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Research / Completed Projects / Brahim Nadri

Brahim Nadri - Completed Project


Brahim Nadri
My Project

I am a PhD research student from Morocco . My research project is entitled “ Diffraction studies and finite element analysis of cold expanded holes ”.

Before I started my PhD at The Open University, I gained a French degree (DESS) specialized in “Analysis and treatment of surfaces” at the University of Reims . The diploma course has qualified me to continue my research in the field of materials engineering.

I am very delighted to have the opportunity to study at The Open University. It offers an excellent environment for learning. The OU has good research facilities including laboratory equipment, numerical, analytical software and good library services.

The main objective of my project is to investigate the effect of fatigue crack growth, and compressive overloading, on the beneficial compressive residual stresses introduced by the split-sleeve cold expansion process. The cold-working process of holes has been widely practised to enhance the fatigue resistance of aerospace structures due to propagating cracks. Fatigue loading experiments were carried out to grow a number of cracks from cold expanded holes. The effects of the residual stress field of the fatigue crack propagation were also studied, Fig. 1 shows the process.

In parallel, this work involves modelling of the whole cold expansion process using finite element method (ABAQUS). Several 2D and 3D finite element models have been simulated to predict the resulting residual stress fields. These stresses were then validated using a number of experimental techniques, such as laboratory and synchrotron X-rays as well as neutron diffraction, at various experimental facilities in France (ESRF and LLB) and UK (ISIS).


click above

video of the hoop residual stresses simulation of a 3D elasto-plastic finite element model of a 4% cold expanded hole.

The results of my work are very interesting and hopefully these findings will be useful for the aircraft industries for the prediction of fatigue life of components containing cold-expanded holes.

1. B. Nadri, L, Edwards, M. E. Fitzpatrick and A. Lodini “ Analysis of residual stresses following overloading of cold expanded holes using the X-ray diffraction technique and finite element method ” (pdf file). Journal of Neutron Research , January-September 2004: 12 (1-3): 219-224.

2. D. Stefanescu, A. Steuwer, R. A. Owen, B. Nadri, L. Edwards, M. E. Fitzpatrick and P. J. Withers “Elastic strains around cracked cold expanded fastener holes measured using the synchrotron X-ray diffraction technique”. The Journal of Strain Analysis for Engineering Design , 1 September 2004:39(5): 459-469.

 

Supervisors Dr Mike Fitzpatrick , Prof Lyndon Edwards and Prof Alain Lodini.


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