Statistical Characteristics Of Avalanche Dynamics And Its Application Based On Acoustic Emission Of Rock Brittle Fracture

Avalanche dynamic behavior is a series of intermittent and across multiple-scale dynamic responses of physical systems to external stimuli.These reactions are nonlinear and non-continuous,which we call avalanche signals.When an out of equilibrium system governed by disorder is externally driven,the evolution of internal variables changes from local short-range to long-range correlation.This process is a collective behaviour adiabatically quick known as avalanche.Avalanche dynamics are associated to the transformation of spatial domains in different scales.Now avalanche dynamics is also an interdisciplinary topic involved in the complex system evolution,material science,the return prices of stock markets,the neuron networks,the biological evolution and earth science.Avalanche behaviors have the characteristics of scale invariance and criticality.The physical mechanism obeys a similar distribution law in all observational scales.Avalanche dynamics follow some empirical laws and have been improved or unified in their respective fields,ultimately reducing the complexity of systems to simpler mathematical models.In this doctoral thesis,avalanche dynamics was applied into the instability rupture of quasi-brittle coal-rock materials,and use acoustic emission monitoring technology to obtain the damage signals caused by external mechanics.Due to the similarity between the internal fracture mechanism of the rock and the trigger mechanism of the earthquake,the seismic statistic laws are also suitable for this series of discrete small-scale avalanche signals.Therefore,we have conducted systematic research and discussion on the laboratory scale “seismic signals”.The structure of the doctoral thesis are as follows:Chapter 1 introduces the application of avalanche dynamics in solid catastrophic and its research progress.Describe in detail the research status of avalanche dynamics in deformation test and numerical calculations of solid materials.Introduce the framework,technical route and main research contents of this thesis.Chapter 2 defines the basic properties and concepts related to the point process of avalanche,and establishes a detecting method for temporal correlation based on the point process.For the scale-free behavior of avalanche events,a robust critical exponential estimation method—maximum-likelihood estimation is introduced.This chapter provides theoretical support for the statistical and test methods of the following chapters.Chapter 3 introduces the working principle of acoustic emission equipment,and summarizes the seismic statistical experience law((1)Gutenberg-Richter law;(2)Waitting-time;(3)O'rime law)of rock avalanche with acoustic emission signal as the research object.Combining the correlation parameters of the labquake with the earthquake,and verifying the scale-free characteristics and universality of the statistical distribution,finally testing the time-correlation.In Chapter 4,based on the difference of maximum-likelihood distribution caused by non-fixed critical point behaviors of avalanche for rock,three types distribution model of critical exponents of maximum-likelihood are proposed:(1)Pure power-law;(2)Exponential mixing;(3)Exponential damping.The three types of model are demonstrated with the results of rock acoustic emission experiments.In Chapter 5,the composite rock mass of coal and sandstone is taken as the research object,exploring the critical fixed point interaction mechanism of two different media with acoustic emission energy as the information carrier.Firstly,verify scale-free characteristics of the power-law at different scales;Then,it explores the distribution characteristics of the maximum-likelihood curve of composite rock failure,and combines the theoretical results of Chapter 4 to reveal the critical exponential mixing mechanism.Finally,analyze the discipline of signal transmission between media and investigate the interaction mechanism between media.Chapter 6 reveals the non-fixed critical point behavior of rock fracture during uniaxial compression.Taking into account the influence of different stress paths and the acoustic emission overlap effect on the statistical results,the rocks avalanche statistical investigate of creep and cyclic loading are carried out to understand the floating characteristics of exponent under different stress paths.Chapter 7 introduces two applications of avalanche in rock damage process based on the correlation between the internal state and the critical exponent:(1)Influence of drying-wetting cycles on microstructure degradation of shaly sandstone using nuclear magnetic resonance and acoustic emission;(2)Study on micro-cracking characteristics of granite by thermal damage using acoustic emission.The experimental results show that the damage degree reflected by the avalanche critical exponent has similar variation trend with the rock mechanics parameters and NMR parameters,and there are corresponding functional relationship between the parameters.Finally,Chapter 8 summarizes the main conclusions and innovations of the overall study.In addition,the shortcomings and the needs for improvement of this research,as well as the future research prospects,are discussed.