Research On Monitoring The Internal Force Of Pins Based On Nonlinear Ultrasonic Theory

Pin connection is a common connection method for nodes such as bearings,supports,beams,columns,and cables in engineering structures.With the construction of major projects such as large-span structures,pin connections are more and more widely used.The pin connection node is an important part of the structure to transmit internal force.Its excessive load or damage will directly affect the safety of the overall structure.Therefore,it is very important to determine the force state of the structure during service.Aiming at the problem that the linear ultrasonic method cannot identify the minor changes in the state of the pin connection interface,this paper proposes a method of monitoring the internal force of the pin based on the nonlinear ultrasonic theory,and conducts related theoretical and experimental research.The main content and conclusions of this article are as follows:(1)According to the characteristics of the piezoelectric sensor and the force characteristics of the pin connection,a method for monitoring the internal force of the pin based on the piezoelectric wave method is proposed.This method pastes piezoelectric sheets on the surfaces of the pin and the lug plate.One is used as a driver to emit ultrasonic signals,and the other is used as a sensor to receive ultrasonic signals passing through the contact interface of the pin.The characteristics of the received signal are analyzed to identify the Internal force of the pin connection.Based on the linear theory,the relationship between the ultrasonic transmitted wave and the pin connection interface pressure is analyzed.Finally,an experimental study on the internal force monitoring of the pin connection was carried out.The results show that the method can identify the internal force of the pin within a certain load range,but when the load condition of the test is large,the method cannot accurately identify the internal force of the pin.(2)Aiming at the problem that the linear ultrasonic method is not sensitive to small changes in the contact state of the pin connection interface,a method of monitoring the internal force of the pin based on the nonlinear ultrasonic theory is proposed.Based on nonlinear ultrasonic theory and rough surface contact stiffness model,the relationship between nonlinear characteristic parameters and interface pressure is established,and the sensitivity of linear and nonlinear characteristic parameters to interface pressure changes is compared through numerical simulation.The results show that nonlinear characteristic parameters are more sensitive to minor changes in the interface state than linear characteristic parameters.(3)Based on theoretical analysis,an experimental study using nonlinear characteristic parameters to identify the internal force of pin-shaft connections was carried out.Under different load conditions,the time-frequency domain of the received signal is analyzed,which verified the correctness of the nonlinear ultrasonic theory.The test results of using linear and non-linear characteristic parameters to identify the internal force of the pin-shaft connection are compared,and the results show that the linear characteristic parameters cannot identify small changes in the state of the pin-shaft connection.The nonlinear characteristic parameters based on the second harmonic can effectively identify the changes in the state of the pin connection under all test load conditions.