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Title: Developing the 'Theory of Critical Distances' for practical integrity assessment of real-life structural components
Author: Louks, Richard
ISNI:       0000 0004 5992 1357
Awarding Body: University of Sheffield
Current Institution: University of Sheffield
Date of Award: 2016
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This PhD thesis details the research conducted to answer three questions in the field of fracture and fatigue engineering. The opening chapters provide fracture and fatigue background theory as well as a more comprehensive review of the Theory of Critical Distances (TCD), a theory proven to be successful in the assessment of components containing stress concentration features. Chapter 4 details an engineering approach based on the TCD for the static assessment of engineering components containing stress concentrators made of brittle, quasi-brittle and ductile materials; and loaded by any combination of static forces. To validate the method, 1744 experimental data was taken from technical literature is provided in Annex A. Each data was modelled using FE software, the extracted stress data was then post-processed using this reformulation of the TCD. The results obtained were compared to the commonly used Hot-Spot Stress-Method, across the same set of data there was an order of magnitude improvement in accuracy, the TCD Point Method giving an average error less than 30% whilst the HSSM gave an average error greater than 300%. Chapter 5 is concerned with the use of the linear-elastic TCD to assess notched metallic components in the high-cycle fatigue regime at elevated temperatures. Full details of two experimental programmes are provided, notched samples of a low carbon steel C45 and an aluminium alloy A319 T7 was tested, the results are provided in Annex C. Additional experimental data was taken from technical literature to further validate the method. The results showed that the approach was highly accurate with errors falling within ±20%. The 6th Chapter gives account of a study into the combined use of the TCD and the Modified Wöhler Curve Method (MWCM) to accurately and efficiently assess metal engineering components IV containing complex 3D stress raisers experiencing complex load histories that resulted in fatigue failures in the medium- and high-cycle fatigue regime. The method is based on critical plane theory which assumes that fatigue cracks initiate on the material plane experiencing the maximum shear stress amplitude. The method was proven to be successful independent of the stress raiser geometry and the complexity of the load history, typically returning errors of ±20%. Chapters 4-6 each have their individual conclusions and suggestions for further work, chapter 7 gives a summary of the conclusions and chapter 8 provides some suggestions for further work.
Supervisor: Susmel, Luca ; Askes, Harm Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available