Initial Stage Of Damage Research Articles

Experimental study on energy and damage evolution of dry and water-saturated dolomite from a deep mine

The deformation and failure of a rock is closely related to the strain energy consumption during the load process of rock. To investigate the effect of water on energy evolution and damage characteristics of dolomite samples from a deep mine, the uniaxial compression tests were carried out on dry and water-saturated dolomite samples at different burial depths (900 m–1200 m). The effects of water on the evolution characteristics of elastic and dissipative energy ratios ( Ue/ U and Ud/ U) during rock deformation and failure was analyzed. Based on the variation rate of damage factor ( Df), a new brittleness index is proposed, which can effectively characterize the brittleness characteristics of water-bearing dolomite. The results show that the uniaxial compressive strength and elastic modulus of the water-saturated dolomite are significantly reduced compared to dry sample. The energy and damage evolution process of dolomite can be divided into four stages: initial damage stage, stable damage stage, pre-peak accelerated damage stage and post-damage stage. The variation rate of damage factor of the rock samples in the stable damage stage and the pre-peak accelerated damage stage appeared to increase significantly after water saturation treatment. Compared with water-saturated samples, more pronounced energy hardening characteristics and brittleness characteristics were observed in dry samples. In addition, the possible impact on the stability of deep rock engineering after the deterioration of rock mechanical properties and energy storage properties caused by water was analyzed. Groundwater can somewhat reduce rock burst proneness. However, it also has the potential to lead to greater rock engineering destabilization and failure hazards.

The Effect of Wetting–Drying Cycles on the Deterioration of the Physical and Mechanical Properties of Cemented Paste Backfill in Open-Pit Coal Mines

To promote the sustainable exploitation of open-pit coal resources, waste is used as backfill material to realize the comprehensive utilization of solid waste mine resources. We proposed a mining method that is a combination of the highwall mining and filling mining methods. Cemented paste backfill (CPB) samples were prepared with high-clay-mineral-content marl particles as aggregate and normal Portland cement, sulfoaluminate cement and gypsum as cementing materials. The physical and mechanical properties and microstructural evolution of CPB with different binder ratios under wetting–drying cycles were measured. The results showed that the CPB with 0–3 wetting–drying cycles underwent shear and tensile coalescence, and that with 4–10 cycles underwent shear coalescence. The unconfined compressive strength (UCS) and elastic modulus (EM) decreased exponentially with increasing number of wetting–drying cycles but decreased exponentially and cubically with increasing porosity, respectively. The EM is more sensitive to gypsum content than the UCS. CPB deterioration was divided into an initial deterioration stage and a secondary deterioration stage. The evolution curve of the total damage variable presents an ‘S’ shape, with an initial damage stage, an accelerated damage expansion stage, a decelerated damage expansion stage and an end damage stage. The research results provide a basis for improving the recovery rate of resources under highwall conditions, and the extensive utilization of stripping materials, and promote the coordinated development of coal resource exploitation and environmental protection.

Performance of Pulsating Heat Pipe with a stimulus of auxiliary heat load for Battery Thermal Management System

Stimulus strategy is proposed to enhance the heat dissipation performance of Pulsating Heat Pipe (PHP) at low heat load for local hot spot regression in Battery Thermal Management (BTM). An auxiliary heat load is applied to stimulate the start-up of PHP. The performances of PHP with and without stimulus are compared and the properties of PHP after stimulus are discussed. It is concluded that the application of auxiliary heat load is able to stimulate the start-up of PHP in experiments. The strategy is mainly based on the phase-change mechanism as well as the hysteresis of working medium. Thermal resistance and the evaporator temperature are significantly reduced, if PHP starts operation after stimulus. Long period of stimulus and strong auxiliary heat load are favored for the reduction of thermal resistance and the shortening of period for start-up. The thermal resistance may be reduced by 29.1 ∼ 69.6 % and the temperature may be regressed by around 8 °C. However, PHP may suffer from temperature uplift and overshot to the maximum evaporator temperature. Therefore, high interference temperature coupled with weak auxiliary heat load and long period of stimulus are suggested as the optimal strategy. The verified strategy offers a new method for local hot spot regression and a possible way to mitigate the risk of thermal runaway, since the heat dissipation is enhanced at the initial stage of damage or destruction.

Study on interlaminar fracture toughness of unidirectional composites

Carbon fiber composite is widely used in the nuclear industry and other fields due to their lightweight and high strength. There are various forms of failure in composite, including resin cracking, fiber fracture, and resin fiber interface debonding. At the initial stage of damage, they all exhibit the form of microcracks. As cracks propagate and fuse, they ultimately lead to macroscopic fracture of composite components. For safety reasons, it is necessary to study the fracture toughness of composite. This article uses a combination of winding method and double cantilever beam method to study the interlayer fracture toughness characteristics of high-strength (or high modulus) fiber epoxy resin composite under type I load. Choose a more suitable propagation GIC as a measurement metric. The results indicate that under the same resin matrix, the interlayer fracture toughness of high-strength fiber composite is much higher than that of high modulus fibers, which is related to the high surface chemical activity of high-strength fiber monofilament. Finally, combined with finite element analysis, its application in laminated structures was briefly analyzed.

Bio-inspired beam lattice materials with sacrificial bonds

We consider the controlled non-localized brittle fracture of a periodic beam-lattice subjected to tensile loading. The specific lattice architecture ensures overstress of a periodic group of sacrificial beam elements prior to the macrocrack appearance. Thus, at the initial stage of damage, the lattice material implements the borrowed from nature ”partially break but not fail” paradigm. Consequently, it becomes less stiff and absorbs energy, while still remaining intact. We find several two-dimensional lattices characterized by this feature and examine their elastic and fracture behavior. For the lattices with triangular cells it is found that the anisotropic lattice with the beams of uniform thickness and different lengths is a better energy absorber than the isotropic one where the beam elements of the same length have different thicknesses. Moreover, both configurations are inferior in this regard to the bone-microstructure inspired lattice with rectangular cells.

Quantitative investigation on localized deformation process of rocks by uniaxial test and digital image correlation

Determining the localized deformation mechanism is of vital importance to understand the failure processes of geomaterials in practical engineering. In this study, uniaxial monotonic and cyclic loading tests of slate samples were conducted and the failure processes were recorded by using the AE system and digital image correlation (DIC). The results show that the deformation field variance increases significantly in the initiation of the macro-scale failure stage. Under cyclic loading, the shape of the stress-variance hysteresis curve varies with increasing upper limit stress, and four types of stress-variance hysteresis curves were revealed. Increasing lag time of variance indicates gradual accumulation of damage to the sample. The comprehensive analysis of the evolution process of damage variables defined by cumulative AE counts and variance reveals that the rock failure process can be divided into crack closure stage, initial damage stage, stable development stage, accelerated development stage and failure stage. By proposing the differentiation rate, it is found that there are apparent failure precursor points under monotonic and cyclic loading.

Bending-damaged fracture criterion and numerical implementation of limestone beam under three-point bending test

To study the characteristics of tensile cracking by rock-bending damage, the bending stress–strain curves and the cumulative ringing counts were obtained by a three-point bending test and acoustic emission (AE) monitoring of limestone beams. Based on the Lemaitre strain equivalent principle and the continuous damage theory, the bending damage variable D was defined by the AE cumulative ringing counts, and the bending crack damage evolution equation was established according to the Weibull distribution of the rock element strength. To realize the numerical test of the bending deformation, the damage variable D was used as the intermediate variable, and the specific process of damage bending stress transformation and the realization of the tensile crack criterion were secondary developed by FISH language in FLAC3D. According to the results, the central part of rock beam deforms downward under the action of bending stress, and both ends tilt up. Therefore, the bending failure begins with the tensile crack at the bottom of the rock beam and gradually extends to the compression zone. The maximum damage value is about 0.402 before the peak stress. The compressive stress in the x direction increases from the neutral layer to the top of the rock beam, and the tensile stress in the x direction increases from the neutral layer to the bottom of the rock beam. The maximum tensile stress is distributed in the center of the bottom of the specimen, where the bending effect is obvious. The stress–time curve was divided into the (Ⅰ) compaction stage, (Ⅱ) expansion stage, and (Ⅲ) penetration stage, accordingly, and the evolution of damage equation was divided into three stages: initial damage stage, slow damage stage, and accelerated damage stage. The curves of the experimental result, theoretical model prediction result, and numerical simulation result were in good agreement with each other, which indicates that the numerical simulation based on the criterion of rock damaged fracture can better reflect the bending process of rock beams under three-point bending stress.

Triaxial mechanical behaviour and energy conversion characteristics of deep coal bodies under confining pressure

To understand more about damage, failure, and transformation of coal, this paper performed triaxial loading tests on coal samples obtained from a deep coal mine in China. Results showed that the brittle failure characteristics of the specimens were obvious under single-axis loading, and that the ductile failure characteristics of the specimens increased as confining pressure increased. The ultimate strength and residual strength of the samples exhibited a sound linear growth relationship with confining pressure. And according to the change trend of damage variable with axial strain, the damage process of coal body is divided into four stages: initial damage stage, stable damage stage, rapid damage stage and damage failure stage. The energy conversion characteristics of the samples were thoroughly analysed and it was found that with the increase of confining pressure, the proportion of elastic energy of coal samples increases, while the proportion of dissipated energy decreases, indicating that confining pressure can inhibit the expansion of fractures and strengthen the energy storage capacity of coal samples. It was also discovered that the greater the confining pressure, the greater the ultimate elastic energy of the samples. This study is of great significance for mastering high energy level disasters in deep mines.

Three-point bending properties of 3D_C/C_TiC_Cu composites based on acoustic emission technology

Ceramic matrix composites with three-dimensional (3D) braided structures have been become one of the research hotspots owing to their excellent properties such as high strength and high-temperature resistance. In this study, acoustic emission (AE) as a non-destructive technique was utilised to monitor the three-point bending process of 3D_C/C_TiC_Cu composites and investigate the damage change of the materials under different bending stress. Firstly, the sentry function is used to divide the damage stages. Then the acoustic feature parameters are used to evaluate the damage condition. Finally, the time–frequency characteristics of damage signals are compared to verify the damage type of the composites at different stages. The results demonstrate that the sentry function can effectively distinguish the four stages of the damage process: the initial damage stage, the damage developing stage, the rapid damage stage and the failure stage. By analysing the acoustic feature parameters and time–frequency characteristics of the signals, the damage mechanism and the damage state of the composites can be obtained qualitatively. Consequently, the AE technique is an effective tool for evaluating damage evolution of 3D_C/C_TiC_Cu composites.

Research on the Characteristics of Coal Bump and Monitoring and Early Warning in Hujiahe Coal Mine

Under the high intensity mining disturbance, coal bump is easily triggered by the sudden release of large amount of elastic energy contained in the coal body, which seriously affects coal mine safety production. Triaxial experiments were used to study the damage characteristics of coal samples subjected to loading at the 401103 working face of Hujiahe coal mine, and the critical value of peak strength of coal samples was investigated. Based on the characteristics of the mechanical damage behavior of coal samples obtained from the triaxial experiment, the statistics of the occurrence of coal bump events at the 401103 working face were conducted through numerical simulation and field monitoring to study the areas that need to be focused on prevention and control, with a view to providing basic research for deep coal mining. The results show the following: (1) the strength of coal samples is “weakened” by stress loading, and the fracture penetrates the coal body interface leading to the formation of tensile-shear damage of coal samples. The value of the damage variable for the coal sample in the initial damage stage is 0; at the damage stabilization stage, the values of damage variables were derived to be located at 0.03~0.14. The bearing capacity of the coal sample decreases rapidly during the accelerated development period. (2) According to the simulation and field monitoring, it is known that 0~100 m in front of the coal mining face belongs to the key monitoring area. (3) With the advancement of the working face, different coal pillar widths have obvious effects on the vertical stress, and stress increase and decrease zones appear on both sides of the coal column, and the peak stress shows the characteristics of increasing first and then decreasing with the advancement of the working face. The width of the working face has a great influence on the change of vertical stress. When the sensitivity of the vertical stress to the width of the working face increases, the stress concentration phenomenon will occur, and a large amount of elastic energy gathered in the coal body is suddenly released to induce coal bump.

Attenuation of Cigarette-Smoke-Induced Oxidative Stress, Senescence, and Inflammation by Berberine-Loaded Liquid Crystalline Nanoparticles: In Vitro Study in 16HBE and RAW264.7 Cells.

Cigarette smoke is considered a primary risk factor for chronic obstructive pulmonary disease. Numerous toxicants present in cigarette smoke are known to induce oxidative stress and airway inflammation that further exacerbate disease progression. Generally, the broncho-epithelial cells and alveolar macrophages exposed to cigarette smoke release massive amounts of oxidative stress and inflammation mediators. Chronic exposure of cigarette smoke leads to premature senescence of airway epithelial cells. This impairs cellular function and ultimately leads to the progression of chronic lung diseases. Therefore, an ideal therapeutic candidate should prevent disease progression by controlling oxidative stress, inflammation, and senescence during the initial stage of damage. In our study, we explored if berberine (an alkaloid)-loaded liquid crystalline nanoparticles (berberine-LCNs)-based treatment to human broncho-epithelial cells and macrophage inhibits oxidative stress, inflammation, and senescence induced by cigarette-smoke extract. The developed berberine-LCNs were found to have favourable physiochemical parameters, such as high entrapment efficiency and sustained in vitro release. The cellular-assay observations revealed that berberine-LCNs showed potent antioxidant activity by suppressing the generation of reactive oxygen species in both broncho-epithelial cells (16HBE) and macrophages (RAW264.7), and modulating the genes involved in inflammation and oxidative stress. Similarly, in 16HBE cells, berberine-LCNs inhibited the cigarette smoke-induced senescence as revealed by X-gal staining, gene expression of CDKN1A (p21), and immunofluorescent staining of p21. Further in-depth mechanistic investigations into antioxidative, anti-inflammatory, and antisenescence research will diversify the current findings of berberine as a promising therapeutic approach for inflammatory lung diseases caused by cigarette smoking.

Study on Damage Characteristics of Deep Coal Based on Loading Rate Effect

In this paper, the uniaxial compression tests of coal under different loading rates are carried out by using the MTS rock mechanics loading system and the DS5 acoustic emission instrument, and the mechanical parameters and damage characteristics of coal samples under five loading rates are studied. The conclusions are as follows: The uniaxial compressive strength and the elastic modulus of the sample increase with the increase in the loading rate, whereas the strain at the peak point of stress decreases with the increase in the loading rate; at a low loading rate, the AE ring count of the coal samples is widely distributed, but the maximum AE ring count value is small. At a high loading rate, the AE ring count of the coal samples decreases, whereas the maximum AE ring count value increases significantly. With the increase in the loading rate, the maximum AE ring count and cumulative AE ring count of the sample increase. According to the damage variable curves of the coal samples under different loading rates, the damage evolution process of the samples before the stress peak is roughly divided into three stages: initial damage stage, stable damage development stage and rapid damage development stage. It is found that when the loading rate is low, the deformation time of the coal sample is relatively sufficient, whereas when the loading rate is high, the micro cracks have no time to develop and expand, the sample is destroyed instantly and the destruction of the coal sample is sudden. Therefore, with the increase in the loading rate, the damage variable value at the peak stress of the coal sample generally shows an increasing trend.

Tensile damage evolution of 2D SiC(f)/BN(i)/(SiC-B4C)(m) composites based on acoustic emission pattern recognition

The tensile test of 2D SiC (f) /BN (i) /(SiC-B 4 C) (m) , with acoustic emission (AE) online monitoring, was carried out to study the mechanical properties and failure mechanism. Using the pattern recognition technique to find out the relationship between AE signals and damage mechanisms, an improved sentry function was proposed by choosing the AE energy of fiber breakage instead of the AE energy in its definition. Combined with the cumulative trend of each class of the AE signals, the damage evolution process was identified. It is found that the entire loading process includes four stages: (a) the linear elastic stage, there have sporadic AE events; (b) the initial damage stage, the matrix cracking contributes 80.4% of the AE energy and leads to the non-linear behavior of the stress-displacement curve; (c) the damage development stage, in which all types of damage continuously happen; and (d) the damage acceleration stage, dominated by fiber breakage that accounts for 60.1% of the AE energy. The improved sentry function has a decreasing trend during the fourth stage, which provides an early warning before failure, and gives a reliable ultimate strength.

Study on Acoustic Emission Characteristics and Damage Evolution Law of Red Sandstones under Different Loading Rates

Uniaxial compression experiments with different loading rates and acoustic emission tests were conducted to study the loading rate effects on the mechanical and acoustic emission characteristics of red sandstones. The mechanical and acoustic emission parameters of red sandstones were analyzed with varying loading rates. Furthermore, the red sandstone damage evolution model was established based on the acoustic emission cumulative ringing count. The results show that: (1) The elastic modulus decreases linearly with the increase of the logarithm of loading rate, while the peak strength generally shows a gradually increasing trend with the logarithm of the loading rate. (2) With the increase of loading rate, the AE event rate’s peak value increases gradually, and the cumulative number of AE events decreases. (3) The evolution law of the characteristic stresses determined by the AE event rate and cumulative AE event number is the same as that of the loading rate. That is, with the increase of the loading rate, it shows a gradually decreasing evolution trend. (4) The damage evolution model of red sandstone can better describe the damage evolution process of red sandstone. According to the evolution characteristics of damage variables, the damage evolution process of red sandstone can be divided into three stages: the initial damage stage, the damage stable development stage, and the damage accelerated stage. (5) The damage variable at the damage stress point can reflect the actual damage degree of rock, and the size of the damage variable is closely related to the initiation, propagation, and transfixion of microcracks inside the rock. When the loading rate is low, the damage degree of red sandstone at the damage stress is usually more prominent because the rock’s microcrack develops more fully.

Stability Analysis of Slope Considering the Energy Evolution of Locked Segment

Researches on the energy evolution of the key blocks is helpful to reveal the failure process of locked-segment type slope, whose stability is governed by the locked segment along the potential slip surface. In order to study the failure mechanism of the locked segment in the process of slope progressive failure due to strength attenuation, a series of stability analysis on the numerical models of locked-segment type slope were implemented to record the relationship curve between energy and strength reduction coefficient. Then, according to the variation law and characteristic of energy evolution, the failure process of the locked segment was divided into four stages: elastic stage, initial damage stage, extensive damage stage and failure stage. And the reduction coefficient corresponding to the peak of the energy evolution curve was employed to achieve landslide warning. In addition, the method to determine the safety factor of locked-segment type slope was given, and its reliability was verified by comparing with other traditional methods. Finally, the formula for calculating the initial sliding velocity was presented based on the residual strain energy which is defined as the elastic strain energy of the locked segment when the slope is unstable.

Study on characteristic stress and energy damage evolution mechanism of cemented tailings backfill under uniaxial compression

This study attempted to explore, at curing age, the characteristics stress and energy evolution of the cemented tailings backfill (CTB) under uniaxial compression. Based on the energy consumption theory, the energy parameters at the characteristic stress varing with the curing age was analyzed. Furthermore, the evolution law of energy distribution and the energy damage mechanism of the CTB were revealed, and the failure criterion of the CTB was established based on the elastic energy consumption ratio. The results showed that the characteristic stress of the CTB follow an exponential function increasing law with the increase of curing age and the characteristic stress of the CTB with larger cement-to-tailings (c/t) ratio increases more rapidly when the curing age is 3d ~ 14d. The total energy, elastic strain energy and consumption energy at the peak stress point of the CTB all follow the exponential function increasing law with the increase of curing age, and the increase of cement-to-tailings (c/t) ratio and curing age can significantly improve the energy storage limit of the CTB. The deformation and failure of the CTB mainly go through five stages: initial crack compaction stage, linear elastic deformation stage, steady development stage of microcrack, accelerated crack expansion stage and post-peak failure stage. According to the damage value D of the CTB and the growth law of dissipated energy, elastic strain energy and axial strain, the loading damage of cemented CTB can be divided as follow: initial damage stage, damage stationary stage, damage stable stage, damage rapid stage and damage failure stage. The slow growth and abrupt change of the elastic energy consumption ratio K in the post-peak stage can be used as the criterion for strength instability of the CTB.

A Study of the Structural Evolution and Strength Damage Mechanisms of PishaSandstone Cement Soil Modified with Fly Ash

In the present study, in order to investigate the effects of fly ash on the structural evolution and strength damage mechanism of Pisha-sandstone cement soil, unconfined compressive strength tests of Pisha-sandstone cement soil with different fly ash content levels and various ages were carried out. The apparent morphology, microstructures, and chemical compositions of the samples were observed and analyzed using ultra-depth three-dimensional microscopy, scanning electron microscopy, and XRD methods. The results revealed that the unconfined compressive strength levels of Pisha-sandstone cement soil samples displayed increasing trends with the increases in fly ash content and age. For example, when the fly ash content levels were increased from 12% to 15%, the strength of Pisha-sandstone cement soil had only slightly increased under the curing ages of 7, 28, and 60 days. In addition, the unconfined compressive strength levels of the samples with 15% fly ash content only increased 0.02%, 0.51%, and 0.54%, respectively, when compared with the samples containing 12% fly ash. It was observed that with the increases in the fly ash content, the number of pores on the outer surfaces of the samples were significantly reduced. Also, the height differences of cross-sectional gullies were reduced, and the apparent morphology was observed to be flatter. Since cement hydration creates a strong alkaline environment for reaction systems, the active degrees of the pozzolanic reactions of the fly ash were stimulated in this study. Moreover, a significant amount of the C-S-H gel phase and the stable five-membered ring structure of the mordenite and ettringite were generated, which connected the loose Pisha-sandstone particles to form a skeleton. The internal microstructures were then observed to be denser and more uniform. At the same time, the micro-pores were filled and refined by the unreacted micro-bead fly ash. Consequently, the defects in the internal microstructures were improved. Also, based on the Weibull distribution, a damage evolution model of the Pisha-sandstone cement soil was established. The analysis results of the damage variable D values during the initial damage stage, damage evolution stage, and residual damage stage of the damage process showed that the damage variables during all three stages displayed decreasing trends with the increases in the fly ash content levels and age. Therefore, based on this study’s findings, it was considered that the incorporation of fly ash could effectively improve the damage degrees of Pisha-sandstone cement soil under external force conditions.

On acoustic emission characteristics, initiation crack intensity, and damage evolution of cement-paste backfill under uniaxial compression

The objectives of this study are as follows: To establish the relationship between the acoustic-emission (AE) parameters and mechanical-failure mechanism of tantalum-niobium tailings cemented paste backfill (CPB), to better understand the damage-evolution trend of CPB, to investigate the damage-evolution process of the CPB and AE time-effect mechanism, using an AE monitoring system combined with the stress–strain relationship, and to experimental study the damage-evolution and AE characteristics of tantalum–niobium tailing CPB under uniaxial compression. First, we discussed the crack-initiation and damage strengths, and then analyzed the AE characteristics of the CPB. Then, we proposed a damage variable based on the modified AE energy rate. We developed a CPB damage model based on the AE characteristics under uniaxial compression. The damage-evolution curve and equation of the CPB were obtained. Our results show: that the AE information reflects the damage to the CPB, which is closely related to the evolution of the internal microcracks and initiation, propagation, and penetration of new microcracks. The AE characteristics of the CPB can better describe its deformation and damage-evolution trend. The rationality of the damage model based on the AE characteristics is verified. The evolution process of the damaged CPB under uniaxial compression can be divided into three stages: initial damage stage, stable evolution of the damage and damage development stage, accelerated damages stage. The deformation to destruction of the CPB can be regarded as a gradual process. The entire process consists of the initiation and development of deformation and damage to the occurrence of macrocracks, and finally to failure.

Fatigue-Damage Evolution Characteristics of Interbeded Marble Subjected to Dynamic Uniaxial Cyclic Loads

In this work, uniaxial fatigue tests combined with post-test X-ray computed tomography (CT) scanning were conducted on marble samples with different interbed orientations, in order to reveal the anisotropic damage evolution characteristics during rock failure. The dynamic elastic modulus, damping ratio, fatigue deformation, damage evolution, accumulative damage modeling and crack pattern were systematically analyzed. The testing results indicate that the interbed structure in marble affects the damage evolution and the associated dynamic mechanical behaviors. The damage curve in “S” style indicates three-stage trend, namely, initial damage stage, steady damage stage and the accelerated damage stage. The damage index during cyclic deformation for marble presents obvious discrepancy. In addition, a fatigue damage prediction models was employed numerically as double-term power equations based on the experimental data. It is found that the selected damage model is suitable in modeling the rapid damage growth in the early and final stage of rock fatigue lifetime. Moreover, post-test CT scanning further reveals the anisotropic damage characteristics of marble, the crack pattern in the fractured sample is controlled by the interbed structure. What is more, the most striking founding is that the fracture degree is in consistent with the damage accumulation within the steady damage stage. Through a series of damage mechanical behavior analysis, the internal mechanism of the effect of interbed orientation on damage evolution of marble is firstly documented.

Understanding the damage evolution of sapphire under scratching from AE signals

In this paper, the study on damage evolution of sapphire induced in scratching process using acoustic emission (AE) technology was carried out. Single-grit scratches with ramp scratch depth were conducted on C-plane of sapphire with AE signal monitoring. Groove microstructure after scratching shows that the damage evolution process is mainly determined by the interactions among cracks, specimen surface and groove boundary. To evaluate the damage evolution, the AE waveform indexes, i.e. fractal and frequency characteristics, were fully analyzed and correlated with groove microstructure of specimen after tests. It is found that the fractal dimension (FD) can identify the three basic damage modes as well as various damage behaviors during scratching process. In addition, the model of damage evolution is further proposed. The frequency characteristics of AE signals are distinctive to various damage behaviors during their evolution, especially to the occurrences of the critical damages and removal modes. Furthermore, the characteristic frequency band (CFB) of AE signals was extracted. It is found that FD of the reconstructed AE signals in CFB (86.8–161.4 KHz herein) can highlight damage details and features during initial damage stage of sapphire in scratch test effectively.