TY - THES

T1 - Validation of a New Method to Compute the Gearing Tooth Root Failure

AU - Neururer, Maximilian

N1 - embargoed until 22-09-2027

PY - 2022

Y1 - 2022

N2 - The hardening process is a common method to increase the mechanical strength of machine parts by microstructural transformation. This thesis examines two mechanisms that are assumed to be the key drivers for the change of mechanical properties; on the one hand the increased hardness of the surface material and on the other hand the residual pressure stress produced by volume expansion during martensitic transformation. The developed computation method considers those two effects and yields a simplified method to predict the static strength of pinions. At the current stage of computer aided engineering complete process chain simulations yield are used to model a hardened pinion. The effort and the number of required parameters is huge. The new computation method bypasses that costly procedure. The goal is to synthetically produce a finite element model that features both a realistic hardening pattern as well as a residual stress state. The comparison of a finite element simulation and experimental results of static breakage tests shows the accuracy of the developed method. Four different versions of the pinion are tested. They differ in hardening treatment. Pinion 1 features a surface hardness of 650 HV, a surface hardening depth of 0.8 mm and was manufactured by a supplier. Thus, its specifications conform with the serial part. The simulation model reaches an accuracy of under 2.2 %. Comparing the result of pinion 1 to the other 3 pinion types yields the following conclusions. The simulation model can reproduce the effect of different surface hardness levels. However, the simulation model consistently predicts a strength increase with a higher hardening depth, whereas the breakage tests conducted show a strength decreasing behavior with increasing hardening process duration. It was assumed that residual stress is the key mechanism behind this behavior. However, according to the simulations conducted residual stress has no influence on the static strength. At the current state of knowledge the observed strength decreasing effect is not explainable. It turned out that there must be a mechanism that is not considered yet and causes the difference between simulation and experiment.

AB - The hardening process is a common method to increase the mechanical strength of machine parts by microstructural transformation. This thesis examines two mechanisms that are assumed to be the key drivers for the change of mechanical properties; on the one hand the increased hardness of the surface material and on the other hand the residual pressure stress produced by volume expansion during martensitic transformation. The developed computation method considers those two effects and yields a simplified method to predict the static strength of pinions. At the current stage of computer aided engineering complete process chain simulations yield are used to model a hardened pinion. The effort and the number of required parameters is huge. The new computation method bypasses that costly procedure. The goal is to synthetically produce a finite element model that features both a realistic hardening pattern as well as a residual stress state. The comparison of a finite element simulation and experimental results of static breakage tests shows the accuracy of the developed method. Four different versions of the pinion are tested. They differ in hardening treatment. Pinion 1 features a surface hardness of 650 HV, a surface hardening depth of 0.8 mm and was manufactured by a supplier. Thus, its specifications conform with the serial part. The simulation model reaches an accuracy of under 2.2 %. Comparing the result of pinion 1 to the other 3 pinion types yields the following conclusions. The simulation model can reproduce the effect of different surface hardness levels. However, the simulation model consistently predicts a strength increase with a higher hardening depth, whereas the breakage tests conducted show a strength decreasing behavior with increasing hardening process duration. It was assumed that residual stress is the key mechanism behind this behavior. However, according to the simulations conducted residual stress has no influence on the static strength. At the current state of knowledge the observed strength decreasing effect is not explainable. It turned out that there must be a mechanism that is not considered yet and causes the difference between simulation and experiment.

KW - induction hardening

KW - residual stresses

KW - Induktionshärten

KW - Eigenspannungen

M3 - Master's Thesis

ER -