Tooth flank breakage

  Image of a tooth break Copyright: © Valérian Iss


Valérian Iss © Copyright: IWM


Valérian Iss

Group Heat Treatment


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An economically relevant type of damage that can occur in gear wheels is flank fracture. In the case of oscillating loads, it occurs at high cycle numbers in the material depth. The fracture is dependent on residual stresses that are built up during the heat treatment of case hardening. Due to local differences in cooling conditions and phase transformations, residual stresses are generated in the steel. The damage pattern from flank fracture is associated with this residual stress condition. As the relevant residual stresses are in a deep range, hardly any verified data and results are available. This is due to the complicated and costly measurements, which are not always 100% guaranteed.


  • Development of the targeted correlation between geometry, heat treatment process, material and residual stresses
  • Extension of calculation approaches for flank fracture load capacity (conspicuous features of flank fracture mechanisms), which take into account the residual tensile stresses in the material depth

Project contents

  1. carrying out heat treatments
  1. IWM Aachen
    1. Material characterisation for heat treatment simulation
    2. For the modelling
  2. Material data as a function of temperature, carbon concentration, phases
    1. Measurements of data using dilatometry
      1. determination of flow curves
      2. thermal expansions
      3. transformation behaviour Phase transformation behaviour/ determination of phase transformation characteristics
  3. Residual stress simulation / residual heat simulation
    1. Gears heat-treated by the IWT are calculated by the IWM on the basis of measured data of the treatments and the modelling of the heat treatment with the determined material data
    2. The calculation of the residual stress state in the component and the simulation of the residual stress states follows
  4. project partners: IWT (Leibniz Institute Bremen)
    1. Manufacturing and heat treatment of gears by means of different variants of carburizing and subsequent creation of different carbon profiles in depth
    2. Testing of various quenchants
    3. Testing of different geometries
    4. Production of real components and gears
  5. Munich
    1. Development of calculation methods for flank break
  6. Combination of residual stresses of flank break risk by means of mathematical approaches
    1. Analysis of the correlation between heat treatment process, geometry, residual stress state and flank breakage by parameter studies