DEM-FEM Coupling Simulation of Residual Stress Improvement for Q235B Welded Joint via Shot Peening

To overcome the welding-induced residual tensile stress of Q235B welded joints, a sequential thermal-mechanical welding and DEM-FEM dynamic shot peening coupled model is established. The Goldak double-ellipsoidal heat source model is adopted to simulate welding temperature evolution, and the discrete element method fully considers random shot ejection and shot–shot collision energy attenuation, which addresses the simplification defect of traditional single-shot finite element models. The effects of shot diameter d, incident angle θ, initial shot velocity v and mass flow rate rm on the residual compressive stress layer are systematically analyzed. Results reveal that larger shot diameter and initial shot velocity deepen the residual compressive stress layer. Meanwhile, the maximum residual compressive stress first increases and then decreases with the increase in rm and θ. The optimal parameter combination is determined as d = 1 mm, θ = 60°, v = 60 m/s, rm = 9 kg/min. Under these parameters, the maximum residual compressive stresses reach −306 MPa (σx) and −310 MPa (σz), with the depths of the residual compressive stress layer being up to 0.78 mm for σx and up to 0.66 mm for σz, respectively. Different from previous simplified simulations, this study quantifies the collision energy attenuation caused by shot trajectory overlap. This proposed model can provide guidance for post-weld surface strengthening of low-carbon steel engineering structures.