Numerical Limit And Shakedown Analyses Of The Pressure Vessels With Part-Through Slots

This thesis investigates the effects of part-through slots to the pressure vessel strength by using limit and shakedown analyses as well as a number of experimental tests. Until recently, many attempts have been made to address the issues at limit and shakedown analyses as well as related safety assessment methods of the pressure vessels with part through slots. These attempts represent the state-of-the-art and cutting edge of research and development in the field of the safety analysis of the pressure vessels, and have significant and extensive application background.This thesis presents a general computational approach for the limit and shakedown analyses, by using dimension deduction strategy, that is used to investigate the effects of various part-through slots to the limit and shakedown loads acting various structures, which results in a series of computational curves as well as the fit formulae for the stress concentrating factors, and limit and shakedown loads. The approach, called GAFLSA (General computational Approach For the Limit and Shakedown Analyses), is based on the following steps:(1) Melan theorem-based decomposition of the structural shakedown analysis into the search for optimal self- equilibrium stress field and the non-linear optimization of maximum load factor;(2) determination of the piecewise search method for dimension deduction-based iteration process, that is facilitated by identifying the spatial characteristics of the self-equilibrium stress field described in Step (1);(3) identification of the subspace for searching for optimal self-equilibrium stress field described in Step (1), that results from the elastic — plastic equilibrium iteration process by using the method described in Step (2);and(4) simplification of the non-linear optimization problem with multiple constrains into a unconstrained optimization problem, that is achieved by utilizing the structural characteristics of the formulae obtained in Step (3).GAFLSA can make the space and time resources required much less, and make the convergency better. As a result, GAFLSA can provide a more promising future for limit and shakedown analyses of many large scale structures with defects.In light of GAFLSA, the effects of various part-through slots to the limit and shakedown loads acting various structures are investigated and evaluated. First, the elastic stress fields and their stress concentrating factors are calculated for various combination of structural and defect cases. The structural cases include plates, spherical shells, and cylindrical shells. And the defect cases include single spherical, ellipsoidal, or rectangular part-through slots, or slot groups on the external or internal surfaces of the structures. Second, GAFLSA focuses on the effects of various part-through slots to the limit and shakedown loads acting various structures, the expansion regularities of the plastic areas at defect location, and the diverse failure modes of the pressure vessels with part-through slots. In the end, the relationships between the structural limit and shakedown loads and the stress concentrating factors are discussed.This research has lead to a series of computational curves as well as the fit formulae for the stress concentrating factors as well as limit and shakedown loads, and a multiple level safety assessment method of the pressure vessels with part-through slots. Comparing with current codes and standards, this method can provide less severe allowable values of the part-through slots, which is expected to be able to achieve significant economical benefit.