Experimental Study On Acoustic Emission Characteristics Of Concrete Under Cyclic Loading

Concrete is widely used as a durable material,but it is lack of detection for its damage degree after long-term use.The mechanical properties of concrete under cyclic load will deteriorate to different degrees,which will cause fatigue damage,and eventually lead to the decline of the overall bearing capacity of the building and damage.Therefore,the nondestructive testing of concrete shall be strengthened to master the damage process of concrete The evolution law of the system is very important.At present,the research ideas of acoustic emission detection technology to explore the evolution law of damage process are relatively new.Therefore,by using acoustic emission technology and mechanical characteristics,this paper explores the law of acoustic emission characteristics of concrete under periodic load,so as to make the research of acoustic emission characteristics of concrete be supplemented and improved accordingly.The main work and research results of this paper are as follows:(1)The laboratory test is carried out to study the concrete under horizontal periodic loading and unloading by using three variables of load amplitude,water content and strength.It is found that the ringing count of acoustic emission signal has strong regularity with the periodic change of load,but the regularity of energy and load periodic change is not strong,but the energy value has great influence on the macro cracks of concrete specimen In the whole process of cyclic loading,the average ringing count and average energy value increase with the increase of the strength range of the specimen;the acoustic emission parameters of concrete under cyclic loading have obvious fractal characteristics,and the change trend of its fractal dimension reveals the change process of the internal damage development of concrete from disorder to order and finally disorder.(2)There are three types of time-domain waveform of concrete acoustic emission under periodic load: weak burst,continuous and strong burst;different wavelet denoising methods can get different results in denoising concrete acoustic emission signal,and the best denoising methods are: DB9 wavelet basis,2-layer decomposition,rigid sure denoising rule,hard processing method and non white The best denoising methods for continuous signal are: db5 wavelet basis,2-layer decomposition,rigid sure denoising rules,hard processing method and scaled noise white noise level.After denoising,the signal-to-noise ratio of the original signal can be significantly improved.(3)The noise removal method can significantly reduce the influence of noise signal on the spectrum characteristics of original signal.The spectrum characteristics of acoustic emission signals have strong correlation characteristics with stress level.The main frequency is low frequency signal at low stress,and the main frequency is high frequency signal in high stress;the energy proportion of characteristic frequency band in different stress levels and the soul ring frequency of load are relative to the Soul Ring under the periodic load of natural state test piece The number has strong correlation,and the characteristic frequency band of acoustic emission signal is not obvious when the saturated sample is at the stress mean and valley level.The amplitude of characteristic frequency band of acoustic emission signal has obvious fractal characteristics.The change of fractal dimension D reveals the process of internal damage development from disorder to order and final disorder when concrete is damaged under load.