130,556 research outputs found
Lezioni di fondamenti e tecnica della progettazione meccanica
No full textIn questo volume sono raccolte le lezioni tenute dal Prof. Dario Croccolo negli insegnamenti di Fondamenti di Progettazione ed Ingegnerizzazione di Prodotto L e di Tecnica delle costruzioni meccaniche L attivati, rispettivamente, presso i Corsi di Laurea in Ingegneria Gestionale ed Ingegneria Meccanica della prima e della seconda Facoltà di Ingegneria dell’Università degli Studi di Bologna.
Tale raccolta è stata concepita e realizzata con l’intento di ampliare i lucidi proiettati in aula e di facilitare la preparazione delle prove d’esame. A tal fine sono stati, perciò, sviluppati ed approfonditi gli argomenti affrontati a lezione senza, però, avere la pretesa di offrirne una trattazione completa per la quale si rimanda ai testi indicati in bibliografia. I contenuti dell’opera sono stati più volte controllati ed aggiornati al fine di adattarli alla recente riforma degli Ordinamenti e dei Regolamenti Universitari e, dunque, le lezioni teoriche curate dal Prof. Croccolo sono state arricchite da molti esempi e calcoli eseguiti anche con metodi numerici agli elementi finiti, curati dall’Ing. Vincenzi, al fine di migliorare la comprensione degli argomenti e rendere il volume il più possibile moderno ed allineato con i recenti strumenti e metodi di calcolo.
Poiché i contenuti fanno riferimento a due insegnamenti di base offerti in Corsi di Studio differenti (Laurea in Ingegneria Meccanica ed in Ingegneria Gestionale) potranno esservi parti di programma già proposte in altri insegnamenti del Corso di Laurea in Ingegneria Meccanica oppure che non saranno mai affrontate e trattate a lezione per il corso di Laurea in Ingegneria Gestionale; in ogni caso tutti gli argomenti, pur essendo tra loro correlati, sono fruibili indipendentemente e, dunque, possono essere compresi e studiati dagli studenti di entrambi i corsi, soprattutto se decidano di frequentare e seguire le lezioni.
Tutti i risultati numerici sono stati arrotondati per eccesso o per difetto in modo da rimanere sempre a favore di sicurezza e da ottenere cifre significative che possiedono valore ingegneristico
The design and the optimization of the fork-pin compression joints in front motorbike suspensions
No full textThe design of the fork-pin compression-fit joints of front motorbike suspensions is uncertain mainly because of the poor knowledge about the starting friction coefficient μll and about the mean coupling pressure p. The axial releasing force Fll=μll∙p∙A, which is the fundamental design parameter, depends on the mentioned two factors, usually unknown, and on the coupling surface dimension, usually known. For these reasons, we decided to develop a generalized methodology which may be able to calculate the parameters (μll and p) of fork-pin joints like those reported in Figure 1 and produced by Paioli Meccanica S.p.A.. In a previous work [Croccolo, 2002], the mathematical model useful to calculate the starting friction coefficient μll has been defined as a function of the production and assembly specifications which are the resting time, the presence of humidity, and the presence of protecting oil. Instead, the definition of the coupling pressure is more difficult because it requires the help of numerical (FEM) analyses. In fact, cause to the not axial symmetric geometry of the fork, the tensile state on the coupling surfaces does not result constant as shown by the different contours of the images of the Figure 2 and therefore it is not possible to apply the high thickness pipe theory. Furthermore, the FEM analysis needs to use many contact elements which increase the computational time and which often do not provide any solution. On the other hand, the pin has, normally, a perfect axial symmetric geometry which is simple to study with the theoretical formulas. Therefore, we decided to separate the strain contribution of the pin and of the fork going on improving the methodology presented in [Croccolo, 2002] and [Croccolo, 2003] which allows to continue in applying the theoretical formulas appropriately corrected. The mathematical models of μll and p are, therefore, implemented in a program which is useful to quickly perform the design and the verification of the joint without using the FEM analyses
Editorial: bolted joints and mechanical connections of components
No full textThis special issue, dedicated to bolted joints and mechanical connections, offers an attractive selection of the recent and modern findings on mechanical fastening and their products. It is widely demonstrated that fastening systems play a fundamental role for all engineered products especially because they are, nowadays, driven by the continuously pursuit of highest strength to weight ratios. Structural components are getting lighter by taking advantage of the favorable features offered by high strength steels, titanium, aluminum and magnesium alloys as well as fiber reinforced plastics. Among the wide range of fastening systems, which have to withstand increased thermal, mechanical and environmental impacts, threaded components are the most common and dominant solution for structural joining of different materials. Bolted joints have to be considered as important machine elements which will also play a major role for efficient products in future
Adhesives: Mechanical properties, technologies and economic importance
No full textIn this book, some interesting technologies and applications dedicated to adhesives are presented and discussed. First, the interference fitted and adhesively bonded joints are extensively studied as an effective means to increase the transferable load while reducing both the weight and the stress level of the joined components. In such type of joints, the influence of the assembly technique on the shear strength of the joints has been investigated. Therefore, the shear strength of hybrid joints realized by �press fitting�, by �shrink fitting� or by �cryogenic fitting� were compared in order to suggest the best way of joining both for technological and economic importance. Then, some design aspects for practical application (for instance in the automotive steel wheel) were analyzed. The adhesive and interference contributions to the resultant resistance of the hybrid joint were carried out with particular attention to the phenomena occurring at the interface. The effect of the adhesive nature, its curing technology and its mechanical response were strongly related to the type of adhesive exploited. Also, the static and fatigue strength properties of press fitted and adhesively bonded joints was studied by considering their Engagement Ratio, which is the ratio between the coupling length and the coupling diameter. Coupling and decoupling tests have been performed both on press-fitted and adhesively bonded specimens and on pin-collar samples, considering four different levels for the Engagement Ratio. The study shows that the Engagement Ratio has a negligible effect on the shear strength of the adhesive and also on the relationship between the decoupling and the coupling forces. Then, the assessment of the adhesive performance of two binders for reassembling fragment porous stones and, more specifically, the effect of nano-titania in the hydration and carbonation of the derived mortars was investigated. The mechanical characterization indicated that the mortars with the nano-titania addition showed improved mechanical properties when compared to the specimens without nano-titania. This property can be exploited in the fabrication of mortars for reassembling fragments of porous limestones from monuments, where the presence of humidity controls the mortar setting and adhesion efficiency. Based on the physico-chemical and mechanical characterization of the studied adhesive mortars with nano-titania, binders of metakaolin-lime and natural hydraulic lime have been selected as the most appropriate formulations for the adhesion of fragment porous stones in restoration applications. Furthermore, the adhesive crack propagation was investigated for some load bearing applications. It was determined that fatigue cracks, either induced by defects or by applied stresses, may appear and propagate, thus becoming potentially harmful for the structural integrity of a part or a whole structure. Case studies are presented and discussed for adhesively bonded single lap joint (SLJ). Finally, a numerical method able to reproduce three-dimensionally the fatigue debonding and/or delamination evolution in bonded structures is proposed in this book in order to improve their performances. The cohesive zone model previously developed by the authors to simulate fatigue crack growth at interfaces in 2D geometries is extended to 3D cracks under mixed-mode I/II loading
EFFECT OF THE ENGAGEMENT RATIO ON THE SHEAR STRENGTH AND DECOUPLING RESISTANCE OF HYBRID JOINTS
No full textPress fitted and adhesively bonded joints give several advantages: among others, they lead to smaller constructions for a given load capacity, or to stronger constructions for a given size. For that reason, the static and fatigue strength properties of these joints have been studied extensively. Studies dealing with the influence of the Engagement Ratio (i. e. the coupling length over the coupling diameter) are still limited. This work aims at filling the gap, limited to the case of a single component anaerobic adhesive. Coupling and decoupling tests have been performed both on press-fitted and adhesively bonded specimens and on pin-collar samples, considering four different levels for the engagement ratio. The study shows that the engagement ratio has a negligible effect on the shear strength of the adhesive and also on the relationship between the decoupling and the coupling forces. Moreover, the obtained results show that a too high interference level in press-fitted and adhesively bonded joints may have a detrimental effect on the adhesive strength
Esercizi di Comportamento meccanico dei materiali ed Elementi delle macchine
No full textIn questo libro sono raccolti 15 esempi di esercizi proposti come temi d’esame o come problemi applicativi durante le esercitazioni nei corsi di Comportamento Meccanico dei Materiali e di Elementi delle Macchine tenuti presso la sedi di Bologna e di Forlì della Scuola di Ingegneria ed Architettura dell’Università degli Studi di Bologna.
Le tracce di soluzione proposte sono state realizzate considerando che il lettore sia già a conoscenza degli argomenti teorici trattati nei corsi citati, con particolare riferimento a quelli contenuti nel libro di testo: Dario Croccolo, Nicolò Vincenzi, “Lezioni di Fondamenti e Tecnica della Progettazione Meccanica”, Soc. Ed. Esculapio, Bologna. Ciò nonostante vi sono frequenti riferimenti e commenti ad aspetti teorici al fine di migliorare la comprensione delle procedure di calcolo e di aiutare il lettore alla preparazione complessiva delle prove d’esame.
Gli esercizi, e le relative soluzioni, sono stati suddivisi e raggruppati in tre capitoli che corrispondono, nella sostanza, a tre dei principali argomenti teorici affrontati durante le lezioni. Il capitolo 1 riguarda le strutture isostatiche: viene mostrato come ricavare le caratteristiche della sollecitazione ed il coefficiente di sicurezza nel punto maggiormente sollecitato. Il capitolo 2 verte sulla determinazione di baricentri e momenti d’inerzia, per arrivare alla stima delle tensioni normali e tangenziali in alcuni punti di sezioni di travi. Il capitolo 3 riguarda le strutture iperstatiche e mostra la procedura per il calcolo delle incognite iperstatiche, fino alla verifica strutturale. Ciascun esercizio proposto risulta, in ogni caso, indipendente dagli altri e risolvibile anche se considerato singolarmente.
Tutti i risultati numerici sono stati arrotondati per eccesso o per difetto in modo da rimanere sempre a favore di sicurezza e da ottenere cifre significative che possiedono valore ingegneristico
Esercizi di Costruzione di macchine e Tecnica delle costruzioni meccaniche
No full textIn questo libro sono raccolti 25 esempi di esercizi proposti come temi d’esame o come problemi applicativi durante le esercitazioni nei corsi di Costruzione di Macchine e di Tecnica delle Costruzioni Meccaniche tenuti presso la sedi di Bologna e di Forlì della Scuola di Ingegneria ed Architettura dell’Università degli Studi di Bologna.
Le tracce di soluzione proposte sono state realizzate considerando che il lettore sia già a conoscenza degli argomenti teorici trattati nei corsi citati, con particolare riferimento a quelli contenuti nel libro di testo: Dario Croccolo, Nicolò Vincenzi, “Lezioni di Fondamenti e Tecnica della Progettazione Meccanica”, Soc. Ed. Esculapio, Bologna. Ciò nonostante vi sono frequenti riferimenti e commenti ad aspetti teorici al fine di migliorare la comprensione delle procedure di calcolo e di aiutare il lettore alla preparazione complessiva delle prove d’esame.
Gli esercizi, e le relative soluzioni, sono stati suddivisi e raggruppati in cinque capitoli che corrispondono, nella sostanza, a cinque dei principali argomenti teorici affrontati durante le lezioni. Il capitolo 1 riguarda strutture isostatiche più complesse di quelle studiate nell’altro volume, perché aventi sviluppo nello spazio. I capitoli 2 e 3 vertono sul progetto e sulla verifica di collegamenti per bullonatura e saldatura, di impiego molto comune nella pratica dell’Ingegnere Meccanico. Il capitolo 4 riguarda la verifica a fatica di alberi intagliati, eseguita con un metodo avente validità generale, anche in presenza di combinazioni di sollecitazioni. Il capitolo 5 riguarda infine l’opportuna scelta dei cuscinetti volventi da montare sugli alberi e la stima della relativa vita di funzionamento. Ciascun esercizio proposto risulta, in ogni caso, indipendente dagli altri e risolvibile anche se considerato singolarmente.
Tutti i risultati numerici sono stati arrotondati per eccesso o per difetto in modo da rimanere sempre a favore di sicurezza e da ottenere cifre significative che possiedono valore ingegneristico
INFLUENCE OF THE ASSEMBLY PROCESS ON THE SHEAR STRENGTH OF SHAFT–HUB HYBRID JOINTS
No full textInterference fitted and adhesively bonded joints, also known as hybrid joints, are an effective means to increase the transferable load while reducing both the weight and the stress level of the joined components. Many researches evaluated the strength of hybrid joints in dependence of several variables, such as the assembly pressure level, the type of materials in contact, the curing methodology, the operating temperature, and the loading type. To the authors’ best knowledge, no data are available about the influence of the assembly technique on the shear strength of hybrid joints. This paper aims at filling the gap, by comparing the shear strength of hybrid joints realized by ‘press fitting’, by ‘shrink fitting’ and by ‘cryogenic fitting’
Motorbike equilibrium
No full textThis chapter aims at defining the equations that govern the motorbike equilibrium and are useful for designing the front and the rear suspensions. Such equations are, in some case, non-linear and implicit so that they can be solved by recursive methods applied and presented in the Chap. 3 of this book. The mathematical models can be applied to different types of motorbike but they are developed for the peculiar case of those that adopt a single braking disk installed on front suspension and with a unique arm for the rear suspension
The front suspension
No full textIn this chapter, the authors introduce the telehydraulic fork, which has become, across the years, the most common kind of front suspension for motorbikes. In chronological order, some noteworthy patents are presented, which help the reader following the main steps of the technical evolution which gave front motorbike suspensions their current shape. Then, the behaviour of some key structural elements of the fork is examined, under the assumption that the fork is subject to a bending moment acting on the front wheel mid-plane. Such a noteworthy loading condition is frequently encountered during the life cycle of a motorbike: consider, for instance, an emergency braking manoeuvre. Tests which simulate the effect of a hard braking on the fork are also part of the product validation programmes of the main motorbike producers. It is illustrated an analytical model useful for calculating the stress state of the fork legs under said loading condition. Such a model takes into account some architectural configurations as well as some characteristic geometrical parameters of the fork and of the motorbike. The model was validated referring to some production forks, both by finite element analyses and by experimental tests on the road. In the case of forks equipped with a single brake disc, the load unevenness between the legs during braking is analysed, and some strategies aimed at reducing such loading unbalance are suggested. The model presented herein could be helpful for designers who are developing new fork models, because it allows foreseeing critical issues due to legs dimensioning since the early phase of product development, when FEA techniques may be difficult to implement
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