Experimental and numerical prediction of collapse of flatbar stiffeners in aluminum panels

Flatbar stiffeners are attractive in stiffened plates from a fabrication point of view. Flatbars are susceptible to torsional buckling and collapse. Current approaches to assess torsional buckling strength are uncertain. For instance, formulations for torsional buckling of stiffeners in steel panels are still debated. Compared to steel structures, the strength of aluminum structures is influenced not only by the residual stresses and initial imperfections, but also reductions in mechanical properties in heat-affected zones (HAZ). In the present paper, an experimental and numerical investigation of the torsional buckling strength of longitudinal stiffeners in aluminum (aluminum alloy 5083-H116 and 6082-T6) panels subjected to axial compression is conducted. The experimental results are presented and compared with numerical predictions by using finite element method code ABAQUS, considering the influence of the HAZ and actual initial deflections. The effect of the HAZ on the torsional buckling strength of the stiffened panels is discussed. It is found that the torsional buckling strength of the stiffened panels is affected by the HAZ and the reduction of ultimate strength is up to 34% when the HAZ is accounted for in numerical prediction for AA6082-T6. The load eccentricity also affects the ultimate strength significantly. The ultimate capacity is not found to be sensitive to welding residual stresses in aluminum stiffened panel.