Research On Vibration-Based Damage Monitoring And Fatigue Test Of Fiber-Reinforced Composite Materials

The excellent material properties of fiber-reinforced resin-based plastics(FRP)make it widely used in various aerospace,vehicles,ships,pressure vessels and automation equipment.And it began to be applied to a large number of critical load-bearing structure,showing the integration,large-scale trends.These equipment in the actual service will inevitably bear complex,random vibration load.The equipment structure under these load excitation,resulting in vibration response,and then lead to vibration fatigue problems.However,for a long time,research on FRP fatigue has focused on a simple fatigue phenomenon under constant amplitude load,such as Tension-Tension(T-T),Tension-Compression(T-C),and Compression-Compression(C-C).The fatigue life under the uniaxial load during laboratory experiments is much different from that under realistic and irregular service load.The load in the actual service for all kinds of engineering structures is not the constant amplitude load commonly used in the conventional fatigue test,but the random load with complex amplitude.Currently,however,there is very little literature on the fatigue life of composite structures under random and complex load.All kinds of equipment in the service process need to perform a variety of complex tasks,so the equipment structure design of lightweight,high reliability and long-life requirements are getting higher and higher,which leads to the vibration fatigue problem of a large number of applications on the structure of FRP under complex random load gradually become more prominent.To study the vibration fatigue problem of composite materials,it is necessary to monitor the derivative and development state of fatigue damage of composite materials in real time.However,the current damage detection means for the fiber-reinforced resin-based composite material is substantially off-line.Aiming at above problems,this paper firstly analyzes the vibration characteristics of the typical damage of the composite material by simulation and experiment,and explores the on-line damage monitoring method during the vibration fatigue test of FRP based on the vibration signal.On the basis of that,the factors that affect the fatigue life of composites were completely studied by means of dynamic simulation analysis and practical experiment,respectively,from two different technical perspectives: structural stress response analysis and actual vibration fatigue test.The main contents and conclusions are as follows:1.On-line damage monitoring technology of fiber reinforced composite based on vibration signal was studied.Firstly,the simulation method and the modal test were used to analyze the vibration characteristics of the typical damage of the composite material,and the relationship between the initiation of typical damage and the vibration characteristics of the structure was established.On the basis of this,the damage monitoring of FRP during vibration fatigue test was designed and realized in vibration test system.2.The stress response of fiber reinforced composite under complex random load was analyzed.This paper explored the transient dynamics simulation method of the typical carbon fiber-reinforced composite cantilever laminate structure.Through the large-scale time domain calculation,the structural stress response under complex random base-excitation is analyzed systematically.The structural stress-strain calculation method was explored.The strain test method in the vibration test of the laminates was proposed and the simulation results are verified.Simulation analysis of stress response of typical structure under non-Gaussian random vibration base-excitation was realized.3.The factors influencing the vibration fatigue life of fiber-reinforced composites were systematically studied.The vibration fatigue behavior of the composites was verified by the actual vibration fatigue test,and the factors that affected the vibration fatigue life of the carbon fiber-reinforced composites,such as the kurtosis,root mean square(RMS)value,power spectrum density(PSD)magnitude,bandwidth and other load factors,were revealed.The methods and conclusions of this paper can lay the foundation for the damage monitoring,life evaluation and structural optimization design of fiber-reinforced composite materials,and provide support for ensuring the safe and reliable service of FRP.