NONLINEAR FINITE ELEMENT ANALYSIS OF COLLAPSE LOADS OF CYLINDRICAL SHELLS SUBJECTED TO COMBINED THERMAL LOADS AND EXTERNAL PRESSURES

摘要

The inner tube of the double-tube reactors used in some chemical process units must be designed to resist buckling. When the inner tube is operated at a higher temperature and at a lower pressure and outer tube is operated at a lower temperature and at a higher pressure, the inner tube will be subjected to combined thermal loads and external pressure. ASME Code Sec. Ⅷ Div. 1 provides a design procedure for shells, based on a B-chart, to ensure against buckling under external pressure, however, additional consideration should be made where plastic deformation may occur due to very large longitudinal thermal loads. In this study, nonlinear finite element analyses_-were performed to investigate the collapse of thick-walled cylindrical shells subjected to combined thermal loads and high external pressures. Two nonlinearities, a material nonlinearity (elastic-plastic behavior) and a geometric nonlinearity (large deformation), were considered in these analyses. The effects of initial imperfection in the shells (out-of-roundness) as well as of thermal loads were studied. The results showed that the longitudinal thermal loads reduce the plastic collapse load especially when the thermal loads are tensile. It was also shown that the loading sequence has a large effect on the collapse load especially when the thermal stress was larger.