Infrared Radiation Temperature Research Articles

Infrared temperature evolution law and thermal effect mechanism of concrete impact failure

Concrete impact failure can occur quickly and cause severe failure, which is of great significance for effective monitoring of concrete impact failure. Infrared thermal imaging technology possesses the merits of high sensitivity, noncontact, and nondestructive monitoring, rendering it extensively employed in monitoring the stability of concrete structures. However, the infrared radiation temperature (IRT) evolution law and thermal effect mechanism of concrete impact failure are not clear at present. In this study, infrared monitoring experiments were conducted on concrete impact failure and static load failure using drop hammer (DH) testing machines, pressure testing machines, and infrared thermal imagers. The infrared thermal images and the IRT change law of concrete subjected to DH impact failure were analysed. The infrared thermal effect difference and mechanism between DH impact and static load failure were compared. The results indicate that there is an infrared high-temperature point at the impact location of concrete DH impact failure, and both average infrared radiation temperature (AIRT) and maximum infrared radiation temperature (MIRT) increase suddenly. The increase in the MIRT is tens of times that of the AIRT. Compared with that of static load failure, the infrared high-temperature area of concrete DH impact failure is concentrated, while the IRT of static load failure increases overall, and the heating area is large. Moreover, the change in the IRT under DH impact failure is much greater than that under static load failure. The infrared thermal effect of concrete under DH impact failure was mainly composed of the thermoelastic effect, frictional thermal effect and tensile failure endothermic effect. The infrared data obtained for concrete impact failure should focus on the highest and lowest IRT change indicators. The highest IRT corresponds to the impact failure point, and the lowest IRT corresponds to the tensile failure position. The research results provide a new infrared thermal effect approach for monitoring the stability of concrete under impact failure.

Method for rock fracture prediction and early warning: Insight from fusion of multi-physics field information

Understanding the precursors leading to rock fracture is crucial for ensuring safety in mining and geotechnical engineering projects. To effectively discern these precursors, a collaborative monitoring approach that integrates multiple sources of information is imperative. This paper considered a rock multi-parameter monitoring loading system, incorporating infrared radiation and acoustic emission monitoring technologies to simultaneously track the rock fracture process. The study delves into the spatiotemporal evolution patterns of infrared radiation and acoustic emission in rock under loading. Utilizing stress, cumulative acoustic emission count, and average infrared radiation temperature (AIRT), the paper establishes a comprehensive evaluation model termed “acoustic-thermal-stress” fusion information, employing principal component analysis (PCA). The research reveals that the sensitivity to rock sample damage response follows the sequence of cumulative acoustic emission count, AIRT, and stress. Furthermore, a novel method for identifying rock fracture precursors is proposed, based on the first derivative of the comprehensive evaluation model. This method addresses the limitations of single physical field information, enhancing the robustness of monitoring data. It determines the average stress level of fracture precursors to be 0.77σmax. Subsequently, the study defines the probability function of rock damage during loading and fracture, enabling the realization of probability-based warnings for rock fracture. This approach introduces a new perspective on rock fracture prediction, significantly contributing to safety monitoring and warning systems in mine safety and geotechnical engineering. The findings of this research hold paramount engineering significance, offering valuable insights for enhancing safety measures in such projects.

The law of infrared radiation generation and evolution of coal-rock fracture under load

In order to study the formation mechanism and evolution law of infrared radiation (IR) of coal-rock. A mathematical model of pressure-IR for coal-rock under loading conditions was developed based on theories such as frictional heat generation and heat conduction. The results indicate that: (1) IR and stress exhibit a one-dimensional quartic function relationship, which is consistent with the strong correlation shown by the experimental data curve. As the loading stress increases, the infrared radiation temperature of the coal-rock surface increases. (2) From the simulation results, it can be seen that the increase in surface temperature of coal-rock is essentially influenced by the heat transfer of internal heat sources. The trend of temperature fluctuations is similar for both, with both increasing with ambient temperature and loading rate. And this characteristic change is independent of external loading factors. (3) The IR temperature varies in stages under different loading conditions. In addition, the surface temperature of the coal-rock before fracturing is affected by the frictional heat generation between cracks, resulting in an overall upward trend. When it is about to break, a precursor to the fracture appears. The final IR on the surface of coal-rock increased by 0.04–0.13 °C, which is consistent with the simulation results. It is consistent with the simulation results and reveals the evolution law of IR. The results of this work provide theoretical evidence for the prediction of dynamical disasters in coal and rocks.

2013–2020年海河流域农田水热碳通量及气象要素观测数据集

The present study area was located in the cropland ecosystem near Guanting Reservoir in Haihe River Basin. We conducted long-term observations of the multi-scale fluxes and meteorological elements, using various observation systems, including lysimeter, eddy covariance, large aperture scintillometer and automatic weather station/gradient of meteorological elements. This dataset consists of multi-scale fluxes (meter, hundred-meter, and kilometer-meter) and meteorological elements data. Observation items include ecosystem net carbon exchange, latent heat flux/evapotranspiration, sensible heat flux, air temperature, relative humidity, wind speed, wind direction, downward/upward shortwave radiation, downward/upward longwave radiation, net radiation, atmospheric pressure, precipitation, infrared radiation temperature, photosynthetic effective radiation, soil temperature, soil moisture, soil heat flux, and average soil temperature, etc. This dataset is processed carefully and can be used to study the effects of reservoir expansion and shrinkage on the circulation of carbon and water or other substances in the surrounding ecosystem. Additionally, it can serve as a powerful data basis for the research on relevant remote sensing estimation and model simulation.

Study on the acoustic-thermal effects and damage models during uniaxial compression failure process of phosphorite with different H/Di

Determining the size of ore pillars is crucial for the stability of mining structures and the recovery rate in mining design. To investigate the damage characteristics of phosphorite under different height-to-diameter ratios (H/Di), uniaxial compression tests were conducted on phosphorite specimens with varying H/Di. The effects of these H/Di on the mechanical properties and acoustic-thermal signals were analyzed, leading to the establishment of a joint acoustic emission-infrared damage model. Results showed: (1) Peak stress and ultimate strain of phosphorite specimens were negatively correlated with the H/Di, with compressive strength decreasing and stabilizing as the H/Di increased. (2) Increasing H/Di led to a transition from tensile to shear crack dominance during specimen failure, with cumulative acoustic emission energy and ringing counts positively correlated with H/Di. (3) Infrared radiation temperature before instability failure showed a cyclic pattern of slow increase, sudden rise, and sudden decrease, reaching a peak at failure. Using these findings, separate damage models for different H/Di were established based on two characteristic signals, correcting for monitoring losses, and finally merged into a joint acoustic-thermal damage model. The resulting model aligned well with experimental data, validating its rationality and significantly improving damage prediction accuracy. Thus, the model holds promising application prospects for calculating recovery rates, designing ore pillar sizes, managing goafs, and maintaining abandoned mine stability in phosphate mining design.

The infrared thermal effect of coal failure with different impact types and its relationship with bursting liability

There are significant differences in the infrared thermal effect of coal failure with different impact types. It will be of great significance to determine the bursting liability of coal by using the infrared thermal effect characteristics of coal failure. In this paper, the infrared monitoring experiments of coal failure with different impact types is carried out. The infrared thermal effect characteristics of coal failure with different impact types are analyzed, and the quantitative relationship between the thermal effect index and the bursting liability index is established. The results show that the infrared radiation temperature (IRT) changes of coal failure with different impact types have great differences. With the increase of bursting liability, the increment of IRT gradually increases, and the infrared high temperature area (IHTA) gradually increases and concentrates. The average infrared radiation temperature (AIRT) increment of the strong and weak impact coal is 2.38 times and 1.62 times that of the no impact coal, respectively. The maximum infrared radiation temperature (MIRT) increment is 12.95 times and 5.42 times that of the no impact coal. The percentages of IHTA in coal with no, weak, and strong impact are 3.49 %, 57.83 %, and 81.43 %, respectively. Based on the quantitative relationship between AIRT, MIRT, IHTA and bursting liability index, the type of bursting liability of coal can be determined. For the uniaxial compressive strength index (RC), when the AIRT and MIRT are greater than 0.19 °C and 0.87 °C, and the IHTA is greater than 59.60 %, the coal belongs to the strong bursting liability. The research results propose a new approach to use infrared thermal effect characteristics to determine the bursting liability of coal, which is of great significance for improving the theory and method of infrared monitoring and early warning of rock burst.

Predicting Sandstone Brittleness under Varying Water Conditions Using Infrared Radiation and Computational Techniques

The brittleness index is one of the most integral parameters used in assessing rock bursts and catastrophic rock failures resulting from deep underground mining activities. Accurately predicting this parameter is crucial for effectively monitoring rock bursts, which can cause damage to miners and lead to the catastrophic failure of engineering structures. Therefore, developing a new brittleness index capable of effectively predicting rock bursts is essential for the safe and efficient execution of engineering projects. In this research study, a novel mathematical rock brittleness index is developed, utilizing factors such as crack initiation, crack damage, and peak stress for sandstones with varying water contents. Additionally, the brittleness index is compared with previous important brittleness indices (e.g., B1, B2, B3, and B4) predicted using infrared radiation (IR) characteristics, specifically the variance of infrared radiation temperature (VIRT), along with various artificial intelligent (AI) techniques such as k-nearest neighbor (KNN), extreme gradient boost (XGBoost), and random forest (RF), providing comprehensive insights for predicting rock bursts. The experimental and AI results revealed that: (1) crack initiation, elastic modulus, crack damage, and peak stress decrease with an increase in water content; (2) the brittleness indices such as B1, B3, and B4 show a positive linear exponential correlation, having a coefficient of determination of R2 = 0.88, while B2 shows a negative linear exponential correlation (R2 = 0.82) with water content. Furthermore, the proposed brittleness index shows a good linear correlation with B1, B3, and B4, with an R2 > 0.85, while it shows a poor negative linear correlation with B2, with an R2 = 0.61; (3) the RF model, developed for predicting the brittleness index, demonstrates superior performance when compared to other models, as indicated by the following performance parameters: R2 = 0.999, root mean square error (RMSE) = 0.383, mean square error (MSE) = 0.007, and mean absolute error (MAE) = 0.002. Consequently, RF stands as being recommended for accurate rock brittleness prediction. These research findings offer valuable insights and guidelines for effectively developing a brittleness index to assess the rock burst risks associated with rock engineering projects under water conditions.

Prediction of rock loading stages using average infrared radiation temperature under shear and uniaxial loading

Accurately predicting geologically rock loading phases under varying water levels is crucial to prevent rock engineering operations from severe geological hazards. Acoustic emission (AE) traditionally determines these phases, but machinery in rock projects can disrupt AE sensors, leading to imprecise data and potential accidents. To address this, our study tested a novel approaches using AE, Average Infrared Radiation Temperature (AIRT), Critical Slow Down Theory (CSDT), and Convolutional Neural Networks (CNNs) to predict rock loading phases accurately under different water conditions. The research findings are: (1) AE analysis divides the stress–strain curve into four phases: crack closure, elastic deformation, and stable and unstable crack propagations. Each phase exhibits distinct characteristics in terms of AE signal behavior. (2) AIRT analysis reveals specific patterns during different loading phases. The AIRT and cumulative AIRT have distinct trends in different phases. (3) The AIRT sequence's fractal dimension shows distinct trends during loading phases: it initially rises during the elastic phase and then declines. Fractal dimensions for crack closure, elastic deformation, and stable crack propagation increase, while that for unstable crack propagation decreases with water content. 4) The stress–strain curve phases were successfully predicted by using AIRT and CSDT, demonstrating a strong correlation with actual stress levels. Notably, this marks the first-time prediction of phases through non-destructive tests (IR and CSDT), where CSDT fluctuations at each stage can serve as early indicators of rock failure.5) The proposed CNNR model achieves high accuracy (98%) in predicting different phases of the stress curve using AIRT. It particularly performs well in the elastic deformation and stable crack propagation phases, with only a few instances of false negative predictions. The model shows promising potential for effective and safe geological projects, especially under varying water conditions. The findings contribute to the understanding of rock behavior and offer insights for the design of safer and more efficient rock engineering projects.

Visual characterization of coal gas desorption using infrared radiation

Gas monitoring is an important means of preventing gas disasters in coal mines. Correct gas monitoring methods can be used to locate abnormal areas of gas emission on the surface of coal bodies. Therefore, an infrared radiation (IR) testing system of coal gas adsorption and desorption is established in the present work, and the IR-based measurement of coal gas desorption is conducted. The corresponding relationship between amount of gas desorption and the infrared radiation temperature (IRT) difference in coal gas desorption process is studied. The general formula of amount of gas desorption of coal based on the average infrared radiation temperature (AIRT) difference is established, and the visual characterization of amount of gas desorption of coal based on IRT difference is realized. The results show that the process of coal gas desorption is a cooling process, and AIRT difference, in the process of coal gas desorption shows a downward trend. There is a linear relationship between the amount of gas desorption of coal and the AIRT difference. The gas desorption curve of coal based on the AIRT difference is consistent with the measured curve. The cloud diagram of coal gas desorption under different adsorption equilibrium pressures can better reflect the variation characteristics of gas desorption in the process of coal gas desorption, and quantitatively characterize the distribution of gas desorption in different regions of the coal. The research results will help to accurately grasp the regional distribution characteristics of coal gas emissions and provide theoretical support for accurate monitoring and control of gas disaster risk at the mining face.

Investigating average infrared radiation temperature characteristics during shear and tensile cracks in sandstone under different water contents

Shear loading and water contents can accelerate rock deformation and fracturing during loading and mining activities. The prediction of the patterns of cracks in rocks under shear loading is thus crucial for the safe and efficient execution of these activities. Previously, crack patterns were classified using Acoustic Emission (AE). Determination of the type of crack patterns on site is not only cumbersome, but may also lead to inaccurate results due improper execution of the AE procedures. Also, there is no proper experimental study which truly reflects the relationship between Average Infrared Radiation Temperature (AIRT) and crack type. In this study, AE and AIRT were used to examine the crack patterns followed by determination of the effect of sandstone crack formation, under varying water and loading conditions, on AIRT. It was found that the increase in water contents lowers AE and strain, and increases shear stress. A linear decrease in AIRT with loading time followed by a sudden increase at the point of failure was observed in dry rocks contrary to a nonlinear trend in rocks with increasing water content. The absolute rate of AIRT increases shear and decrease in tensile crack. Moreover, Shear cracks dominated pre-set shearing tests, and the ratio of acoustic fracturing to radial cracking varied with the level of water contents and loading method. Furthermore, the employed machine learning models (Random Forest (RF), Decision Tree (DT), Support Vector Machine (SVM)) demonstrated accurate classification of shear and tensile cracks with both AIRT and RF data. Based on performance metrics i.e., precision, recall, and F1 score, RF fared better than AIRT with performance metrics (precision = 1, recall = 1, and F1 score = 1). The research offered valuable guidelines for experts to predict cracks and rock failure in rocks, aiding efficient relevant engineering project monitoring and execution.

Quantitative characterization of constitutive model of mudstone under uniaxial loading after immersion in acid solution by infrared radiation

The fracturing of coal and rock is a fundamental cause of mine disasters, such as coal pillar instability,water inrush and rock failure. To prevent the occurrences of these failures, it is important to accurately monitor and detect stress fractures in coal and rock. Furthermore, it is also essential to develop stress–strain constitutive models for an accurate and effective monitoring, early warning of coal and rock stress fracture process. The development of stress–strain constitutive model is the important basis for effectively realizing water conservation mining and rock strata control in mines. In this research, mudstone samples were collected from coal mining sites and mining faces. The mudstone samples were subjected to chemical corrosion using both strong acid and neutral solutions, followed by conducting infrared radiation observation experiments during uniaxial loading. The research findings revealed that 1) strong acid can promote the infrared radiation of the mudstone surface. The Average Infrared Radiation Temperature (AIRT) value of the mudstone corroded by the solution with pH 1.3 during uniaxial loading fracture is changed and noted 6.71 times to the solution with pH 7.3. 2) strong acid has an significant impact on the failure of mudstone samples. The mudstone corroded by the solution with pH 1.3 is mainly damaged by tension and shear composite cracks, while the mudstone corroded by the solution with pH 7.3 is primarily damaged by tension cracks. 3) A nearly linear relationship between the strain of mudstone during uniaxial loading and AIRT was found. This relationship defines a new index of deformation infrared radiation coefficient, allowing for the quantitative characterization between strain and infrared radiation. 4) A one-dimensional statistical damage constitutive model based on AIRT is established using Weibull distribution, while considering the stress–strain compaction stage. This model effectively predicts the stress of mudstone during uniaxial loading. The research results lay a theoretical and practical foundation for the monitoring and evaluation of rock stability in underground engineering such as coal mines, subways and tunnels.

Study on the Specific Expression of Infrared Radiation Temperature on the Body Surface of Acupoint in Rats with Chronic Myocardial Ischemic Injury.

Infrared thermal imaging technology was used to observe the changes in infrared radiation temperature at acupoints in rats caused by chronic myocardial ischemia injury. This study aims to compare the difference of body surface infrared radiation temperature information of three groups of acupoints: bilateral Neiguan (PC6), bilateral Yanglingquan (GB33), and bilateral Sham Acupoints (SA) in the pathological state of myocardial ischemia injury, and to explore the relationship between acupoints and viscera state. SPF adult Wistar male rats (n = 20) were randomly divided into a control (CTL; n = 10) and an isoproterenol group (ISO; n = 10). Chronic myocardial injury was induced in rats by subcutaneous injection of isoproterenol hydrochloride for 14 d. On the second day after the establishment of the model, the serum levels of cardiac troponin (cTnI) and creatine kinase isoenzyme (CK-MB) were measured by enzyme-linked immunosorbent assay (ELISA). The morphological changes of the myocardial tissue in the two groups were observed by hematoxylin-eosin (HE) staining and their pathological scores were evaluated, which was then used to determine the myocardial ischemic injury. Two days before and after the establishment of the model, the electrocardiograms (ECG) of the two groups of rats were recorded by the (ECG) data acquisition system, and the infrared thermal imaging platform was used to detect the temperature of the six acupoints. 1. After subcutaneous injection of isoproterenol hydrochloride for 14 days, the ST segment of the ECG decreased in the ISO group compared with that of the CTL group; 2. Myocardial tissue injury was serious in the ISO group compared to the CTL group; 3. Serum cTn-I and CK-MB were significantly increased (P <0 01) in the ISO group, compared to that in the CTL group; 4. The infrared radiation temperature on the body surface of bilateral Neiguan (PC6) acupoints decreased significantly in the ISO group, compared to that of the CTL group. Infrared thermal imaging technology can be used to detect the changes in the energy state of acupoints. Chronic myocardial ischemic injury can cause a decrease in IR temperature on the body surface of bilateral Neiguan (PC6) acupoints, suggesting that visceral diseases can lead to changes in the energy metabolism of acupoints.

Water vapor-heat-carbon fluxes and meteorological observation matrix dataset in 2012 over Zhangye oasis-desert area

The oasis-desert ecosystem is a unique landscape in arid/semi-arid regions, and the observation and research of its water vapor, heat, and carbon fluxes are of great significance to the stability and sustainable development of oases. This study focuses on the oasis-desert area of Zhangye City, Gansu Province, in the middle reaches of the Heihe River Basin. Based on the state-of-art flux observation matrix experiment conducted in the region in 2012, we processed the water vapor-heat-carbon fluxes and meteorological data from the experiment in two nested matrices (30 km × 30 km and 5.5 km × 5.5 km). There are a total of 22 eddy covariance systems and 21 automatic weather stations within the 21 observation sites as well as 4 group large aperture scintillometer and 3 group thermal dissipation probe observations in the two nested matrices. The observation parameters encompass a wide range of elements, including ecosystem net carbon exchange, latent heat flux, sensible heat flux, air temperature, relative humidity, wind speed, wind direction, downward/upward short wave radiation, downward/upward long wave radiation, net radiation, atmospheric pressure, precipitation, infrared radiation temperature, photosynthetic effective radiation, soil temperature, soil moisture, soil heat flux and average soil temperature, tree transpiration, etc. This meticulously processed dataset can be used to study the characteristics and impact mechanisms of water vapor, heat, and carbon changes in oasis-desert areas. Moreover, it can provide a strong data foundation for model simulation or remote sensing estimation results.

Experimental study on infrared thermal response characteristics of water-bearing concrete under drop hammer impact

The dynamic impact damage of concrete will lead to serious safety accidents, and the water environment will aggravate the degree of damage. In this paper, an infrared monitoring experimental system for drop hammer impact damage of water-bearing concrete was designed and established. The mechanical properties, infrared radiation temperature (IRT) and infrared thermography of concrete impact damage with different soak time were tested and analyzed. The influence of water on the infrared generation mechanism of concrete was discussed. The results show that water has an initial weakening effect on concrete, which weakens the cementation between concrete particles and aggregate strength, resulting in a decrease in concrete strength. Compared with dry concrete, the infrared temperature of water-bearing concrete increased more during impact damage. With the increase of soak time, the average infrared temperature (AIRT) and the maximum infrared temperature (MIRT) of water-bearing concrete decreased. When dry concrete was damaged, tensile cracks were mainly produced and accompanied by heat absorption. When water-bearing concrete was damaged, high temperature shear cracks appeared. The high temperature generated at the moment of impact failure of water-bearing concrete may be caused by the cavitation phenomenon of water in the microscopic pores of concrete during the drop hammer impact and the combined effect of concrete microstructure damage. The research results are of great significance for monitoring and evaluating the stability of the dynamic evolution process of concrete structures.

A method for identifying precursors information on infrared radiation of instability and failure in wood

Anomalies in infrared radiation temperature (IRT) are usually accompanied via the sprouting and expansion of cracks. Precursor information of crack sprouting and extension is essential for predicting the condition as a material of structural fields. In order to investigate the precursor information of instability and failure of wood, the infrared radiation characteristics of wood during failure were analyzed by a three-point bending test. Based on the IRT probability distribution conforming to the Gaussian distribution, an indicator is defined in this paper: the peak probability density (PPD) of IRT. The changes in PPD were combined with the four stages of typical damage to determine the precursor information, and identified a precursor point on the PPD-time curve. The relations between IRT indicators and wood fracturing were also investigated to explain the anomalies in IRT indicators, the precursor point characterize the transition zone from the elastic to the plastic phase of deformation when the wood is under pressure. Besides, the samples before and after the precursor point were also compared by macroscopic (digital image correlation, DIC) and microscopic (scanning electron microscope, SEM), the results proved the validity of the precursor information. Comparison with other IRT indicators, the IRT indicator proposed in this paper has a higher sensitivity to IRT abnormalities in the failure process of wood structures.

Development and performance study on low strength and high rockburst tendency similar simulation material of coal

The current similar simulation materials (SSM) are featured with the contradiction between low strength and high rockburst tendency (RT), thus being unable to simultaneously realize the qualitative rockburst of small size specimen and the impact damage restoration of large size model. In this case, this study developed a new SSM of low strength and high RT by using water glass (WG) as cement, talcum powder (TP) as aggregate and adding curing agent sodium silicofluoride (SSF). Under the requirements of initial set volume shrinkage rate (IVSR), long-term volume decay rate (LVDR), uniaxial compressive strength (UCS) and modulus index (MI), the optimal ratios of SSF and TP were obtained 20% and 70% by orthogonal experiment and multiple linear regression method, respectively. Micro-macroscopic experiments such as uniaxial compression, scanning electron microscope (SEM), acoustic emission (AE) and Infrared thermal imager were utilized to monitor in real time the energy-temperature-strength synergistic change characteristics and similarities between this material and the coal with a strong RT. The experimental results show that: the UCS value of this material is 6.11 MPa and its MI is 11.57, which meets the requirements for low strength and high RT. Meanwhile it satisfies a certain similar proportionality between its physical parameters and those of coal. In the whole process of uniaxial compression, there are energy and temperature homologous changes in the characteristics of consistency, and both materials conform to the stress–strain phase law. The infrared radiation temperature displays a trend of “slowly decreasing-gradually warming-continuously cooling-suddenly warming-sharply cooling”. The AE energy count rate shows a trend of “calm transition and sudden increase before and after the stress peak”. All are characterized by strong RT. There is still some difference between the two specimens during energy and temperature changes, due to their different molding characteristics and load-bearing capacity. The feasibility of the material was confirmed in terms of physical parameters, degree of rockburst and homologous energy and temperature characteristics. Meanwhile, this study revealed the multi-parameter precursor characteristics of rockburst damage in the specimen, which can lay a foundation for the prevention and study of impact ground pressure disaster.

Development and characterization of a high-emissivity reference blackbody radiation source with V-grooves and large aperture at low-temperature

A high-emissivity blackbody radiation source can improve the measurement level of infrared radiation temperature, which is critical for applications in high-value industries and human health monitoring. In this study, a new high-emissivity blackbody source with V-grooves and large aperture was redesigned and developed, which can be used as a radiation temperature reference source for the calibration of secondary blackbody sources and precision radiation thermometers in the temperature range from −10 ℃ to 100 ℃, including the temperature range of human body infrared radiation considered in the study of people exhibiting fever symptoms. The wavelengths of the infrared spectral radiation temperatures involved in the study were in the range of 8–14 μm. The blackbody source consisted of a blackbody cavity, a jet-stirred precision constant-temperature bath, a standard platinum resistance thermometer, a high-precision digital multimeter, a frost-proof cover, and an auxiliary test frame. The cavity was cylindrical and conical with a diameter of 60 mm, a conical top angle of 120°, and a total length of 300 mm. The V-grooves with an angle of 50° on the inner wall were coated with high-emissivity coatings. The cavity was then completely immersed in a thermostatic bath. The radiation temperature of the blackbody source was traced to the International Temperature Scale of 1990 using a standard platinum resistance thermometer, which was calibrated at fixed-points of the Ar, Hg, H2O, Sn, and Zn. The experimental results revealed that the normal effective emissivity of the blackbody measured by the thermal cavity reflectometer method was 0.999 751, which is consistent with the theoretical calculation results based on the Monte Carlo method using optical ray tracing technology. In addition, the accuracy of the radiation temperature was verified by comparing it with a reference blackbody source from the National Institute of Metrology (NIM), China. The temperature stability of the blackbody source did not exceed 0.005 ℃ within 30 min, the axial temperature uniformity of the blackbody cavity did not exceed 0.048 ℃, and the temperature uniformity at the bottom of the cavity was better than 0.053 ℃. The combined standard uncertainty of the radiation temperature of the blackbody radiation source was evaluated from 0.010 ℃ to 0.032 ℃. The novel design with 50° V-grooves allowed for the blackbody source to provide the combination of a large aperture and high emissivity, which improved radiance temperature measurements. The reliability of the new design was experimentally verified. This design provides a novel method and experimental basis for the future design of compact light-weight blackbody sources, which is useful for the development of compact spaceborne blackbody sources.

Laboratory study on the damage characteristics of shale under different liquid nitrogen injection rates

Liquid nitrogen (LN2) is an environmentally sustainable fracturing fluid that is used in oil and gas field. LN2 flow rate has a significant impact on the cryogenic damage effect. A sequence of laboratory experiments was carried out to explore the cryogenic damage characteristics of shale under different LN2 flow rates (0.05 L/min-0.20 L/min) in this paper. LN2 was injected into a shale borehole for 20 min. The infrared radiation temperature (IRT) system and the acoustic emission (AE) system were applied to monitor the magnitude of the cryogenic damage in real time. After LN2 pre-conditioning, the shale samples were broken in uniaxial compression condition or fractured in high temperature (100 °C) and triaxial stress (12 MPa) condition. The differences in microscopic characteristics of shale with and without LN2 pre-treatment were observed by the scanning electron microscope (SEM). The experimental results show that a low temperature region around the borehole grew with increasing LN2 flow rates. There were many new microcracks generation between the laminations during LN2 injection. The cumulative AE energy increased by at least 15 times when the LN2 flow rates increased from 0.05 L/min to 0.20 L/min. The uniaxial compression strength (UCS) of shale decreased by 22.33% and the elastic modulus decreased by 24.43%. High LN2 flow rate is favorable for in-situ cryogenic damage, but the economic efficiency decreased. The reduction in average breakdown pressure (BP) increased and then decreased with increasing LN2 flow rate. When the IRT of shale didn't change, the cryogenic damage would not increase any longer. It is necessary to co-ordinate the LN2 flow rate and the LN2 injection time for better cryogenic damage effect. The study provides evidence of the advantages of LN2 assisted fracturing and valuable perspectives on the characteristics of cryogenic damage at different LN2 flow rates.

Fabrication of sandwich-structured infrared camouflaged and flexible anti-aging composite for thermal management

The design and preparation of infrared stealth materials that meet the application in complex environments is urgently demanded in military fields. In this paper, composites with low emissivity and thermal insulation are designed to be used for indoor and outdoor infrared stealth. Thereinto, nanoPE-MXene, yttrium oxide coated hollow glass microspheres (HGMs@Y2O3) and polypropylene nonwoven (PPF) were used as low emission, insulation, and antifouling layers, respectively. The sandwich-structured composite reduce the infrared radiation temperature of the 80 °C heat source object to 33.9 °C, and the average infrared emissivity of 3-15 μm is only 0.17. In addition, the infrared stealth performance of the composite is not affected by environmental changes. More importantly, the composite exhibits excellent anti-fouling and ageing resistance performance, which lays the foundation for the practical application of efficient stealth infrared materials.

Precursors of Cyclic Loading and Unloading Sandstone Failure Based on “Acoustic-Thermal” Loading–Unloading Response Ratio

Coal mining often causes periodic disruption in the rock mass around the stope. The study of the deformation and failure characteristics of cyclic loading and unloading sandstone is very critical for gaining a thorough understanding of the mechanisms of rock damage, degradation, and failure. This kind of investigation is very helpful in determining the precursors of rock failure and the instability of engineering structures. In this research study, the properties of acoustic emission and infrared radiation of cyclic loading and unloading sandstone are explored using a cyclic loading and unloading sandstone experiment. Based on acoustic emission and infrared radiation, the loading–unloading response ratio of rock is established. It is found that the response variables of sandstone during the loading stage based on acoustic emission (AE) counts and the loading–unloading response ratio based on average infrared radiation temperature (AIRT) both rise suddenly in the last cycle, which may be a precursor of “acoustic-thermal” approaching rock failure. On this basis, the quantitative analysis index of infrared radiation of differential infrared energy change rate (DIECR) is proposed, that is, the change of square of ΔAIRT in unit time, and based on AE counts and DIECR, the loading–unloading response ratio of “acoustic-thermal” is defined. It is found that the “acoustic-thermal” loading–unloading response ratio suddenly increases during the penultimate cycle of loading and unloading. This feature can be taken as the initial precursor of rock failure. Together with the “acoustic-thermal” imminent failure precursor of rock, it constitutes the “initial precursor-imminent failure precursor” combined with the internal fracture and surface infrared radiation temperature field during the cyclic loading and unloading process of rock, realizing the hierarchical monitoring and early warning of cyclic loading and unloading rock failure. The research results lay a theoretical and practical foundation for using infrared radiation to monitor engineering disasters caused by rock fracture and failure in mining engineering.