The materials used in advanced ultra-supercritical (AUSC) applications will be subjected to different loads and temperatures depending on operating conditions. Any pre-existing defect or incipient damage during service conditions can lead to crack extension due to synergistic interaction of creep and fatigue/fracture conditions. It is necessary to estimate the life of such components by simulating the application conditions by carrying out creep-fatigue crack growth tests. Creep-Fatigue Crack Growth (CFCG) experiments have been carried out using CT specimens following ASTM E 2760 standard. CFCG tests were conducted at different load ratios, temperatures and holding durations at peak load of cycle. The CFCG data in terms of (da/dt) avg vs. (Ct) and da/dN vs. ΔK are generated for alloy 617 forged material at 650°C & 710°C and for P91 material at 600°C. It is observed that the CFCG behavior of samples subjected for higher loading conditions & temperatures and longer hold times tend to emphasize the role of high temperature in prolonging the crack growth phenomenon, thereby underlying the fact that new deformation mechanisms are coming into picture, which were not evident under lower temperatures and subdued loading parameters.
Dr. N. Narasaiah, Dept. of Metallurgical & Materials Engineering, National Institute of Technology, Warangal, India
Prof. N. Narasaiah obtained Bachelor’s Degree in Mechanical Engineering from The Institution of Engineers (India) in 1998, M.Tech. (2000) and Ph.D. (2004) from Indian Institute of Technology, Kharagpur, India. After obtaining Ph.D, he joined as Scientist in the CSIR – National Metallurgical Laboratory, Jamshedpur in 2004. After serving the CSIR-NML up to 2012, Dr. Narasaiah joined as a faculty member in the Department of Metallurgical and Materials Engineering, National Institute of Technology – Warangal. Dr. Narasaiah works in the area of fatigue and fracture behaviour of materials. His other interests include failure analysis, creep-fatigue crack growth behaviour, remaining life assessment and component integrity evaluation. He is the recipient of BOYSCAST fellowship for the year of 2007-2008 from Ministry of Science and Technology, India. During this period he worked at Stuttgart University, Germany on ‘stretch zone forming in ductile fracture of metallic materials’. He has published more than 50 publications in journals. He has carried out more than 30 research projects worth of Rs. 27.62 Crore. He served as Head of Department of Metallurgical and Materials Engineering, Professor In-charge of Center for Advanced Materials and Associate Dean (Planning & Development) at NIT Warangal.