Fatigue Crack Growth Behaviour of Nitrogen Bearing Austenitic Stainless Steel and its Weld: Analysis using Unified Approach By MATCHA NANI BABU Enrolment No. : ENGG02201504004 Indira Gandhi Centre for Atomic Research, Kalpakkam A thesis submitted to the Board of Studies in Engineering Sciences In partial fulfillment of requirements for the Degree of DOCTOR OF PHILOSOPHY of HOMI BHABHA NATIONAL INSTITUTE OCTOBER, 2019