Disparate Contact Stress Behavior of Thermoplastic Gears against Steel Gear using 2D and 3D FEA

Based on the applications, the polymer gears are paired with different gear pair combinations such as Polymer - Polymer, Polymer - Steel, and Steel - Polymer. Finite Element Analysis is one of the effective techniques utilized to investigate the contact stress behavior of those gear pairs. Depending upon the selected conditions, such as two-dimensional finite element analysis with plane stress, plane strain conditions, and 3D FEA, the surface and subsurface contact stress occurrence between the gear pairs were observed. And, no proper explanations have arrived on such behaviors till date. Thus, the present study aimed to do a detailed 2D and 3D FE analysis for various thermoplastic gears with different gear pair combinations (S - P, P - S, and P - P) and investigated the occurrence of surface-subsurface stresses among the selected gear pairs. A comparison was done between the 2D and 3D FE analysis and validated with the assumed condition with regard to the face width. A gear with face widths of 5 and 20 mm has opted to reproduce the 2D plane stress and plane strain conditions, and their results were compared with 3D FEA. The contact stress data were extracted at 10 subsequent face width planes along the face width of a gear tooth. Higher directional stresses were noticed at the gear tooth mid-surface and reduced stress on the edges of the gear tooth for all the thermoplastic materials paired with all gear pairs. Surface stress for 2D FEA and subsurface stress for 3D FEA were detected for all the gear pair combinations. The maximum stress occurrence of 5 mm face width Steel - PP, Steel - ABS, Steel - DELRIN, ABS - Steel, DELRIN - Steel gear pairs exhibit a minimum depth value of 0.135 mm whereas 20 mm face width PC - Steel gear pair exhibits a maximum depth value of 0.3 mm. The maximum contact stress increases as a function of depth according to the proportional limit to elastic modulus dimensionless ratio.