Browsing by Author "Dias, Nicole Gomes"
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- A methodology to develop shallow cracks for qualification of a NDT techniquePublication . Dias, Nicole Gomes; Gamboa, Pedro VieiraInspection and maintenance are important processes in the aeronautical field. The processes suffered a significant evolution over the years, due to the strong development and growth of aeronautical fleets. To guarantee aircraft safety, all critical damage should be intercepted in due time before it become an irreversible damage and compromise the entire structure. In this dissertation a methodology to create fatigue cracks of a certain dimension to be used on the qualification of NDT processes was developed. The methodology was developed based on numerical approaches, working with 2mm thick cracked specimens. For the qualification of the NDT process, the objective was to create a shallow fatigue crack on a specimen. A fourpoint bending test was modelled to restrain the crack propagation direction through thickness. Abaqus®, a finite element method software, is used to determine the stress intensity factor along the crack propagation, followed by a mathematical approach using Paris Law which is also presented to determine the crack growth along with the number of cycles. Using the software NASGRO® it was possible to determine the number of fatigue cycles that are needed for a crack starting at the initial notch to achieve the desired dimensions. The results portrayed indicate that the four-point bending test is an appropriate choice to create the crack with the imposed dimensions. By the use of the finite element method software, it is observed that the stress intensity factor is higher in the crack tip and it assumes the lower value in the notch tip. With the values of stress intensity factor, a verification study of the values was made in the Paris Law domain. A relation between the number of fatigue cycles and the values of stress intensity factor was achieved, meaning that, with the increase of fatigue cycles, the stress intensity factor also increases and consequently, the crack tends to develop into the thickness specimen.