Creep behavior analysis, optimization and reliability evaluation for bolted joints of engine rotor

The connecting bolt is widely adopted joint method in turbine engine structure design, and some important bolts are of decisive influence on the reliability of the turbine engine. Stress relaxation caused by creep is a major failure mode for turbine engine rotor bolts. The preload, temperature and vibration in the practical environment are most critical factors affecting creep behavior. The objectives of this paper include stimulating the early creep defect of bolted joint structure and improving the reliability of bolted joint by retightening after early creep stage. The creep curve can be obtained by the high temperature creep test of engine rotor with actual working conditions, and the burn-in time before the bolted joint reached the steady stage can also be obtained. Under the initial preload, the axial forces of the rotor connection structure are collected in real-time by self-designed test device. The degradation mechanism of bolt's preload under the initial preload and the high temperatures is studied. Reliability enhancement testing is performed to stimulate the defect of bolt assembly to accelerate the early stage of creep process so that the bolted joint structure can rapidly reach the steady stage of creep behavior before it come into service. The retightening operation is applied to the initial preload at the turning time from the rapid stage to the steady stage. According to the retightening operation mechanism and the stress relaxation model, the reliability of the bolt is evaluated and the reliable lifetime of bolted joint could be predicted quantitatively.