Simplified limit load determination for integrity assessment

Adibi-Asl, Reza (2008) Simplified limit load determination for integrity assessment. Doctoral (PhD) thesis, Memorial University of Newfoundland.

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Abstract

The codes and standards in the pressure vessels and piping areas of the energy, petrochemical and related industries are based on the identification of potential modes of failures and a strategy for their avoidance. Instantaneous failures, specifically limit state and fast fracture, in the components and structures, can lead to catastrophic events. Therefore, integrity assessment of components and structures is required. -- Inelastic finite element method is widely used to conduct failure analysis. However, it can often be complicated, time consuming and expensive. As well, accurate results are dependent on the specification of adequate mesh density and an assurance of numerically stable solutions. Independent verification methods that are alternatives to inelastic finite element methods are often required for engineering designs. The methods discussed in this thesis, based on elastic modulus adjustment procedures (EMAP), provide rapid and stable solutions at a relatively lower cost. -- The elastic modulus adjustment methods rely on the convergence of the specific moduli adjustment procedure. A criterion for assessing the degree of convergence of EMAP is developed, and a procedure for achieving improved convergence is studied in this thesis. Also, simplified methods are developed in order to estimate the limit load in components and structures using iterative linear elastic methods. One of these procedures is the concept of reference volume that can be used to identify the kinematically active volume and dead zones in the components or structures. The reference volume method is shown to give a more accurate prediction of limit loads comparing to available traditional methods based on total volume. Furthermore, by invoking the concept of reference volume the systematic procedures are proposed to estimate the lower bound limit load solutions with high accuracy. This is very helpful for limit load analysis of the components/structures with stress razors such as notches and cracks. -- The concept of equivalence of "static indeterminacy" that relates a multidimensional component configuration to a "reference two-bar structure" is introduced for rapid estimation of the limit loads in components or structures. The procedures and methods discussed in this thesis are applied to some practical components (including cracks and notches) in order to verify their effectiveness in analyzing different geometries. Based on the proposed methods, integrity assessment analysis of different crack configurations, including multiple cracks and three dimensional effects, are studied in this thesis.

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