Different Failure Mechanisms in Keyed Shaft-Hub Connections under Dynamic Torque Load

Keyed shaft-hub connections are a very popular way to transmit torque via form fit in drive technology. Still in use for decades, they seem to be well known and current in design, although multiple field failures show existing gaps and uncertainties in the design. For this reason, numerous keyed shaft-hub connections were experimentally investigated and analyzed for their failure due to torsional loading. Keyed shaft-hub connections can be designed due to two different criteria: On the one hand, there is the maximum permissible contact pressure in the keyways that, if exceeded, causes a failure via an unacceptable plastic deformation of the keyway. On the other hand, there is the fatigue strength of the shaft or more specifically the connection. The results are based on a large amount of experiments of keyed shaft-hub connections under dynamic torque load. The experimental results of the investigations were analyzed with regard to different failure mechanisms and their dependencies. Most of the investigations focused on the failure caused by inadmissibly high plastic deformation of the shaft keyway. Furthermore, the transition from an unacceptable plastic keyway deformation to the initiation of different cracks are shown. The experimental results reveal that the decisive design criterion for keyed shaft-hub connections is dependent from the shaft material strength. Keyed shaft-hub connections with shafts made of low-strength steel fail via maximum permissible pressure in the keyway, thus consequently via an unacceptable plastic deformation of the keyway. Keyed shaft-hub connections with shafts made of higher strength steel fail via a crack at the shaft without prior relevant plastic deformation of the keyway. Both design criterions can be handled in the design of keyed shaft-hub connections with different internationally recognized German standards (DIN 743 and DIN 6892). Both standards have their miscellaneous shortcomings and potential improvements will be pointed out. In addition, the strong notch effect causes that the higher material quality of the shaft material does not result in a higher load capacity of the entire component.