Finite element investigation of mechanical behavior in composite bolted flange assemblies with conical collars

Fiber-reinforced polymer (FRP) flanges are becoming increasingly adopted in piping systems owing to their corrosion resistance. However, current design standards for flanged joints are derived from those of metallic materials, neglecting the anisotropic behavior of composite laminates. This study develops a 3D anisotropic finite element model to investigate the mechanical behavior of FRP bolted flange assemblies with conical collars. The composite flanges were modeled using a ply-by-ply approach in ANSYS Composite PrepPost, while the bolts and gasket were represented using nonlinear elastic material models. The numerical procedure captures the coupled response of the flange, bolts, and gasket during pre-tightening and pressurization. Fourteen flange configurations, ranging from NPS 1 to NPS 36 and pressure classes 50 and 150, were analyzed. The results reveal that flange rotation at the ring–collar junction governs stress concentration, laminate deformation, and sealing performance. Failure analysis based on the Tsai-Hill criterion identifies critical plies and failure modes, highlighting configurations that exhibit a risk of laminate failure under operating conditions. Additionally, the evolution of bolt stress and gasket contact pressure sheds light on the mechanisms that control joint leakage risk. The proposed model enables a thorough investigation of the structural integrity of FRP flanged joints with conical collars. The findings provide design guidance for improving laminate architecture, bolt configuration, and joint reliability, and provide a basis for extending composite flange design frameworks beyond the limitations of current metallic-based standards.