Dr.-Ing. Thomas Tobie

Dr.-Ing. Thomas Tobie studied mechanical engineering at the Technical University of Munich (TUM), Germany. Today he is head of the Load Carrying Capacity of Cylindrical Gears department at the Gear Research Centre (FZG), where he specializes in gear materials, heat treatment, gear lubricants and gear load carrying capacity research. Concurrently, Tobie brings to that work a particular focus on all relevant gear failure modes such as tooth root breakage, pitting, micropitting and wear, as well as sub-surface-initiated fatigue failures.  (Bio last updated 2016-01-01 Contact Randy Stott, Managing Editor, with changes.)

Articles by Thomas Tobie

  • Increased Tooth Bending Strength and Pitting Load Capacity of Fine-Module Gears (September/October 2016)
    The common calculation methods according to DIN 3990 and ISO 6336 are based on a comparison of occurring stress and allowable stress. The influence of gear size on the load-carrying capacity is considered with the size factors YX (tooth root bending) and ZX (pitting), but there are further influences, which should be considered. In the following, major influences of gear size on the load factors as well as on the permissible tooth root bending and contact stress will be discussed.
  • Influences on Failure Modes and Load-Carrying Capacity of Grease-Lubricated Gears (January/February 2016)
    In order to properly select a grease for a particular application, a sound knowledge of the influence of different grease components and operating conditions on the lubrication supply mechanism and on different failure modes is of great benefit.
  • Tooth Flank Fracture - Basic Principles and Calculation Model for a Sub-Surface-Initiated Fatigue Failure Mode of Case-Hardened Gears (August 2015)
    Cracks initiated at the surface of case-hardened gears may lead to typical life-limiting fatigue failure modes such as pitting and tooth root breakage. Furthermore, the contact load on the flank surface induces stresses in greater material depth that may lead to crack initiation below the surface if the local material strength is exceeded. Over time the sub-surface crack propagation may lead to gear failure referred to as “tooth flank fracture” (also referred to as “tooth flank breakage”). This paper explains the mechanism of this subsurface fatigue failure mode and its decisive influence factors, and presents an overview of a newly developed calculation model.