Predictive Modeling and Analysis of Thermal Failure in Plastic and Composite Gears Using VDI Method Approach

Abstract

A method for predicting surface thermal failure of gears made of plastic materials and their natural fiber composites is developed with the “Verein Deutscher Ingenieure (VDI)” “Association of German Engineers” method, and a simulation is made for these gears. The simulation is carried out for Duracon acetal gears and composite material of high density polyethylene (HDPE) with 40% birch wood fiber (HDPE40B) gears. The simulation is carried out with the same meshing characteristics that were used to carry out the tests on the gear test bench in real simulated operation to study the thermo-tribo-mechanical behavior of HDPE40B gears. From the predefined operating temperature, the torque-speed (C-ω) limiting curve is established using the computer program for predicting operating temperatures. Then the heat map is established using the same temperature calculation program by determining the equilibrium temperatures in the tooth and instantaneous temperatures on the profile according to the normalized positions S/pn. The induced surface contact stresses are then determined according to the normalized positions S/pn with the VDI method and are compared with the limit allowable stress. The results show that more severe operating conditions give comparatively lower induced stresses, but they are nevertheless the ones that will fail first at surface thermal failure compared to less severe operating conditions. In other words, the results show that the more severe the operating conditions, the shorter the operating cycles become before surface thermal failure occurs. The results also show that the surface thermal failure behaviors for plastics and composites gears are similar and the higher the melting temperature of the material, the butter it can stand surface thermal failure in more severe working conditions.