Internal Gas Pressure Research Articles

Forced oscillation dynamics of surface nanobubbles.

Surface nanobubbles have potential applications in the manipulation of nanoscale and biological materials, waste-water treatment, and surface cleaning. These spherically capped bubbles of gas can exist in stable diffusive equilibrium on chemically patterned or rough hydrophobic surfaces, under supersaturated conditions. Previous studies have investigated their long-term response to pressure variations, which is governed by the surrounding liquid's local supersaturation; however, not much is known about their short-term response to rapid pressure changes, i.e., their cavitation dynamics. Here, we present molecular dynamics simulations of a surface nanobubble subjected to an external oscillating pressure field. The surface nanobubble is found to oscillate with a pinned contact line, while still retaining a mostly spherical cap shape. The amplitude-frequency response is typical of an underdamped system, with a peak amplitude near the estimated natural frequency, despite the strong viscous effects at the nanoscale. This peak is enhanced by the surface nanobubble's high internal gas pressure, a result of the Laplace pressure. We find that accurately capturing the gas pressure, bubble volume, and pinned growth mode is important for estimating the natural frequency, and we propose a simple model for the surface nanobubble frequency response, with comparisons made to other common models for a spherical bubble, a constant contact angle surface bubble, and a bubble entrapped within a cylindrical micropore. This work reveals the initial stages of growth of cavitation nanobubbles on surfaces, common in heterogeneous nucleation, where classical models based on spherical bubble growth break down.

The in-situ testing and modeling on sealing strength deterioration of lithium-ion pouch cell

The pouch cell is of great potential application among a variety of power batteries, because of its higher energy density and lower weight. Due to the existence of internal gas generation in the long lifetime of the pouch cell, the slowly increasing internal gas pressure will cause a time-dependent fracture in its package sealing edge. This process significantly affects the remaining useful life and reliability. In this paper, an in-situ experiment was performed and a modified cohesive zone model (CZM) was proposed to describe the seal strength degradation behavior. Firstly, the in-situ tensile test was conducted to measure the sealing strength curve, and the exponential CZM was used to characterize the constitutive relation of the sealing area based on the load-displacement data. Secondly, constant stress accelerated degradation tests (CSADT) were carried out to simulate the degradation process, where the action of gas pressure on sealing area was converted to accelerated tensile load. Then, the exponential CZM was modified to account for the strength degradation behavior with the effect of constant load duration, based on the traction-separation relationship. The fracture energy was calculated by area integral under the load-displacement curve, whose reduction represented the degradation phenomenon. Finally, the proposed model was validated by the testing data, and a good agreement was observed.

Measurement of gas pressure inside large-format prismatic lithium-ion cells during operation and cycle aging

In this study we investigate the influence of the state of charge (SOC), temperature and aging on the gas pressure inside prismatic lithium-ion cells with a LiNi1/3Mn1/3Co1/3O2 cathode and a graphite anode. The internal gas pressure inside lithium-ion cells has so far been only investigated for small cells using large-size laboratory measurement equipment. We show for the first time that measuring the internal gas pressure is also possible for large-format prismatic cells and by using miniaturized pressure sensors that can be integrated into a battery pack. We also show that this measurement method enables the monitoring of the gas pressure during long-term cycling without leading to premature battery failure or accelerated aging. The gas pressure depends on the SOC in a non-linear way. This is caused by the dependence of the electrode volumes on the degree of lithiation. The gas pressure also correlates non-linearly with temperature, and the magnitude of temperature dependence increases with aging. During long-term cycling, the pressure irreversibly increases, which is most likely due mainly to gas formation. The increase in pressure correlates with a loss of capacity, which basically qualifies internal gas pressure for an indicator for state of health.

Expansion Properties and Diffusion of Blowing Agent for Vinylidene Chloride Copolymer Thermally Expandable Microspheres.

Vinylidene chloride copolymer microspheres were synthesized by in situ suspension copolymerization of vinylidene chloride (VDC), methyl methacrylate (MMA), and/or acrylonitrile (AN) in the presence of a paraffin blowing agent. The effects of shell polymer properties including compositions, glass transition temperature (Tg), crosslinking degree, blowing agent type, and encapsulation ratio (Er) on the expansion properties of copolymer microspheres were investigated. Moreover, the diffusion properties of blowing agent in copolymer microspheres were studied. The results show that VDC-MMA-AN copolymer microspheres exhibited excellent expansion properties, and the volume expansion ratio (Ev) and the apparent density were decreased over 40 times, but it was difficult to expand for the VDC-MMA copolymer microspheres. In addition, the moderately crosslinked inside of the polymer shell enhanced the Ev more than 30 and the stable expansion temperature range (Tr) was about 30 °C by adding 0.2–0.4 wt% of divinyl benzene. The Tg of the shell polymer must be higher than the boiling point of the blowing agent as a prerequisite; the lower the boiling point of the blowing agent, the higher the internal gas pressure driven microsphere expansion, and the wider the Tr. By increasing the Er of blowing agent improved the Ev of the microspheres. The diffusion of pentane blowing agent in VDC-MMA-AN copolymer microspheres were divided into Fick diffusion and non-Fick diffusion.

Study of liquid spurt caused by hydrodynamic ram in liquid-filled container

When a high-velocity penetrator impacts a liquid-filled container, such as a fuel tank, the phenomenon of hydrodynamic ram occurs. The cavity formed in the liquid and the resultant complex pressure field may cause the liquid to spurt from the penetration orifices. In this study, an experiment in which a high-velocity fragment impacts a liquid-filled container is conducted to examine the resulting liquid spurt. The characteristics of the liquid spurt are investigated. It is revealed that both the impact velocity of the fragment and the shape of the penetration orifice affect the characteristics of the liquid spurt. The expansion and contraction of the cavity are direct causes of the liquid spurt. Moreover, the relationship between the liquid spurt velocity and the pressure in the liquid is analyzed, and the theory of the pressure distribution that exists during the cavity oscillation is preliminarily proposed. The change in the cavity volume during the oscillation and the initial internal gas pressure in the cavity contribute significantly to the pressure field in the liquid.

Effect of reduced gas pressure on yield of biogas and other physicochemical parameters

The internal gas pressure is one of the major parameters affecting the microclimate of the anaerobic digester. The effect can be described by Henry’s Law and Ideal Gas law. In this experiment, the effect of reduced gas pressure on the yield of biogas and its composition was observed. The pressure of gas was reduced by displacement of a piston connected to the balancing weight, to maintain constant reduced pressure. As the piston is displaced to its maximum point due to gas generation, then the gas is transferred to the gas storage tank for further analysis. The gauge pressure applied was 0, $$-100$$ , and $$-200$$ mmHg for systems A, B, and C, respectively. The specific gas yield of systems A, B and C was 26.09, 70.41, and 246.5 L/kg (on dry basis). The production of methane was increased with a decrease in internal gas pressure. The corresponding average methane content of systems A, B and C was 38.33, 44 and 63.97%. The $$\hbox{BOD}_{5}$$ removal efficiencies were 6.25, 33.33 and 70.83% for systems A, B, and C, respectively. The pH of the substrate was stable in the system C. The rate of Total Solid (TS) reduction was high in System C. The TS reduction efficiency of systems A, B, and C was 14.7, 16.64, and 22.19%, respectively. The reduction in internal gas pressure can be a new effective and efficient process control strategy. The reduced-pressure system reduces the chemical cost incurred by the addition of alkalinity to maintain the pH.

In situ micro gas tungsten constricted arc welding of ultra-thin walled 2.275 mm outer diameter grade 2 commercially pure titanium tubing

Ultra-thin walled cooling tubes for heat exchangers and condenser units have applications in multiple high-value manufacturing industries. Grade 2 commercially pure titanium (CP-2 Ti) requires far less mass to achieve the same mass flow handling abilities as stainless steel tubing yet it is more challenging to join, particularly at wall thicknesses less than 500 μm (termed ultra-thin walled tube). This paper presents a single-pass joinery method that produces reliable welds on 2.275 mm outer diameter (OD), 160 ± 10 μm wall thickness tubing with a service life of 20 of more years. This is achieved through an automated orbital gas tungsten constricted arc welding (GTCAW) process incorporating enveloping low-mass sleeves used in tandem with a buttressing internal gas pressure to support the molten metal and maintain consistent internal diameter inside the tube. The industrial applicability is demonstrated through the production of a 1:1 scale mock-up of a fixed geometry CO2 cooling circuit for a next-generation particle detector. The tensile strengths of the joints, 403.8 ± 4.2 MPa, exceed the tensile strength of the parent CP-2 Ti.

Influence of precast foam on the pore structure and properties of fly ash-based geopolymer foams

This paper proposed a new type of fly ash-based geopolymer foams (FAGF) designed for wall insulation in buildings. The first part investigated the pore structures and properties of FAGF such as porosity, average Feret diameter (AFD), and roundness via a variation of the mix ratios and contents of precast foam. Then the results were further supported by the microstructures of pores, leading to the optimization of mix formulations of precast foam in terms of FAGF. The second part of this study explored the relationship between precast foam properties and FAGF performance. Then the influence of foam content on the pore structure parameters, fluidity, dry density, compressive strength and thermal conductivity of FAGF were measured and analyzed, revealing the mechanism of pore forming within FAGF. The results indicated that the foam in the paste was mainly controlled by five kinds of forces: surface tension Fst, internal gas pressure Pi, drainage force Fd extrusion binding force Fc and buoyancy Fb. When these forces were balanced, the foam was in a relatively stable state in the paste, resulting in the uniform pore size distribution and the excellent macro properties of FAGF.

Investigation on the Continuous Wave Mode and the ms Pulse Mode Fiber Laser Drilling Mechanisms of the Carbon Fiber Reinforced Composite.

The near infrared (NIR) laser drilling of a carbon fiber reinforced polymer (CFRP) composite in the continuous wave (CW) mode and the ms pulse mode was investigated by an experiment and a numerical simulation. The relationships between the laser penetrating time, entrance hole diameter, surface heat affected zone (HAZ) width, and material ablation rate and the laser irradiation time and laser peak power densities were obtained from the experiment. For the same average power density of the laser output, 3.5 kW/cm2, it was found that the ms pulse laser mode, which had a higher peak power density, had a higher drilling efficiency. When drilling the same holes, the pulse laser mode, which had the highest peak power density of 49.8 kW/cm2, had the lowest drilling time of 0.23 s and had the smallest surface HAZ width of 0.54 mm. In addition, it was found that the laser penetrating time decreased sharply when the peak power density was higher than 23.4 kW/cm2. After analyzing the internal gas pressure by the numerical simulation, it was considered that a large internal gas pressure appeared, which resulted from polymer pyrolysis, causing a large amount of the mechanical erosion of the composite material to improve the drilling efficiency. Therefore, the ms pulse laser showed its potential and advantage in laser drilling the CFRP composite.

Influence of surface treatment with infrared nanosecond laser on adhesion performance of adhesion-bonded carbon fiber/epoxy composite

The surface treatment of carbon fiber/epoxy composites with a pulsed infrared (1064 nm wavelength) nanosecond (7 ns pulse duration) laser has been investigated. It is found that single 1064 nm laser pulse can remove the polymer matrix from composite surface to expose the carbon fibers by expansion of the pyrolysis gas resulting from laser-induced polymer degradation. The influences of laser power density and scan strategy on matrix removal process have been studied. The bonding strength of laser processed, adhesion-bonded CFRP (carbon fiber reinforced plastic) increase with lower matrix residues on the fibers and a linear relation is found. The adhesion-bonding strength of CFRP surfaces, tested by lap-joint shear test, exceeds the strength measured for untreated and abrasion treated (SiC paper) samples. The main origin of fiber damage of the laser-treated surface is mechanical fracture rather than thermal damage as found by laser scanning confocal microscope and scanning electron microscope. The characteristic morphologies and failure modes of shear-tested surfaces are analyzed. The obvious improvement of adhesive strength is achieved by the laser-treated surfaces attributed to matrix removal and carbon fibers protruding. A 1 D model is established to describe temperature and internal gas pressure of the irradiated surface. The new laser treatment method needs less laser energy and low pulse numbers and prove the way to an efficient, low-cost surface treatment for preparation of high quality adhesion bonded CFRP components.

О влиянии внутреннего давления на колебания цилиндрического газового пузырька

Natural and forced oscillations of a gas bubble are studied. The bubble has the shape of a round cylinder in the state of equilibrium. It is bounded in the axial direction by two parallel solid surfaces and is surrounded by an incompressible liquid of a finite volume with a free outer surface. The entire system is under an alternating pressure field. The velocity of the contact line of three media (gas-liquid-solid substrate) is proportional to the deviation of the contact angle from the equilibrium value. The frequency of eigenmodes of a gas bubble can increase with an increase in the Hocking parameter, in contrast to the frequencies of an incompressible liquid drop, which only decrease. It is shown that radial oscillations of a cylindrical bubble are possible only in a finite volume of liquid. The effect of crossing the modes of natural oscillations is considered for the dissipative case. The amplitude-frequency characteristics are constructed for different values of the internal gas pressure. Resonance phenomena are found. It is shown that the external influence excites, first of all, volumetric oscillations of the bubble. Variations in shape are caused by the movement of the contact line. Expressions are found for the vibration amplitude in the case of a fixed contact line and a fixed contact angle.

Modeling atomic force microscopy and shell mechanical properties estimation of coated microbubbles.

We present an extensive comparison with experimental data of our theoretical/numerical model for the static response of coated microbubbles (MBs) subject to compression from an atomic force microscope (afm). The mechanics of the MB's coating is described in the context of elastic thin shell theory. The encapsulated fluid is treated as compressible/incompressible pertaining to a gas/liquid, while the thinning of the liquid film between the MB and the afm cantilever is modeled via introduction of an interaction potential and the resulting disjoining pressure. As the external force increases, the experimental force-deformation (f-d) curves of MBs covered with polymer have an initial linear response (Reissner regime), followed by a non-linear curved downwards response (Pogorelov regime) where buckling takes place. On the other hand, the f-d curve for MBs covered with lipid monolayers initially follows the Reissner regime, but buckling is bypassed to a curved upwards regime where internal gas pressure dominates. The elastic properties, namely Young's modulus and shell thickness, for MB's covered with polymer can be estimated by combining the buckling point and the slope of the Reissner regime or the slopes of Reissner and Pogorelov regimes. Comparison of the present model with afm f-d curves for polymer shows satisfactory agreement. The area dilatation and bending moduli are shown to be the appropriate independent elastic parameters of MBs covered with phospholipid monolayers and are estimated by combination of the transition from Reissner to pressure dominated regime. Simulations and experiments in this case are in excellent agreement.

The Morphology of the Volume Plasticity Zones at the Gas-Filled Pores in Cast and Powder Steels under Stress Corrosion

Purpose of research . The purpose of this work is to develop a method for calculating parameters of volumetric zones of plasticity in powder and cast steels, occurring in the vicinity of pores under external tensile stress and internal gas pressure. Methods . The problem was solved on the basis of the analysis of the distribution of stress tensor components in the vicinity of discontinuities (pores) of different shapes. A sample under tensile stresses ( σ ), containing a single stress raiser - a spherical pore with radius a, and a pore in the form of a biconvex lens, was studied stepwise. The choice of pores morphology was determined by their experimental observation in the structure of real commercial steels, and the presence of a solution for estimating the stress field near the spherical pore, performed by L. D. Landau and E. M. Lifshitz. In comparison with such stress raisers as a tight crack or a pore in the form of a biconvex lens, the stress concentration near a spherical pore is weaker. However, for the processes of diffusion of atoms through the zone of increased stress, not only the intensity of stress is important, but also the size of the zone itself. Near the spherical cavity, the size of the overstressed zone is the largest, so the analysis of its morphology was taken as a basis. In this paper, we used the modeling of functions describing the stress distribution around the pores similarly to the velocity field of an ideal fluid. Results . As a volume object, the described zones of plasticity are the surfaces of a spheroid and an ellipsoid surrounding spherical and lenticular pores. It is obvious that the smaller the ratio h/l for the pore is, the further in the transverse direction the plasticity zone (more than p max -l) spreads, becoming tighter and tighter (z 1 is approximately proportional to h). The following geometric parameters of the plasticity zones near the lenticular pore were determined as characteristic ones: its greatest length in the radial direction from the apex; the characteristic thickness of the zone ( ρ max – l)l/a; the area of the lens; the volume of the zone and its share of the volume of the lens. The development of plasticity zones near pores of different morphologies in steels under stress-corrosion conditions stimulates the change (increase) of the kinetic characteristics of the metal and the creation of favorable conditions for accelerated diffusion (decarburization). In the area of plasticity zones in the vicinity of pores under external and internal (gas pressure) stresses, the creation of channels of facilitated diffusion forms places of nucleation of submicrocracks at points D, B and C. Juvenile free surfaces formed in radial directions create zones of realized accommodation opportunities of the medium - zones of plasticity. Along with the growth of radial cracks to their tops from the pore under high pressure, gases diffuse rapidly. Conclusion . The stress distribution analysis algorithm proposed in this paper allows predicting the intensity of plasticity zones (crack formation) development depending on the ratio of parameters β ( β = σ T/ σ ) and s (s = p/ σ ), that is, on the ratio of external stress values, steel yield stress and gas pressure in the pore. The calculation made it possible to clarify the place of nucleation, the shape and scale of the development of zones of plasticity (cracking) in the vicinity of pores of different morphology depending on the ratio of external stress and gas pressure in the pores.

Stability study and optimization design of small-spacing two-well (SSTW) salt caverns for natural gas storages

Abstract A small-spacing two-well salt (SSTW) cavern is a relatively new type of cavern. As this type of cavern is less frequently used in underground natural gas storages, study on its stability is quite limited. To promote the application of this type of cavern and accelerate the construction of underground salt cavern gas storages, stability analysis and optimization design of this type of cavern are indispensable to the security of underground natural gas storages. In this paper, numerical calculation and parameters analysis were performed to analyze the effects of internal gas pressure and ratio of long axis to short axis (RLS) on the stability of SSTW caverns. The results show that internal gas pressure has an influence on the stability of SSTW caverns and low pressure should be limited in terms of duration and magnitude. And the ratio of long axis to short axis (RLS) has limited influence on the stability of a SSTW cavern by ways of volume loss rate and roof settlement. Overall, the SSTW cavern behaves similar stability state with that of a SW cavern. In addition, a flatter roof shape appears under greater Ratio value (RLS) and thus a thicker roof salt rock thickness is suggested for engineering design. The most different between them are the waist displacement along short axis, therefore the pillar width close to the adjacent cavern should be a certain lengthened at this direction.

Structure Optimization Design for Evaporation Substrate in Natural Cooling System Based on the Application of Power Electronics Equipment

Based on simulation, the structure optimization of a Cu evaporation substrate in natural cooling system is conducted, which can be used in power electronics equipment. The relationship between the welding area ratio and stress of evaporation substrate is investigated. The evaporation substrate is one of the most important components in a natural cooling system. Through utilizing phase-transition technology, heat dissipation is realized by a natural cooling system. During operation of evaporation substrate, increase in internal gas pressure, caused by the evaporation of working fluid, leads to deformation of evaporation substrate. Therefore, strengthen-columns are introduced to reinforce the evaporation substrate. Both Pro/E simulation outcomes and experimental results based on structure optimization of evaporation substrate indicate that the optimal design is achieved at a welding area ratio of 1.844%, namely the arrangement of strengthen-columns is 11 × 14 × 3 mm. With this arrangement, the minimum stress on welding surfaces of strengthen-columns and minimum deformation of the evaporation substrate are achieved, which can meet the engineering requirement.

In-Service Welding Simulation of 28” Pipeline Using Finite Element Method

To maintain the integrity of the gas pipeline, the repairing of pipeline system with common method such as cut and replaces method by conducting hot tap and bypass or clamp method is conducted. Both methods require in-service welding in the process. During in-service welding, the process affects the structure strength. The structure then needs to be analysed during the welding process. There are two common problems associated with in-service welding. Firstly, the high gas flow in pipe causes the weld rapidly to cool due to the convective transfer of heat. The other problem is burn-through during in-service welding. Pressurized natural gas imposes a significant stress on the pipe wall, and since the pipe strength is decreased during welding, this cause failure in pipe wall. Burn-through occurs when the region around the weld pool has insufficient strength to withstand the internal gas pressure. This paper shows the finite element analysis procedure of In-Service Welding Analysis to avoid burn-through failure. A thermal-mechanical based Finite Element model had been conducted to assess the risk. The model is simulated using three-dimension (3D) mechanical, thermos-elastic-plastic-metallurgical finite element computational procedure. The temperature, stress and strain parameters of inner surface were used to assess the model. The temperature and strain check are below the allowable value while the stress check with some applicable method which are based on either stress or strain based.

Investigations on a typical small modular PWR using coupled neutronic-thermal-mechanical evaluations to achieve long-life cycle-length

The main purpose of this study was to design small modular PWR with power of 150 MWth for long life operation, based on the coupled neutronic and thermal-mechanical evaluations. In this regard, pitch and fuel rod diameter were changed from 0.9 cm to 2.5 cm and 0.6 cm–0.96 cm, respectively; and desirable pairs (pitch - fuel rod diameter) were obtained. Neutronic parameters such as excess reactivity, maximum to average ratio of the radial neutron flux and fuel burnup were calculated using MCNP code. Also, thermal-mechanical parameters of the fuel rod including fuel centerline temperature, cladding hoop stress and fuel rod internal gas pressure were computed using FRAPCON code. Independency of results from number of axial nodes in FRAPCON code was analyzed. The number of axial nodes was considered 40 to ensure the accuracy of the FRAPCON results. Neutronic and thermal-mechanical cost values for each pair were calculated and Pareto front of the desirable pairs were obtained. Based on the results, eight desirable pairs were selected. By assuming equal importance for neutronic and thermal-mechanical parameters, total cost value was defined and pair of (1.1, 0.64) was selected as the most desirable one. Finally, fuel cycle lifetime was assessed for desirable pair considering neutronic (criticality and burnup) and thermal-mechanical (cladding strain, oxidation and hydriding as well as fuel rod internal gas pressure) limits. It was observed that fuel cycle lifetime was enhanced to 1750 days (40 GWD/ton).

Electro-Mechanical Design and Creep Analysis of Proposed Enclosure for Flexible Gas Insulated Line Regarding Subsurface Metropolitan Applications of High-Voltage Transmission Lines

Land shortage in metropolitan vicinities entails subsurface implementation of power transmission lines (PTLs) which demand structural flexibility, as well as substantial load bearing capability. Thus, development of a flexible gas insulated transmission line (FGIL) necessitates its strength degradation analysis, regarding the synergistic effect of aging and mechanical loadings. Moreover, correlation of conductor and enclosure dimensions of FGIL apropos field distribution, requires careful consideration regarding their dimensional specifications. In this research, a comprehensive electro-mechanical design is performed for the proposed flexible-thermoplastic-enclosure of a 132 kV FGIL by considering the synergistic impact of time and temperature-based aging, along with the effect of external and internal loadings, such as dead load, live load and internal gas pressure. Additionally, a recursive design algorithm for the proposed scheme regarding electro-mechanical aspects, along with aging perspectives is developed. Comparative analysis of proposed and conventional schemes regarding electro-mechanical and aging aspects revealed that the proposed enclosure exhibits the required structural strength, as well as flexibility for trenchless subsurface application of FGILs in metropolitan areas.

Temperature‐dependent effect of gas pressure on electrical tree in XLPE cable

Cross-linked polyethylene (XLPE), which is an important material in the cable insulation, faces the challenge of high temperature with high internal gas pressure during the process of overload. To clarify the impacting mechanism of temperature and gas pressure, this study presents the characteristics of electrical trees and partial discharge (PD) under different gas pressure and different temperature in XLPE cable. Experiments were conducted using XLPE cable insulation as samples. The results show that gas pressure has different effects on the initiation and propagation of electrical trees at different temperatures. XLPE is in the glassy state at low temperature, and the gas pressure suppresses the development of electrical trees during the growth period. When XLPE is in the elastomeric state, the high temperature accelerated the PD under high gas pressure. The analysis shows that more trapped charge and more branch channels will exist at high temperatures with high gas pressure, which is the primary cause behind the development of streamer, thus accelerating the progress of PD. XLPE cable in the case of high temperature and high gas pressure should cause more attention.

Test and analysis of mechanics and permeation properties of raw coal

AbstractIn this paper, we investigated the mechanics and permeation properties of the raw coal sample during loading and unloading process, and come to some conclusions: the permeability of the sample increases nonlinearly during the unloading confining pressure process. The larger the gas pressure is, the greater the increase range of the permeability will be. The larger the confining pressure unloading amplitude is, the greater the increase range of the permeability will be. In the loading process, the permeability and the axial strain of the specimen change in a “V” shape. As the gas pressure increases, the peak strength of the specimen gradually decreases, and fitted the gas pressure and the peak strength are accordance with the linear relationship. As the confining pressure increase, the peak strength of the sample gradually increases, and fitted the confining pressure and the peak strength are accordance with the exponential function. The internal friction angle of the coal sample was 43.22°, and the cohesion was 3.77 MPa. The relationship between the fitted gas pressure and internal friction angle, gas pressure and cohesion is in line with linear functions. Maintain an axial stress constant, unloaded confining pressure to a constant state of target value, the permeability of specimen shows a constant pressure boosting flow zone, the relationship between permeability and deviatoric stress is accordance with the ExpDec1 function during the process of unloading confining pressure and prepeak loading axial stress.