Research activities 1999 - 2009

From November 1999 to August 2009 i was working at the University of Glasgow. My work supported development of fitness for service procedures for structures containing crack-like flaws in the energy sector. My specialization are multiple flaws and flaw characterisation (flaw combination, flaw alignment). My work is fundamental in revisions of the BS 7910 code and ASME Boiler and Pressure Vessel code, Section XI, Appendix C. 

I am actively contributing to the top level advisory groups, such as TAGSI in the UK and ASME Boiler Code in the USA and have benefited from a long term support from the domestic and overseas utilities and the UK research councils. 

I am a an Associate member of the Institution of Mechanical Engineers in the UK, Member of the FESI and ESIS - UK and EU forums for Engineering Structural Integrity and  Affiliate member of the American Society of Mechanical Engineers.  

I am a member of the British Standard Institution' committee WEE/37 on fracture. I am also a member of the ASME Boiler code, Working group on Pipe Flaw Evaluation and Working Group on Flaw Evaluation. I have strong links with industry through Serco Assurance ltd and BAE Systems in the UK and Hitachi Research Laboratories in Japan. 

I have expertise in the use of finite element software ABAQUS for stress analyses in support of design and fitness-for-service evaluations. Thought the last 10 years i have led several experiment intensive projects using multi purpose testing equipment the Materials Laboratory at the University of Glasgow and am well versed in the hands-on investigation too.  

From  September 2009 I am moving into oil & gas sector in Aberdeen. I am still happy to provide consultancy services to other industries. I can be contacted on bbezensek@hotmail.com 

PAST PROJECTS (from my PhD):

Defect Re-characterisation 

Safety cases for components containing defects of complex shapes, such as evolve from merger of two adjacent surface breaking defects, to the first approximation rely on substituting real defect geometry with a simplified bounding defect, typically of a semi-elliptical shape. The project examined failures from complex defects with re-entrant sectors (Figure 1) and assessed appropriateness of using a simplified assessment procedure under conditions of brittle and ductile fracture. 

Main conclusions were that complex defect evolve in a similar manner in fatigue and ductile tearing, making the re-characterisation procedure of R6/4 and BS7910 conservative. In cleavage in ductile-brittle transition the constraint effects and statistical size and shape corrections (ASTM E1921 extended to complex defects) can be invoked to make the assessment more realistic and conservative. On the lower shelf, constraint effects are weak and size effects are insufficient to make the bounding defect more detrimental than the real complex defect: the re-characterisation is non-conservative.

Constraint effects and temperature margins 

Shallow cracked geometries typically exhibit higher fracture toughness  in contained yielding due to loss of in-plane constraint, compared to deep cracked data. Stress fields in such geometries are self similar and differ by a hydrostatic term. This allows unconstrained field to be matched with high constraint field by J or by yield stress, thus quantifying the margins on toughness due to constraint loss in safety cases (Anderson&Dodds approach). 

A procedure has been developed using the Ritchie-Knott-Rice and Weibull stress based techniques which allows constraint loss be expressed in terms of a temperature margins in ductile-brittle transition. 

For this project I have performed extensive fracture toughness testing of mode I and mixed-mode crack configurations on mild steel under conditions of cleavage fracture. 

The results show that the crack deviates into the material of lowest apparent toughness adjacent to the crack tip and propagates down the toughness gradient. Charpy tests differed in that the crack consistently propagated into the softer material, and extended down the yield strength gradient adjacent to the tip. Charpy tests thus give misleading information about the fracture behaviour of mismatched weldments, such that crack path deviations may not expose a potentially low toughness weld metal. Recommendations are given on supplementing Charpy weld characterisation with the fracture mechanics tests to ensure conservatism in mismatched weldments (see publications).