Effect of bolt assembly conditions on fatigue strength

Bolted joint is one of the most commonly used separable joint types utilised for gas turbine engines. The modules of gas turbine engines must be easily assembly and disassembly during field maintenance operations. Also, maintaining its function and integrity under operational loads is one of the important design criteria. During the assembly of the connections, torque is applied to the nu tor bolt and a preload is created on the bolt and this preload force ensures that the connection is kept in the desired condition without loosening. Preload plays a major role in the operation of bolted connections. The strength and durability of the connection cannot be fully ensured unless adequate pre-loading is provided. However, preloads due to over-torque may also combine with operational loads and cause plastic deformation. In the literature and standards for bolts with the same thread size, different torque values are specified. This study is carried out to investigate and analyze the effect of mounting parameters used in gas turbine engines on bolt life. Calculations and analyzes are made for 10 different mounting conditions with various torque, nut factor and lubrication methods. It is observed that the assembly parameters (torque, nut factor, lubrication) affect the preload force and as the preload force increases, the bolt life strength increases.