Stress-reducing geometry optimization of short-fiber reinforced polymer gears to increase the tooth root load capacity

• Applicants: Professor Dr.-Ing. Oliver Koch; Professor Dr.-Ing. Karsten Stahl
• Subject Area: Engineering Design, Machine Elements, Product Development
• Term: since 2024
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 545926895

The tooth root load capacity of polymer gears is an essential factor for their service life. The geometry of polymer gears used today is usually based on conventional steel gears, which are bound to the restrictions of classic production tools in the machining of gears. The design freedom available through the injection molding process and the associated potential for using load-bearing capacity-optimized geometry variants without additional manufacturing effort have so far remained largely unused. When using fiber-reinforced polymers, the orientation of the reinforcing fibers has a decisive influence on the mechanical strength properties of a polymer gear. The correlations between fiber orientation and optimal design of the tooth root fillet to increase the load-bearing capacity have not been researched at present. In addition, the range of validity of the calculation methods available in practice for optimized root geometries and, in particular, the transferability of the calculation methods and test results on steel gears to polymer gears with and without fiber reinforcement is not sufficiently known. In this research project, the focus is on identifying tooth root geometries for gears made of fiber-reinforced polymer, with the help of which an increased tooth root load-bearing capacity can be achieved. Furthermore, the possible increase in load-bearing capacity will be quantified. In addition, an extension of the existing calculation methods for the reliable determination of the tooth root load capacity of gears made of fiber-reinforced polymer is being developed within the project. This should be applicable independently of the shape of the tooth root fillet. Based on a theoretical evaluation of different geometry concepts, promising geometry variants are modeled and investigated in detail. The focus of the investigations is in particular the consideration of the specific properties of fiber-reinforced polymers and their influence on the stress distribution in the tooth. In a further step, test gears with the most promising tooth root geometry are manufactured from short glass fiber-reinforced PA46 and PEEK to validate the theoretical investigations experimentally. To characterize the deformation behavior and the achievable load-bearing capacity, both pulsator tests and tests using rotating gears are carried out. Finally, influencing parameters on the tooth root load capacity that have not been considered so far will be integrated into common calculation methods according to the state of the art (such as VDI 2736). After the research project has been completed, there are not only comprehensive findings on the ideal design of the tooth root geometry of fiber-reinforced polymer gears but also statements on the validity and limits of the different theoretical calculation models as well as the analytical calculation approaches.

• DFG Programme: Research Grants