Thermal failure of rubber bushing of a Positive Displacement Motor: A study based on thermo-mechanical coupling

• Material testing of a kind of nitrile-butadiene rubber was carried out to get Mooney–Rivlin parameters for calculation.
• Finite element method was used to calculate the thermo-mechanical coupling effect on PDM rubber bushing.
• The mud pressure, rotor rotation speed and formation temperature effects on bushing temperature rise were studied.
• The rubber bushing's heat failure modes in engineering practice are consistent with the calculation results.

Viscoelastic hysteresis of the rubber material often causes thermal failure of PDM (Positive Displacement Motor) stator bushing. Combining heat transfer modeling with material testing, finite element method was used to calculate the temperature field and thermal stress of the bushing, and their sensitivity to Poisson ratio, mud pressure, rotor speed and formation temperature. The results show that the maximum thermal stress occurs at the bottom of the arc of the bushing, and the maximum deformation occurs at the arc top. The distribution of temperature field appears oval-shaped and the temperature gradient is large. Bushing's temperature decreases with the increasing of formation temperature, but increases with the increasing static pressure and the rotor speed. The rubber bushing's thermal failure modes observations in practice are consistent with the calculation results.