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Borislava Yordanova - Developing Correlations for Estimating Fracture Toughness of Thick Sections
NSIRC student in the lab with equipment - landscape header image

Developing Correlations for Estimating Fracture Toughness of Thick Sections

Borislava Yordanova
University of Edinburgh
Research Title:
Developing Correlations for Estimating Fracture Toughness of Thick Sections

Use of high strength steels is becoming more and more popular in offshore structures and ship construction to obtain weight and manufacturing cost savings without sacrificing structural performance. During the material selection for ship hulls, leg structures of mobile offshore units and lifting appliances, high strength steels with yield strength of the order of 690 MPa and beyond in thicknesses up to 220mm are increasingly being adopted. However, fracture resistance becomes a problem. Currently, the fracture toughness of a material obtained from small scale standard fracture mechanics test is used in fracture mechanics based assessments of structures to evaluate flaw tolerance. However, the thickness of the actual structural component is greater than the thickness of the test specimens; it is not certain that the measured fracture toughness from the former can represent the toughness of the latter.


Furthermore, is it very well-known that the fracture toughness of the materials decreases as the thickness of the section increases. The aim of this study is hence to develop new, validated correlations for the determination of fracture toughness of thick high strength steel sections based on the material properties obtained from smaller specimens of this material. Current existing correlations include statistical relationship of fracture toughness in terms of geometry, which allows predicting of fracture toughness of any size based on previously known values. The PhD aims to further review constraint loss effects with thickness and how to separate them from the statistical effect for two parent steels and welds. SEN(B) and SEN(T) tests are to be conducted over a range of thickness: 12.7, 25.4, 50.8 100. The experimental work is accompanied by numerical modelling to optimise the testing programme and analyse constraint loss in small and large scale specimens and be at a level to allow for comparison between numerical and experimental results and lead to improvement in existing correlations.