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%.

与复合材料夹层材料相反，对于均质和各向同性材料，螺栓连接中的构件刚度已得到广泛研究。因此，在ANSYS软件中进行了基于增强拉格朗日算法解决接触问题的数值模拟，以研究具有碳和玻璃层压板以及两种类型泡沫芯的各种预载夹层螺栓接头。测试样品显示，当施加的预紧力显着增加时，最大剪切应力与最大主应力之比会增加，这会提高核心失效的风险，此外，提出了预紧力刚度的解析近似，为此，使用了搜索算法推导被测接头构件的等效弹性模量表达式，并应用距离相关法确定所引入的刚度模型的理论公式，通过分析其数学近似的均方根误差（RMSE）结果来优化其精度，除具有最大弹性模量 (209 GPa) 的最刚性蒙皮的样本外，所有测试样本均确保所选模型的收敛性。此外，Zhang 和 Poirier 提出的有关导致螺栓接头分离的拉伸载荷的方程经过调整和验证，百分比误差小于 13%。