Study On Thermo-Structure Coupling Fatigue Behaviour Of Turbopump Rotor

Turbopump rotor is the key part of liquid rocket motor.Its working environment is harsh and high reliability is required.The start-up process is a stage of frequent failures,which is mainly affected by centrifugal,thermal load and prone to low-cycle fatigue problems,then cracks are generated and propagate until the structure fails.Therefore,it is necessary to study the fatigue of the start-up process.In this paper,based on the finite element method,the effect of temperature on the natural frequency and modal of the rotor is simulated and thermo-structure coupling simulation calculation is carried out.The stress,displacement and temperature change of the rotor under the action of mechanical load alone,thermal load alone and thermo-mechanical load together are studied and compared.and the calculation results of the constant and change of the sink temperature under the action of thermal load alone are analyzed.At the same time,the difference between the calculation results of complete and sequential thermo-structure coupling method is explored,besides the load change during the rotor start-up process is clarified,which lays the foundation for the subsequent estimation of lowcycle fatigue and crack propagation life.The commonly used low-cycle fatigue life prediction methods are described,and the most commonly used life prediction model(MansonCoffin formula)is used to calculate typical examples,and the calculation results adopting different correction methods are compared.Simultaneously,considering that the turbopump rotor under the thermo-mechanical load dose not yield during the start-up process.Then based on the asymmetric cycle counting method,obtained equivalent strain amplitude by considering the notch effect and high temperature endurance strength of the material.According to the strain life curve of the material,the low cycle fatigue life of the rotor under different start-up process is estimated.Combining the results of sequential thermo-structure coupling finite element analysis to obtain the dangerous position of the rotor,then a specific size crack is prefabricated in the dangerous position,the stress intensity factor in the crack propagation process is calculated by using FRANC3 D software,and the rotor crack growth rate under different startup process and crack depth is studied.Finally,based on the Paris crack growth life prediction model,the effects of start-up process and crack depth on rotor crack growth life are obtained.