Acoustic Emission Perception And Characteristic Behavior Of Asphalt Mixture During Cracking Failure

The repeated vehicle loading and temperature condition create stress in asphalt pavements as a result microcrack gets developed in the asphalt mixtures.Understanding the failure mechanism and mechanical response of asphalt mixtures is essential to improve performance design and structure optimization of asphalt pavement,and then prolong the service life of asphalt pavements.As a dynamic non-destructive testing method,the acoustic emission technology could conduct dynamically observation of minor damage in the material or structure realize the diagnosis of the damage source location and the evaluation of the material performance.The purpose of this paper is to explore the relationship between the mechanical behavior and the acoustic emission process in the failure process of asphalt mixture,and to achieve the position diagnosis,damage feature analysis and damage state evaluation of the acoustic emission source of asphalt mixture by utilizing the source location algorithm,signal feature extraction and dimensionality reduction expression,damage theory derivation and numerical simulation.Firstly,the pencil-lead-break tests are conducted on asphalt mixture beams to explore the propagation characteristics of AE signals.The wavelet threshold denoising method is utilized to extract effective information from AE signals associated with the pencil-lead breaks on the surface of asphalt mixture beam by simultaneously considering the wavelet basis functions,decomposition levels and threshold rules.An effective time difference of arrival estimation method combining noise reduction,wavelet decomposition and cross-correlation processing is established to accurately locate the damage source of asphalt mixtures.The results of 3d localization reveal the crack propagation trend in the failure process of asphalt mixture.Secondly,the relevant tests of asphalt mixture under different loading modes are carried out.The law of acoustic emission activity under different load levels is discussed.The relationship between acoustic emission parameters and fatigue damage is analyzed,and the importance of embrittlement point temperature in evaluating material state transition is expounded.Thirdly,the local tangent space arrangement method is used to obtain the low-dimensional embedding of the high-dimensional feature data set,and the pattern recognition of the acoustic emission signal type by the support vector machine is realized.Finally,this paper discusses the mechanism of acoustic emission source and mechanics behavior.The relationship between acoustic emission energy parameters is constructed and its damage in the process of the quantitative relation between the damage factor,calibrating the fatigue damage evolution model of Weibull distribution parameters,and through numerical simulation,based on the acoustic emission parameter is verified the validity of the calibration of the fatigue damage evolution model.The following major conclusions are achieved from this study.(1)The results show that there is less serious attenuation of amplitude and energy of acoustic emission parameters and frequency spectrum of acoustic emission waveforms within the range of 100 mm in asphalt mixtures.The larger signal-to-noise ratio and the smaller root mean square error of denoised acoustic emission signals indicate that the threshold denoising method optimized by the Fruit Fly Optimization Algorithm is more effective for acoustic emission detection of asphalt mixtures.The improved time difference of arrival estimation method could obtain a minimum time difference value,and the calculated locations of acoustic emission events are closer to the actual pencil-lead-break points.(2)Under the condition of monotone loading,there are obvious differences in acoustic emission activities at different load levels,which indicates that the characteristics of acoustic emission signal can be used as the basis to distinguish the changes of material properties during the failure of asphalt mixture.Under the condition of fatigue load,acoustic emission activity is closely related to the fatigue damage state of asphalt mixture,and the variation of acoustic emission amplitude and energy parameters is helpful to further understand the damage behavior of materials.Under the condition of temperature load,the temperature corresponding to the sudden change point of acoustic emission parameters is called the embrittlement temperature,which can be used to judge the state transition of asphalt mixture under the condition of low temperature.(3)Acoustic emission accumulative parameters show a periodic distribution pattern in the failure and failure process of materials,which can be used as the evaluation index of the failure stages.acoustic emission signal characteristics reflect the failure mechanism of damage sources,and the local tangent space arrangement method can better extract the low-dimensional embedded features of the high-dimensional features of different types of signals,so as to identify the types of ae signals in the failure process of materials and achieve the pattern recognition in the failure stage.(4)The energy parameters of acoustic emission signal can reflect the fatigue damage process of asphalt mixture,and the parameters of the fatigue damage evolution model are calibrated by the damage factors defined in the acoustic emission signal.It is found by numerical simulation that the fatigue damage evolution model can better reflect the damage process of the material in trabecular fatigue test.The research results provide a method of acoustic emission signal perception and source location suitable for asphalt mixture,and clarify the characteristics of acoustic emission signal in the failure process of asphalt mixture,which would hopefully to provide support for diagnosing defects and evaluating the performance of asphalt pavement structure.