Variational principles based methods for integrity assessments

The assessment of load carrying capacity under applied loads is an important goal in designing mechanical components and structures. Limit analysis is carried out to determine the load at which uncontained plastic flow occurs in the component under consideration. Lower bound limit loads are vital from the structural integrity standpoint and are germane to fitness-for-service assessments. -- The existing lower bound limit load determination methods using elastic modulus adjustment procedures (EMAP) such as the classical and mα-multiplier methods have a dependence on the maximum equivalent stress. These methods are therefore sensitive to localized plastic action, which occurs in components with thin or slender construction, or those containing notches and cracks. The lower bounds obtained using the present methods have an oscillatory behavior during successive elastic iterations. -- The mβ-multiplier method developed in this thesis is obtained by considering a distribution of stress rather than a single maximum equivalent stress. As a result, good limit load estimates can be obtained especially for shape-sensitive structures and components with cracks and notches. -- The applicability of the m fJ -multiplier method is extended such that the method can determine limit loads of pressure components exhibiting anisotropy. As a result, collapse load analysis can be performed for perforated heat exchanger tubesheet that is currently modeled as an equivalent solid plate with anisotropic properties. -- Simplified procedures for fitness-for-service assessment, suitable for use by plant engineers, is also developed. A variational formulation in plasticity is used to develop these procedures. The concept of "integral mean of yield" is utilized to problems involving locally thinned areas and local hot spots in the context of industrial pressure vessels and piping. -- The lower bound limit loads obtained by the mβ-method and the fitness-for-service assessment methods are compared with corresponding results of inelastic finite elastic analyses