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

Compression molding of reused in-process waste – effects of material and process factors

Effective strategies for the reuse and recycling of in-process prepreg waste are needed to reduce economic and environmental costs. In this paper, we investigate the compression molding of prepreg waste converted into scrap “chips” (or strands). Material is randomly distributed within a lab-scale closed mold and cured with control of temperature and pressure. Material properties and process parameters such as chip geometry, fiber bed reinforcement, resin state, and cure cycle are varied and shown to influence porosity and thickness. These experiments clarify the phenomena governing microstructural quality and identify manufacturing pathways for high-quality parts. In addition, mechanical properties are measured for laminates with high and low defect levels. The study demonstrates the viability of prepreg reuse. Furthermore, the resulting insights provide a basis for practical science-based optimization of the reuse of production prepreg waste