Luís Magalhães

Experimental observations of contact fatigue crack mechanisms for austempered ductile iron (ADI) discs

Abstract Collected from several twin-disc contact fatigue tests, images concerning crack development at ADI surfaces and sub-surfaces are presented. Several auxiliary surface analysis techniques were used (electronic scanning microscopy, video imaging and perfilometry). Defects found at these ADI samples are characterised and related to operating conditions. Elastohydrodinamic theory was used to evaluate surface tribological performance, involving parameters such as lubrication, roughness and general operating conditions. Results concerning a quick procedure to allow the evaluation of fatigue resistance properties among different ADI sample discs are also presented.

Influence of tooth profile on gear power loss

Purpose – The purpose of this paper is to develop innovative geometry for gears aiming low power loss and easy manufacturing.Design/methodology/approach – New gear profiles were developed and studied, and gears were built accordingly and then tested using an FZG machine.Findings – Results from the experimental tests revealed the influence of the profile modifications on the operating temperature, thus on the efficiency of gears (in terms of power loss).Research limitations/implications – Studied cases were limited to experimental gear models compliant to the FZG machine.Practical implications – Low‐loss gears can be produced using common technologies and tools. Its design includes power loss minimization besides mechanical strength. The new gears are more environmentally friendly and can operate with lower power consumption, lower temperature, increasing gear and gear oil life.Originality/value – This work contributes to the development of the “low‐loss gears” concept, adapting it to low‐cost manufacturin...

Comparison of tooth profiles and oil formulation focusing lower power losses

Environmental awareness, lower consumption of raw materials and longer life of equipment are main concerns nowadays and are leading to the research and development of lubricants and equipment to access those requirements. In this study, the power loss performance of three different tooth profile geometries, developed with the purpose of decreasing power losses while keeping the predicted life, were tested and evaluated in a FZG test rig. The path to reduce power losses was based on the decrease of the module, the increase of the helix angle and increase of the addendum modification coefficients in order to reduce the path of contact, i.e. the sliding velocity. The power loss behaviour of two different lubricants was also evaluated for each tooth profile geometry considered. The influence of the oil level in the gearbox was also evaluated. One of the lubricants has an ester base while the other has a polyalphaolefin base and both are fully formulated. An energetic model was developed for the FZG test gearbox and applied to these tests to improve the knowledge about the influence of tooth geometries as well as lubricant formulation in the power losses and coefficient of friction between gear teeth. The developed geometries showed that the path followed for the reduction of power losses produced the expected results and can be implemented with success on gear design.

Contact fatigue behaviour of artificially indented austempered ductile iron (ADI) discs

Abstract A complete study of Austempered Ductile Iron (ADI) contact fatigue resistance would require long-cycle fatigue testing for each austempering variety, a process that could take several months or even years until enough data is gathered. Having this problem in mind, short contact fatigue test methods have been proposed by some authors [1,2,3,4] when approaching the same problem concerning steel components analysis. Contact fatigue tests using artificially indented ADI discs were performed in a twin-disc machine, as a quick procedure to characterize and evaluate the fatigue resistance properties of ADI. The tests were followed-up using several auxiliary surface analysis techniques such as electronic scanning microscopy, video imaging and profilometry. The obtained results allowed the characterization of the main contact fatigue mechanisms around indentations, and how the operating conditions affect those mechanisms. The post-test analysis of surfaces and sub-surfaces at zones away from the indentations allowed the characterization of other contact fatigue mechanisms, such as surface and sub-surface cracking, crack propagation and spalling, and how these phenomena are influenced both by the graphite nodules, foundry defects and Hertzian contact pressure.

Low torque loss gears: austempered ductile iron versus carburized steel

Low-loss power transmission gears operate at lower temperature than conventional ones because their teeth geometry is optimized to reduce friction. The main objective of this work is to compare the operating stabilization temperature and efficiency of low-loss austempered ductile iron (ADI) and carburized steel gears. Three different low-loss tooth geometries were adopted (types 311, 411 and 611, all produced using standard 20° pressure angle tools) and corresponding steel and ADI gears were tested in a FZG machine. The results obtained showed that low-loss geometries had a significant influence on power loss, gears 611 generating lower power loss than gears 311. At low speeds (500 and 1000 rpm) and high torque ADI gears generated lower power loss than steel gears. However, at high speed and high torque (high input power and high stabilization temperature) steel gears had better efficiency.

Contact Fatigue Behaviour of Artificially Indented Austempered Ductile Iron Discs

Artificial indentations have been used as an auxiliary method to study metallic surfacesx92 contact fatigue behaviour since the early 90x92s. In this work indentation techniques based on hardness measurements were tested on the surface of austempered ductile iron (ADI) discs. These discs were tested on a twin-disc machine. The evolution of the areas around indentations (in this work these areas are called ZAF Zones Affected by Fatigue) was followed during each twin-disc test and the surface condition of such artificially indented zones was characterized. These zones suffered intense plastic deformation and wear in early test stages and were then progressively damaged by contact fatigue. A coherent growth of each ZAF was observed along each contact fatigue test. It is shown that ZAFsx92 growth follows a trend simmilar to Paris law, revealing that the use of artificial indentations can be used as an auxiliary method to study contact fatigue phenomena.