Abstract: Aiming at the problem of debonding failure of the stator rubber bushing of the screw motor, the failure mechanism of the stator bushing of the 7/8 head conventional and equal wall thickness screw motor was studied. The principle of rubber-metal interface cohesion was adopted in the study. Through rubber-metal bonding mechanics test and rubber uniaxial tensile test, and finite element and numerical analysis, the interface shear stress was found to be the main factor causing the bushing bonding failure, and the minimum arc radius $R$ of the bushing profile was the main reason for the change of the maximum interface shear stress. The drilling fluid and interference have a significant effect on the shear stress at the interface of the equal wall thickness bushing. When the drilling fluid pressure increases from 15 MPa to 60 MPa, the maximum shear stress at the interface of the equal wall thickness bushing increases by 146%, and the equal wall thickness screw motor is more prone to bonding failure. Finally, the different wall thickness bushing structure is proposed. The interface shear stress of the different wall thickness bushing is less than that of the equal wall thickness bushing, and decreases with the increase of the minimum arc radius $R$, which has good heat dissipation. The service life of the bushing with different wall thickness is proportional to the minimum arc radius when fatigue failure occurs. The maxi-mum service life is predicted to be 240.99 h when fatigue failure occurs. The first fatigue failure area is the inner cavity arc top of the bushing, which is consistent with the actual failure phenomenon. This paper provides a theoretical basis for the design optimization of screw motor, and makes an important contribution to improve the working life of screw motor.

Key words: cohesive zone model, interface shear stress, bonding failure, different wall thickness bushing, fatigue life prediction