Mesh Generation of Uptools for Stretch Forming Simulation of Aircraft Skins

To keep the consistency of meshes for the finite element analysis of aircraft skins stretch forming,a process of generating the uptool meshes from downtool meshes is proposed,which consists of several steps such as cutting downtool mesh,adjusting defective elements,creating fillet elements and wall elements,renumbering elements and nodes and offsetting along thickness direction.Firstly,whether each element of the downtool surface is on the uptool surface is checked by the relative position of the elements and their nodes to the cutting planes,and then the elements and their nodes are processed according their positions.Secondly,the elements with defective shapes or with incorrect normal directions are adjusted.Thirdly,the fillet elements are created on the cutting edge according to the given fillet width,and then the wall elements are created with the given height and numbers.Fourthly,the nodes and elements are renumbered by applying graph theory.At last,the elements are offset along the thickness direction with the given sheet thickness.The meshes of several stretch forming tools for complex aircraft skins such as S-shaped skin,inlet skin and wingbody skin are generated with the proposed method,and it is proved that the method is effective in creating uptool meshes consistent with the downtool meshes.