|The design of structural components that are subjected to high temperatures requires understanding the relationship between a range of possible failure modes and the history of temperature and mechanical loading. Traditionally this relationship has been made through the use of structural mechanics concepts, and expressed in terms of failure laws and rules that form the fabric of current design codes and life assessment methods. These codes and methods are usually based on results from linear elastic FE assessments, which produce too conservative solutions. An alternative detailed simulation allows the investigation of any type of load cycle, but inevitably involves significant computer effort for complex practical structures. For high temperature power plant, where the geometries are highly varied and the loading history may not be known in detail, simplified methods still dominate. In life assessment methods there is the further issue that available material data may be limited and the presence of cracks and welds needs to be taken into account.
New methodologies have been proposed to combine the convenience and efficiency of rule-based methods with the accuracy of detailed simulation techniques. These form the basis for the current development of the Linear Matching Method (LMM), and stem from explorations in the early 1990s of computational methods to provide highly accurate limit load solutions for problems of structural components containing cracks, as an input to life assessment methods. The basis of the LMM is through an idea of representing histories of stress and inelastic strain as the solution of a linear problem, where the linear moduli are allowed to vary both spatially and in time. The LMM has been formulated and implemented for various cyclic problems encountered in current structural integrity assessment methodologies, including shakedown and limit analysis, Ratchet Limit Analysis, Creep Rupture Analysis, Low Cycle Fatigue, Creep And Fatigue Interaction.[Chen H (2013) Development of the Linear Matching Method and it's Software Tool for the Design and Life Assessment of Mechanical Structures]