Finite element modeling of folding during the superplastic forming of corrugated core panels

Abstract

Corrugated core panels manufactured by methods of superplastic forming concurrent with diffusion bonding (SPF / DB) are promising for the production of high specific strength articles. One of serious problems arising in forming of corrugated core panels is concerned with the formation of outer folds. The cause of folding is uneven deformation of the skin sheets. In this study, the process of forming a corrugated core panel from a titanium alloy VT6 (analogue of Ti-6Al-4V) by computer simulation is considered. Finite element modeling is carried out using ANSYS software. The formulation of the boundary value problem is stated in terms of the theory of creep. It is shown that after completion of the formation of stiffening ribs, it is possible to increase the working pressure to a maximum without damaging the structure. The results of numerical simulation show that increasing the pressure and holding time allows one to eliminate folds. However, the pressure value is technically limited, and increasing the holding time reduces the economic efficiency of the process. It is noted that the process of forming a corrugated core panel has two characteristic stages. In the first stage, the core sheet is deformed under the conditions of superplasticity, stiffening ribs are formed. The first stage continues until the skin sections joined to the core touches the surface of the die. The second stage proceeds under conditions of creep up to smoothing the outer folds.

Influence of the inclination angle of stiffeners on folding during superplastic forming of corrugated core panels

“…In [18] it is shown that at an inclination angle of 35°, the formation of folds can be avoided by choosing the mode of holding the structure under pressure. The purpose of the present study is to determine the degree of influence of the angle of inclination of the stiffeners of the corrugated structure on folding.…”