Numerical modelling of multi-scan and multi-pass laser ablation for residual stress prediction in structural steel

Nanosecond laser ablation generates steep thermal gradients and residual stresses that influence the performance of structural steel. This study develops a finite element (FEM) framework for multi-pulse, multi-scan laser ablation, extending beyond conventional single-spot models to more realistically capture industrial practice. Experiments were performed on Sydney Harbour Bridge steel using a 1000 W Q-switched Nd:YAG laser. Residual stresses were characterized by X-ray diffraction (XRD) and neutron diffraction (ND), with back-surface temperatures were also recorded for validation. XRD measurements revealed ∼220 MPa tensile stress at the surface, in close agreement with the FEM prediction of ∼215 MPa when averaged over the XRD sampling depth. Beyond 0.5 mm, ND measurements indicated negligible residual stresses within ±30 MPa, a trend also reproduced by the simulation. These results demonstrate that laser-induced residual stresses are confined to the top ∼0.5 mm of the material. Furthermore, the simulated back-surface temperature after 20 laser passes (363 K) closely matched the experimental value (369 K), confirming the model's thermal accuracy. This combined experimental–numerical approach provides a validated framework for predicting residual stresses in laser-processed steels and supports the optimization of short-pulse laser processing for both research and industrial applications. • Computationally efficient 3D FEM model developed for multi-pulse, multi-scan laser ablation • Experimental validation achieved for both residual stress and temperature • The model captured the trends of residual stress, with XRD used for near-surface comparison and ND for in-depth comparison.