1 PhD Scholarship in fracture mechanics in Belgium | Ghent University

Welds produced in the field will almost unavoidably contain flaws from which cracks can initiate and grow until failure of the construction occurs. Standardized procedures aimed at assessing the integrity of flawed welds do not take into account the complex variation of microstructures in fusion welds and their adjacent heat-affected zones, which gives rise to strongly heterogeneous material properties. Instead, ‘idealised’ welds having homogeneous properties and straight fusion lines are assumed.

Soete Laboratory and University of Limerick, Ireland, have recently developed a technique to translate complex heterogeneous welds into idealised welds, that can serve as an input for a standardized engineering critical assessment. Focus is given to the heterogeneous nature of constitutive (i.e., stress-strain) characteristics. This technique, however, is preliminary and fundamental questions remain to be answered. This is the goal of the current project, which runs in collaboration with the University of Maribor, Slovenia.

The project has analytical, numerical and experimental components and work in all three fields will be required.

Firstly, the weld homogenisation technique is based on a slip line field analysis of cracked structures. This analysis is based on severe assumptions such as homogeneous, perfectly plastic material behaviour and simplified boundary conditions. The extension of slip line field analysis to three-dimensional complex heterogeneous welds is a major challenge and is considered to be the end goal of this work. Different analysis tiers with variable degrees of accuracy and complexity should be proposed, thus providing the end user with the necessary flexibility to meet project specific boundary conditions.

Secondly, the developed analytical procedure should be soundly validated. To that end, parametric studies will be performed using commercial finite element software. This requires the development of finite element models that incorporate heterogeneous weld properties.

Thirdly, the reliability of the developed numerical models should be evaluated on the basis of experiments. Focus will be given to tension loaded welds. Soete Laboratory has the necessary equipment to perform tests on a small (150 kN) to component (2.5 MN) scale. Further, the experimental characterization of weld heterogeneity requires carefully executed miniature scale tests (hardness mapping, minitiature tensile testing).

Qualifications:

• you have a strong motivation for conducting scientific research and working with complex questions;
• it’s natural for you to solve problems in a structured and thorough way and you often come up with ideas and new ways of working;
• you possess good analytical and technical skills and take responsibility for the development of your work, solving problems independently;
• you work well independently as well as in team.
• experience with analytical, experimental and numerical work is a clear advantage;
• you have excellent communication skills in English, both orally and written. Knowledge of Dutch is an advantage;