Conventional analysis of tubesheets in nuclear steam generators involves elastic analysis of a solid plate with equivalent properties. It has recently been recognized that alternate design techniques such as inelastic finite element analysis would lead to substantial cost reductions in material and manufacturing. Due to the anisotropy, arriving at yield criteria for an equivalent solid tubesheet is more complicated than for an isotropic solid. In addition, applying plastic finite element analysis in design is significantly more complex and time-consuming than elastic analysis. This paper proposes a relatively simple method to perform tubesheet collapse analysis. An anisotropic yield criterion is applied in conjunction with the classical lower-bound theorem of limit analysis and repeated elastic analyses involving elastic modulus modification. Two yield criteria are examined, namely Hill’s yield criterion and a recently suggested compressible fourth-order yield function. The collapse load predictions of the lower-bound equivalent solid methods are compared with the elastic-plastic finite element collapse load of the equivalent solid and of the actual perforated tubesheet.
Robust methods for estimating limit loads of symmetric and non-symmetric plate structures are presented. The methods proposed in this paper for determining limit loads are (1) the r-node method and (2) the semi-circle construction technique. Analytical methods for estimating the limit loads of plate structures are feasible only for simple configurations. Also, determination of limit loads based on assumed collapse mechanisms may not always give upper bound estimates. Limit analysis using inelastic finite element analysis is often elaborate and time consuming. The methods described in this paper circumvent these difficulties. The methods are applied to several configurations of symmetric and non-symmetric plate structures and the limit load estimates are found to be satisfactory.
A simple procedure uses the r-nodes to achieve minimum weight design of mechanical components and structures. The method is based on two linear elastic finite element analyses (or more) in order to arrive at a component configuration that would correspond to the minimum weight design. The proposed method is applied to pressure component configurations of practical interest.
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