PSI - Issue 60

Md Rakim et al. / Procedia Structural Integrity 60 (2024) 136–148 Md Rakim et al. / Structural Integrity Procedia 00 (2023) 000 – 000

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Y. Guo et al. (2013), M.S. Rahman et al. (2009)], low cycle fatigue (LCF) [C. Cabet et al. (2013), V. Shankar et al. (2017), S.J. Kim et al. (2014), I. Sah et al. (2023)] and high cycle fatigue (HCF) [A.K. Karnati et al. (2019), A. Sarkar et al. (2020)]. Moreover, at elevated temperatures, components of the plant undergo considerable minute cracks along with voids that may have harmful effects. Studies suggest that fatigue crack growth (FCG) investigations on alloy 617M are somewhat limited. The analytical approach of linear-elastic fracture mechanics (LEFM) accurately estimates crack extension. Understanding the concept of fatigue damage behaviour along with crack initiation and propagation at elevated temperature ranges is important in maintaining the structural integrity aspects of boilers and super heaters that are based on the approach of “ damage tolerance ” [ T.L. Anderson (2017), G.E. Dieter (2013)]. Microstructural damage characterization at critical levels which leads to fatigue-crack propagation under cyclic loading conditions is a serious concern regarding the structural component’s integrity of boilers and super heaters. Investigations suggest that the behaviour of HCF for alloy 617M is carried out by several authors to enlighten the effects of high temperature at a particular stress level to evaluate fatigue life. Hence, investigation results disclose the S-N curves generation and Haigh diagrams for constant life [A.K. Karnati et al. (2019), A. Sarkar et al. (2020)]. The correlation between fatigue crack growth rates ( ⁄ ) with stress intensity factor range ( = − ) has been used for the quantification of material capability regarding “ damage tolerance ” [T.L. Anderson (2017), G.E. Dieter (2013)]. This technique analyses crack growth of different domains in material engineering over four decades [S. Suresh (1998)]. However, this approach is empirical and does not consist of the physical methodology of the deformation in the crack tip, particularly the cyclic plasticity that controls the crack growth behaviour for metallic alloys. Several factors influence FCG namely microstructural aspects, environmental impact, temperature conditions, load ratio ( R ), crack closure, ageing duration and frequency of cyclic loading, etc. [M.N. Babu and G. Sasikala, (2020)]. Temperature effects and aged conditions particularly on crack growth behaviour at the near-threshold are much more effective compared to the Paris regime. Herein, temperature and ageing time effects on FCG behaviour for alloy 617M within the threshold regime are represented. During cyclic loading conditions, a necessitated method of “damage tolerant” design is developed which is based on threshold crack-propagation, . Most of the researchers have studied the effect of LCF behaviour on base metals [L.J. Carroll et al. (2013), X. Chen et al. (2014), T.C. Totemeier and H. Tian (2007), K.B.S. Rao et al. (1988), M.A. Burke and C.G. Beck (1984)] but there is limited information regarding welded forms of alloy 617M [T.C. Totemeier (2007)]. For extremely high temperature LCF conditions, investigations on welded materials of alloy 617M and also for austenitic stainless steels have shown low service life [T.C. Totemeier (2007), G.V.P. Reddy et al. (2008)]. Most of the mechanical structures consist of unavoidable welded components and these are merged using several weld methods. However, these weld materials are much more brittle compared to base metal which comprises various defects [W.G. Kim et al. (2013)]. Moreover, these are heterogeneous welded structures both in micro-structural and mechanical aspects that may develop a potential location for fatigue failure. So, mechanisms of fatigue damage namely initiation of fatigue crack