Effect of Rim Thickness on Fatigue Breakage in Plastic-Gear Teeth

In the present paper, fatigue tests were carried out using spur and helical POM-C gears with various rim thickness in order to investigate the effect of the rim thickness on bending stress of plastic gear teeth. As a result, it was confirmed that variations in rim thickness brought the changes of crack directions in the tooth root and the service life of POM-C gears decreased with decreasing rim thickness. And service life of POM-C gears correlated greatly with the maximum principal stress on the tooth root obtained by the finite element analysis with tooth flank film elements (TFFEs). In order to determine the rim thickness factor in the equation of the tooth root stress, maximum principal stresses on POM-C gear flank were obtained by FEA for the gears with changing the number of teeth, gear ratios, profile shift coefficients, and helix angles. And bending strength of POM-C gears and life factor in load capacity of POM-C gears were discussed with calculation of tooth root stress in considering with determined rim thickness factor.