Influence Of Mechanical Joints Contact Stiffness Of CT Specimens On Average Load Of Resonance Fatigue Test And Online Compensation

The study shows that a large number of fractures are closely related to the initiation and propagation of fatigue cracks.The fatigue crack propagation test has been used to study the fracture characteristics of the material,which is very important to improve the reliability and service life of mechanical products.The electromagnetic resonant fatigue crack propagation test device based on resonance principle are used to measure the fatigue crack propagation characteristics of metallic materials and their components.The standard compact tension(CT)specimen is the most common specimen in fatigue crack propagation test.In order to ensure the accuracy of the test results,it is necessary to accurately measure and control the test load(amplitude and average load)acting on the specimen during the test.In the process of fatigue crack propagation test,the change of average load caused by the change of mechanical joints contact stiffness of CT specimens needs to be compensated online.In this paper,the influence of mechanical joints contact stiffness of CT specimens on average load of resonance fatigue test and online compensation are analyzed theoretically and experimentally.It has theoretical and applied value.The main work of this paper is as follows:1.The online average load compensation system for electromagnetic resonance fatigue test is established,including the online fatigue crack detection system and the testing load control system.An online average load compensation method is proposed,and the fuzzy control technology is used to control and compensate the average load online.2.The mechanical joints contact stiffness model of CT specimen,the mechanical model of linear multi-degree-of-freedom vibration system for electromagnetic resonant fatigue test and the mechanical model of static loading system for resonant fatigue test are established.Hertz contact theory is used to analyze and calculate the normal contact stiffness of CT specimens.The finite element analysis method was used to establish the calculation model of CT specimen,force sensor,main vibration and exciting spring stiffness,and the variation law of specimen stiffness with crack length was analyzed.The source of average load error is further analyzed,and the expression of average load error is derived,and the influence of various factors on average load error is discussed in detail.3.An experimental system for on-line measurement and compensation of average load in resonant fatigue test was built,and the software and hardware of the experimental system were designed.Finally,relevant experiments were carried out and the methods proposed in this paper were implemented,analyzed and verified through experiments.