Review and Case Study of the Linear Matching Method Framework for Structure Integrity Assessment

The Linear Matching Method Framework (LMMF) consists of a number of simplified direct methods for generating approximate inelastic solutions and answering specific design related issues in pressure vessel design codes using standard finite element codes. Currently, all the LMM procedures have been implemented in ABAQUS through user subroutines with powerful user-friendly plug-in tools. The LMM ABAQUS user subroutines and plug-in tools for structural integrity assessment are now in extensive use in industries for the design and routine assessment of power plant components. This paper presents a detailed review and case study of the current state-of-the art LMM direct methods applied to the structural integrity assessment. The focus is on the development and use of the LMMF on a wide range of crucial aspects for the power industry. The LMMF is reviewed to show a wide range of capabilities of the direct methods under this framework, and the basic theory background is also presented. Different structural integrity aspects are covered including the calculation of shakedown, ratchet and creep rupture limits. Furthermore, the crack initiation assessments of an un-cracked body by the LMM are shown for cases both with and without the presence of a creep dwell during the cyclic loading history. Finally an overview of the in house developed LMM plug-in is given. Its implementation in ABAQUS finite element solver through an intuitive Graphical User Interface is presented. The efficiency and robustness of these direct methods in calculating the aforementioned quantities are confirmed through a numerical case study, which is a semi-circular notched (Bridgman notch) bar. A 2D axisymmetric finite element model is adopted, and the notched bar is subjected to both cyclic and constant axial mechanical loads. For the crack initiation assessment, different cyclic loading conditions are evaluated to demonstrate the impact of the different load types on the structural response. The creep dwell impact is also investigated to show how this parameter is capable of causing in some cases a dangerous phenomenon known as creep ratcheting. All the results in the case study demonstrate the level of simplicity of the LMMs but at the same time accuracy, efficiency and robustness over the more complicated and inefficient incremental finite element analyses.