When laser processing materials, the transient heat flow density is extremely high, generating significant temperature differences and causing localized thermal stresses, which can lead to material cracking in severe cases. The large energy density of the laser beam causes uneven local heating of parts and large changes in temperature gradient, leading to the concentration of thermal stresses, cracks, and even ruptures, causing serious safety hazards. This is particularly serious for reactive materials with strong thermal sensitivity. Therefore, it is of great significance to study the generation and characterization of thermal stress during laser processing and its influence on processing to improve the application of laser technology in reactive material processing. Although many scholars have studied the stress field of laser ablation, most research is limited to the surface stress distribution. Few studies have focused on internal stress changes during laser processing, making it difficult to observe the influence of internal stress evolution on material processing. Therefore, it is necessary to study the thermal stress characteristics inside the material during laser ablation.

To study the process of laser ablation of reactive materials, we establish a thermodynamic coupling model in a two-dimensional cylindrical coordinate system. When the material is heated to a sufficiently high temperature during laser irradiation, it melts or even evaporates, and part of the material may also change directly from the solid phase to the gas phase, which is the ablation phenomenon of the material. The material interface moves downward at a certain speed. The finite element software COMSOL Multiphysics is used to simulate the heat transfer and thermal stress characteristics inside the material during laser processing of reactive materials. The simulation results are compared with the experimental results to prove their feasibility. Then, the variation rules of each stress along the radial and axial directions are analyzed, and the influence of the laser power on the generation of thermal stresses and their change characteristics is further explored.

During laser irradiation, the material absorbs laser energy when its temperature reaches the melting point. The high temperature of the laser path causes the material to melt and vaporize, resulting in the formation of ablation channels (Fig. 3). The trend of thermal stress change varies in different directions. With increasing r, the circumferential stress gradually transforms into tensile stress, which increases over time. The axial stress is small in the center of laser ablation due to the softening and ablation occurring in this region. Material deformation is a dynamic process, with the thermal expansion zone gradually shifting back over time. This implies that the region of tensile deformation also moves back and the stretching range expands (Fig. 5). The radial and circumferential stresses along the z-direction are similar and change differently than in the radius direction. The transformation of radial and circumferential stresses from compressive to tensile stresses becomes more obvious with time, with tensile stress increasing and the effect of tensile deformation expanding (Fig. 6). The trends of thermal stress maxima in different directions also differ. Along the radial direction, the maxima of both radial and circumferential stresses first increase, but their compressive stress trends are not the same over time; radial stress continuously decreases, while circumferential stress decreases first and then increases. Along the axial direction, the maximum values of all three stresses first increase and then decrease, gradually stabilizing (Fig. 7).

Based on the theory of heat conduction and thermoelasticity, we establish a thermodynamically coupled two-dimensional transient thermoelastic model to study the heat transfer characteristics and thermal stress distribution during the interaction between the laser and the Al/PTFE material. The study explores the influence of various laser parameters on thermal stresses within the material. When the laser beam irradiates the material, a large amount of transient heat flux density is generated near the laser spot, leading to a localized high-temperature gradient in the region, which induces localized transient high thermal stresses. The range of influence gradually enlarges over time. For stresses in the radial direction, radial and circumferential stresses show stress peaks during ablation as the laser action time progresses, while axial stress increases. For stresses along the axial direction, radial and circumferential stresses are similar, and all three thermal stresses show a maximum during the ablation process. Reducing the laser power can narrow the region of thermal expansion, mitigate the effect of thermal stresses on material processing, and even weaken the tensile deformation of the material near the radius of the laser spot, providing appropriate theoretical guidance for the application of the actual machining process.