Numerical Insights into Laser Ablation: A Pathway to Optimised Steel Cleaning for the Sydney Harbour Bridge

Abstract

This doctoral thesis addresses critical issues in maintaining the structural and aesthetic longevity of significant infrastructures, exemplified by the Sydney Harbour Bridge, through advanced laser cleaning techniques. The focus is on understanding the intricacies of laser-material interactions and subsequent stress states within the materials. A fully coupled thermo-mechanical Finite Element Method (FEM) model and Computational Fluid Dynamics (CFD) simulations were developed to offer a more holistic and realistic representation of pulsed laser ablation. Thermo-elastoplastic analysis and a novel element deletion subroutine were incorporated to advance traditional ablation modelling techniques.

The research extensively employs multi-modal validation techniques, involving Scanning Electron Microscopy (SEM), X-ray Diffraction (XRD), and Neutron Diffraction (ND), to corroborate the simulation parameters and outcomes. This thesis introduces a simplified analytical equation, formulating the Intensity Fluence Factor (IFF), a novel parameter for surface temperature estimations.

Furthermore, the study investigates the influence of various laser parameters on residual stress formation, demonstrating the model's capabilities in predicting directional trends in stress with high precision. The findings have vital practical implications in terms of cost reduction, enhanced safety measures, and establishing an empirical foundation towards industry-wide standards. Overall, this research makes a substantial contribution to the fields of material science and engineering by transforming laser cleaning methods from 'experience-based tacit knowledge' to a framework anchored in 'explicit knowledge,' setting a new benchmark for efficiency and reliability.