THERMOMECHANICAL BEHAVIOR OF IN718 BOLTED JOINTS IN AEROSPACE PROPULSION AT ELEVATED TEMPERATURES

In recent years, the need for advanced fasteners has increased significantly in state-of-the-art engineering topics such as the aerospace and defense industries. The components and assemblies used in these sectors must operate under extremely severe conditions with the required performance and reliability. Literature reviews examine the behavior of bolted joints at room and moderate temperatures; however, comprehensive analyses and calculations conducted across a wide range of temperatures, from low to high, are limited. This study focuses on the thermomechanical behavior of superalloy bolted joints used in the assembly of structural parts of gas turbine engines. Analytical and numerical evaluations of flanged bolted joints operating at room temperature 24°C and 700°C were conducted. This study also completed the determination of bolt preload, axial stiffness, and stress distribution on the joint under thermal and mechanical loading. Furthermore, the aim was to compare the results obtained from Finite Element Analysis (FEA) and exact solution. The results indicate that a decrease in bolt preload and joint stiffness occurs due to thermal expansion mismatch and temperature-dependent compliance effects resulting from elevated temperature. Additionally, significant changes were observed in the tensile stresses of 12-point M10x1.25 aerospace-standard bolts at 700°C operating condition, indicating the onset of critical conditions for joint integrity. Analyses also confirm that maintaining adequate preload and stiffness during operation is essential to maintain joint integrity and prevent loss of structural stability. This study provides a comprehensive assessment of the high-temperature mechanical behavior of superalloy bolted connections. The findings contribute to the design and optimization of bolted joints used in aerospace propulsion systems by providing practical insights into ensuring safety, durability, and performance under extreme thermal conditions.