Infrared Radiation Temperature Research Articles

Infrared radiation quantification of rock damage and its constitutive modeling under loading

The root cause of the infrared radiation (IR) change in rock is the failure of microelements during its evolution. However, the quantified relationship between the two parameters remains unclear. This paper, therefore, presents a quantification approach to investigate the internal damage evolution of loading rock through the surface IR. Multiparameter observation experiments were conducted primarily in coal rock samples. The change in related parameters within the rock sample during the evolution of the damage was recorded. The IR noise from the reference (unloaded) samples was taken as the threshold of the sudden change in the IR temperature. Thus, the noise signal and the sudden change in IR temperature were separated through these threshold values. On this basis, a quantitative index of infrared radiation, the IR counts was adopted. It was found that there was a synchronous sudden change between the IR and Acoustic ringing counts. According to the occurrence of sudden change in the IR counts and the differential infrared radiant thermal image sequence at the corresponding time, the damaged area of the rock can be accurately determined. Taking the IR counts as the characterization parameter of the rock damage variable, the quantitative characterization method of the evolution of coal-rock damage by IR and the stress-strain constitutive model was established. The IR calculated stress (σIR) can reflect the failure process of rock transition from the linear elastic to the plastic deformation stage.

Short- and Medium-Wave Infrared Drying of Cantaloupe (Cucumis melon L.) Slices: Drying Kinetics and Process Parameter Optimization

The main objective of the present work was to study the drying kinetics and obtain the optimum process parameters of cantaloupe slices using short-and medium-wave infrared radiation (SMIR) drying technology. The effect of three independent variables of infrared radiation temperature (55–65 °C), slice thickness (5–9 mm) and radiation distance (80–160 mm) on the L value, color difference (∆E), hardness and vitamin C content were investigated by using the Response Surface Methodology (RSM). The results showed that the Page model can adequately predict the moisture content between 55 and 65 °C (R2 > 0.99). The effective moisture diffusivity (Deff) varied from 5.26 × 10−10 to 2.09 × 10−9 m2/s and the activation energy (Ea) of the SMIR drying was 31.84 kJ/mol. Infrared radiation temperature and slice thickness exerted extremely significant effects on L value and color difference (ΔE) (p < 0.01), with higher infrared radiation temperature and thin slice thickness leading to a decrease in the L value and an increase in ΔE. Hardness and vitamin C content were significantly affected by infrared radiation temperature, slice thickness and radiation distance, of which the slice thickness was the most distinct factor affecting the hardness value. Higher infrared radiation temperature and larger slice thickness and radiation distance resulted in higher vitamin C degradation. For the given constraints (maximized vitamin C content and L value, minimized ΔE and hardness value), the optimum drying parameters were infrared radiation temperature 58.2 °C, slice thickness 6 mm and radiation distance 90 mm. Under the optimum drying combination conditions, the experimental values were 65.58 (L value), 8.57 (∆E), 10.49 N (hardness) and 106.58 mg/100 g (vitamin C content), respectively. This study is beneficial to the development of the cantaloupe food processing industry and provides more insights for the application of SMIR drying technology to improve the drying rate and product quality of cantaloupe.

Investigation of the microstructure damage and mechanical properties evolution of limestone subjected to high-pressure water

The water-weakening effect is one of the most important causes for changes the physical and mechanical characteristics of rock materials, triggering large deformations and failures in rock engineering. To investigate the degradation effect of high-pressure water on a rock material, this study performed laboratory tests on limestone specimens. Scanning electron microscopy (SEM) and mercury intrusion porosimetry (MIP) were used to examine limestone subjected to different water pressures, and the results showed that with the water pressure increasing, the dissolution degree and porosity of a limestone specimen increased. Meanwhile, an infrared radiation thermal (IRT) imager was used during uniaxial loading to study the temperature evolution laws of the limestone materials under different water pressures. The phase development characteristics of the stress–strain curve were more obvious, and the average infrared radiation temperature (AIRT) rose in a fluctuating manner during different stages. The AIRT reached an extreme value suddenly before the peak stress and gradually returned to the room temperature after a structural failure. The strength and temperature differences for the specimens continuously decreased with water pressure increasing, with temperature decreases of 5.71%, 12.86%, 18.57%, 22.86% and 24.29% respectively under 2–10 MPa water pressure compared to 0 MPa. In addition, the IRT images intuitively reflected the spatial evolution process for the specimen temperature. There were high temperature anomalies on the IRT image before structural failure, which could be used as the omen of the limestone structure failure.

Identification method of infrared radiation precursor information of coal sample failure and instability under uniaxial compression

This study is aimed at investigating the effective precursory information of coal sample instability and failure under uniaxial compression. To achieve this aim, first, the infrared radiation temperature (IRT) variations of coal sample under the same loading mode were analyzed. Next, the variations of IRT counts on the coal sample surface, numbers of IRT points in high-temperature and low-temperature zones and IRT differences in the two zones were analyzed based on the infrared thermal image. Furthermore, the variations of variance and autocorrelation coefficient of IRT were explored with reference to the critical slowing down theory. The following results were obtained. The changes in IRT exhibit different characteristics in different stages of loading. Before the main rupture occurs, both the maximum infrared radiation temperature (MIRT) and the average infrared radiation temperature (AIRT) present a cooling precursor and an IRT rise buffer section. When the main rupture occurs, the MIRT surges, while the AIRT plunges. The high-temperature zone in the infrared thermal image keeps expanding with the increase of stress, and the low-temperature zone also expands considerably before the main rupture. The number of IRT points in the high-temperature zone decreases first and then increases with the increase of stress, while the number of IRT points in the low-temperature zone increases continuously with it. The IRT differences in the high-temperature and low-temperature zones vary in a basically consistent way with the number of IRT points in the two zones, respectively. The MIRT curve, and the curve of number of IRT points in the high-temperature zone and the variance curve of MIRT can all be taken as the precursor signal for identifying coal sample instability and failure. Among the three, the variance curve of MIRT boasts the most superior effect.

Estimation of moisture migration in rammed earth based on entropy theory.

In the field of cultural relic protection, the migration of moisture will cause a series of adverse effects, such as disruption and crater eruption. Assessment of water migration status is the key to early warning and prevention of these problems. In an attempt for a solution, the whole process of moisture migration in rammed earth is studied by using the moisture migration initiation criterion based on entropy. We analyzed and compared the entropy change law of the infrared radiation temperature in the two main migration stages, and we made a judgment on whether the moisture state is in the steady equilibrium or in the process of dynamic migration. The results show that the moisture migration status can be identified quickly and in real time by using the moisture migration initiation criterion based on entropy. The results of this study provide a new method for judging the state of moisture migration in geotechnical engineering, especially in the field of cultural relic protection, which has very important practical significance.

Localized Enhancement of Infrared Radiation Temperature of Rock Compressively Sheared to Fracturing Sliding: Features and Significance

Previous experiments indicated that infrared radiation temperature (IRT) was applied in monitoring rock stress or rock mass fracturing, and abnormal IRT phenomena preceding rock failure or tectonic earthquakes were frequently reported. However, the characteristics of IRT changing with rock fracturing and frictional sliding are not clear, which leaves much uncertainties of location and pattern identification of stress-produced IRT. In this study, we investigated carefully the localized IRT enhancement of rock compressively sheared to fracturing and sliding (named as CSFS) with marble and granite specimens. Infrared thermogram and visible photos were synchronously observed in the process of rock CSFS experiment. We revealed that localized IRT enhancement was determined by local stress locking, sheared fracturing, and frictional sliding, and the relations between the Kcv of IRT and the shear force are almost linear in wave length 3.7–4.8 μm. In the process of rock CSFS, the detected ΔIRT which resulted from thermoelastic effect is 0.418 K, while the detected ΔIRT resulted from friction effect reaches up to 10.372 K, which is about 25 times to the former. This study is of potential values for infrared detection of rock mass failure in engineering scale and satellite remote sensing of the seismogenic process in the regional scale.

Infrared radiation test on the influence of water content on sandstone damage evolution

The rock mechanics uniaxial compression testing system and a thermal imaging camera were used to research the influence of water on sandstone damage evolution and the concurrent infrared radiation (IR) characteristics on sandstone samples with different water contents. The field of view of the thermal imaging camera divided the sandstone surface into several small areas of equal area. When one of the small areas of sandstone ruptured (that was when a damage point was generated in the sandstone) the IR information from that area underwent abrupt changes. Based on this monitoring, a quantitative index of infrared radiation, the IR count (IRC), was adopted and investigated as the indicator for damage evolution of rocks that also linked damage intensity with the corresponding IR temperature. The research results showed that when the sandstone stress experienced a stress drop, the IRC will simultaneously undergo a sudden increase indicating that the IRC was controlled by the stress. However, this stress control on IRC decreased with increasing water content due to the softening effect of water on the sandstone. Among them, the control effect of stress on IRC reaches 100% for dry sandstone, which is reduced to 75% for sandstone with a water content of 0.5% and 66.7% for sandstone with a water content of 1.5%. The control effect of stress of saturated sandstone on IRC is 57.1%. For sandstones with other water contents, but at the same damage evolution stage, the average IRC (IRC¯) for sandstones showed an upward trend as the water content increased. Compared with other damage evolution stages, the IRC¯ of the water-bearing sandstone had the most significant difference in the failure stage, indicating that water had the most significant influence on the damage evolution of the sandstone in the failure stage. This IRC was generated at the location of a new damage point on the sandstone surface. Therefore, based on the instant of time node when the sandstone IRC suddenly increased, the IRC spatial distribution map at that corresponding time was drawn to accurately locate the sandstone damage and fracture area. The characteristics of the damage evolution process of sandstones with different water contents were the same over the time before the sudden increase in IRC, the damage points formed were disorderly distributed, and the number of damage points was less. The difference was that as the water content increased, the number of sandstone damage points became larger and more concentrated.

Variation Law of Infrared Radiation Temperature of Unloading Fracture of Composite Coal-Rock

For composite mining coal-rock dynamic disaster, combining the theory of thermodynamics, damage mechanics, and other disciplines, the thermodynamic coupling mathematical model of composite coal-rock under an unloading condition is deduced, and the simulation model of composite coal-rock is established for numerical simulation. And the variation law of thermal infrared radiation under triaxial loading and unloading of composite coal-rock is analyzed and verified by experiments. The results show the following findings: (1) The distribution of thermal infrared radiation temperature of composite coal-rock is different in different stages of stress. The overall temperature of the temperature field is lower than the initial temperature field in the three-dimensional stress loading stage and the stage of stress-keeping pressure, but the internal temperature of the coal body is the highest. In the first stage of “loading and unloading,” the temperature of a coal seam increases slightly, and the temperature of other parts of the rock layer increases except for the circular low-temperature zone. In the second stage of “loading and unloading,” an alternating zone of high and low temperatures appears in the rock mass, and the temperature field is enhanced, among which the temperature field reaches the strongest after unloading the confining pressure. After jumping over the maximum stress, the temperature field decreases as a whole at the instability and rupture stage. (2) The variation of surface average thermal infrared radiation temperature ( T ave ) of composite coal-rock can be divided into the initial fluctuation stage, the linear heating stage, the local decline stage, the temperature sudden increase stage, and the fracture decline stage. At three different unloading rates of 0.003 MPa/s, 0.03 MPa/s, and 0.05 MPa/s, the T ave of coal body, floor rock, and roof rock reach the maximum before composite coal-rock instability and fracture, and the temperature change of the coal body is the most obvious. (3) Under different confining pressure unloading rates, the T ave of roof rock, coal body, and floor rock shows a strong linear relationship with stress after linear fitting. And the correlation between simulation and experimental results after fitting is above 0.89. The larger the confining pressure unloading rate is, the shorter the peak time of T ave arrives, and the larger the peak value. The comparison between the experimental results and the simulation analysis shows that the two results are consistent, and the research results can provide a theoretical basis for the prevention and control of dynamic disasters in coal and rock mining.

Abnormal Precursory Information Analysis of the Infrared Radiation Temperature (IRT) before Sandstone Failure

To study the abnormal precursory information of rock before failure, uniaxial compression tests were carried out on sandstone specimens; meanwhile, the infrared thermal camera was utilized to monitor the infrared radiation temperature (IRT) variation of the specimen surface synchronously during failure process. The test results show that with the increases of strain, the average infrared radiation temperature (AIRT) decreased gradually; when strain raises to a certain degree, the AIRT increased abruptly; thereafter, the AIRT decreased gradually with increasing strain. Therefore, the mutation point of AIRT can be regarded as the abnormal precursory information of sandstone before failure. Through analysis, the average stress at the abnormal point was 79.93% of the uniaxial compression strength of the sandstone specimens tested in this paper, and the average strain at this point was 0.9%. In addition, due to the end effect, the IRT field distribution of the sandstone specimen surface presented a decreasing tendency from top to bottom at the initial loading stage. As strain increases, the IRT field distribution tended to be high in middle and low in two ends. Closing to failure, a Y-shaped high-temperature band caused by the shear failure of the specimen appeared in the infrared thermal image. After comparison, the position of the Y-sharped high-temperature band is basically corresponding to the actually failure position of the specimen. With the increases of strain, the IRT distribution ranges decreased and the IRT frequency distribution histogram form gradually approached to the normal distribution.

Experimental study on the infrared precursor characteristics of gas-bearing coal failure under loading

The stress and gas pressure in deep coal seams are very high, and instability and failure rapidly and intensely occur. It is important to study the infrared precursor characteristics of gas-bearing coal instability and failure. In this paper, a self-developed stress-gas coupling failure infrared experimental system was used to analyse the infrared radiation temperature (IRT) and infrared thermal image precursor characteristics of gas-free coal and gas-bearing coal. The changes in the areas of the infrared temperature anomalous precursor regions and the effect of the gas on the infrared precursors were examined. The results show that high-temperature anomalous precursors arise mainly when the gas-free coal fails under loading, whereas the gas-bearing coal has high-temperature and low-temperature anomalous precursors. The area of the high-temperature anomalous precursor is approximately 30%–40% under gas-bearing coal unstable failure, which is lower than the 60%–70% of the gas-free coal. The area of the low-temperature abnormal precursor is approximately 3%–6%, which is higher than the 1%–2% of the gas-free coal. With increasing gas pressure, the area of the high-temperature anomalous precursor gradually decreases, and the area of the low-temperature anomalous precursor gradually increases. The high- and low-temperature anomalous precursors of gas-bearing coal are mainly caused by gas desorption, volume expansion, and thermal friction. The presence of gas inhibits the increase in IRT on the coal surface and increases the difficulty of infrared radiation (IR) monitoring and early warning for gas-bearing coal.

Multifield Coupling Mechanism of Unloading Deformation and Fracture of Composite Coal-Rock

The deformation and fracture evolution of coal and rock under unloading are prone to sudden instability or dynamic damage. To solve the problem, this paper combines interdisciplinary theories such as damage mechanics and electromagnetic field theory. The mathematical model of multiphysics coupling during loading and unloading of composite coal-rock is deduced. In addition, numerical simulations along with experimental verification are carried out to study multi-physical field variation and coupling mechanisms. The composite coal-rock deforms and ruptures under unloading, and the brittle failure of the rock body becomes more sudden when the confining pressure is unloaded. Macroscopically, many microcracks are generated and expanded during the loading and unloading of composite coal-rock. Microscopically, the internal old molecular chains are broken to form new molecular chains by the force. Simulation results show that, during the loading and unloading process, the three physical fields of the composite coal-rock all change regularly. During the unloading of coal and rock, there is a transition period in which the temperature increases sharply and reaches the maximum. Then, the temperature decreases due to the gradual decrease of its bearing capacity. Besides, the electromagnetic field is strongest on the surface of the coal body, and its propagation in the air decays exponentially. There are small fluctuations that appear at the junction of the coal body and the air. The experimental results show that the internal infrared radiation temperature of the composite coal-rock decreases during the initial stage of loading and unloading due to the discharge of internal gas. In the first stage of “loading and unloading,” it increases with the increase in stress, and the temperature suddenly increases in a short time after unloading. The electromagnetic radiation fluctuates in small amplitudes at the initial stage. When the stress is about to reach the peak, the electromagnetic radiation intensity increases and reaches the peak suddenly. Then, the coal-rock ruptures, the stress decreases, and the electromagnetic radiation weakens. The experiment and simulation results are consistent. The multiphysics coupling model is used to study the characteristics of coal and rock unloading under complex conditions, providing a theoretical basis and new method for the prediction and forecast of coal and rock mining dynamic disasters.

Electrical and optical characterizations of a rotating gliding arc plasma-enhanced combustion dome in an aero-engine combustor

A gliding arc discharge is a typical method of producing non-equilibrium plasma, presenting excellent advantages in the field of enhanced combustion. In this study, a rotating gliding arc (RGA) plasma was combined with an aero-engine combustor dome to develop a RGA plasma-enhanced combustion dome. Experiments were conducted to investigate discharge, spectral, and infrared radiation temperature characteristics in the RGA plasma-enhanced combustion dome. Experimental results showed that two different discharge modes occurred during the RGA discharge process, the breakdown gliding mode and the steady arc gliding mode. The results had major implications for understanding the effects of the airflow rate and input voltage on the arc gliding mode transformation. The breakdown voltage, the average power, and the gliding arc rotational velocity increased with an increase in the airflow rate and a decrease of the input voltage. The spectral emission intensities of OH, O2, and O and vibrational temperature of N2 (C3Πu→B3Πg) were relatively high at a high airflow rate. Additionally, the RGA discharge had a weak temperature rise effect on electrode, which had no obvious impact on the discharge process. These characteristics could be important for future applications for controlling plasma-enhanced combustion process.

Dynamic measurement and correction of infrared radiation temperature for rocket motor exhaust plume

The dynamic measurement and correction of infrared radiation temperature for rocket motor exhaust plume was established based on Stefan-Boltzmann formula under the assumption that the colorimetric temperature is regarded as the real value. The relationship between the spectral emissivity of the exhaust plume and time is obtained, and the temperature distribution measured by the infrared thermal imager is corrected in real time. During the stable working period of the rocket motor, the maximum value of the infrared radiation temperature distribution curve and the average value corresponding to the time are used to represent the maximum and average infrared radiation temperature of the motor exhaust plume field. This method is applicable to the real-time determination of the spectral emissivity of the exhaust plume and the accurate measurement of the infrared radiation temperature distribution at static or rocket sled flight state, and is of great significance to the development of the low-signature rocket motor and propellant charge.

Independent dual-responsive Janus chromic fibers

Daily exposure under solar ultraviolet (UV) and infrared (IR) is prone to cause skin cancer and photoaging. Real-time monitoring of the environmental UV index and IR radiation temperature during outdoor activities can enhance awareness and strengthen personal protection. It is a challenge to design flexible, wearable devices (with measurement capabilities) that can be integrated with apparels. Here, microfluidic spinning technology (MST) was used for the continuous and large-scale fabrication of eco-friendly coresheath Janus fibers with a well-defined axially symmetric Janus core. One side of the core was sensitive to UV light and the opposite was sensitive to IR radiation. Textiles woven with Janus fibers showed excellent independent reversible color responses to dual-wavelength stimulation. Such textiles switched among four colors under UV and IR irradiation, both individually and in combination. The color gradient of the textiles changed significantly with increasing UV intensity (UV index). After 60 cycles of UV/IR stimulation and 50 washes, the change rate of the comprehensive chromatic aberration (ΔE*ab) of the textiles under different conditions was only 0.42%–4.71%. This was attributed to the unique structure of the fibers. The three-line striped textiles demonstrated the potential of the fibers to be used as wearable energy-free real-time visual monitors of the UV index and IR radiation temperature.

Experimental investigation on infrared radiation features of fracturing process in jointed rock under concentrated load

In case of earthquakes and crustal movement, the concentration of impounding load over a large region of crust can cause disturbances to the stratum. In order to quantitatively investigate crack initiation, propagation and coalescence processes of jointed stratum based on thermal variations caused by concentrated load, a series of indentation tests were performed on jointed granite specimens, failure process was respectively recorded by synchronized digital image correlation system and infrared camera. Then, strain and infrared radiation temperature of mixed shear-tensile and tensile conical crack were analyzed. In the initiation process, experimental results indicate that the abnormities in the temperature concentration factors are caused by the frictional-thermal effect for mixed mode crack and the thermoelastic effect for tensile mode crack. Subsequently, in the propagation process, these two cracking types followed newly proposed criteria, namely, the maximum temperature gradient criterion for mixed mode crack and the minimum temperature gradient criterion for tensile mode crack. In addition, the intensity of temperature concentrations in crack initiation stage and coalescence stage are more pronounced than that of crack propagation stage. The new findings from the infrared radiation temperature distributions provide some fundamental references for geophysical prospecting in jointed rock mass.

Experimental investigation on rock mechanical properties and infrared radiation characteristics with freeze-thaw cycle treatment

The effect of freeze-thaw weathering cycles caused by diurnal and seasonal temperature changes is a significant disadvantage in the stability of rock engineering in cold regions. To investigate the evolution rule of rock strength and infrared radiation characteristics of igneous, metamorphic, and sedimentary rock subjected to freeze-thaw weathering cycles, freeze-thaw weathering cycle treatment was conducted on coarse-grained granite, fine-grained marble and soft red sandstone from cold regions in Western China. The nondestructive detection technique of nuclear magnetic resonance (NMR) was used for rock damage detection. Infrared thermography was used to monitor the rock debris movement, crack propagation and average infrared radiation temperature (AIRT) during unconfined compressive strength (UCS) testing. The mechanisms of rock damage and change in AIRT induced by freeze-thaw weathering cycles were carefully analyzed. According to the UCS evolution rule, the ranking order (from high to low) of the results of rock resistance to freeze-thaw weathering processes is as follows: marble, granite and sandstone. An indicator called the infrared radiation rate was proposed to measure the rate of increase in infrared radiation temperature with increasing stress during the UCS tests. The rank order (from high to low) of the infrared radiation rate results is as follows: sandstone, marble and granite. Based on the infrared images and photographs of the failed rock specimens, the failure patterns and processes of the different rock types are investigated.

Failure mechanics and infrared radiation characteristics of soft coal at various moisture contents

Soft coal is characterized by low strength and weak bonds, which play a key role in the occurrence and development of dynamic disasters. A more thorough understanding of the failure mechanics and infrared radiation characteristics of soft coal at various moisture contents is needed. In this study, infrared radiation experiments were conducted for soft coal at various moisture contents. The results indicate that moisture content affects compressive strength and elastic modulus of soft coal with compressive strength and elastic modulus being highest at moderate. Moisture has a substantial influence on the infrared radiation of compressed coal samples. Soft coals with high moisture contents show a smaller fluctuation of the average infrared radiation temperature curve and a stronger direct relationship of temperature and stress in the linear elastic stage. The coal samples with various moisture contents show a warming trend during loading. The increased amplitude of infrared radiation temperature per unit stress shows a linear relationship with moisture content. A large number of high temperature red spots appear along the diagonal line of coal samples with 0% moisture content before fracture, while changes in the infrared thermal image of the coal sample with 4% moisture content were negligible during loading.

Study on the breaking process of jointed rock mass by disc cutters based on digital image correlation and infrared thermography

Jointed rock masses are frequently encountered during the TBM excavation. To investigate the rock breakage mechanism of jointed rock mass by disc cutter and precursory information before rock failure, a series of indentation tests were performed on shear rheological test system. During the test, breaking process of specimens were recorded by digital image correlation system and thermal infrared imager simultaneously. Therefore, the strain fields and thermal infrared images of jointed rock mass by disc cutters were obtain. The experimental results show that the failure process of jointed rock mass can be divided into four stages: compaction stage, linear elastic stage, residual failure transition stage and post-failure stage. Besides, the characteristic of strain fields shows a good accordance with that of infrared radiation temperature fields at each stage. The failure of rock samples is dominated by shear failure, and the localized temperature rise is an important infrared precursor of rock fracture and instability. The experimental results are of great significance to the deep understanding of the breaking mechanism of jointed rock mass and warnings of engineering disasters.

Cyclic fatigue characteristics of rock failure using infrared radiation as precursor to violent failure: Experimental insights from loading and unloading response

AbstractIn this research paper, a new method is developed that can be used as a precursor of violent rock failure. It is based on measuring the characteristics of rock failure using infrared radiation (IR) under uniaxial cyclic loading and unloading. The loading–unloading response ratio (LURR) is determined based on IR indexes such as average infrared radiation temperature (AIRT) and infrared radiation temperature rate (IRTR). The results show that the LURR based on AIRT revealed an overall rising trend and mutation that occurred in the last cycle, which can be used as a precursor of the imminent rock failure. By contrast, the LURR based on IRTR has a noticeable ‘mutation‐rapid decrease’ in the middle and later periods of cyclic loading and unloading, which can also be considered as an early precursor of rock failure. Combined with the precursors of the imminent rock failure, the categorized warning of rock failure is recognized.

An experimental study of infrared radiation characteristics of sandstone in dilatancy process

The rock failure process is always accompanied by dilatancy. This study investigated the average infrared radiation temperature (AIRT) characteristics in the rock dilatancy process. An Infrared Radiation (IR) dilatancy precursor point was found prior to the failure of the rocks under load. During the uniaxial loading process, the stress levels of upward-AIRT and downward-AIRT rock samples at the initial point of rock dilatancy were 0.74 σmax and 0.80 σmax, respectively. After rock dilatancy, the AIRT change rate of upward-AIRT sample increased by 1.48 × 10−4°C⋅s−1, and AIRT change rate of downward AIRT sample dropped by 1.29 × 10−4°C⋅s−1. From the initial point to the process reached rock failure, the AIRT change was almost linearly correlated with volumetric strain increment. Based on the IR thermogram, the IR hot spot was defined, and a new index—high temperature point scaling factor (HTPSF)—was proposed for qualitative analysis. The calculated HTPSF values of upward-AIRT and downward-AIRT rock samples at the IR dilatancy precursor point were 0.4 and 0.6, respectively. This study provides a new thought to determine the initial point of rock dilatancy.