Progressive buckling: a numerical study to prevent evolution of geometrical imperfections

A parametric numerical study has been undertaken to get an estimation of the value of the cyclic loading, below which the evolution of an imperfection can be considered negligible, that is buckling analysis can be led with the initial geometry. This study was performed on cylindrical structures modelled with nonlinear shell elements, in the hypothesis of axisymmetrical imperfections and a material with linear kinematic hardening. Calculations were run with the following variable parameters: the shell thickness t; the magnitude of initial imperfection do; the intensity of a permanent axial load P; the amplitude of a moving temperature step Δ T. In each case, the evolution of the imperfection was investigated until stabilization (after about five cycles) and for each value of t, do, P, the minimum amplitude of the step Δ T thr needed to obtain a significant evolution of the imperfection (10% of do) was assessed (threshold loading). Evaluation the maximum efficient primary stress corresponding to the threshold loading, an approach, similar to the efficiency rule of RCC-MR for ratcheting, is proposed to ensure that the imperfection does not grow up. (author). 2 refs., 2 figs., 2 tabs