18. Distortion Control and Mitigation

Out-of-plane distortion results from buckling and angular deformations of panel edges as well as in the panel in between the stiffeners. The most effective way of reducing distortion is to control the formation of plastic stains produced in regions near the weld. If the appropriate distortion control is applied, the final distortion will be reduced. On the other hand improper control may lead to higher distortion. Control of distortion needs to start from implementation of appropriate design and fabrication techniques. Reducing welding heat input reduces all types of weld-induced distortions. Distortion mitigation through heat sinking involves removal of heat from the welded region such that it does not get spread in the plates away from the weld zone thus reducing residual stresses and distortion. Mitigation of buckling distortion of stiffened panels can be done by applying an active distortion mitigation technique known as Thermo-Mechanical Tensioning (TMT). In this method through the use of restraining and tensioning lugs, the tensile residual stress field generated by welding of stiffeners is reduced. This leads to reduction of the balancing compressive stress field.