The influence of the interface coefficient of friction upon the propensity to judder in automotive clutches

This paper presents an investigation of the driveline torsional vibration behaviour, referred to as judder, which takes place during the clutch engagement process, particularly on small trucks with diesel engines. A non-linear multibody dynamic model of the clutch mechanism is employed to study the effect of various clutch system and driveline components on the clutch actuation performance. The paper demonstrates that judder is affected by driveline inertial changes, variation in the coefficient of friction, μ, of the friction disc linings with slip speed, v, and the loss of clamp load. The results of the simulations show that various friction materials with different μ–v characteristics produce torsional self-excited vibrations of the driveline. The results also show that loss of clamp load relating to the speed of clutch actuation also contributes to judder. Furthermore, it is shown that the simulation results conform closely to the experimental findings

Heat generation and transfer in automotive dry clutch engagement

Dynamic behaviour of automotive dry clutches depends on the frictional characteristics of the contact between the friction lining material, the flywheel, and the pressure plate during the clutch engagement process. During engagement due to high interfacial slip and relatively high contact pressures, generated friction gives rise to contact heat, which affects the material behaviour and the associated frictional characteristics. In practice excess interfacial slipping and generated heat during torque transmission can result in wear of the lining, thermal distortion of the friction disc, and reduced useful life of the clutch. This paper provides measurement of friction lining characteristics for dry clutches for new and worn state under representative operating conditions pertaining to interfacial slipping during clutch engagement, applied contact pressures, and generated temperatures. An analytical thermal partitioning network model of the clutch assembly, incorporating the flywheel, friction lining, and the pressure plate is presented, based upon the principle of conservation of energy. The results of the analysis show a higher coefficient of friction for the new lining material which reduces the extent of interfacial slipping during clutch engagement, thus reducing the frictional power loss and generated interfacial heating. The generated heat is removed less efficiently from worn lining. This might be affected by different factors observed such as the reduced lining thickness and the reduction of density of the material but mainly because of poorer thermal conductivity due to the depletion of copper particles in its microstructure as the result of wear. The study integrates frictional characteristics, microstructural composition, mechanisms of heat generation, effect of lining wear, and heat transfer in a fundamental manner, an approach not hitherto reported in literature

Application of compact laser-driven accelerator X-ray sources for industrial imaging

X-rays generated by betatron oscillations of electrons in a laser-driven plasma accelerator were characterised and applied to imaging industrial samples. With a 125TW laser, a low divergence beam with 5.2±1.7 × 107photonsmrad−2 per pulse was produced with a synchrotron spectrum with a critical energy of 14.6±1.3keV. Radiographs were obtained of a metrology test sample, battery electrodes, and a damage site in a composite material. These results demonstrate the suitability of the source for non-destructive evaluation applications. The potential for industrial implementation of plasma accelerators is discussed

Study of the effect of contact force model on the dynamic response of mechanical systems with dry clearance joints : computational and experimental approaches

The main objective of this work is to present a computational and experimental study on the contact forces developed in revolute clearance joints. For this purpose, a well-known slider-crank mechanism with a revolute clearance joint between the connecting rod and slider is utilized. The intra-joint contact forces that generated at this clearance joints are computed by considered several different elastic and dissipative approaches, namely those based on the Hertz contact theory and the ESDU tribology-based for cylindrical contacts, along with a hysteresis-type dissipative damping. The normal contact force is augmented with the dry Coulomb’s friction force. In addition, an experimental apparatus is use to obtained some experimental data in order to verify and validate the computational models. From the outcomes reported in this paper, it is concluded that the selection of the appropriate contact force model with proper dissipative damping plays a significant role in the dynamic response of mechanical systems involving contact events at low or moderate impact velocities.Fundação para a Ciência e a Tecnologia (FCT

SoTL Research Fellows: Collaborative Pathfinding through Uncertain Terrain

From 2014-2016, Scholarship of Teaching and Learning (SoTL) Research Fellows at a mid-sized Canadian research-intensive, medical-doctoral university undertook to study their own formation as scholars of teaching and learning, as well as benefits and challenges of their cross-appointment to our central teaching and learning institute from their home academic departments. Findings from surveys and focus groups identified themes such as identity, community, access, transfer, and structural elements (each with benefits and challenges to practice). Our autoethnographic work confirms assertions in the literature about the uneasy relation between SoTL and traditional scholarship, while also bearing out the need for departmental support, and for key interventions along the path from novice to practitioner identity. Some discussion of the ambassador or translator role that can flow from such arrangements is included. De 2014 à 2016, les chercheurs en Avancement des connaissances en enseignement et en apprentissage (ACEA) d’une université canadienne médicale-doctorale de taille moyenne ayant un coefficient de recherche élevé ont entrepris une étude portant sur leur propre formation en tant que chercheurs érudits en matière d’enseignement et d’apprentissage, ainsi que sur les avantages et les défis de leur nomination conjointe à notre institut central d’enseignement et d’apprentissage tout en enseignant dans leur propre département universitaire. Les résultats des sondages et des groupes de discussion ont permis d’identifier certains thèmes tels que l’identité, la communauté, l’accès, le transfert, ainsi que des éléments structuraux (chacun présentant des avantages et des défis concernant la pratique). Notre travail autoethnographique confirme les assertions présentes dans la documentation existante concernant la relation difficile qui existe entre l’ACEA et la recherche traditionnelle, tout en tenant compte de la nécessité du soutien départemental ainsi que pour les interventions clés sur la voie qui consiste à passer de l’identité de novice à celle de praticien. L’article contient également des discussions sur le rôle d’ambassadeur ou de traducteur qui peut découler de tels arrangements

SoTL Research Fellows: Collaborative Pathfinding through Uncertain Terrain

From 2014-2016, Scholarship of Teaching and Learning (SoTL) Research Fellows at a mid-sized Canadian research-intensive, medical-doctoral university undertook to study their own formation as scholars of teaching and learning, as well as benefits and challenges of their cross-appointment to our central teaching and learning institute from their home academic departments. Findings from surveys and focus groups identified themes such as identity, community, access, transfer, and structural elements (each with benefits and challenges to practice). Our autoethnographic work confirms assertions in the literature about the uneasy relation between SoTL and traditional scholarship, while also bearing out the need for departmental support, and for key interventions along the path from novice to practitioner identity. Some discussion of the ambassador or translator role that can flow from such arrangements is included. De 2014 à 2016, les chercheurs en Avancement des connaissances en enseignement et en apprentissage (ACEA) d’une université canadienne médicale-doctorale de taille moyenne ayant un coefficient de recherche élevé ont entrepris une étude portant sur leur propre formation en tant que chercheurs érudits en matière d’enseignement et d’apprentissage, ainsi que sur les avantages et les défis de leur nomination conjointe à notre institut central d’enseignement et d’apprentissage tout en enseignant dans leur propre département universitaire. Les résultats des sondages et des groupes de discussion ont permis d’identifier certains thèmes tels que l’identité, la communauté, l’accès, le transfert, ainsi que des éléments structuraux (chacun présentant des avantages et des défis concernant la pratique). Notre travail autoethnographique confirme les assertions présentes dans la documentation existante concernant la relation difficile qui existe entre l’ACEA et la recherche traditionnelle, tout en tenant compte de la nécessité du soutien départemental ainsi que pour les interventions clés sur la voie qui consiste à passer de l’identité de novice à celle de praticien. L’article contient également des discussions sur le rôle d’ambassadeur ou de traducteur qui peut découler de tels arrangements