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Fatigue crack characterization by image correlation.

Lopez-Crespo, Pablo (2007) Fatigue crack characterization by image correlation. PhD thesis, University of Sheffield.

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The structural integrity of many materials from aircraft structures, pressure vessels and offshore structures is closely related to the cracks existing in the component. The stress intensity factor is widely recognized as a major parameter for assessing the severity of a crack, and is extensively used in fatigue lifetime predictions. This work presents a new methodology for experimental determination of the effective stress intensity factor from image correlation data. In addition, the methodology allows the reconstruction of the full stress field. Based on a multi-point over-deterministic method, the full-field displacement information collected from the neighbourhood of the crack tip is combined with an elastic model based on Muskhelishvili's complex variable formulation to determine the opening and the sliding mode stress intensity factors. Utilization was made of edge-finding routines for locating the crack tip coordinates from the displacement fields. The technique was applied successfully to study real fatigue cracks in different aluminium alloy specimens, subjected to static and cyclic loads. Good agreement was also obtained for a crack emanating from a hole, where complex passing stress fields exist. Different factors such as crack face contact and rubbing effects, local mixed-mode arising from wedge opening or tilting of the crack front are identified as being responsible of the differences between the nominal and measured values. Finally the non-contacting tool was extended to the analysis of crack face interaction and crack closure problems, and it was found to be able to estimate the opening load.

Item Type: Thesis (PhD)
Academic Units: The University of Sheffield > Faculty of Engineering (Sheffield) > Mechanical Engineering (Sheffield)
Identification Number/EthosID: uk.bl.ethos.485887
Depositing User: EThOS Import Sheffield
Date Deposited: 18 Nov 2016 16:40
Last Modified: 18 Nov 2016 16:40
URI: http://etheses.whiterose.ac.uk/id/eprint/14917

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