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•Experimental tensile and bending tests performed on polyoxymethylene samples.•Anand viscoplastic model used for polymer gear meshing mechanical analysis.•Contact response found to be ...influenced by the viscoplastic material component.•Low influence of viscoplastic properties on generated frictional heat found.•For steel-polymer pairs the heat partition coefficient is a time dependent function.
The nonlinear material properties of thermoplastics like polyoxymethylene (POM) can influence the thermo-mechanical response of polymer gears to applied running loads. In the presented study, the non-elastic strain rate- and temperature-dependent mechanical characteristics of POM are examined, along with their influence on the mechanical response of the polymer gear at the tooth root and contact interface, and the resulting heat generation driving the commonly exhibited temperature rise during gear meshing/running. A detailed experimental study of these properties was conducted, employing standardized and partly customized tensile and bending tests. Using a suitable viscoplastic constitutive material model, calibrated based on the obtained experimental results, a numerical structural-contact analysis of the gear meshing process was performed, which could subsequently be used for a more detailed evaluation of the generated frictional heat and resulting temperature rise during gear running. While a significant influence of the viscoplastic material properties on the mechanical contact response and the flash temperature rise on the POM gear was identified, no major impact on the long term nominal temperature rise was recognized.
Acetal gears are the most widely applied type among these polymer gears. Acetal gears may suffer from many failure forms such as severe wear, tooth breakage or tooth surface cracks depending on the ...loading conditions and the lubrication and temperature environment. The contact fatigue performance of acetal gear relates to many factors including temperature and load, however, their influences on the mechanical properties and fatigue parameters of the acetal material are still not fully understood. In this work, the thermo-elastic-plastic constitutive equations are derived to describe the acetal material behavior during gear meshing process, and the modified Brown-Miller multi-axial fatigue criterion is proposed to estimate the polymer gear contact fatigue life. Durability tests of acetal gear against steel gear are conducted based upon a developed test rig. Results reveal that the temperature rise could significantly reduce the contact pressure of acetal gear due to the decay of the modulus, but still jeopardize the fatigue life on tooth flank because the fatigue properties are also affected by the temperature rise. The predicted location of fatigue failure zone on the tooth and the lifespan agree well with experimental observation.
•Temperature effect on fatigue life of acetal gear is considered.•Thermo-elastic-plastic constitutive equations of acetal gear is derived.•The predicted fatigue lifespan agree well with test results.
This paper will concentrate on acetal gear wear behaviour and its performance prediction based on the extensive investigations on the gear thermal mechanical contact both experimentally and ...numerically. It has been found from the tests that acetal gear wear rate will be increased dramatically when the load reaches a critical value for a specific geometry and running speed. The gear surface will wear slowly with a low specific wear rate if the gear is loaded below the critical one. The possible reason of the sudden increase in wear rate is due to the gear operating temperature reaching the material melting point under the critical load condition. Gear surface temperature has been then investigated in details through three components: ambient, bulk and flash temperatures. Through extensive experimental investigations and modelling on gear surface temperature variations, a general relation has been built up between gear surface temperature and gear load capacity. An approach for acetal gear transition torque prediction has been proposed and this method is based on the link between polymer gear wear rate and its surface temperature. The method has been related to test results under different operating speeds and gear geometries. Good agreements have been achieved between the proposed method predictions and experimental test results.
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