Finite Element Analysis and Fatigue Life Assessment of AISI 4130 Frame Steel Tubes Based on TIG Welding

This study systematically investigates the mechanical properties and fatigue characteristics of AISI 4130 chassis steel tubes under TIG welding processes, focusing on the U20 roll cage welding right-angle butt joint specimens from the China SAE Baja Competition. A thermomechanical coupled finite element model based on the Goldak double ellipsoid heat source was constructed to dynamically simulate the welding temperature field and residual stress field using ANSYS Workbench. A multiaxial fatigue life evaluation system integrating the mean stress-corrected Morrow model and the E-N curve method was established via nCode Design Life. Innovatively adopting response surface methodology to optimize welding parameters, a three-factor three-level orthogonal experiment revealed that optimal weld quality is achieved at a torch speed of 3 mm/s, welding duration of 20 s, and power density of 40 W/mm². Under these conditions, the weld penetration reached 3.2 mm, with an 18% improvement in weld width uniformity, a residual stress peak reduction to 285 MPa, and a maximum deformation of 0.08 mm, representing a 23% enhancement in forming quality compared to conventional parameters. Microstructural analysis indicated refined grain sizes (12–15 μm) in the weld zone and a 37% reduction in hardness gradient within the heat-affected zone. Multibody dynamics-based load spectrum analysis demonstrated spatially graded fatigue life distributions: the minimum life of 7.37×10^7 cycles occurred at 15 mm from the loading point, while regions beyond 30 mm exhibited a maximum life of 7.311×10^8 cycles, compliant with SAE J1099 standards. Experimental validation confirmed a prediction error of less than 9.2% for the finite element model. The study establishes a quantitative mapping relationship among welding parameters, microstructural properties, and fatigue life, providing a damage tolerance design-based framework for selecting process windows in high-strength steel racing chassis optimization.