INTRODUCTION1.1BackgroundFailure accounts for at least half of this mechanical

INTRODUCTION1.1BackgroundFailure due to repeated loading, that is fatigue, has accounts for at least half of this mechanical failure. No exact data is available, but many books and articles have suggested that between 50 to 90 per cent of all mechanical failures are due to fatigue, most of this is unexpected failures 1. In many situations a beam experiences fluctuating loading conditions. This may initiate and propagate a crack. The monitoring and modeling of fatigue crack growth is more significant for the stability and safety of machines components, bridges, aircraft and structures. In this project (EN8) medium carbon steel beam is used. In fatigue fracture the stress is generally below the yield stress. In general ductile material deforms before fracture and gives warning before failure of a component but in case of fatigue failure the ductile materials fails suddenly. This becomes more significant when failure is related to automobile sectors or machinery parts in which heavy loads or continuous work being done. In a dynamic world, however, failure occurs at stresses much below the material„s ultimate strength or yield strength. This phenomenon, failing at relatively low stresses, came as quite a surprise to most engineers in the early years of metal component design and manufacturing. The other frustrating aspect is that the material exhibited no sign of its tiredness or fatigue and could fail without much warning. This could be more dangerous if proper selection of design criteria is not selected and validation of those criteria with experiment is not done. There are many areas where the fatigue criteria should be in mind before designing the component.1.2 ObjectivesThe objective of present work is: To develop compliance correlation of a-N data and estimation of fatigue crack propagation life by using exponential model.1. To conduct fatigue crack propagation test of supplied (EN8) medium carbon steel under constant amplitude loading condition with different stress ratios.2. To propose an exponential model to predict fatigue crack propagation in single edge notched cracked beam.31.3 Thesis structureThe concept of present investigation is presented through six chapters. The first chapter presents an introduction of present work, 2nd chapter presents a brief review of literature. Chapter-3 describes the details of experimental procedure. Chaper-4 describes generation of crack profile and calibration of COD gauge, Chapter-6 describes the formulation and validation of proposed exponential model under constant amplitude loading condition with different stress ratios. Chapter-7 and Chapter-8, describes conclusion and possible future work respectively.