Explore the vast range of titles available.

The purpose of this study is to identify the crack initiation and damage stress thresholds of granite from the Korea atomic energy research institute’s Underground Research Tunnel (KURT). From this, a quantitative damage evolution was inferred using various methods, including the crack volumetric strain, b value, the damage parameter from the moment tensor, and the acoustic emission (AE) energy. Uniaxial compression tests were conducted, during which both the stress–strain and AE activity were recorded simultaneously. The crack initiation threshold was found at a stress level of 0.42–0.53  σ c , and the crack damage threshold was identified at 0.62–0.84  σ c . The normalized integrity of KURT granite was inferred at each stress level from the damage parameter by assuming that the damage is accumulated beyond the crack initiation stress threshold. The maximum deviation between the crack volumetric strain and the AE method was 16.0 %, which was noted at a stress level of 0.84  σ c . The damage parameters of KURT granite derived from a mechanically measured stress–strain relationship (crack volumetric strain) were successfully related and compared to those derived from physically detected acoustic emission waves. From a comprehensive comparison of damage identification and quantification methods, it was finally suggested that damage estimations using the AE energy method are preferred from the perspectives of practical field applicability and the reliability of the obtained damage values.

Effective methane extraction in underground coal seams can improve the efficient utilization of fossil energy and reduce the risk of safety accidents in coal mines. Pulsating nitrogen fatigue fracturing technology is proposed as a novel and effective method to enhance gas production in low-permeability coal seams and improve gas extraction efficiency. In this study, a pulsating gas test system was established to apply fatigue fracturing of pulsating nitrogen to low-permeability coal. Mercury intrusion tests, wave velocity tests, and triaxial compression tests were used to reveal the changes in microstructure and mechanical properties of low-permeability coal under fatigue fracturing tests. Results show that the residual deformation of the coal changes considerably under fatigue fracturing. The strain of the coal is characterized by a periodic “expansion–contraction” variation with the intrusion and discharge of the pulsating nitrogen, and the residual strain increases gradually in this process. After fatigue fracturing, facilitates the seepage of gas and the development of micropores and transition pores toward mesopores and macropores enhances the permeability of the coal. The specific surface area of the pores is considerably improved in the transition pores and mesopores. The pore fractal dimension of the coal tends to decrease under fatigue fracturing, resulting in a more uniform distribution of pores and enhanced interpore connectivity within the coal. The fatigue period is negatively correlated with the strength and wave velocity evolution of the coal, and the peak intensity first decreases rapidly and then gradually stabilizes. The fatigue fracturing results in a substantial increase in the spatial complexity and connectivity of the fracture distribution throughout the specimen. On the basis of the evolution characteristics of residual volumetric strain, a fatigue damage model was constructed to analyze the characteristics of fatigue deformation and failure of coal.HighlightsThe pulsating nitrogen fatigue test of low-permeability coal was carried out.The change of residual deformation of coal under pulsating nitrogen fatigue is obtained.The influence mechanism of pulsating nitrogen fatigue on pore structure is analyzed.The macromechanical parameters and damage evolution characteristics under pulsating nitrogen fatigue are evaluated.

The occurrence of various types of disasters in deep underground engineering is related not only to the strength of the rock mass but also to the crack propagation capacity (CPC) under corresponding stress conditions. The deep-seated rock mass is generally in the stress state of σ1 > σ2 > σ3, and the CPC under differential stress is very important to evaluate the brittle failure of rock. Therefore, based on the deformation characteristics of Baihetan (BHT) basalt under true triaxial compression (TTC), the evaluation index (IP) of the CPC is established, which considers the characteristics of stress-induced deformation anisotropy and the propagation angle of volumetric strain. The evaluation indexes of JP marble, BS granite and BHT basalt under TTC are analysed and compared. When the stress exceeds the crack initiation stress, the evaluation index of the CPC decreases with the increase of σ2, but increases with the increase of σ3, and the effect of σ3 on the CPC index is greater than that of σ2. Under TTC, the CPC of JP marble is the largest, followed by that of BS granite and BHT basalt. The analysis shows that the evaluation index (IP) proposed in this study is also suitable for conventional triaxial compression and uniaxial compression conditions. In addition, the test result shows that there is divisibility between the failure mode and IP under TTC. The relationship between IP and the failure mode of BHT basalt shows that splitting failure occurs when IP < 0.3, that shear failure occurs when IP > 0.4, and mixed failure occurs when IP is between these values. The evaluation index of the CPC proposed in this paper can provide a theoretical reference for evaluating the failure of surrounding rock near the opening boundary of deep underground rock engineering.

Background A ductile material, such as a polymeric material, releases energy during deformation. The dissipated energy can be evaluated as entropy generation. If the thermodynamic entropy generation can be measured, the stress state can be evaluated by the thermodynamic entropy generation. Objective In this study, the thermodynamic entropy generation of Polyamide 6 (PA6) was obtained using differential scanning calorimetry (DSC) for a material subjected to arbitrary strain. Methods Thermodynamic entropies were measured at the beginning and at each strain state of tensile tests by using DSC, and the volumetric strain was measured with Digital Image Correlation Method. Results At the 25% strain just before the necking behavior, the volumetric strain of PA6 was ~4.8%, and the entropy was ~56 kJ/K∙m 3 . Furthermore, the thermodynamic entropy generation of PA6 in carbon fiber reinforced plastics was evaluated under tensile conditions. The results showed that the thermodynamic entropy generation just before the transverse cracking (as same as necking in matrix resin) was ~69 kJ/K∙m 3 and the volumetric strain of PA6 in composite was ~ 3.56 %. As the results, the entropy generation and volumetric strain of PA6 showed almost same values in pure PA6 and PA6 in composite. Conclusions Consequently, thermodynamic entropy generation can be measured the volumetric strain of matrix resin.

Traditional railway substructure materials (i.e., natural crushed rock aggregates used for ballast and capping layers) degrade under service loads, incurring higher periodic maintenance costs compared to recycled materials. Using recycled waste materials such as coal wash and rubber crumbs for infrastructure upgrades not only reduces construction and maintenance costs but also supports environmental sustainability. By exploring unconventional avenues, earlier studies have delved into the viability of blending rubber crumbs (RC) and coal wash (CW) as an innovative substitute for traditional railway substructure materials, with a specific focus on the capping layer. This study introduces a semi-empirical constitutive model to simulate the response of mixtures of coal wash and rubber crumbs (CWRC) using the bounding surface plasticity framework. The novelty of this study is that a modified volumetric strain expression is introduced to capture the compressibility of rubber, thus enabling a more accurate representation of the internal deformation of rubber within the granular matrix. The variation of rubber content in the mixture is captured by the corresponding critical state void ratio surface and the hardening modulus. The theoretical model is then calibrated and validated using static drained triaxial test data for CWRC mixtures as well as mixtures of steel furnace slag, coal wash, and rubber crumbs (SFS + CW + RC).

When the fault in a focal area enters the critical state, nonlinear accelerated deformation and disturbance changes may occur during tide-induced loading and unloading. In this study, the anomalies in the Korla volumetric strain caused by earth tide were investigated using a theoretical model of tidal force. Results show that the step changes in the Korla volumetric strain may be triggered by tidal force within a short time frame, ranging from a few to tens of days, prior to a moderate earthquake. The azimuthal angles at the time of step changes are mainly distributed in the ranges of 124-158° and 185-228°, and the azimuth angle at the time of many nearby medium-to-strong earthquakes occurring in this step concentration area, suggesting that the step anomalies in the Korla volumetric strain are closely related to the horizontal tide-induced force in a specific direction. Using the Schuster method, it was found that the tide-induced azimuth angle of the step changes occurred mostly at the minimum value of the solid tide, providing evidences of the modulation of the solid tide. These results may present new ideas for using crustal deformation observations for short-term earthquake predictions.

Modernized technological processes or increasing demands on building materials force the scientific community to analyze in more detail the suitability of individual raw materials and deposits. New or modernized research methodologies make it possible to better understand not only the geometrical structure of the pore space of materials but also the processes taking place in them and the interaction of many factors at the same time. Despite the extensive literature in the field of research on capillary-porous materials, scientists still face many challenges because not everything is known. Carbonate rocks are the most common (one-tenth of Earth’s crust) sedimentary rocks. Analysis of the test results obtained with the use of the modernized differentia analysis of volumetric strain (DAVS) methodology allows for a better adjustment of rock deposits to the products that can be produced from them. In this manner, it is possible that it will contribute to a more rational use of exhaustible rock deposits and not only carbonate ones. This research subject is of great importance for modern science, which was also noted in many of science publications.

Water has a great influence on rock fracture process, and it is necessary to explore the activity of cracks for saturated rocks at key stress points. By uniaxial compression test and acoustic emission (AE) tests, four key points of stress-strain curve for dry and saturated marble specimens are determined. Those four key stress points include: crack closure stress (point A ), crack initiation stress (point B ), crack damage stress (point C ) and peak stress (point D ). By analyzing dominant frequencies and amplitude of AE waveforms of the whole loading process and in the vicinity of key points, the fracture process of samples was studied. The results show that there are two concentrations of dominant frequency bands in both dry and saturated marble, and the ranges of dominant frequency bands of the saturated seem wider. Due to the existence of water, the number and energy of AE waveforms decrease relatively during the whole test. This phenomenon indicates that water enhances the ductility and creep characteristics of rock. The appearance of lots of AE waveform signals with low dominant frequency is the precursor information of intense crack propagation and failure for dry rock, and the effects of water increased the number of micro-tensile failures for saturated rock in the vicinity of each key point. From point A , point B , point C to point D , the proportions of H-type bands in the vicinity of each key point for dry rock show a trend of increasing — decreasing — sharply decreasing, while those for saturated rock follow the law of increasing — decreasing — increasing.

Digital volume correlation, an experimental method for volumetric strain measurement, has experienced a growth in technique development and application since its introduction in 1999. This has largely been the result of more accessible volumetric imaging methods and greater speed and capacity of computational facilities. This paper reviews recent work using the method and presents examples from the author's laboratory. The emerging message is that, although closely related to the surface-oriented method of digital image correlation, the volume method is distinct due to its predominant reliance on naturally occurring image texture for displacement tracking. This requires careful tuning for successful application with different materials, and therefore the appropriate focus should not be on developing the ‘best’ digital volume correlation method, but on developing a set of tools that can be selected from and adjusted to specific mechanics problems.

Experimental and numerical investigations were conducted to study adsorption and desorption of pure and multicomponent gas on coal, and the sorption-induced volumetric strain and permeability change of the coal. This paper presents the experimental work. Using CO 2 , N 2 , and CO 2 and N 2 binary mixtures of different composition as injection gases, the measurements were conducted on a cylindrical composite coal core at varying pore pressures and constant effective confining pressure. Sorption was measured using a volumetric method. The initial and equilibrium system pressure and gas phase composition were measured. The total amount of adsorption and the composition of the adsorbed phase (for adsorption of binary gas mixtures) were calculated based on material balance. During the process of sorption, the volume of the core was monitored by recording the volume of the water in the confining pressure vessel. Sorption-induced strain was calculated as the ratio of the sorption-induced volumetric change to the initial volume of the core. After adsorption equilibrium was reached, the permeability of the core was measured based on the Darcy equation for gas flow. Sorption and permeability measurements were conducted for each test gas at first increasing and then decreasing pressures. Volumetric strain was only measured while pore pressure increased. To our knowledge, this is the first study measuring adsorption, volumetric strain, and permeability on the same piece of core with the same apparatus.