Numerical Investigation of Member Stiffness in Composite Sandwich Bolted Connections

Member stiffness in bolted connections has been widely studied for homogenous and isotropic materials contrary to composite sandwich ones. Therefore, a numerical simulation based on the augmented Lagrangian algorithm to solve contacts problems is conducted in ANSYS software to investigate various preloaded sandwich bolted joints with carbon and glass laminate skins and two types of foam cores. Tested samples show a rise of the ratio of maximum shear stress to maximum principal stress when the applied preload increases considerably which improves the risk of core failure, additionally, an analytical approximation of stiffness at preload is proposed, for that, a search algorithm is used to deduce the expression of the equivalent elastic modulus of tested joint members and a distance correlation method is applied to determine the theoretical formulation of the introduced stiffness model whose accuracy is optimized through analyzing results of root mean square error (RMSE) of its mathematical approximations , the convergence of the chosen model is ensured for all tested samples except the ones having the most rigid skins with the greatest elastic modulus (209 GPa). Furthermore, the equation introduced by Zhang and Poirier concerning the tension load causing a bolted joint separation is adapted and validated with a percent error less than 13%.