Objective As a new type of material with carbon fiber as the reinforcing material and epoxy resin as the matrix, carbon fiber/epoxy resin composite materials have been widely employed in aerospace, automotive manufacturing, and other fields in the past decade. Laser technology serving as a novel material processing means has found widespread applications in various fields. However, the mechanism of laser interaction with carbon fiber/epoxy resin composite materials, such as irradiation and material processing, is not fully understood. Therefore, research on the resistance of carbon fiber/epoxy resin composite materials to laser irradiation has emerged. Currently, research on laser irradiation of carbon fiber/epoxy resin composite materials both domestically and internationally is mainly experimental. However, the anisotropy of the physical properties of composite materials and the differences in material component physical properties make it challenging to build theoretical models that accurately represent the materials. Consequently, existing theoretical models are often simplistic and do not fully align with the actual behavior of carbon fiber/epoxy resin composite materials under laser irradiation, resulting in difficulties in studying the effects of laser irradiation on these materials. Therefore, we aim to address the physical structure and properties of carbon fiber/epoxy resin composite materials by building a novel stepped variation model in physical parameters such as thermal conductivity. The research focuses on simulating the laser irradiation of carbon fiber/epoxy resin composite materials from two dimensions of parallel fiber orientation and vertical fiber orientation to provide insights into the behavior of these materials under laser irradiation. Methods We propose and build a novel stepped variation model for laser irradiation of carbon fiber/epoxy resin composite materials based on their complex internal woven and stacked structures. This model constructs new expressions for thermal conductivity, density, and specific heat capacity of the composite materials, with partial material decomposition before and after heating taken into account. Additionally, the physical process of continuous laser irradiation and ablation of carbon fiber/epoxy resin composite materials is established based on the principles of laser energy absorption and heat conduction equations. The absorption coefficient of the materials for laser radiation is derived based on their physical properties. Finally, by adopting this model and combining it with COMSOL simulation, we analyze the laser irradiation behavior on the materials. The analysis includes simulations of the temperature field, ablation depth, and heat response resulting from Gaussian continuous laser irradiation from two dimensions of parallel and vertical fiber orientations. Results and Discussions We build a stepped variation model for the physical parameters of carbon fiber/epoxy resin composite materials. By taking thermal conductivity as an example, the core expression is represented by k = k(1)center dot epsilon (T-T-C)+ k(2)center dot[1 - epsilon(T - T-C)], where k(1) and k(2) are the stepped variations of thermal conductivity in the material's stacking direction, and embedded within a step function to realize physical parameter changes of the material before and after the thermal decomposition of epoxy resin. A general expression for the material's absorption coefficient of laser is derived based on the material's physical properties, thereby determining the numerical value of the absorption coefficient of carbon fiber/epoxy resin composite materials for laser. Simulation studies are conducted based on the built model for Gaussian laser irradiation of materials in the parallel and vertical fiber orientations. The results show that when the laser irradiation spot diameter is 10 mm and the irradiation time is 10 s, for laser irradiation in the parallel fiber orientation with output powers of 400, 600, 800, and 1000 W, the resulting ablation depths are 0.642, 1.721, 2.846, and 3.990 mm respectively. Meanwhile, the corresponding ablation rates of 0.088, 0.202, 0.315, and 0.426 mm/ s, exhibiting linear growth (Fig. 8). Under laser irradiation in the vertical fiber orientation with output powers of 800 W and 1000 W, the resulting ablation depths are 0.567 and 1.243 mm respectively, with ablation rates of 23333.3 and 46666.7 K/s (Fig. 11). This indicates weaker ablation capabilities than the former case, which can be attributed to shallow heat accumulation, stepped variation of the composite material's thermal conductivity, and ablation difficulty due to epoxy resin thermal decomposition. Conclusions We build a model of longitudinal and transverse thermal conductivity differences based on the structural characteristics of carbon fiber/epoxy resin composite materials to simulate the radial and axial thermal conductivity differences. Additionally, a step-change model for parameters such as thermal conductivity in the vertical fiber orientation is built based on the layered structure of epoxy resin and carbon fiber within the material microstructure. By adopting COMSOL, we combine the above models to simulate the temperature rise and ablation removal processes of materials under laser irradiation. By analyzing materials irradiated by lasers in parallel and vertical fiber orientations within the material, we provide numerical simulation results of temperature fields and ablation morphologies of materials under different output powers of Gaussian continuous lasers with determined spot sizes. The results indicate that under laser irradiation in the vertical fiber orientation, the axial thermal conductivity of the material is affected by not only the alternating stacking of epoxy resin layers and carbon fiber layers but also epoxy resin pyrolysis. Finally, weaker ablation capabilities than the scenario with laser irradiation in the parallel fiber orientation are caused.
