Effect of Microwave Heating On The Mechanical Properties and Energy Dissipation Characteristics of Hard Rock

To study the effect of microwave on the weakening mechanism of hard rock, uniaxial compression tests were conducted on granite samples after microwave treatment, and an acoustic emission system was established to monitor the fracture evolution in such rock samples. The effects of microwave irradiation on the stress-strain curve, acoustic emission characteristics, and energy dissipation characteristics of granite were investigated in the experiment. The results show that: 1) With the continuous increase of microwave irradiation power and time, the compaction stage and crack development stage of the sample gradually increase, and the elastic stage gradually becomes shorter; the trend of post-peak stress drop becomes slower, changing from “cliff type” to multi-step type “. The failure of the sample indicates that they become less brittle and more ductile; 2) Microwave irradiation reduces the strength. The overall acoustic emission count rate is weak before the peak and increases rapidly near the peak. The count rate has also changed from sparse to dense, and with the increase in the irradiation power and time, the total acoustic emission count rate increases; 3) From the energy point of view, the weakening of granite by microwave irradiation will not only decrease the energy-storage limit of granite and increase the proportion of dissipated energy in the failure process, but also decrease the rate of release of elastic energy after the peak. Therefore, microwave irradiation will not only reduce the mechanical energy dissipated during damage, but also reduce the intensity of potential dynamic disasters.

Study on Pressure Relief Effect and Rock Failure Characteristics with Different Borehole Diameters

Rock burst is a common tunnel and mine dynamic disaster, especially for deep buried tunnels, which often leads to tunnel construction delay and even induces tunnel collapse and subsidence of strata. Rock drilling is one of the effective pressure relief methods to prevent these disasters. In order to study the influence of borehole diameter on rock mass pressure relief effect, indoor acoustic emission characteristics and numerical simulation of rock samples with different borehole diameter were studied. The research result shows that with the increase in borehole diameter, the effect of borehole pressure relief is better. Different borehole diameters do not change the overall trend of acoustic emission evolution, but it will lead to different acoustic emission count characteristics of rock damage and failure, especially the maximum acoustic emission count characteristics and corresponding strain values. The existence of drilling will lead to the failure stress of rock in advance. Moreover, the existence of drilling causes a great change in the failure mode of the specimen.

Study on Multiparameter Precursory Information Identification of the Fracture of Yellow Sandstone

In order to explore the disaster caused by uncontrollable instability of coal and rock mass, a multiparameter fusion system is constructed to predict and predict disasters more accurately by identifying the mechanical and acoustic precursors of coal and rock fracture. In order to explore the precursor information of yellow sandstone rupture, the damage evolution process of yellow sandstone is analyzed from the four aspects of rock mechanics, acoustic emission time domain, frequency domain, and characteristic parameters, and the body strain, dissipated energy and acoustic emission counting, acoustic emission energy, average frequency, peak frequency, b value, and entropy value precursor information identification points are obtained, and 8 parameters are analyzed by time series fusion. The specific conclusions are as follows: body strain in the violent stage of damage evolution, the slope is zero, the zero end point is the precursor information identification point, the dissipative energy curve overall shows the “s” type, the early growth rate is faster—the medium-term stability—the later period is slowed down, and the upper slope boundary point of the “s” type curve is used as the precursor information identification point. In the violent stage of damage evolution, the layered features of the acoustic emission count are obvious, the specific gravity shift is more obvious, and the high count appears as the precursor information identification point; the acoustic emission energy accumulates the high-energy signal and is accompanied by the steady and rapid growth of energy as the precursor information identification point. The effects of shearing main cracks, shear microcracks, tensile cracks, and composite cracks on the acoustic emission count and energy in the damage evolution process are analyzed. The increase of medium- and high-frequency signals and the reduction of high-frequency signals predict the rupture. The average frequency signal change law is continuous high frequency-blank-continuous high frequency, with the blank period end point as the damage precursor identification point; the b value damage evolution stage shows a continuously steady increase to a rapid increase, with the continuous stable growth starting point as the crack identification point. In the process of damage evolution, the sample entropy presents an orderly, chaotic, disordered, and orderly process. The end of chaos and the beginning of disorder are used as the prejudging demarcation points. Based on the time sequence, an eight-parameter comprehensive early warning system is constructed. The indicators are classified into five levels for early warning in the stage of severe damage evolution. The identification of multiparameter precursory information of yellow sandstone provides a new research idea and analysis angle and method for the failure of other coal and rock masses.

Monitoring Acoustic Emissions from Finger-Joints from Tropical African Hardwoods for Predicting Ultimate Tensile Strength

Summary The patterns of acoustic emissions generated during tension test of finger-joints from three tropical African hardwoods, Obeche (Triplochiton scleroxylon), Makore (Tieghemella heckelii) and Moabi (Baillonella toxisperma) were evaluated to assess their potential usefulness for non-destructively predicting ultimate tensile strength. The acoustic emission patterns generated were observed to differ depending on the type of finger profile and the wood species. Regression coefficients from cumulative acoustic emission count versus applied stress squared functions also varied with the profile and species type. When ultimate tensile strength was correlated with these regression coefficients, for stresses applied up to 50% of mean ultimate strength, the logarithmic regression model developed could predict finger-joint strength accurate to ±12%, ±13% and ±18% for Obeche, Makore and Moabi, respectively. The model was also sensitive to the type of finger profile used for all three tropical African hardwoods. The results indicate that this acoustic emission monitoring procedure could be useful for non-destructively predicting ultimate tensile strength of finger-joints from the three tropical African hardwoods.

Wear Process Description Based on Acoustic Emission

Since acoustic emissions are generated by fundamental mechanical processes, they can provide insight into the basic processes which determine friction and wear behavior. Descriptions of acoustic emission generated by plastic deformation and fracture were developed, and wear tests were performed, during which acoustic emission activity was measured. This work demonstrates that acoustic emissions can be used to track the wear process in terms of the energy dissipation mechanisms acting. The results show that acoustic emission count rate and amplitude distribution correspond to wear rate and that the amplitude distribution also indicates the active processes contributing to wear.