e provata su vettura, dando la possibilità di verificare i risultati ed operare un’approfondita attività di correlazione del modello di calcolo per i consumi. Il beneficio ottenuto in termini di autonomia è stato decisamente significativo con riferimento sia ai cicli di omologazione europei, che a quelli statunitensi. Sono state inoltre analizzate le ripercussioni dal punto di vista delle prestazioni ed anche in questo caso i numerosi dati rilevati hanno permesso di migliorare il livello di correlazione del modello di simulazione per le prestazioni.
La vettura con la nuova rapportatura proposta è stata poi confrontata con un prototipo di Maserati Quattroporte avente cambio automatico e convertitore di coppia. Questa ulteriore attività ha permesso di valutare il differente comportamento tra le due soluzioni, sia in termini di consumo istantaneo, che di consumo complessivo rilevato durante le principali missioni su banco a rulli previste dalle normative.
L’ultima sezione del lavoro è stata dedicata alla valutazione dell’efficienza energetica del sistema vettura, intesa come resistenza all’avanzamento incontrata durante il moto ad una determinata velocità. Sono state indagate sperimentalmente le curve di “coast down” della Quattroporte e di alcune concorrenti e sono stati proposti degli interventi volti alla riduzione del coefficiente di penetrazione aerodinamica, pur con il vincolo di non alterare lo stile vettura.The present research is focused completely on the fuel consumption reduction for a high performance sports vehicle, specifically, the Maserati Quattroporte. The scenario in which this research takes place is that of a strong push to reduce greenhouse gases (notably, carbon dioxide, CO2), in accordance with the Kyoto protocol’s statements. The necessity in containing CO2 emissions are conditioning each field of our society: from heating of private houses to industrial buildings; from energy generation to production processes in general. Within this context, automotive OEM ( Original Equipment Manufacturer ) are clearly called on because of the high amount of CO2 produced every day by automobiles all over the world.
Beside the delicate issue of emissions, there is another, perhaps even more urgent and contingent one pertaining to the socio-economic situation: fossil fuels, are recognised as a non-renewable source of energy and their availability is connected with specific areas of the world.
Moreover, the socio-political situation that Middle East is facing and the increasing demand due to growth of new markets, have recently made the price of oil rise at an alarming rate. For this reason, energy efficiency in general and low fuel consumption are becoming evermore appreciated and important marketing factors, even for the high class vehicles.
During this work, the fuel consumption problem has been approached as a consequence of the overall car efficiency, searching for the best trade off among the different functional areas constituting the whole vehicle. An important part of the research was spent on the development and optimisation of a simulation model, which allowed evaluation and sensitivity of different parameters which influence the vehicles fuel consumption to be investigated. Several calculations were performed and their results were exploited in order to suggest a modification to the original gear ratios. The new ratios proposed for the electro-actuated transmission, were thought to best optimise the compromise between fuel consumption and performance, with special attention not to penalise the latter too much. The new solution was actually built and tested on a prototype which showed an important benefit in terms of fuel consumption reduction, both in the European and American Standard cycles ( NEDC, FTP 75 ). The experimental results were used to improve the correlation of the theoretical model whose global reliability has proved to be efficient and robust.
The new gear ratios were also evaluated from the point of view of car performance and the global response was definitely acceptable. The accuracy of the calculation model was increased further by these new activities and due to the high amount of experimental information collected.
Another part of the work was dedicated to the comparison between the new version of electro-actuated transmission and a prototype Maserati Quattroporte with automatic drive and torque converter. Thanks to this activity it was possible to analyse the different behaviour of the two solutions in terms of instantaneous and global fuel consumption during the standard tests.
The final section was focused on the evaluation of the energy efficiency of the vehicle system referring to the resistance that the car has to overcome in order to maintain a certain constant speed. The “coast down” curves for the Maserati Quattroporte and for some other models of the same market segment were acquired experimentally. This enabled suggestions to improve the aerodynamic resistance to be made, with the strict constraint of keeping the vehicle style and outer appearance absolutely unchanged
High-Speed Laser Processing of Thin Single and Multi-Layer Films
No full textTheoretical models are developed for the continuous-wave and pulsed laser incision and cut of thin single and multi-layer films. A one-dimensional steady-state model establishes the theoretical foundations of the problem by combining a power-balance integral with heat flow in the direction of laser motion. In this approach, classical modelling methods for laser processing are extended by introducing multi-layer optical absorption and thermal properties. The calculation domain is consequently divided in correspondence with the progressive removal of individual layers. A second, time-domain numerical model for the short-pulse laser ablation of metals accounts for changes in optical and thermal properties during a single laser pulse. With sufficient fluence, the target surface is heated towards its critical temperature and homogeneous boiling or "phase explosion" takes place. Improvements are seen over previous works with the more accurate calculation of optical absorption and shielding of the incident beam by the ablation products. A third, general time-domain numerical laser processing model combines ablation depth and energy absorption data from the short-pulse model with two-dimensional heat flow in an arbitrary multi-layer structure. Layer removal is the result of both progressive short-pulse ablation and classical vaporisation due to long-term heating of the sample. At low velocity, pulsed laser exposure of multi-layer films comprising aluminium-plastic and aluminium-paper are found to be characterised by short-pulse ablation of the metallic layer and vaporisation or degradation of the others due to thermal conduction from the former. At high velocity, all layers of the two films are ultimately removed by vaporisation or degradation as the average beam power is increased to achieve a complete cut. The transition velocity between the two characteristic removal types is shown to be a function of the pulse repetition rate. An experimental investigation validates the simulation results and provides new laser processing data for some typical packaging materials
Study of bending and torsional stiffness behavior of a composite frame for sport car
No full textLo studio svolto in merito alle tecniche di produzione di componenti strutturali in materiale composito ha permesso il raggiungimento di una precisa consapevolezza dello stato dell’arte del settore, in particolare in riferimento ai processi attualmente utilizzati per l’industrializzazione in media-grande serie.
Con l’obiettivo di sintetizzare i principali vantaggi delle tecnologie suddette e permettere la realizzazione di forme più complesse, si è proceduto all’analisi di fattibilità, attraverso uno studio funzionale e una prima progettazione di una tecnologia di produzione per nastratura automatizzata di componenti strutturali in materiale composito.
Si è voluto quindi dimostrare la flessibilità e la consistenza del processo disegnando un telaio nastrato in carbonio, intercambiabile al telaio FSAE 2009 in tubolare d’acciaio (stessi punti di attacco motore, punti di attacco telaietto posteriore, attacchi sospensioni anteriori) e che garantisca un sostanziale vantaggio in termini di peso, a pari rigidezza torsionale.
La caratterizzazione di tale telaio è stata eseguita mediante l'utilizzo del calcolo strutturale, validato da prove sperimentali.The study done on the techniques of structural components production made in composite materials has permitted the achievement of a precise knowledge of the state of art, particularly in reference to the processes currently used for the industrialization in medium-large series.
With the aim to synthesize the main advantages of these technologies and to allow the production of more complex shapes, the feasibility was examined, through a functional study and a first design of a production technology for automated taping of structural components in composite material.
The flexibility and consistency of the process was demonstrated by drawing a frame interchangeable with the 2009 FSAE chassis with tubular steel (same engine attachment, same rear frame attachments and same front suspension attacks), and which guarantees a substantial advantage in terms of weight, maintaining the same torsional stiffness.
The characterization of such frame has been made through Cae analisys, validated by experimental tests
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