Research On Defect Detection Of Coil Spring Based On Ultrasonic Guided Wave

Due to its excellent performance,the coil spring is widely used in various mechanical structures,such as the mechanical watch movement,the spiral coil spring and the high-voltage circuit breaker spring operating mechanism.The material properties and mechanical properties of the coil spring have a great influence on the stability and safety of the mechanism.High-voltage circuit breaker energy storage coil springs are prone to fatigue cracks and other damage after long-term operation,which has a great impact on the stable operation of high-voltage circuit breakers.In this paper,according to the structural characteristics of energy storage coil spring,the research method of circumferential guided wave of thick-walled pipeline is applied to damage detection of coil spring in high-voltage circuit breaker,which provides guidance for circumferential guided wave detection of coil spring.The main work of this paper includes:(1)Based on the basic theory of ultrasonic guided waves,the main characteristics of ultrasonic guided waves and the principle of ultrasonic guided waves applied to structural damage detection are analyzed.According to the particularity of the structure of the coil spring,the coil springs are approximated as thick-walled pipeline structures.The propagation characteristics of the guide waves in the laps of the coil springs are studied by referring to the research method of the inner-wall guided waves of thick-walled pipelines.(2)By using the wave equation combined with the knowledge of elastic mechanics to calculate the circumferential guided wave dispersion equation of thick-walled pipe,the numerical solution method of the dispersion equation is used to analyze and solve the coil springs,then the dispersion curves of the coil springs are obtained.By analyzing the dispersion curves of each lap,it can be seen that there is a negative correlation between the shape parameters representing the bending degree of the coil spring and the dispersion degree of each lap,and the feasibility of testing the coil spring by exciting single-mode circumferential guided waves is explored.(3)By analyzing and comparing the dispersion degree of each mode in each circle,the first mode with the lowest dispersion degree in each circle is selected as the mode of coil spring guided wave detection,and the frequency and incidence angle of the sensor exciting the mode are obtained by solving and analyzing the relationship curve between the first mode excitation frequency and incidence angle of four circles.(4)By studying the working principle of the spring operating mechanism,the force analysis of the coil spring in the actual work is analyzed.The finite element analysis method is used to analyze and solve the energy storage process of the coil spring,and the stress distribution of each lap of the coil spring is obtained.From the stress distribution,the conclusion that the outermost ring of the coil spring is most prone to stress damage(5)Taking the outermost lap of the coil spring which is most vulnerable to damage as the detection object,two prefabricated defects on the outer lap of the coil spring are detected by using a single circumferential guide wave excited by the sensor with selected frequency and incidence angle.Through the analysis of the echo signal of the coil spring,it is verified that the selected sensor excites the required guided wave mode,and the spring defect is identified and located by the modal guided wave.(6)According to the characteristics of coil spring structure and the requirement of in-service detection,a sensor structure for coil spring circumferential guided wave detection is designed,and the parameters of piezoelectric wafer material,wedge material and angle of the sensor are optimized.Three groups of guided wave sensors with different backing are developed.By comparing the performance of the sensors,the high tungsten powder ratio containing graphene is obtained.Sensors are more suitable for detecting coil spring defects.In this paper,the circumferential guided wave is applied to the damage detection of coil spring structure for the first time,and the propagation characteristics of the circumferential guided wave in coil spring are explored,which provides a basis for the further study of the damage detection of coil spring.