Theoretical definition of a new custom finite element for structural modeling of composite bolted joints

The general definition of a novel finite element for structural analysis of composite bolted joints is presented. The work aims to define an accurate and computationally efficient simulation tool for multi-jointed composite structures characterized by a low entry of degrees of freedom. The modeling approach exploits the full stiffness evaluation of the bolted region from the analytical standpoint. Two main stiffness contributions are defined: the first one is the elasticity of the plates around the bolt that is evaluated by means of an original theoretical approach based on the FSDT of composite plates and the Ritz method. The second one is associated with the stiffness of the bolt and is related to its shank, bolt head and bolt-hole bearing deformation. This methodology can further precisely assess friction, preload and radial clearance effects. The user-defined Composite Bolted Joint Element (CBJE) is obtained by transferring the stiffness of composite laminates to a set of radially arranged custom beam elements, whose tailored stiffness matrix is expressly derived, whereas bolt stiffness values are taken into account through beam and spring elements. The proposed methodology is verified with experimental data from literature; results are in remarkable agreement. Sensibility analysis of FE models featuring the CBJE are reported in comparison with refined 3D FE models.