Simulazione numerica della brunitura a sfere su lega di alluminio 2024 utilizzando metodo ibrido esplicito-implicito degli elementi finiti.

Aluminium 2024 alloys are widely used in the manufacturing of aircraft structural components due to high strength-to-weight ratio, excellent resistance to fatigue crack propagation, good fracture toughness, and good machinability. However, the combined effect of local corrosion and cyclic loading leads to crack initiation and propagation during service, ultimately reducing the fatigue life of the component. To address this challenge, mechanical surface treatment (MST) methods, particularly ball burnishing, have emerged as promising post-machining finishing processes. This method induces surface compressive residual stresses, which are used to enhance fatigue performance and improve service life. The present thesis aims to develop an efficient 3D Finite Element Model for the ball burnishing process applied to Aluminium 2024 through a hybrid Explicit-Implicit FEM approach for accurate residual stress prediction. The dynamic explicit analysis is performed to replicate the physical ball burnishing process by designing a modified geometry of the burnishing component, simulating one tool pass to study the thermo-mechanical response during interaction. In contrast, the Implicit FEM approach is developed through the INP file modification technique using the normal stress generated during the Dynamic Explicit analysis to simulate multiple tool passes for residual stress prediction. The 3D FEM model prediction proves that the burnishing force is directly proportional to the generation of compressive residual stress, both at the surface and subsurface stress-affected zone. At applied burnishing force 348N, the tool sliding condition produces a surface axial and lateral compressive residual stress -146.24 MPa and -473.05 MPa, respectively, while the tool rolling condition generates -209.39MPa axial and -478.36 lateral compressive residual stress for an average stable burnished zone. The residual stress prediction shows a good agreement with XRD measurement. At applied burnishing force 275 N and tool sliding condition, the optimum FEM surface axial residual stress was obtained, with 7.8% deviation from XRD measurements.