Detectability of fatigue cracks in metals.

Master's thesis in Structural EngineeringThe repetitive cyclic loading are the main cause of fatigue in metals and consequently their failure. Furthermore, the defects due to fatigue such as surface breaking and sub-surface, drastically effects the integrity of the structures. Therefore, to achieve high-quality performance and profitability of the structure or a component, they need to be detected and characterize on time concerning their type, location, length, depth, width, and orientation. For this purpose, a lot of detection techniques have been introduced and employed widely. However, the role of Non-Destructive Testing (NDT) methods is vital in this regard due to its high reliability and versatility. This thesis work aims to evaluate the different types of NDT techniques, to detect the fatigue cracks in metals. For this reason, several most common NDT techniques including electromagnetic and contact/non-contact types are thoroughly described and compared in the light of the previous researches done by many researchers. Namely Ultrasonic Testing (UT), Magnetic Particle Inspection (MPI), Radiographic Testing (RT), Acoustic Emission (AE), Eddy Current (EC), Liquid/Dye Penetrant Testing (DPT), Alternating Current Field Measurement (ACFM), Visual Inspection (VI) and Thermographic Testing. Moreover, efforts are made to bring out the detection capabilities and limitations, primarily to enable the selection of an appropriate technique for a specific application such as automated testing capability, derived from an operator-independent concept, with the potential of complete characterization of defects in a material