Fatigue of welded structures

Transport and the Environment

University of Southampton

Many large structures such those deployed in ships and bridges are fabricated from welded steel plates with stiffeners. Ships are growing bigger in size. Operational demands impose high levels of structural loadings. Operational economics dictate that the payload to structural weight ratio should be high leading to requirements of weight minimisation. Thus this coupled action of higher loads and lighter, thinner structures leads to structures being subjected to higher stresses for larger portions of their operational lives. This has implications on the initiation of defects such as cracks in ship structures and their subsequent propagation. Ship owners and ship safety regulators have an obligation to examine ships for cracks and prescribe remedial action. The current philosophy is to accept no defects or cracks; that is, if a ship surveyor detects a crack then the instruction is to repair and rectify that defect regardless of its location and significance (potentially consuming resources and energy unnecessarily). There is a need to examine this philosophy in a fundamental manner and create a safe-ship approach based on rational examination of defects and their implications on ship structural integrity.

This project focuses on a fundamental understanding of multi-scale modelling of defects such as cracks under cyclically loaded regimes through the deployment of advanced imaging techniques such as X-ray tomography and full-field strain and stress characterisation methods such as TSA and DIC to link the growth of defects in and around weldments, with varying material make-up, effects of differing boundary conditions and load directions. This experimentally derived data set will underpin numerical modelling of the fatigue and fracture responses of the welded structures and eventually be linked to rules for constructing and operating ships in a safe manner.  This project will be aligned with that sponsored by Lloyd’s Register.

This EngD project is being funded through sponsorship by TWI 

Enquiries:  engd@soton.ac.uk