Improvement of buckling resistance of thin sheets by local laser treatment

Lightweight thin walled structures are primarily dimensioned for stiffness of the whole construction and less for material resistance. Usual design concepts for improving the stability behaviour of metal sheets introduce the configuration of fins, stiffeners, beads or embossing patterns. However these methods not only increase the moment of inertia but also the weight of the component. In this paper an alternative method for inserting residual stresses is presented and the influence of the static and dynamic behaviour is shown. Local laser spots and laser lines are introduced in order to achieve proper distributions of residual stresses. The effect on fundamental frequency and buckling resistance was investigated on steel sheets of 280 mm x 280 mm and a thickness of 0.75 mm in a special testing rig. Buckling load and mid-point displacement were measured by a LVDT-system. Correlations between residual stresses, fundamental frequency and buckling resistance could be found. During buckling tests the uniaxial applied load vs. mid-point deflection was measured. In order to illustrate the improvements of the buckling load, fundamental frequency and residual stresses have been analysed. In conclusion, the laser treatment and the insert of residual stress patterns by laser treatment, respectively, is a promising method to increase the static and dynamic behaviour for thin walled metal sheets.