Deep Cryogenic treatment: a bibliographic review

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 different materials reporting laboratory tests results, microstructural investigations and hypothesis on CT strengthening mechanisms have been published. The removal of retained austenite combined with fine dispersed η-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 formation 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 com

Experimental characterization of a Si-Mo-Cr ductile cast iron

High temperature-resistant ductile cast irons behaviour is highly interesting for the manufacture of components, such as exhaust manifolds for automotive applications. In the present paper the temperature-dependent static, high cycle and low cycle fatigue behaviour of a heat-resistant Si-Mo-Cr ductile cast iron (Fe-2.4C-4.6Si-0.7Mo-1.2Cr) is investigated. Tensile and high cycle fatigue properties, in terms of elastic modulus, yield stress, elongation at break, fatigue limits, and the stress-life Basquin’s curve parameters have been determined at room temperature, 160 °C, 500 °C and 800 °C, thus covering the usual temperature range to which actual components, obtained with this kind of material, are subjected. The alloy showed good monotonic properties at low temperature, but showed to be fragile during fatigue tests, due to the high Silicon content in the alloy. At 500 °C mechanical properties are still good, with a 40% decrease with respect to 160 °C, and ductility is increased. The last temperature level of 800 °C has caused a noticeable drop of the cast iron strength, due to softening and oxidation effects

Proposal of a stress-based isothermal LCF life model for Aluminium alloy cylinder heads

The paper presents and discusses the calibration procedure and the results related to a new easy-to-use low cycle fatigue (LCF) life prediction empirical stress-based model. The model was applied to a commercial Aluminium alloy diesel engine cylinder head. The material characterization was carried out on commercial cylinder heads made by primary AlSi9Cu1, investigating the mechanical properties on sets of specimens obtained from layers positioned at different distances from the gas face of the cylinder heads. The results of mechanical characterization and LCF model calibration parameters are presented for each layer. The material characterization was carried out at room temperature to assess the procedure and validate the model. The life assessment performance of the model was compared with the corresponding Basquin-Manson-Coffin model. The model prediction fitted the experimental data trend with a determination coefficient ranging from 0.75 to 0.98, which is globally higher with respect to the parameter fitting obtained with the Basquin-Manson-Coffin calibration. Furthermore, all life forecasts are close to the experimental results with a variance lower than 55%. A future development of the research work with further material characterization at different temperature will allow to validate and discuss the temperature dependence of the model parameters and to investigate its thermo-Mechanical Fatigue (TMF) life assessment performance

Finite Element Thermo-Structural Methodology for Investigating Diesel Engine Pistons with Thermal Barrier Coating

Traditionally, in combustion engine applications, metallic materials have been widely employed due to their properties: castability and machinability with accurate dimensional tolerances, good mechanical strength even at high temperatures, wear resistance, and affordable price. However, the high thermal conductivity of metallic materials is responsible for consistent losses of thermal energy and has a strong influence on pollutant emission. A possible approach for reducing the thermal exchange requires the use of thermal barrier coating (TBC) made by materials with low thermal conductivity and good thermo-mechanical strength. In this work, the effects of a ceramic coating for thermal insulation of the piston crown of a car diesel engine are investigated through a numerical methodology based on finite element analysis. The study is developed by considering firstly a thermal analysis and then a thermo-structural analysis of the component. The loads acting on the piston are considered both separately and combined to achieve a better understanding of their mutual interaction and of the coating effect on the stress state. The thermal analysis pointed out a decrease of temperature up to 40°C in the upper part of the piston for the coated model. Despite the lower deformations induced by the reduced thermal load, the stiffening effect provided by the TBC results in higher peak stress. However, the lower temperature field inside the piston compensates by allowing higher yielding stresses for the component and reducing the impact on the safety factor. The methodology is validated by comparison of the model results with numerical data available from the literature; limitations and potential future improvements are also discussed

CFD analysis of internal ventilation in high-speed Human Powered Vehicles

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 analyze 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 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

An Overview of Engine Components Friction Modeling

Development of efficient internal combustion engines (ICEs) is receiving wide attention due to increasing environmental legislation limits and fuel and emission costs. In order to improve ICEs performance, it is vital to gain insight of lubrication mechanism and tribological performance of engine reciprocating and rotating components. Analytical modeling of engine components such as piston ring assembly (PRA), connecting rod big eye and main journal bearings tribological behavior widely accepted as reliable tool by researchers and car industries. The principle aim of this paper is to briefly describe technical aspects and governing equations as well as numerical approaches apply to simulat

Smart Manufacturing in Rolling Process Based on Thermal Safety Monitoring by Fiber Optics Sensors Equipping Mill Bearings

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

Design and Construction of a Moving Cassette Electronic Gear-Shift for Human Powered Vehicles

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

Gas escape to crankcase: impact of system parameters on sealing behavior of a piston cylinder ring pack

Abstract 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