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Mechanical vibrational energy, which is provided by continuous or discontinuous motion, is an infinite source of energy that may be found anywhere. This source may be utilized to generate electricity to replenish batteries or directly power electrical equipment thanks to energy harvesters. The new gadgets are based on the utilization of piezoelectric materials, which can transform vibrating mechanical energy into useable electrical energy owing to their intrinsic qualities. The purpose of this article is to highlight developments in three independent but closely connected multidisciplinary domains, starting with the piezoelectric materials and related manufacturing technologies related to the structure and specific application; the paper presents the state of the art of materials that possess the piezoelectric property, from classic inorganics such as PZT to lead-free materials, including biodegradable and biocompatible materials. The second domain is the choice of harvester structure, which allows the piezoelectric material to flex or deform while retaining mechanical dependability. Finally, developments in the design of electrical interface circuits for readout and storage of electrical energy given by piezoelectric to improve charge management efficiency are discussed. [ABSTRACT FROM AUTHOR]

This paper investigates the dynamic behavior of a rolling mill during variable gauge rolling. Considering that the variation of rolling process parameters and the movement of hydraulic cylinder are the remarkable features of the variable gauge rolling process, the dynamic rolling force model and the hydraulic cylinder dynamic model were established respectively, and the rolling mill dynamic model was established based on the structure-process coupling strategy. The Incremental Harmonic Balance Method (IHBM) is used to solve the amplitude–frequency characteristics of the rolling mill system, and the Runge–Kutta method is used to solve the vibration characteristics. The results indicate that as the piston of the hydraulic cylinder is displaced, the stiffness of hydraulic cylinder changes and exhibits nonlinear features. The nonlinear characteristics of the hydraulic cylinder affect the dynamic behavior of the rolling mill, which presents different dynamic behaviors when the piston is in different initial positions for variable gauge rolling. The results provide a theoretical reference for the analysis and control of rolling mill dynamic behavior during variable gauge rolling. [ABSTRACT FROM AUTHOR]

Vibration energy harvesting using piezoelectric cantilevers has been widely studied during the past decade. As an alternative to piezoelectric cantilevers, plate-like energy harvesters can be much more effective in marine, aerospace, and automotive applications. This work presents an exact two-dimensional model that can be used for analyzing thin, moderately thick, and thick piezoelectric bimorph plate vibration harvesters. The model allows to consider for the substrate layer both homogenous materials, and those with varying properties along the thickness direction. For the latter case, porous materials with various porosity distributions are herein considered, and the piezoelectric layers are assumed to be wired in both parallel and series configurations. Rayleigh damping assumptions are also used to model the structural damping of the harvesting system. Using Hamilton's principle and Gauss's law, the energy harvesting model is established based on the first-order and the third-order shear deformation theories. Applying an analytical procedure to the electromechanical governing equations, closed-form steady-state response expressions, which relate the voltage output and the vibration response of the harvester to harmonic input force, are derived. Finally, the proposed model is validated, and the power generation performance of the plate harvester is discussed through conducting extensive parametric studies, covering the effect of design parameters, such as the applied electric load, porosity characteristics, electrical configuration, and geometrical parameters. [ABSTRACT FROM AUTHOR]

The Intelligent Fault Diagnosis of rotating machinery calls for a substantial amount of training data, posing challenges in acquiring such data for damaged industrial machinery. This paper presents a novel approach for generating synthetic data using a Generative Adversarial Network (GAN) with cycle consistency loss function known as cycleGAN. The proposed method aims to generate synthetic data that could effectively replace real experimental data. The generative model is trained to transform wavelet images of simulated vibrational signals into authentic data obtained from machinery with damaged bearings. The utilization of Maximum Mean Discrepancy (MMD) and Fréchet Inception Distance (FID) demonstrates a noteworthy resemblance between synthetic and real experimental data. Also, the generative model enables the synthesis of data that may have been entirely lacking from the experimental observation, indicating generative zero-shot learning capabilities. The efficacy of synthetic data in training diagnosis algorithms by means of Transfer Learning (TL) on Convolutional Neural Networks (CNNs) has been demonstrated to be comparable to that of real data. The study has been validated by means of the test rig for medium-sized industrial bearings accessible at the Politecnico di Torino. [ABSTRACT FROM AUTHOR]

The Intelligent Fault Diagnosis of rotating machinery currently proposes some captivating challenges. Although results achieved by artificial intelligence and deep learning constantly improve, this field is characterized by several open issues. Models' interpretation is still buried under the foundations of data driven science, thus requiring attention to the development of new opportunities also for machine learning theories. This study proposes a machine learning diagnosis model, based on intelligent spectrogram recognition, via image processing. The approach is characterized by the employment of the eigen-spectrograms and randomized linear algebra in fault diagnosis. Randomized algebra and eigen-spectrograms enable the construction of a significant feature space, which nonetheless emerges as a viable device to explore models' interpretations. The computational efficiency of randomized approaches provides reading keys of well-established statistical learning theories such as the Support Vector Machine (SVM). Machine learning applied to spectrogram recognition shows to be extremely accurate and efficient as compared to state of the art results. [ABSTRACT FROM AUTHOR]

The aerospace industry is one of the leading figures in the development and improvement of techniques for the design of new products. One of the most promising developments of the last decades is the exploitation of digital models that make it possible to evaluate design solutions and simulate the behavior of the individual systems and their interactions. The goal is to be able to predict and analyze all aspects an aircraft much in advance of its industrialization in order to heavily reduce the time and costs of product development and to guarantee flexibility to test a multitude of solutions. The main issue in this context is the complexity of creating models that are capable of accurately sizing and simulating multiple interacting systems, thus considering the constraints imposed by the need for their mutual compatibility. The present contribution introduces two interconnected models regarding an aircraft system, in particular, the landing gear, that make it possible to size its main components and subsystems and to use the found parameters to populate a dynamic model that simulates the behavior of the aircraft during landing. These models provide a preliminary digitalization of the system itself and of the design process as well, thereby making it possible to define a potential configuration and to test it in a dynamic virtual environment, thus taking into account the interaction between the individual subsystems. The model was tested through three use cases, differentiated by class and scope, which made it possible to compare and validate the obtained results with actual values. [ABSTRACT FROM AUTHOR]

The current numerical study aims to examine the single and combined effects of various piston bowl geometries, diesel main Start of Injection (SOI) timing, and syngas energy ratio on the combustion characteristics, specific emissions (g/kW·h), energy distribution, and exergy of a heavy-duty off-road Reactivity-Controlled Compression Ignition (RCCI) diesel engine. The examined geometries include the stock chamber (baseline combustion chamber), wide-shallow chamber, dual-swirl chamber, stepped-lip chamber. The main SOI timing was varied from −20 to −5 Crank Angle (CA) After Top Dead Center (ATDC) with 5 CA steps. Also, syngas energy ratio including 0% Conventional Diesel Combustion (CDC) mode, 20%, 40%, and 60% of total fuel energy per cycle. To accomplish this goal, the SAGE combustion model coupled with a reduced chemical kinetic mechanism consists of 360 reactions, and 72 species was applied to conduct this investigation. The numerical findings showed that the use of the wide-shallow chamber extended the engine operable range under diesel-syngas combustion operating conditions. In comparison to the baseline CDC case, the application of the dual-swirl chamber under CDC conditions, and main SOI timing of −15 CA ATDC led to reduction of Carbon Monoxide (CO), Hydro-Carbon (HC), Particle Matter (PM), Carbon Dioxide (C O 2 ), Indicated Specific Energy Consumption (ISEC), Gross Indicated Efficiency (GIE), and exergy efficiency but with a Nitrogen Oxides (NOx) penalty rate. In general, an increase in the bore to bowl diameter ratio caused a shorter ignition delay period and combustion duration. The utilization of the stepped-lip chamber at both CDC and diesel-syngas combustion operating modes resulted in a shorter ignition delay period, but a longer combustion duration. Nonetheless, the stepped-lip combustion chamber reduced the diffusive flame temperature. Also, it is noteworthy that the utilization of the stock chamber along with the main SOI timing at −5 CA ATDC under diesel-syngas 60% combustion mode is a suitable technique to pass EURO-VI PM and HC emissions regulations. [ABSTRACT FROM AUTHOR]

In recent years, the methodology of Model-Based System Engineering (MBSE) has become relevant to the design of complex products, especially when safety critical systems need to be addressed. It allows, in fact, the deployment of product development directly through some digital models, allowing an effective traceability of requirements, being allocated upon the system functions, components, and parts. This approach enhances the designer capabilities in controlling the product development, manufacturing and after-market services. However, the application of such a methodology requires overcoming several technological barriers, especially in terms of models integration. The interoperability and management of several models—developed within different software to cover multiple levels of detail across several technical disciplines—is still very difficult, despite the level of maturation achieved by Systems Engineering. This paper describes a possible approach to provide such a connection between tools to allow a complete multi-disciplinary and heterogeneous simulation to analyse complex systems, such as safety-critical ones, which are typical of aerospace applications. Such an application is within a defined industrial context, placing particular attention on the compatibility of the approach with the legacy processes and tools. [ABSTRACT FROM AUTHOR]

Although the effectiveness of machine learning (ML) for machine diagnosis has been widely established, the interpretation of the diagnosis outcomes is still an open issue. Machine learning models behave as black boxes; therefore, the contribution given by each of the selected features to the diagnosis is not transparent to the user. This work is aimed at investigating the capabilities of the SHapley Additive exPlanation (SHAP) to identify the most important features for fault detection and classification in condition monitoring programs for rotating machinery. The authors analyse the case of medium-sized bearings of industrial interest. Namely, vibration data were collected for different health states from the test rig for industrial bearings available at the Mechanical Engineering Laboratory of Politecnico di Torino. The Support Vector Machine (SVM) and k-Nearest Neighbour (kNN) diagnosis models are explained by means of the SHAP. Accuracies higher than 98.5% are achieved for both the models using the SHAP as a criterion for feature selection. It is found that the skewness and the shape factor of the vibration signal have the greatest impact on the models' outcomes. [ABSTRACT FROM AUTHOR]

InconelTM 718 is widely used for commercial application in aerospace industry and additive manufacturing process allows for versatile design and manufacturing opportunities. In the present research, the results of a wide experimental campaign run on additive manufactured InconelTM 718 specimens obtained with different processing parameters are presented. In particular, the influence of process parameters (for both vertical and horizontal planes with respect to the building direction) on the hardness properties are investigated. A further investigation is performed on the optimal hardness testing procedure for additive manufacturing. The research is extended to as-built and heat-treated specimens. The new insight gained is that the orientation of the printing direction with respect to indentation direction can be responsible for scattering in hardness measurements and indentation size effect. As-built specimens show a strong anisotropy for in-plane and growth directions and an increment of hardness with respect to increasing energy density. The difference between hardness value with respect to the energy density and the measurements scattering are reduced by the heat treatment. A careful handling of hardness data is required when dealing with additive manufactured materials. [ABSTRACT FROM AUTHOR]

Maintenance scheduling is a fundamental element in industry, where excessive downtime can lead to considerable economic losses. Active monitoring systems of various components are ever more used, and rolling bearings can be identified as one of the primary causes of failure on production lines. Vibration signals extracted from bearings are affected by noise, which can make their nature unclear and the extraction and classification of features difficult. In recent years, the use of the discrete wavelet transform for denoising has been increasing, but studies in the literature that optimise all the parameters used in this process are lacking. In the current article, the authors present an algorithm to optimise the parameters required for denoising based on the discrete wavelet transform and thresholding. One-hundred sixty different configurations of the mother wavelet, threshold evaluation method, and threshold function are compared on the Case Western Reserve University database to obtain the best combination for bearing damage identification with an iterative method and are evaluated with tradeoff and kurtosis. The analysis results show that the best combination of parameters for denoising is dmey, rigrSURE, and the hard threshold. The signals were then distributed in a 2D plane for classification through an algorithm based on principal component analysis, which uses a preselection of features extracted in the time domain. [ABSTRACT FROM AUTHOR]

This paper aims to develop analytical solutions for wave propagation and free vibration of perfect and porous functionally graded (FG) plate structures integrated with piezoelectric layers. The effect of porosities, which occur in FG materials, is rarely reported in the literature of smart FG plates but included in the present modeling. The modified rule of mixture is therefore considered for variation of effective material properties within the FG substrate. Based on a four-variable higher-order theory, the electromechanical model of the system is established through the use of Hamilton's principle, and Maxwell's equation. This theory drops the need of any shear correction factor, and results in less governing equations compared to the conventional higher-order theories. Analytical solutions are applied to the obtained equations to extract the results for two investigations: (I) the plane wave propagation of infinite smart plates and (II) the free vibration of smart rectangular plates with different boundary conditions. After verifying the model, extensive numerical results are presented. Numerical results demonstrate that the wave characteristics of the system, including wave frequency and phase velocity along with the natural frequencies of its bounded counterpart, are highly influenced by the plate parameters such as power-law index, porosity, and piezoelectric characteristics. [ABSTRACT FROM AUTHOR]

Innovating new approaches and effective methods to improve the efficiency of mechanical systems in terms of energy losses and environmental effects serve as an attractive domain for researchers and industries. Wet clutches are widely used in power transmission systems in automotive and other tribological mechanisms. The wet clutch has two functional modes; under the engaged state, in which two disks come into contact to each other, and under disengagement the plates are located at a very short distance from each other, and oil flows between them. In disengaged state, the differential speed of driving and driven units causes oil shearing within the clearance which leads to transmission of certain amount of drag torque from the driving to the output shaft. This transferred drag torque is distinguished as power loss in form of heat. The governing physical relation based on continuity equation and Navier–Stokes equations reveals that in a certain rotational velocity, the pressure gradient at the outer radius of the clutch becomes null, and, in this circumstance, aeration occurs that is known as critical rotation speed. Experimental findings provide evidence that geometry manipulation and considering grooves over the frictional disk, reduces the critical rotational speed. But there is a shortage of physical analytical relations to predict the pressure gradient in grooved wet clutches. Therefore, this article is aimed to introduce analytical model to evaluate grooved wet clutches performance in terms of drag torque and critical rotational speed under single-phase flow condition. [ABSTRACT FROM AUTHOR]

The minimization of friction losses in internal combustion engines is a goal of primary importance for the automotive industry, both to improve performance and to comply with increasingly stringent legislative requirements. It is therefore necessary to provide designers with tools for the effective estimation of friction losses from the earliest stages of design. We present a code for the estimation of friction losses in piston assembly that uses semianalytical models that require only strictly necessary geometric and functional inputs for the representation of components. This feature renders the code particularly suitable for the preliminary design phase. Furthermore, models ensure reduced computation times while maintaining excellent predictive capabilities, as demonstrated by the numerical–experimental comparison. [ABSTRACT FROM AUTHOR]

The steel rolling process is critical for safety and maintenance because of loading and thermal operating conditions. Machinery condition monitoring (MCM) increases the system's safety, preventing the risk of fire, failure, and rupture. Equipping the mill bearings with sensors allows monitoring of the system in service and controls the heating of mill components. Fiber optic sensors detect loading condition, vibration, and irregular heating. In several systems, access to machinery is rather limited. Therefore, this paper preliminarily investigates how fiber optics can be effectively embedded within the mill cage to set up a smart manufacturing system. The fiber Bragg gratings (FBG) technology allows embedding sensors inside the pins of backup bearings and performing some prognosis and diagnosis activities. The study starts from the rolling mill layout and defines its accessibility, considering some real industrial cases. Testing of an FBG sensor prototype checks thermal monitoring capability inside a closed cavity, obtained on the surface of either the fixed pin of the backup bearing or the stator surrounding the outer ring. Results encourage the development of the whole prototype of the MCM system to be tested on a real mill cage in full operation. [ABSTRACT FROM AUTHOR]

Today's deep learning strategies require ever-increasing computational efforts and demand for very large amounts of labelled data. Providing such expensive resources for machine diagnosis is highly challenging. Transfer learning recently emerged as a valuable approach to address these issues. Thus, the knowledge learned by deep architectures in different scenarios can be reused for the purpose of machine diagnosis, minimizing data collecting efforts. Existing research provides evidence that networks pre-trained for image recognition can classify machine vibrations in the time-frequency domain by means of transfer learning. So far, however, there has been little discussion about the potentials included in networks pre-trained for sound recognition, which are inherently suited for time-frequency tasks. This work argues that deep architectures trained for music recognition and sound detection can perform machine diagnosis. The YAMNet convolutional network was designed to serve extremely efficient mobile applications for sound detection, and it was originally trained on millions of data extracted from YouTube clips. That framework is employed to detect bearing faults for the CWRU dataset. It is shown that transferring knowledge from sound and music recognition to bearing fault detection is successful. The maximum accuracy is achieved using a few hundred data for fine-tuning the fault diagnosis model. [ABSTRACT FROM AUTHOR]

Theory of Critical Distances (TCD) collects several methods adopted in failure prediction of components provided with stress concentration features. The idea of evaluating stress effect in a zone rather than in a single point was proposed decades ago but, only thanks to relatively recent works, TCD concepts showed to be a successful extension of Linear Elastic Fracture Mechanics (LEFM), able to assess strength and fatigue life. The increasing computational power has made Finite Element Method (FEM) widespread, hence stress fields can be easily extracted and used as input data for fatigue post-processing and durability analyses. In this scenario, TCD reveals as a powerful tool which, thanks to the introduction of a single material parameter (critical distance, L), integrates classical fracture models by considering the presence of microscale phenomena acting in fracture process. In this sense, TCD behaves as a link between continuum mechanics and LEFM. Modalities and reasons for this connection to occur are interesting points of further investigations. Literature on TCD and its theoretical-experimental background is quite extended, nevertheless few industrial applications are available in literature to the best of authors' knowledge. In this paper, an overview of concepts and applications related to TCD are reported highlighting the relevance of theoretical arguments in actual applications. [ABSTRACT FROM AUTHOR]

In the automotive field, the requirements in terms of carbon emissions and improved efficiency are shifting the focus of designers towards reduced engine size. As a result, the dynamic balancing of an engine with strict limitations on the number of cylinders, the weight and the available space becomes a challenging task. The present contribution aims at providing the designer with a tool capable of selecting fundamental parameters needed to correctly balance an internal combustion engine, including the masses and geometry of the elements to be added directly onto the crankshaft and onto the balancing shafts. The relevant elements that distinguish the tool from others already proposed are two. The first is the comprehensive matrix formulation which makes the tool fit for a wide variety of engine configurations. The second is an optimisation procedure that selects not only the position of the mass and centre of gravity of the counterweight but also its complete geometric configuration, thus instantaneously identifying the overall dimensions and weight of the crankshaft. [ABSTRACT FROM AUTHOR]

Condition monitoring of rotating machinery plays an important role in reducing catastrophic failures and production losses in the 4.0 Industry. Vibration analysis has proven to be effective in diagnosing rotating machine failures. However, identifying bearing defects based on vibration analysis remains a difficult task, especially in non-stationary operation conditions. This work aims to automate the process of identifying bearing defects under variable operating speeds. Based on an order analysis technique, three frequency domain features: Spectrum peak Ratio Outer (SPRO), Spectrum peak Ratio Inner (SPRI), and Spectrum peak Ratio Rolling element (SPRR) are updated to perform with non-stationary signals. The updated features are extracted from vibration data of a real ball bearing system. They are retained to build a predictive multi-kernel support vector machine (MSVM) classification model. Therefore, the effectiveness of the proposed features is evaluated based on the performance of the constructed classifier. The updated features deployed have proven their effectiveness in identifying bearing: outer race, inner race, ball, and combined defects under variable speed conditions. [ABSTRACT FROM AUTHOR]

Tool health monitoring (THM) is in great focus nowadays from the perspective of predictive maintenance. It prevents the increased downtime due to breakdown maintenance, resulting in reduced production cost. The paper provides a novel approach to monitoring the tool health of a computer numeric control (CNC) machine for a turning process using airborne acoustic emission (AE) and convolutional neural networks (CNN). Three different work-pieces of aluminum, mild steel, and Teflon are used in experimentation to classify the health of carbide and high-speed steel (HSS) tools into three categories of new, average (used), and worn-out tool. Acoustic signals from the machining process are used to produce time–frequency spectrograms and then fed to a tri-layered CNN architecture that has been carefully crafted for high accuracies and faster trainings. Different sizes and numbers of convolutional filters, in different combinations, are used for multiple trainings to compare the classification accuracy. A CNN architecture with four filters, each of size 5 × 5, gives best results for all cases with a classification average accuracy of 99.2%. The proposed approach provides promising results for tool health monitoring of a turning process using airborne acoustic emission. [ABSTRACT FROM AUTHOR]

This investigation aims to perform a detailed natural frequency analysis of functionally graded porous beams integrated with transverse (d 31) and shear (d 15) piezoelectric layers under short circuit and open circuit electrical conditions. It is assumed that the core layer is made of functionally graded materials containing porosities. Due to the existence of internal pores, the mechanical properties of functionally graded materials are considered according to the modified power-law rule which includes the effect of porosity. The distribution of electric potential within the d 31 and d 15 piezoelectric layers is modeled based on nonlinear variation for both short circuit and open circuit conditions. Employing the classical, the first-order, and the higher-order beam theories incorporated with the virtual work principle as well as Maxwell's equation, the electromechanical equations of motion are derived. The governing equations are then solved analytically for simply supported boundary condition and a parametric study is presented. After validation of the results, some new interesting conclusions covering the effects of porosity volume fraction, porosity distribution, various piezoelectricity modes, power-law index, and the beam theories on short circuit and open circuit resonance frequencies are reported. It is believed that the presented numerical results could provide a benchmark to check the accuracy of the approximated approaches. [ABSTRACT FROM AUTHOR]

Predictive maintenance strategies are established in the industrial context on account of their benefits in terms of costs abatement and machine failures reduction. Among the available techniques, vibration-based condition monitoring (VBCM) has notably been applied in many bearing fault detection problems. The health indicators construction is a central issue for VBCM, since these features provide the necessary information to assess the current machine condition. However, the relation between vibration data and its sources intimately related to bearing damage is not effortlessly definable from a diagnostic perspective. This study discloses a diagnostic investigation performed both on the vibration signal and on the contact pressure signal that is supposed to be one of main forcing terms in the dynamic equilibrium of the damaged bearing. Envelope analysis and spectral kurtosis (SK) are applied to extract and compare diagnostic features from both signals, referring to the Case Western Reserve University (CWRU) case-study. Namely, health indicators are constructed by means of physical considerations based on the effect of faults on the signal power contents. These indicators show to be promising not only for damage detection but, also, for damage severity assessment. Moreover, they provide an invaluable reading key of the link occurring between the contact pressure path and the vibration response. [ABSTRACT FROM AUTHOR]

This article presents a detailed analytical model to evaluate piston skirt tribology under hydrodynamic lubrication. The contribution of the piston ring pack lubrication has been taken into account to study piston secondary motion and tribological performance. A system of nonlinear equations comprising Reynolds equation and force equilibrium is solved to calculate piston ring pack friction force and its moment about wrist pin axis. Instantaneous minimum oil film thickness at piston ring/liner interface has been estimated considering different boundary conditions: full Sommerfeld, oil separation, and Reynolds cavitation and reformation. The ring pack model has capability to be used for a wide range of ring face profiles under boundary and hydrodynamic lubrication. Piston secondary motion is evaluated using lubrication theory and equilibrium of forces and moments, to examine the effect of wrist pin location, piston skirt/liner clearance, and oil rheology. Numerical method and finite difference scheme have been used to define piston eccentricity and hydrodynamic pressure acting over the skirt. [ABSTRACT FROM AUTHOR]

This paper is focused on finite element simulation of cylinder head gaskets. Finite element codes support several methodologies, each of which has its own strengths and weaknesses. One of the key points lies in the influence of the gasket geometry on its final behaviour. Such a contribution can come from the detailed modelling of the gasket or by defining a global non-linear behaviour in which material and geometry non-linearities are summarised. Two approaches were used to simulate the gasket behaviour. The first one consists in using a 2D approach, which allows to model through-thickness non-linear behaviour of gasket. The second one consists in using conventional 3D finite element modelling. The numerical methods have been discussed and compared in relation to the accordance with experimental data, amount of information supplied and computational time required. Finally, a parametric study shows how some geometric parameters influence the compressive load and the elastic recovery of a single-layer steel gasket. [ABSTRACT FROM AUTHOR]

Purpose: The implementation of project-based learning (PBL) activities in the curricula of engineering students has become a consolidated method to improve their skills. The purpose of this paper is to share the experience acquired by the authors from a decennial case-study on a student team PBL activity focused on design and development of human-powered vehicles (HPVs). A review of the project evolution, boundary constraints and management choices could provide inspiration and suggestions to faculty staff that would like to set-up similar experiences for engineering students in their universities. Design/methodology/approach: A student team was funded by the authors in 2008 to gather engineering students interested in design and construction of HPVs. In the past decade, the team has grown from 10 up to 60 students enrolled per year and stimulated to develop a range of HPV designs for sports and mobility. The project management evolved as a consequence to com ply with the growing ambitions of the group and complexity of the goals. Findings: A thorough analysis of factors contributing to the success of the project led to identification of the key factors to increase student participation: persistence of the faculty staff is essential, attending competitions and challenges increases students' recruitment and formal recognition of the activity through credits and the implementation of intermediate assessment steps increase the active participation rate. Bigger teams reduce the negative impact of recruits eventually abandoning the project in an early stage. Ambitious goals keep students motivated for longer periods and enable a virtuous circle by transferring enthusiasm and knowledge to new members. Research limitations/implications: The activity is analyzed starting from a subjective experience perspective and some of the findings/conclusions may be not applicable in a different context. However, such review can suggest strategies on the long-term period to create similar conditions elsewhere. Social implications: In the last part of the paper, it is pointed out how PBL projects can provide a fertile ground for innovation and lead to patents and development of new products aiming at the market. Originality/value: This study contributes to provide an insight view of how a student team PBL activity can grow over a decade if guided by faculty staff. [ABSTRACT FROM AUTHOR]

Mechanical power loss of lubricated and bearing surfaces serves as an attractive domain for study and research in the field of internal combustion engines. Friction reduction at lubricated and bearing surface is one of the most cost-effective ways to reduce gas emission and improve internal combustion engines' efficiency. This thus motivates automotive industries and researchers to investigate tribological performance of internal combustion engines. Piston secondary motion has prime importance in internal combustion engines and occurs due to unbalanced forces and moments in a plane normal to the wrist pin axis. Consequently, piston executes small translations and rotations within the defined clearance during the piston reciprocating motion. Mechanical friction power loss and lubrication at piston skirt/liner and radiated engine noise are dramatically affected by piston secondary dynamics. The lubrication mechanism, piston secondary motion and tribological performance are affected by piston design parameters (piston/liner clearance, wrist pin offset, skirt profile, etc.), lubricant rheology, oil transport mechanism and operating conditions. Therefore, this review is devoted to summarize the synthesis of main technical aspects, research efforts, conclusions and challenges that must be highlighted regarding piston skirt/liner lubrication and piston dynamics and slap. [ABSTRACT FROM AUTHOR]

The paper presents and discusses a low-cycle fatigue life prediction energy-based model. The model was applied to a commercial cast iron automotive exhaust manifold. The total expended energy until fracture proposed by the Skelton model was modified by means of two coefficients which take into account of the effects of mean stress and/or mean strain, and the presence of high temperature. The model was calibrated by means of experimental tests developed on Fe–2.4C–4.6Si–0.7Mo–1.2Cr high-temperature-resistant ductile cast iron. The thermostructural transient analysis was developed on a finite element model built to overtake confidentiality industrial restrictions. In addition to the commercial exhaust manifold, the finite element model considers the bolts, the gasket, and a cylinder head simulacrum to consider the corresponding thermal and mechanical boundary conditions. The life assessment performance of the energy-based model with respect the cast iron specimens was compared with the corresponding Basquin–Manson–Coffin and Skelton models. The model prediction fits the experimental data with a good agreement, which is comparable with both the literature models and it shows a better fitting at high temperature. The life estimations computed with respect the exhaust manifold finite element model were compared with different multiaxial literature life models and literature data to evaluate the life prediction capability of the proposed energy-based model. [ABSTRACT FROM AUTHOR]

Internal combustion engines are the generators of energy for many transportation applications, but they still have an overall low efficiency due to mechanical and thermal losses. The combustion chamber is the core element of the engine and it ought to be perfectly sealed; however, some of the gas leaks toward the crankcase due to imperfect sealing of the rings. This leakage is known as blow-by and affects efficiency, correct lubrication and emissions. The aim of this paper was to understand, in a more detailed way, how some parameters could affect the sealing efficiency of a ring pack. In particular, ring gaps, ring masses and elastic properties, and ring static twists, were varied from the original and investigated for their influence on the inter-ring dynamics and sealing efficiency. The problem, referred to a turbo diesel engine, was formulated in terms of motion equations for the rings and gas equations for the inter-ring crevices, and solved in ©Ricardo RINGPAK solver. The results were compared with the original design and with the reference literature. These results confirm that ring gaps and ring unstable motion have an important role in the phenomenon of gas blow-by. In addition, the second ring emerged to have a more important role on the blow-by reduction with respect to the top ring. However, this phenomenon is complex due to the interaction of several parameters, not all of which were included in this study. Nevertheless, these findings can already be taken into account for further studies or experimental investigations. [ABSTRACT FROM AUTHOR]

Internal combustion engines are at present used as the major power sources for transportation and power generator. Improvement of the internal combustion engine efficiency is expected due to strict environmental standards and energy costs. Any reduction in oil consumption, friction power losses and emissions results in improving engines' performance and durability. Automotive industries have intense passion to increase engines' efficiency to meet the fuel economy and emission standards. Many studies have been conducted to develop reliable approaches and models to understand the lubrication mechanisms and calculate power losses. This review paper summarizes the synthesis of the main technical aspects considered during modeling of piston ring--liner lubrication and friction losses investigations. The literature review highlights the effects of piston ring dynamics, components geometry, lubricant rheology, surface topography and adopted approaches, on frictional losses contributed by the piston ring-pack. [ABSTRACT FROM AUTHOR]

Internal combustion engines are at present used as the major power sources for transportation and power generator. Improvement of the internal combustion engine efficiency is expected due to strict environmental standards and energy costs. Any reduction in oil consumption, friction power losses and emissions results in improving engines' performance and durability. Automotive industries have intense passion to increase engines' efficiency to meet the fuel economy and emission standards. Many studies have been conducted to develop reliable approaches and models to understand the lubrication mechanisms and calculate power losses. This review paper summarizes the synthesis of the main technical aspects considered during modeling of piston ring--liner lubrication and friction losses investigations. The literature review highlights the effects of piston ring dynamics, components geometry, lubricant rheology, surface topography and adopted approaches, on frictional losses contributed by the piston ring-pack. [ABSTRACT FROM AUTHOR]

When dealing with fully faired human powered vehicles (HPVs) for speed or endurance record attempts, the need for internal ventilation of the rider arises. Different solutions have been proposed in the literature and in practice by designers and builders of these bicycles. The present paper proposes an analytical approach to design the frontal air inlet according to the VO $$_{2}$$ max of the rider in speed competitions. A 3D computational fluid dynamics (CFD) model is presented to analyse the external and internal flow interaction with respect to three design parameters: the presence of wheel covers, the location of the rear vent and its geometry. The CFD results predict that the wheel covers save 23 W of aerodynamic power at 125 km/h. A secondary but significant design parameter is the rear vent position that can provide a further reduction of 11 W at 125 km/h if properly located. Finally, the effect of the rear vent geometry was below the model confidence level, resulting in a likely negligible design parameter. [ABSTRACT FROM AUTHOR]

In micro-world applications usually the need to manipulate, handle and measure micro-components becomes an important issue both for production and research reasons. Pointing out the aspect of measurements, the specific contest considerably conditions the technical approach and practical procedure which can be efficiently applied to obtain a reliable and precise measure. The framework of this research concerns the production phase of micro-biomedical components characterized by very small dimensions, high deformability, and sensitivity of surface damage. The main focus has dealt with the definition of an optical procedure to orient and assemble micro-elements. The compromise between the production cadence and the measurement necessity has been one of the main requirements for the research in order to define, implement, and evaluate an ad hoc process to get the expected outcomes. The proposed procedure allows to solve a practical issue by combining a solid vision background to a technical contest solving the specific measuring task and applying the same approach to different practical applications, both in micro and macro world. [ABSTRACT FROM AUTHOR]

The paper presents a magneto-rotordynamic model that allows to obtain the nonlinear equations of motion for all rigid body modes of the Levitron. These equations describe the complete dynamic behaviour of the spinning top and highlight the presence of stability fields related to its spin speed and vertical position of levitation. The developed model takes into account the effect of the aerodynamic drag torque on the sides of the spinning top too. An experimental investigation has been developed to experimentally identify the complex dynamic behaviour of the spinning top; a dedicated test bench and some tests are discussed. By means of the numerical integration of the equations of motion, the spatial trajectories of the spinning top have been computed and validated by comparison with the experimental test results. [ABSTRACT FROM AUTHOR]

The 'micro-world' is a very interesting case of study both for production and research reasons. The use of micro-products and components has had a heavy increase in the last two decades. The manipulation of micro-elements has then become an important need to be satisfied in order to complete production cycles or allow the handling of these components. This paper focuses on a particular case study belonging to the bio-mechanical field. The key point, trigger of the research, has been the need to define a system capable of handling a specific bio-component during a part of its production cycle. In the particular application, the manipulation device has to follow strict requirements of precision, accuracy, and delicacy, because of the dimensions and deformability of the bio-component. The research then has started with an exhaustive analysis of the state of the art, followed by the design and the practical realization of a manipulator matching the specific implementation but whose characteristics could be employed also for other applications. Thanks to the modularity of the design, the device can be easily adapted to any circular micro-element requiring precision and no damaging effects during its manufacturing, motion, or positioning phase. [ABSTRACT FROM AUTHOR]

The remote prognosis and diagnosis of bearings can prevent industrial system failures, but the availability of realistic experimental data, being as close as possible to those detected in industrial applications, is essential to validate the monitoring algorithms. In this paper, an innovative bearing test rig architecture is presented, based on the novel concept of "self-contained box". The monitoring activity is applicable to a set of four middle-sized bearings simultaneously, while undergoing the independent application of radial and axial loads in order to simulate the behavior of the real industrial machinery. The impact of actions on the platform and supports is mitigated by the so-called "self-contained box" layout, leading to self-balancing of actions within the rotor system. Moreover, the high modularity of this innovative layout allows installing various sized bearings, just changing mechanical adapters. This leads to a reduction of cost as well as of system down-time required to change bearings. The test rig is equipped with suitable instrumentation to develop effective procedures and tools for in- and out-monitoring of the system. An initial characterization of the healthy system is presented. [ABSTRACT FROM AUTHOR]

A novel graphical presentation is proposed to convey information about relevant dynamic phenomena and behaviour of a rotor. The ’’orbital tube‘‘ is a three-dimensional plot in which the orbits are stacked in the third dimension at various rotating speeds. It may be conveniently used to represent and analyse data obtained from analytical, numerical and experimental means. Some illustrating examples are reported. [ABSTRACT FROM AUTHOR]

Additive Manufacturing (AM) processes enable their deployment in broad applications from aerospace to art, design, and architecture. Part quality and performance are the main concerns during AM processes execution that the achievement of adequate characteristics can be guaranteed, considering a wide range of influencing factors, such as process parameters, material, environment, measurement, and operators training. Investigating the effects of not only the influential AM processes variables but also their interactions and coupled impacts are essential to process optimization which requires huge efforts to be made. Therefore, numerical simulation can be an effective tool that facilities the evaluation of the AM processes principles. Selective Laser Melting (SLM) is a widespread Powder Bed Fusion (PBF) AM process that due to its superior advantages, such as capability to print complex and highly customized components, which leads to an increasing attention paid by industries and academia. Temperature distribution and melt pool dynamics have paramount importance to be well simulated and correlated by part quality in terms of surface finish, induced residual stress and microstructure evolution during SLM. Summarizing numerical simulations of SLM in this survey is pointed out as one important research perspective as well as exploring the contribution of adopted approaches and practices. This review survey has been organized to give an overview of AM processes such as extrusion, photopolymerization, material jetting, laminated object manufacturing, and powder bed fusion. And in particular is targeted to discuss the conducted numerical simulation of SLM to illustrate a uniform picture of existing nonproprietary approaches to predict the heat transfer, melt pool behavior, microstructure and residual stresses analysis. [ABSTRACT FROM AUTHOR]

The aim of this study is developing an analytical solution for the free vibration of piezoelectric bimorph and unimorph doubly curved panels with a porous substrate. The panel is assumed to be relatively thick, and the effects of its shear deformation are taken into account. Nonlinear models are considered to describe the variation of mechanical properties and of the electric potential within porous host and piezoelectric layers, respectively. Furthermore, short and open circuit electrical conditions are studied to predict the frequency response for sensing and actuation applications. Employing the first-order shear deformation theory (FSDT), in conjunction with the Hamilton's variational principle and Maxwell's equation allows deriving six highly coupled partial differential equations to describe the system dynamics under electromechanical coupling. After analytically solving those equations for simply supported panels, the system frequency response is investigated, for various values of design parameters such as porosity, electrical boundary conditions, and geometry. Moreover, some types of smart panels, including bimorphs and unimorphs layouts, are analyzed. The analysis confirms that the above-mentioned parameters play major roles in the natural frequency response of this system and must be carefully considered in the mechatronic design of this smart structure, although they allow to tailor the system behaviour to the selected application. [ABSTRACT FROM AUTHOR]

Cryogenic treatment is a supplemental structural and mechanical properties refinement process to conventional heat treatment processes, quenching, and tempering. Cryogenic treatment encourages the improvement of material properties and durability by means of microstructural alteration comprising phase transfer, particle size, and distribution. These effects are almost permanent and irreversible; furthermore, cryogenic treatment is recognized as an eco-friendly, nontoxic, and nonexplosive process. In addition, to encourage the application of sustainable techniques in mechanical and manufacturing engineering and to improve productivity in current competitive markets, cryo-treatment can be considered as a promising process. However, while improvements in the properties of materials after cryogenic treatment are discussed by the majority of reported studies, the correlation between microstructural alteration and mechanical properties are unclear, and sometimes the conducted investigations are contradictory with each other. These contradictions provide different approaches to perform and combine cryogenic treatment with pre-and post-processing. The present literature survey, mainly focused on the last decade, is aimed to address the effects of cryogenic treatment on microstructural alteration and to correlate these changes with mechanical property variations as a consequence of cryo-processing. The conclusion of the current review discusses the development and outlines the trends for the future research in this field. [ABSTRACT FROM AUTHOR]

In this article, the design and implementation of an electronic bicycle gear-shift with moving cassette is presented. The niche context where the needs developed is explained and the project evolution over two versions is described. Technical aspects considered in the design phase are discussed and detailed explanations of hardware layout and control software logic are given. Performance of the two implemented versions are compared through data recorded during the target competition (pedaling cadence and torque), highlighting the higher reliability of the second design thanks to mechanical simplification and a more stable position feedback. An additional comparison with cadence data from other competitors in a speed-challenge competition is then presented to highlights the main benefit obtained: a reduced variance in cadence that enables the rider to pedal at his optimal rate since the early stage and through the whole run-up. Finally, the current development of the project under a Proof of Concept grant is presented by discussing its potential application on the standard bicycle market, the need for an assessment of its value proposition and the main obstacles to overcome for complying (or not) with the current market standards. The article offers an overview of practical aspects to be considered when designing high-speed human powered vehicle transmissions, including technical details of an innovative solution and critical considerations about the possibility of such a specific design to develop within the standard bicycle market. [ABSTRACT FROM AUTHOR]

A hydrodynamic lubrication analysis for connecting rod big-end bearing is conducted. The effects of engine speed, operating condition, lubricant viscosity and oil temperature on tribological performance of big-end bearing have been examined. Force equilibrium is solved to define instantaneous eccentricity between journal and bearing to have accurate estimation of oil film thickness at interface of connecting rod big-end bearing and crankpin. Connecting rod big-end is treated as π film hydrodynamic journal bearing and finite difference scheme is applied to calculate generated hydrodynamic pressure and frictional power loss at each crank angle. Beside the development of analytical formulation, well-known Mobility model introduced by Booker has been employed to be compared with the analytical model. The presented analytical model reduces the complexity and the numerical effort with respect to Mobility method, thus shortening the computation time. The simulation results show good agreement between analytical model, Mobility approach and experimental data. [ABSTRACT FROM AUTHOR]