In order to reveal the forming mechanism of assembly stress at the bottom of harmonic gear flexspline of ultrashort cylinder

a spline function is used to express the bending deformation model of the bottom disk of the cylinder

and a theoretical calculation method of assembly stress at the bottom of the cylinder is proposed. The radial

circumferential and axial deformations of flexspline ring are solved by using the semi-moment theory of shell. According to the asymmetric bending model of the bottom of flexspline with center fixed support

the expressions of bending deformation and assembly stress of flexspline cylinder bottom deformation were obtained through boundary conditions and continuous displacement conditions of flexspline cylinder and bottom. The finite element model was established to numerically verify the theoretical calculation method. The comparative study shows that the deflection and normal stress at the bottom of the flexure cylinder are maximum in the long and short axes

and the shear stress is maximum at 45°. The deflection and shear stress of barrel bottom increase with the increasing of polar diameter

while the shear stress decreases with the increasing of polar diameter of barrel bottom. In the assembly state

the principal stress is radial normal stress

and the maximum values of circumferential normal stress and shear stress are 1/3 of the radial normal stress.