For the design of gears the knowledge of the load carrying capacity of the gear tooth root and the gear tooth flank is of main importance. Especially the highest stressed regions in the tooth root at the surface layer have to fulfil high strength requirements. That is why case hardening became one of the surface engineering techniques widely used in the automotive industry for an improvement against different damage and fatigue mechanisms. The aim of this work is an optimization of the carburizing process to save costs by finding the optimum between the oven time and the load carrying capacity of the surface layer. According to second Fick's law, the required oven time for the diffusion of carbon in the component surface increases with the square of the case hardening depth. The main task of the diploma thesis is the evaluation of the load carrying capacity of the case hardening steel 20MnCr5 taking the influence of the case hardened surface layer into account. Therefore the main material parameters - case hardening depth, hardness and residual stress distribution - influencing the local load carrying capacity are analysed and discussed. By means of rotating bending fatigue tests and tests on real components, FZG-C gear wheels, three different case hardening depths are performed. The geometry of the rotating bending specimen is notched to adjust nearly the same local stress concentration factor like in the tooth root of the test gears. The tested components are spur toothed gears, case hardened with three different case hardening depths of 0.3; 0.5 and 0.7 mm. Attendant thereto rotating bending tests, analytical evaluations according to DIN 3990 Part 3 standard and numerical evaluations by finite element simulations are accomplished. For further information about the crack initiation and the fracture behaviour a detailed analysis of the fracture surfaces is arranged. A final discussion about the fatigue test results delivers the influence of the case hardening depth to the load carrying capacity and illustrates a possible way of the transferability from the specimen to the real component.
|Translated title of the contribution
|Life time increase and cost saving through evaluating the optimal case hardening depth for gears due to experimental and numerical investigations
|18 Dec 2009
|Published - 2009
Bibliographical noteembargoed until null
- gear case hardening case hardening depth load carrying capacity