1,721,017 research outputs found
Enhanced brush model for the mechanics of power transmission in flat belt drives under steady–state conditions: Effect of belt elasticity
No full textThe present paper is an extension of a previously published paper by the authors, where the “brush” model was adopted for the contact stresses between the belt and pulleys. In this paper, the axial stiffness of the belt is introduced, while in previous work, particularly suited for belt with stiff reinforcement fibers, the belt was assumed to be inextensible. The complete set of equations is derived in steady state conditions and the relationship between belt tension and belt speed is introduced based on the continuity condition. The belt tension can be obtained by solving a second order differential equation, for which a closed form solution is given. A numerical procedure is, however, necessary for determining the solution of a given transmission with assigned rotational speed at the driving pulley and resistant moment at the driven pulley. It is shown how the contact angle at which stick–slip phenomenon may occur is influenced by the belt stiffness and the way the transmission effiency is reduced. Allowing to analyze the mechanics of flat belt transmission, the model can be considered a useful tool for the designer
Analytical Derivation and Analysis of Vertical and Lateral Installation Ratios for Swing Axle, McPherson and Double Wishbone Suspension Architectures
No full textIn the context of suspension design, the installation ratio (or motion ratio) is a parameter that relates wheel movement with spring deflection, quite an important kinematic property of a suspension. Yet, no study in the literature provides a clear relationship between the installation ratio and the geometrical features of a suspension. This paper employs rigid body kinematics and appropriate geometrical schematics to fill such a gap. Analytical expressions of the installation ratio are derived for three suspension layouts: swing axle, McPherson, double wishbone. Key concepts such as instant center, roll center and camber gain are harnessed to provide insightful analyses for relevant case studies of suspension passenger cars. Among the key results, the typical assumption of a McPherson installation ratio close to 1 is supported by a formal demonstration, and the new concept of “lateral” installation ratio is introduced which, alongside the classical “vertical” installation ratio, further characterizes suspension motion. Numerical results obtained through a multibody software support the findings of this paper. In conclusion, this study provides valuable insights for suspension design engineers
“Brush model” for the analysis of flat belt transmissions in steady-state conditions
Full text linkIn the present work a novel mathematical model for the analysis of the contact actions between belt and pulleys, particularly suited for flat reinforced rubber belt, is presented. The model considers the tension member, composed of the reinforcement fibers, inextensible, and the rubber matrix, which is subjected to tangential stress, as a continuum bed of elastically deformable bristles, fixed to the tension member on one side and in contact with the pulley on the other side. The deformation of the matrix is inversely proportional to the bending stiffness of the bristles, while friction conditions determine the local adhesion/sliding behavior between belt and pulleys. The proposed model can give a detailed description of the contact conditions along the whole contact arc and is able to describe the stick–slip phenomenon which has been experimentally observed by some authors. The model assesses also the power losses due to the contact stresses and to the elastic deformation of the matrix. The results of the model are discussed in comparison with results from classical models, Grashof and Firbank models, available in the technical literature
Analysis of belt transmissions capabilities using the brush model
Full text linkThe mechanics of power transmission is usually modeled by two different theories: the creep theory and the shear theory. Recently, the authors introduced an alternative theory based on the brush model, which allows to compute the tangential stress distribution along the winding arc of pulleys. The brush model is able to predict the speed loss along the driving and driven pulley as a function of the transmission parameters (e.g. pre-load, friction, pulley radii etc.) and the operating parameters (i.e. angular speed and resistant torque). In addition, the energy efficiency of the system is obtained by knowing the speed loss and the energy dissipation; this contribution can be subdivided into energy loss due to friction and energy loss due to the non-recoverable elastic deformation of the bristle.
In the present paper, using the previously developed model, a sensitivity analysis aimed at mapping the transmission capabilities as a function of geometry and operating parameters is proposed. These results, given as look-up table (or contour plot), are very important in mechanical systems simulation (e.g. real-time systems, hardware in the loop systems) since they allow to introduce the phenomenological behavior of the pulley-belt transmission without introducing complex models in the simulation
Validation of the brush model for the analysis of flat belt transmissions in steady-state conditions by finite element simulation
No full textIn this paper a finite element (FE) model for the analysis of the contact stresses in flat belt transmissions was developed, with the intent of comparing the numerical with the theoretical results of the brush model and those of the classical Euler–Grashof (creep) model. The FE model consists of two pulleys and a belt composed of a thin layer of inextensible reinforcement fibers and a rubber matrix in contact with the pulley. The analysis is performed incrementally, under quasi-static conditions; as a consequence, any inertia effect is not accounted for. In the paper, the capabilities of the analyzed models are discussed. The brush model is generally better correlated with the FE results, both in terms of tangential stress along the winding arc and belt tension and it is capable of estimating the power losses due to friction with low computational and time effort. In addition, the effect of the belt thickness on the tangential stress at the entrance and the exit from the pulley, which are generally neglected by simplified model, are highlighted by the FE analysis
Prototyping of Automated Guided Vehicle for Teaching Practical Mechatronics
No full textThis paper presents an innovative approach to teaching mechatronics at the bachelor’s level, using the design and construction of an Automated Guided Vehicle (AGV) as a comprehensive example of a mechatronic system. The course, titled Laboratory of Electronic Systems, is part of a newly established professionalizing bachelor’s degree program at the University of Pisa, focused on techniques for mechanics and production. This program was developed to meet industry demands for technically skilled personnel with an engineering-related background but without the need for a full traditional engineering education. The course is designed to provide students with hands-on experience, integrating fundamental concepts from mechanical, electronic, and control engineering, along with software development. The curriculum emphasizes practical applications rather than theoretical depth, aligning with the program’s goal of preparing students for operational roles in industrial settings. We present the course structure, educational objectives, and the interdisciplinary nature of mechatronics as addressed in this teaching approach. A dedicated section outlines the critical steps involved in the AGV prototype development, highlighting practical challenges and learning opportunities. The effectiveness of the course is assessed through the evaluation of student projects, specifically via a technical report and a final discussion on the design of a mechatronic system. The results demonstrate the value of a project-based learning approach in equipping students with the practical skills and knowledge required for careers in mechatronics and industrial automation
Progettazione di prove sperimentali per la calibrazione del modello di rottura di Johnson-Cook
Full text linkExperimental Bench for the Analysis of Belt Deformation in Belt–Pulley Systems by Digital Image Correlation
No full textBelt–pulley transmissions are a classical topic in mechanical engineering, usually studied following two approaches: the creep theory (Euler or Grashof model) and the shear theory. Recently, the authors introduced a new theory to study the belt–pulley contact mechanics, which is inspired to the brush model used for pneumatic tires. Basing on this theory, the belt is considered as an almost axially rigid tension member connected to a series of bristles, which are, at the other end, in contact with the pulley. In this paper, a test bench is presented and designed to experimentally validate the brush model. The bench is made up of two pulleys connected to two shafts driven by independently controlled motors; a belt is installed between the pulleys, and the shafts are equipped with sensors measuring the angular velocity and the transmitted torque. The belt preload, which is measured by a load cell, can be varied by changing the distance between the two shafts. The belt was painted creating a suitable texture (random speckle pattern) to be interpreted using the Digital Image Correlation (DIC) technique. The first results obtained by carrying out tests at low speed with different transmitted torque values are discussed, appreciating the variation in the tension of the belt along the winding arc and the dependence of the radial compression of the belt from the transmitted torque. The tangential deformation of the belt under the action of different torque values and direction of rotation of the pulleys is also presented, which is consistent with that foreseen by the brush model
Influence of the stress history and of the Lode angle on the determination of the ductile fracture locus for two steel alloys
No full textThe fracture locus of ductile materials is primarily related to the stress triaxiality. Recently, the Lode angle was also found to be relevant in the fracture locus determination. In order to characterize a material in terms of fracture locus, usually several tests, spanning a wide range of stress triaxiality and Lode angle values, have to be performed using different specimen geometries, obtained both from round bars and sheets. In this paper the fracture loci of two steel alloys (S500MC and 22MnB4) are obtained using a simplified procedure, based on the Bai–Wierzbicki model. The procedure considers, for experimental tests, only flat specimens, avoiding the use of round specimen of the same material which were not available. Experimental tests were performed on differently shaped specimens and the results were used to train finite element (FE) models. The triaxiality and Lode angle histories, computed for each test by the FE model, were used to obtain the fracture loci following two different approaches: the proportional loading approach and the non-proportional loading approach. The former does not consider how the stress triaxiality and Lode angle vary during the test, while the latter considers their history in the computation of the fracture locus. The results show how the Lode angle influences the fracture locus, especially for 22MnB4, and how non-proportional loading approach is more accurate to compute the damage for the different specimen geometries
Progettazione di strutture in acciaio con le Nuove Norme Tecniche e con gli Eurocodici: basi concettuali ed esempi di calcolo
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