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Reinforced polymers (RPs) are widely used in structural, industrial, automotive, and engineering applications due to their ecofriendly nature and the potential to manipulate their properties. This article addresses the technical synthesis of RPs, referring to their tribological behavior, to provide insights into the contribution and interaction of influential parameters on the wear behavior of polymers. It provides a brief discussion on the effects of significant parameters on RP tribology. The article describes abrasive and adhesive wear and provides a theoretical synthesis of the literature regarding the wear mechanisms of RPs. It also describes the synthesis of abrasive wear failure of different types of RPs and highlights the contribution of these influential parameters. The article addresses the synthesis of adhesive wear failure of different types of RPs.

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.

In this article, the methodology and results of an experimental campaign on small and slick bicycle tires are presented. The test was developed to compare the rolling resistance of tires to be used in high-speed competitions for streamlined human-powered vehicles. After an explanation of the theoretical background for the measurement, the test-rig and the adopted procedure to measure and subtract aerodynamic effects are presented. The obtained data show that the rolling resistance coefficient has a nonlinear dependency from the speed between 45 and 145 km/h. The data comparison points out a decrease in rolling losses up to 54% by switching from a butyl to latex inner tube on the same tire, whereas no significant difference is detected between the latex tube and tubeless configuration. An estimation of the impact on racing performance is provided, showing that selecting the best option could save up to 19% of the overall effort energetic cost, which means a higher final speed can be achieved with the same rider effort. Finally, a speculative analysis is proposed that considers different functions to fit the obtained data, pointing out the need for experimental measurements on the very-low-speed region to achieve a better understanding of the entire rolling resistance behavior with respect to speed.

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.

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.

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.

Even if it makes a smaller contribution than aerodynamic drag, rolling resistance plays a non-negligible role in the efficiency of human-powered vehicles, whether they are designed for daily commuting or to set speed records. The literature, experimental evidence and models show that the rolling resistance coefficient of cycling wheels strongly depends on the supported load, suggesting that the number of wheels and the load distribution could play a role in vehicle design and in road-test data analysis. Starting with an in-depth look at the relationship between a single wheel and overall vehicle rolling resistance coefficients, an analysis is proposed and discussed with the aim of minimizing the rolling resistance of a vehicle. Finally, a parametric surface response model for rolling resistance is obtained as a function of wheel size and the number of wheels. The overall analysis overturns the popular assumption according to which ‘the more wheels, the more rolling resistance’, at least according to a strict definition of the phenomenon.

A mold insert is an important component of the molds commonly used in die casting processes. Its purpose is to realize particular shapes in castings, like cavities and undercuts. It is also used for improving the cooling system in some critical areas. Each insert has at least one simple cooling channel for controlling the thermal state of the mold and for cooling every hot spot efficiently. The severe cyclical thermal conditions, together with the mechanical stresses due at first to the molten metal cast in the shape and then due to the solidified casting, submit the insert to thermomechanical fatigue. The thermomechanical fatigue is the main cause of the cracks observed on insert surfaces after a certain number of cycles, which makes the component unusable and requests its substitution. This circumstance has a negative influence on direct and indirect costs. In this case, the phenomenon has been studied on a mold insert used for realizing an oil drain channel in an aluminum alloy cylinder block made through die casting process. The aim of the present work is to determinate the zones which are mostly subjected to high temperature and high thermal gradients and to design and analyze a more efficient cooling system by using conformal channels on the same insert realized in additive manufacturing.

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.

Despite the wide literature on the mechanical behaviour of carbon/epoxy composites, it is rare to find practical methodological approaches in finite element design of structural components made by laminate layup. Through the case study of a special bicycle fork needed in a Student Team prototype, this paper proposes a simplified methodology as starting point for educational and manufacturing purposes. In order to compare two manufacturing solutions in terms of stiffness, strength and failure mode, a numerical model was implemented. Since the project requirements imposed to avoid standard destructive testing, the model validation was based on a posteriori linear stiffness comparison with the manufactured component. The slight discrepancies between experimental and numerical results were discussed in order to check their origin and to assess the reliability of the model. The overall methodology, even if complain with only a part of the safety standard requirements, shows to be reliable enough and can be the basis for further extension and refinement.

Coast-down techniques are widely used on bicycles and motorized vehicles in order to estimate retarding forces and respective coefficients. The mathematical model behind coast-down data analysis is usually based on the assumption that both drag and rolling-resistance coefficients do not depend on the vehicle speed. This assumption restricts the model validity to the specifically tested range of speeds and provides averaged values for the force coefficients. In the attempt to overcome this limitation, the proposal of a complete polynomial equation of motion is developed, evaluated and discussed through a human-powered vehicle case study. The analysis points out that the extended model is adequate for experimental data fitting and could potentially provide a more reliable power–speed prediction outside the testing range. However, the expressions included in the model in order to account for speed-dependent coefficients are first approximation with limited capability to represent these complex phenomena. As a consequence, further experimental testing is needed in order to achieve a validation. Advantages and side effects of both the classical and the complete polynomial models are discussed, concluding that the two approaches could be complementary and could answer different needs that specifically depend on the purpose of the coast-down analysis.

The problem of treatment parameter optimization focused on the fatigue resistance is analysed through a case study about Deep Cryogenic Treatment (DCT) of AISI 302 steel. In particular, the possibility to integrate fatigue data fittings through the Maximum Likelihood Estimation (MLE) method in the optimization process is evaluated. Two levels of two parameters (soaking time and temperature) are considered and then expanded to three by proper scaling of their values in order to include the untreated case as a “zero” level. Fatigue focused optimization is then achieved by standard Response Surface Method (RSM) and by MLE with two models for comparison purposes.

The micro-mechanical model for fatigue crack initiation proposed by K. Tanaka and A. Mura in 1981 is analysed and rewritten in a different form, which allows highlighting its formal analogy with an empirical model previously introduced by W. Weibull in 1934. The result is a unified phenomenological model that can be used for both fatigue data fitting and life predictions. Strengths and limitations of the model are discussed and a case study of experimental data fitting is presented. In the example application, the model parameters of 18NiCrMo5 carburized steel are obtained through the likelihood maximization over fatigue test data. A comparison between the estimated parameters for the material in two different conditions (untreated and deep cryogenically treated) is then given to confirm the micro-mechanical changes that should be induced by the cold processing and to point out the direction for further investigations.

The effects of deep cryogenic treatment (DCT) on the static mechanical properties of the AISI 302 austenitic stainless steel were investigated through experimental testing. The results of the tensile and hardness tests are discussed and compared to data and microstructural observations from the DCT literature concerning the same class of steel. In addition, the influence of two important treatment parameters, such as the soaking-time and the minimum temperature, is analysed through a full factorial design of experiments (DOE) and by means of a first approximation model in order to obtain confirmation and suggestions about the possible use of the DCT as a standard practice to improve the mechanical properties of stainless steels. A particular focus is given to the registered changes of the elastic modulus and of the hardness as representative measures of two different deformation mechanisms.

During the last decade, the interest about deep cryogenic treatment (DCT) is grown beyond its successful application on tool steels. The use of such cold treatment has shown positive effects on carburized steel fatigue life and some promising results were also noticed on stainless steels and on other materials. In this article, the DCT effects on fatigue and corrosion resistance of the AISI 302 austenitic stainless steel are analysed starting from the results of an extensive experimental campaign that was performed on both hardened and solubilized material conditions. The analysis includes an evaluation of the influence that the most important treatment parameters have on the final result. Considering their statistical significance at different reliability levels, the results show that the DCT can improve the fatigue behaviour of the solubilized AISI 302, while no important changes are noticed on the hardened material. Moreover, no difference was detected on the corrosion resistance of the cryotreated material, ensuring that such key-property for this class of steel is not compromised by the cryogenic treatment.

After analysing in a previous work the effects of the deep cryogenic treatment (DCT) on the static mechanical properties of the 18NiCrMo5 carburized steel, its influence on the fatigue behaviour of this material is investigated through stair-case experimental testing followed by SEM fractographic observations. The aim of the study is the comparison between different sequences of DCT and tempering to be performed after a conventional carburization. Two levels of the soaking time parameter are considered for the case of the pre-tempering DCT in order to analyse its influence. A careful statistical analysis of the experimental data is performed and the SNP curves are plotted using the Maximum Likelihood method. A substantial effect on the fatigue behaviour is noticed for all the cryotreated groups, with a general remarkable reduction in data scatter, which is in agreement with the DCT induced carbides segregation largely reported by literature. While in the case of the pre-tempering DCT the improvement is counterbalanced by some other changes, perhaps involving the residual stress state, leading to a general loss in fatigue life, the post-tempering DCT revealed no side effects giving a more reliable and durable material behaviour.

In this paper the influence of DCT (Deep Cryogenic Treatment) and a CrN arc-deposited PVD (Physical Vapor Deposition) coating on the fatigue behaviour of AISI 302 stainless steel was studied. Rotating bending tests were carried out on standard specimens to evaluate the fatigue limit at 300000 load cycles. The single and the combined effects of the two treatments were investigated by addressing untreated, PVD-coated and both PVD-coated and DC-treated specimens to the tests. All the series of specimens were also tested statically and laboratory analyses including fracture surface SEM observations and hardness measurements were performed.

In this paper, the influence of deep cryogenic treatment (DCT) on mechanical properties of two commercial steels is analysed. Hardened AISI 302 stainless steel and 18NiCrMo5 carburized steel specimens were subjected to DCT after standard treatments. For both materials, the fatigue behaviour is a key property considering their usual applications requirements. Surface hardness, tensile properties and axial fatigue resistance of both materials were measured and compared with and without DCT. From the analysis of the experimental results and from their interpretation in the light of the previous literature, some useful indications are obtained about the DCT potential fallout on design and construction of structural components.

In consideration of the raising interest about the application of the deep cryogenic treatment (DCT) on materials, its effects on the static mechanical properties of a commercial gear carburized steel (18NiCrMo5) are investigated through hardness and tensile tests followed by optical fractographic observations. The present study focuses on the comparison between the results given by different sequences of DCT and tempering performed after the conventional case hardening. In addition, the soaking time parameter influence is analyzed for the case of the pre-tempering DCT. A special attention is paid to the statistical analysis of the experimental data in order to avoid misinterpretations. The results point out substantial hardness increases (from +0.6 HRC to +2.4 HRC) for all the cryotreated groups and a remarkable enhancement of the tensile strength (+11%) in one case, indicating that different sequences and DCT parameters must be considered depending on the application requirements. The experimental results are then discussed in consideration of the literature about the DCT on similar steels with the aim of correlating the obtained improvements to the microstructural mechanisms that are commonly ascribed to this treatment.

The use of cryogenic treatment (CT) to improve mechanical properties of materials has been developed from the end of the Sixties. At the present time, the initial mistrust about CT has been cleared up and many papers about differ- ent materials reporting laboratory tests results, microstructural investigations and hypothesis on CT strengthening mecha- nisms have been published. The removal of retained austenite combined with fine dispersed � -carbides precipitation have been widely observed and their effects on mechanical properties have been measured. In addition, some recent studies have pointed out a different mechanism for fatigue strengthening of stainless steels, which involves nano-martensite for- mation during the CT. The present paper summarizes the state of art about CT, focusing on methods, parameters, results and assumed microstructural mechanisms, in order to get a starting point for new researches to come. th century, but the actual interest on cryogenic treatment (or cryo- treatment, CT) was developed during the last years of the century. The basic CT consists in a gradual cooling of the compo- nent until the defined temperature, holding it for a given time (freezing time) and then progressively leading it back to the room temperature. The aim is to obtain an improvement of mechanical properties, typically hardness and wear resis- tance, but in recent tests fatigue limit too, and to achieve an optimal ratio between conflicting properties, like hardness and toughness.

Student Team Challenges on specific topics are growing in popularity as efficient ways to stimulate students’ independent work, technical and management learning as well as socialization and internationalization. Many competitions are focused on ground vehicles (SAE Formula, Motostudent, Shell Eco Marathon, Solar Challenge), with different focuses on performance, fuel consumption or other depending on the aim of the event. An interesting approach is proposed in the United States by the ASME HPV Challenge, which is focused on Human Powered Vehicles. This class of vehicles allows not only to set-up a classical competition in terms of design, innovation, presentation, manufacturing and racing, but also to grow the student awareness about speed-energy relation. An HPV gives to the rider a direct feedback on a “human-scale” about energy quantities involved in personal mobility. The main returns by the use of this specific topic for a student challenge are: better understanding of the sustainable mobility problem, awareness about the potential and the limits of human muscular power, development of technical skills about design and engineering of lightweight and efficient vehicles, stimulation of the HPVs market development (the students are both potential future designers/manufacturers and/or customers), promotion of healthy and engaging physical activities. In this context, while Europe is rich of HPVs amateurs and manufacturers and is the usual location of the WHPVA World Championship, there is a lack of an educational framework involving students and teachers. Starting from the end of ZEV-HPV Erasmus Intensive Program 2011–2013, the proposal of creating a specific HPV challenge for the European students was developed by the authors. In particular, it was evaluated that by integrating the Student Challenge in the WHPVA World Championship as a special “Educational” category, many reciprocal advantages could be obtained: logistic and organizational support from the WHPVA and its national representatives, in particular for racing and timing, reciprocal technical and cultural exchange between students, academics and the hundred of amateur rider/designer/builder that were attending the event in the last decade, growth and renewal of the European HPVs community by aggregating young people around the subject and by stimulating the research of innovative solutions. After an in-depth analysis of the arguments reported above, an overview of the rules for the 1st edition of EU HPV Student Challenge will be presented and compared to analogous international competitions from an educational perspective.Copyright © 2014 by ASME

As the use of polymers in structural components and power transmission systems has grown in the last decades, the demand for improved mechanical performances of these materials is increasing. Besides fibre reinforcement, the research about thermal treatments and surface coatings of these materials is focused on obtaining more strength and resistance to fatigue and wear. In this direction, a contribution can be given by unconventional treatments such as cryogenics. The use of deep cryogenic treatment (DCT) on polymers is already claimed as miraculous by some companies. The analysis of peer-reviewed literature shows that it is not all marketing: many pure and reinforced polymers have shown DCT improvements in hardness and in wear resistance under controlled experimental conditions. Starting from these results, a general overview of potential DCT applications on polymeric products is given in order to suggest further developments and research areas.