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Bolted flange joints are the most popular type of connection of pressure vessels and piping equipment because of their ease of assembly and disassembly. However, the initial tightening of their bolts is a delicate operation because it is extremely difficult to achieve the target load and uniformity due to elastic interaction. This study consists of developing an analytical model to evaluate the elastic interaction of bolted flange joints subjected to multi-pass tightening patterns. The proposed analytical model is based on the theory of circular beams on elastic foundation. The parameters such as elastic compliance due to bending, twisting and bearing are involved to describe the effects of elastic interaction during the tightening sequence. The developed model based on the theory of circular beams on elastic foundation is compared to the straight beam on elastic foundation theory. The validity of the approach is supported by experimental tests conducted on a NPS 4 class 900 weld neck bolted flange joint and by finite element analysis on this bolted joint and a 52 heat exchanger flange joint using the criss-cross tightening and sequential patterns. This study provides an attractive alternative to evaluate the bolt tension scatter due to elastic interaction avoiding costly experimental tests and cumbersome FEA simulations. [ABSTRACT FROM AUTHOR]

The initial loss of tension in individual bolts after initial tightening obviously affects the level and the stability of the clamp load in bolted joints. A high-precision instrument to analyze the clamp load loss was developed. In this instrument, an Atlas Copco’s high performance spindle with an accuracy of ±2.5% under the conditions of one million duty cycles was used to tighten the test bolts and nuts. A rotary torque-angle transducer was integrated in the tightening spindle to measure the tightening torque. KMR force washer with a repeatability of < ±1% was applied to monitor the clamping force in real time. Using this instrument, the design of experiment analysis was performed to determine the effect of variables on the initial loss of tension. Those variables included the joint materials, the fastener class, the gasket grade, the lubrication, the surface roughness, the tightening speed, and the number of repeated tightening. The results showed that the tightening speed and the number of repeated tightening had a significant effect on the initial loss of tension. Moreover, a process criterion of eliminating plastic deformation was proposed to minimize the initial loss of tension. The findings presented in this paper will be expected to enhance the reliability and the safety of bolted assemblies, especially in critical applications. [ABSTRACT FROM AUTHOR]

• The analytical model of blade aerodynamic force in aero-engine pressure zone is established. • The contact characteristics of the joint interface under the coupling action of aerodynamic force and bolt preload are analysed. • Aerodynamic and interface contact characteristics are introduced to analyse the self-excited resonance of rotor system. • The aerodynamic force on the interface of bolted connection is complicated, which causes subcritical resonance in the rotor system. • The important influence of aerodynamic force on aero engine rotor system is evaluated. Bolting joint is widely used in aero-engine, but the existing analysis theory of bolting joint interface strength connection completely ignores the aerodynamic load borne by blade and support disks. Therefore, in view of the aero-engine rotor system, we establish a bolt-flange connection blade-disk-drum joint model. Based on the l-stubs strength theory, considering three failure modes of bolt-flange interface stiffness, we study the connection strength of the disk-drum structure under aerodynamic force and bolt preload, and analyse the steady-state response of the rotor system under different connection states. The results show that the aerodynamic load will produce three kinds of yield phenomena on the rotor interface, and reduce the critical speed of the rotor system. Due to the stiffness loss of the connection interface, the critical speed of the rotor decreases and a subcritical resonance phenomenon occurs after the second critical speed. At the same time, the increase of interface contact damping results in the failure of vibration energy transfer between disk and drum, which makes the drum more susceptible to external excitation. By balancing bolt preload and interface friction coefficient, the influence of aerodynamic load on interface contact characteristics can be reduced, and the working efficiency of rotor system can be improved. [ABSTRACT FROM AUTHOR]