Use this URL to cite or link to this record in EThOS: http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.636112
Title: A numerical study of energy criteria in fracture mechanics
Author: Bleackley, M. H.
Awarding Body: University College of Swansea
Current Institution: Swansea University
Date of Award: 1982
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Abstract:
In this study two energy fracture parameters, the Rice J-integral and 'Q' (derived from an elastic-plastic energy balance) have been calculated for several different specimen geometries. These parameters were obtained numerically using an elastic-plastic finite element program and then compared to experimental and analytical solutions to see if any significant trends emerged. The application of Q is invalid for sharp cracks, for it has been shown elsewhere that Q for an elastic-plastic material is a function of crack extension (As) and as pa i 0, Q • 0. This has been borne out numerically in this study, but the numerical results are still inconclusive in depicting the same trend for a plane stress case where substantial plastic deformation and a more distinct crack-tip opening displacement exists. One must interpret with care J-integral curves for different crack lengths of a given geometry, for these curves show different trends depending on how J is calibrated. In various specimens containing a through-thickness edge crack in the weld, no detectable variations of J values were found between evaluations on paths confined to the welded region around the crack-tip or paths traversing the weld/parent interface. Good overall correlation was obtained between numerical and analytical J values except in the single-edge shallow notch homogeneous tension specimen. This numerical study shows that 'backward' extension of plasticity from the crack-tip to the specimen edge occurs in shallow notch specimens. Backward yielding relieves the constraint at the crack-tip prior to general yield across the ligament; this phenomenon may explain recent experimental results showing shallow-cracked bend specimens failing in a ductile fashion and deep cracks in a brittle fashion. A comparison is also made between the discrepancies that can exist between different numerical solutions for the same specimens.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID: uk.bl.ethos.636112  DOI: Not available
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