Effect of wheel diameter on high-adhesion locomotive wheel tread thermo-mechanical stresses

A simplified thermoplasticity tread surface computer model for estimating the resulting stresses and plastic strains in the wheel treads of high adhesion locomotives is summarized. The nature and severity of the thermo-mechanical (TM) tread surface material cyclic loading associated with this new generation of driving wheels is then illustrated for a particular high traction AC locomotive starting operation (45% adhesion @ 10% slip) vs. a typical DC operation (35% adhesion @ 5% slip). A maximum flash temperature rise of 372 deg.C (670 deg.F) is predicted for the AC locomotive vs. 263 deg.C (473 deg.F) for the DC locomotive. The maximum effective TM stress is 33% lower, the residual tensile stress is 86% lower, and the plastic shear strain increment is 66% lower with the DC locomotive. The effect of wheel diameter on the flash surface temperatures and transient thermal stresses is explored theoretically. It is concluded that for any given load and traction conditions the diameter of the wheel has little effect on the magnitude of these tread surface temperatures and stresses. Nevertheless, since the mechanical stresses are moderately smaller for a larger wheel, the lower interfacial mechanical shear stress with the larger wheel will lead to a small reduction in plastic shear strain. For an increase in wheel diameter from 1.016 m (40") to 1.118 m (44"), for instance, the reduction in plastic shear strain is predicted to be only 4.6% for the plastic properties assumed.<
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