Improved thermal stress model and its application in ultraviolet nanosecond laser cleaning of paint

A developed 2D finite element model to describe temperature distribution, stress distribution, and ablation depth by ultraviolet nanosecond (ns) pulsed laser cleaning is presented. In this paper, we indicate that thermal stress is the primary mechanism in the paint removal process by laser cleaning and successfully simulate the ultraviolet nanosecond (ns) pulsed laser cleaning by the finite element method. Notably, the formation of plasma, plasma shielding effect on the incident laser fluence, temperature-dependent absorptivity, and absorption coefficient of the paint layer are crucial factors considered in this model. In addition, the tailored model can predict theoretical cleaning of thresholds based on the mechanism of thermal stress. According to the temperature, stress distribution, and cleaning depth in paint and substrate at various laser fluence in this model, the corresponding cleaning threshold is 7 J/cm(2) in theory. In a word, it is expected that this study could provide a theoretical reference regarding laser cleaning paint layers and pave the way for reducing substrate damage in various industrial applications. (C) 2020 Optical Society of America