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Machine Design
Design Against Static Load
GATE 2008
Hard

A journal bearing has a shaft diameter of 40 mm and a length of 40 mm. The shaft is rotating at 20 rad/s and the viscosity of the lubricant is 20 mPa.s. The clearance is 0.020 mm. The loss of torque due to the viscosity of the lubricant is approximately

  • 0.040 Nm
  • B0.252 Nm
  • C0.400 Nm
  • D0.652 Nm

Explanation

Surface speed U=ωr=20×0.02=0.4 m/s. Shear stress τ=μU/c=0.02×0.4/0.00002=400 Pa. Shear force F=τ×πdL=400×π×0.04×0.04≈2.01 N. Torque=F×r=2.01×0.02≈0.040 Nm.

Source: GATE ME 2008 (2008)

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