Monitoring the Progression of Micro-Pitting in Spur Geared Transmission Systems Using Online Health Monitoring Techniques
Micro-pitting is a fatigue effect that occurs in geared transmission systems due to high contact stress, and monitoring its progression is vital to prevent the eventual failure of the tooth flank. Parameter signature analysis has been successfully used to monitor bending fatigue failure and advanced phases of gear surface fatigue failure such as macro-pitting and scuffing. However, due to modern improvements in steel production the main cause of gear contact fatigue failure can be attributed to surface micro-pitting rather than sub-surface phenomena. Responding to the consequent demand to detect and monitor the progression of micro-pitting, this study experimentally evaluated the development of micro-pitting in spur gears using vibration and oil debris analysis. The paper presents the development of an online health monitoring system for use with back-to-back gear test rigs.
Certification of Engine Health Management Systems: Guidelines for Selecting Software Assurance Levels
The use of Engine Health Management (EHM) systems has been growing steadily in both the civilian and the military aerospace sectors. Barring a few notable exceptions (such as certain temperature and thrust margin monitoring) regulatory authorities around the world have not required these systems to be certified in any way. This is changing rapidly. New airframes and engines are increasingly being designed with the assumption that EHM will be an integral part of the way customers will operate these assets. This leads to a need for better guidelines on how such systems should be certified. The SAE E-32 committee on Propulsion System Health Monitoring is leading an industry-wide effort to develop a set of guidelines for certifying EHM systems.
Up to now, the reliability achieved by COTS components was largely sufficient for avionics, in terms of failure rate as well as time to failure. With the implementation of new and more integrated technologies (90 nm node, 65 nm and below), the question has arisen of the impact of the new technologies on reliability. It has been stated that the lifetime of these new technologies might decrease. The drift is expected to be technology dependent: integration, technology node, materials, elementary structure choices and process pay a key role. Figures have been published, which gives smaller lifetime than the 30 years generally required for avionics. This would of course impact not only the reliability, but also the maintenance of COTS-based avionics. Hence a new policy should be defined for the whole COTS supply chain. Faced with these impending risks, different methodologies have been developed.