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Title: The development of J-integral estimation schemes for shallow cracked geometries under large plastic deformation
Author: Lau, C. L.
Awarding Body: University College of Swansea
Current Institution: Swansea University
Date of Award: 1995
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In maritime applications, structures with cracks must be designed to withstand accidental loads, e.g. as a result of collision or explosion. The presence of cracks in structures acts as stress raisers and large plastic deformation easily occurs under these severe loads. The plastic zones, which are much larger than the crack sizes, usually extend to the other parts of the structure. For large cracks which would reduce the load carrying capacity of the structure, it would be necessary to have the cracks repaired. For small cracks such as when a/W≤0.1, not only are they difficult to detect, it is also doubtful about the benefit of having them repaired as it may make the situation even worse. Thus, assessment of the shallow surface cracks with a/W≤0.1 under different loading conditions becomes the theme of the study. This study provides predictions of J as the crack driving force in homogeneous materials. The J-estimation schemes were developed from the elastic-plastic two-dimensional finite element results for a wide range of power hardening materials and shallow cracks with a/W≤0.1. Pure tension, pure bending and a combination of both are the applied loads for the finite element computations. The design curves predict J for remote strain or applied strain up to ten times the yield strain. Key findings are described as below: 1) A revised J-estimation scheme was proposed for single edge notched specimens in tension (SENT). This estimation scheme, which predicts J to within 5% for medium to low work hardening materials (5≤n≤30), is more accurate than Turner's En-J design curve. 2) Two J-estimation schemes for single edge notched specimens (SENB) using applied and remote strains respectively were proposed. Both schemes provides accurate predictions of J to within 5% for 5≤n≤30. 3) A J-estimation scheme was proposed for SENT specimens with tripartite stress-strain curves, i.e. stress-strain curves with a yield plateau. This J-estimation scheme was aimed at providing a comprehensive treatment for real engineering applications. The J-estimation scheme generally provides accurate and conservative results which are suitable for design purposes.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available