Experimental and analytical study of gear micropitting initiation and propagation under varying loading conditions

Abstract

Micropitting damage is one of the failure modes commonly observed in gears leading to destructive failures, which in turn results in unplanned shutdown and expensive replacement, such as those observed in wind turbine gearboxes. This study investigates gear micropitting initiation and propagation when subjected to varying torque loads under a constant rotational speed. The study employs both experimental gear testing and analytical evaluation based on the ISO Technical Report of Gear Micropitting, ISO/TR 15144-1:2010 and the recently revised ISO/TR 15144-1:2014. Initiation and propagation of micropitting are assessed in testing by quantifying the development of micropits and their progressive rate after specific numbers of running cycles at step-up torque levels. The analytical study is conducted to validate the prediction of micropitting using the ISO/TR recommended procedures by comparing the results with the occurrence of micropits in the tested gears.The gear test results show that micropitting initiates at the pinion dedendum but escalates at the addendum, because of the greater severity of progressive micropitting at the dedendum of the mating wheel where the tip relief area first comes into mesh. The analytical results, based on varying surface roughness measurements obtained from the tested gears, confirm that the maximum contact stresses and minimum specific lubricant film thicknesses occur in these regions. The specific lubricant film thickness varies considerably because of changes of surface roughness after gears are subjected to various running cycles under varying torque levels. It has found that the excessive loading, gear tooth micro-geometry, surface roughness and lubricant film thickness are the main factors affecting micropitting.

A Review on Micropitting Studies of Steel Gears

“…The crucial influence of load condition on the micropitting has been addressed by many studies [25,85]. Fajdiga et al [86] proposed a numerical model to simulate the micropitting growth on the tooth flank under boundary lubrication together with rolling and sliding conditions.…”

“…Long et al [24] from the University of Sheffield, South Yorkshire, UK, carried out an investigation on the influence of load variation on gear tooth surface micropitting based on ISO/TR 15144:2010 [20]. Al-Tubi et al [25] from the same research group studied the gear micropitting initiation and propagation under varying loading conditions based on the ISO/TR 15144:2010 and the revised version ISO/TR 15144:2014 [26]. Although many investigations have been implemented on the gear micropitting issues, and great progressions have been achieved by many researchers and engineers, the detailed mechanisms of micropitting crack initiation and propagation still remain unclear.…”

The evolution of hardness and tribofilm growth during running-in of case carburized steel under boundary lubrication

“…The formulae used to calculate these stresses were developed by Hertz in 1881 and later published in his watershed paper On the contact of elastic solids [37]. contacting gears [38]. Another assumption made in the Hertzian contact model is the contact between two bodies is made from two perfectly smooth surfaces.…”

Tensile Fracture Behavior and Failure Mechanism of Additively-Manufactured AISI 4140 Low Alloy Steel by Laser Engineered Net Shaping

“…AISI 4140 is one of the representative medium carbon and low alloy steels and widely used for manufacturing of many industrial components, such as gears, shafts, and rotors, due to its good hardenability, strength, toughness, and wear resistance [ 1 , 2 , 3 , 4 ]. However, when the components made of this alloy steel are exposed to harsh operating conditions, such as surface rolling and sliding contact, during their service life, they are susceptible to serious surface damage, such as micropitting, abrasive wear, and corrosion, which could accelerate premature failure and shorten the life cycle of these critical and expensive components [ 5 , 6 ]. Thus, it is essential to restore the worn-out or damaged components so as to lengthen their service life [ 7 ].…”