On the elasto-plastic buckling of Integrally Stiffened Panels (ISP) joined by Friction Stir Welding (FSW): Numerical simulation and optimization algorithms

Integrally Stiffened Panels (ISP) structures are composed of a base plate and one (or several) longitudinal stiffness sections of simple or complex shape. When compared to conventional reinforced structures, they present an integral profile, as the stiffened panel is obtained as a whole by means of an extrusion process. The choice of a ISP profile can lead to a more robust and defects-free solution, simultaneously maintaining the possibility to adopt complex reinforcement shapes. In the present work, three algorithms are studied and compared in the cross-section optimization of Integrally Stiffened Panels for aeronautical applications: (i) the classical Levenberg–Marquardt, (ii) the Simulated Annealing methodology, and a recently proposed approach involving (iii) a differential/nature-based algorithm called Hybrid Differential Evolution Particle Swarm Optimization (HDEPSO). Numerical simulation models are introduced for several shapes of ISP. Additionally, the presence of a Friction Stir Weld (FSW) zone is also taken into account, from the joining between distinct ISPʹs. This can allow us to infer about the influence of the heat affected zoned (HAZ) in the overall stability of the structure, under compressive buckling loads within the elasto-plastic regimen. Results show that the use of the proposed optimization algorithm represents a viable option, giving an added insight in terms of the buckling resistance and mechanical design in nonlinear material and geometric scenarios.