Inline monitoring of thermo-mechanical behaviour in laser bending of AISI 1010 steel at elevated Fourier numbers

Laser bending of sheet metals is governed by transient thermo-mechanical interactions that remain difficult to predict, with process design still largely guided by simplified criteria. In particular, the Temperature Gradient Mechanism (TGM) is widely assumed to dominate only at low Fourier numbers (Fo < 1), a threshold that has rarely been critically examined for thin metal sheets. This study presents a high-resolution, synchronised experimental characterisation of thermal and mechanical responses during laser bending of thin AISI 1010 steel sheets, combining in-situ temperature, strain and reaction-force measurements. The results show that bending behaviour consistent with TGM is sustained over a markedly extended Fourier number range ( Fo ≈ 2.4–18.15), well beyond the limits conventionally associated with temperature-gradient-driven deformation. This challenges the prevailing interpretation of Fourier number as a strict mechanism-selection criterion and demonstrates that, in thin-sheet configurations, TGM-consistent behaviour can persist despite significantly increased thermal diffusion. Supporting measurements further indicate that increasing scan speed compresses the temporal spacing between temperature peaks, while local strain evolution exhibits a two-stage response, and reaction forces become more stable as scan speed decreases. These observations are interpreted as manifestations of constrained thermo-mechanical interactions within an extended TGM-relevant regime, rather than as independent phenomena. By providing experimental evidence of deformation behaviour consistent with TGM beyond the classical Fo < 1 condition, this work highlights the limitations of treating the Fourier number as a strict mechanism-selection criterion in thin-sheet laser forming. The findings establish a broader and more flexible process window for thin-sheet applications and provide a robust experimental basis for reassessing Fourier-number-based design strategies in laser-based manufacturing.