The effect of preliminary plastic hardening by tension on the cylindrical shells buckling during torsion

The results of the experimental and numerical analysis of the processes of elastoplastic deformation and loss of stability of tubular specimens from 12Kh18N10T steel under monotonic simple and complex kinematic loading by tensile-torsion are presented taking into account large deformations and non-uniformity of the stress-deformed state. The experimental studies were carried out on a modernized (in the standard version- only tension-compression plus alternating torsion) test complex Z100 ZWICK-ROEL, which allows performing tests for complex loading on tubular samples with simultaneous, synchronized setting of the parameters in the quasistatic loading range: the rate of the longitudinal force change (displacement), the rate of the torque change (angle of twist), the rate of the internal pressure change. Numerical modelling of the samples elastoplastic deformation and loss of stability was carried out in Lagrangian variables. Kinematic relations are formulated in speeds in the metric of the current state, which makes it possible to describe large form changes. The elastoplastic properties of the material are described by the flow theory with nonlinear isotropic hardening. The equation of motion is written in a fixed Cartesian coordinate system and follows from the equation of the balance of virtual powers. The system of equations, supplemented by kinematic boundary and initial conditions, is solved by the finite element method in combination with an explicit integration scheme of a cross type. There is a good agreement of the numerical results with the experimental ones on the residual shape of the samples and the integral characteristics of the deformation process (axial force from axial displacement and torque from the angle of twist). The analysis of the mutual influence of stretching and torsion on the loss of stability of the cylindrical shells has been carried out.