Void Compaction Research Articles

Coupled geomechanical analysis of irreversible compaction impact on CO2 storage in a depleted reservoir

The utilization of depleted gas reservoirs for carbon storage offers substantial advantages. However, it raises concerns related to the geomechanical effects of historic gas extraction on the CO2 sequestration operation. In this study, a coupled thermo-hydro-mechanical investigation is conducted on a multi-layered sedimentary system that includes sealed bounding faults. Our simulations exhibit various levels of reservoir compaction during gas extraction under different pre-consolidation conditions of the sediments, highlighting the pivotal role of reservoir compaction in geomechanical analysis. The results demonstrate the occurrence of strain-hardening compaction behavior in the reservoir during post-yield depletion. This compaction is accompanied by a significant reduction in porosity and permeability, as well as irreversible surface subsidence. Hysteresis in the stress state is induced by the aforementioned irreversible reservoir compaction through two primary mechanisms: poro-elastoplastic stressing and differential compaction on each side of the sealing fault. These mechanisms alter the magnitude and orientation of stress inside and outside the depleted reservoir. Moreover, caprock compaction is impeded and delayed by the irreversible reservoir compaction owing to poro-elastoplastic stressing. This implies that conventional methods relying on the poro-elasticity theory alone may overestimate pressure required to fracture the caprock by approximately 2 MPa. When considering the combined effect of poro-elastoplastic stressing and differential compaction, neglecting irreversible reservoir compaction may lead to underestimation of the critical pressure for inducing fault slip by up to 4.9 MPa. Additionally, regardless of whether plastic void compaction is considered, we recommend increased attention be focused on the sub-vertical faults to mitigate the risk of significant slip that potentially could also lead to upward CO2 leakage. In scenarios where a slip event occurs in a fault during reservoir depletion, the results show that a subsequent CO2 injection operation tends to stabilize the faults. Nevertheless, it is crucial to consider that fault stability could deteriorate rapidly over time, potentially leading to a second slip event during carbon sequestration.

Real-time monitoring of self-sensing cementitious composite incorporating hybrid silicon carbide and graphite for enhanced structural health monitoring

This manuscript presents a comprehensive exploration of Silicon Carbide-Graphite Cement Composites (SCGCCs) by investigating their mechanical, electrical, and self-sensing properties. The study systematically varies SiC and graphite content, leading to remarkable insights. In terms of mechanical strength, specimens S50G1 and S50 stand out, exhibiting impressive enhancements of 15.6 % and 9.8 % in compressive strength, respectively, showcasing the pivotal role of particle content in bolstering structural integrity. Electrical resistivity analysis uncovers a percolation threshold at 25 % SiC and 2 % graphite, resulting in a substantial 97 % reduction in resistivity. This critical finding underscores the delicate balance required for optimal conductive networks within the composite material. The self-sensing capabilities of SCGCCs under flexural stress reveal a synergistic effect between SiC and graphite, with specimen S25G2 displaying the lowest voltage drop. The compressive stress analysis unveils a distinctive conductive path reconstruction behavior, offering valuable insights into the material's response to varying stress levels. Advanced CT scan porosity analysis further refines our understanding, indicating a significant reduction in porosity from 4.2 % to 3.1 % in specimen S25. Furthermore, specimens with lower graphite and SiC proportions exhibit efficient void compaction, resulting in a well-integrated microstructure with porosity as low as 2.5 %. These findings not only contribute to the fundamental understanding of SCGCCs but also offer practical applications in smart materials and structural health monitoring. Moreover, the inherent advantage of real-time monitoring within the context of smart mortar extends to the prognostication of an advanced warning signal for impeding the complete failure of the smart concrete matrix.

Characterizing fatigue damage evolution in asphalt mixtures using acoustic emission and Gaussian mixture model analysis

The identification and investigation of fatigue crack evolution and damage modes in asphalt mixtures are crucial for understanding the corresponding mechanisms and characteristics of fatigue failure. In this study, the four-point bending fatigue tests were performed on the asphalt mixture specimens with precast joints using the acoustic emission (AE) technique to analyze the damage evolution. The failure modes of the asphalt mixtures were identified using the Gaussian mixture model (GMM). The results revealed that the fatigue damage of the asphalt mixtures can be categorized into four stages: Stage I (void compaction), Stage II (microcrack initiation and stable propagation), Stage III (crack aggregation and unstable propagation), and Stage IV (complete fracture). This division was defined based on the inflection points of the axial displacement curves, the cumulative number of AE events, and the cumulative ringing counts. The evolution of the AE b value was found to be correlated with the crack propagation. The rapid decline in the b value in Stage III was considered a harbinger of the eventual complete fracture in the asphalt mixtures. The GMM clustering analysis indicated that the fatigue damage of the asphalt mixtures primarily involved tensile damage (90%), and shear damage made a small contribution of 10%. Existing AE studies have focused on the quantitative evaluation of AE parameters, while research on clustering identification algorithms for these parameters is scarce. The analytical methods and findings of this study enable an effective identification of fatigue damage in asphalt mixtures at the laboratory scale and offer insights into the fatigue damage mechanisms of asphalt mixtures.

Mechanical Properties Damage, Fracture Evolution, and Constitutive Model of Siltstone under the Effect of Moisture Content

In order to study the weakening mechanism of mechanical properties and the evolution of fracture of water-bearing rocks, cylindrical standard siltstone samples with four moisture contents (0, 2.85, 3.87, and 4.25%) were prepared, and the mechanical properties, damage mode, AE characteristics, and fractal law of water-bearing rock samples were studied by means of uniaxial compression test and acoustic emission (AE) monitoring technique, and based on the test findings, a constitutive model of the entire process of rock deformation and damage under uniaxial compression was built with different moisture content of rock. The results show that with the increase of moisture content, the peak stress, the stress threshold of void compaction stage, and the stress threshold of elastic stage of the rock samples decreased linearly, elastic modulus decreased exponentially as a function, and the peak strain, the strain threshold of void compaction stage, and the strain threshold of elastic stage increased linearly. The higher the moisture content, the weaker the AE signal intensity and the smaller the AE count value. From dry to saturated, the damage form of rock samples gradually transitioned from predominantly tensile damage to predominantly shear damage. The fractal dimension of the broken block linearly decreases as the moisture content rises. The model constructed in this paper has good applicability to the deformation characteristics of water-bearing rocks under uniaxial compression before the peak stress; it especially can express the rock void compaction stage, but it cannot accurately describe the postpeak deformation characteristics.

A statistical thermal damage constitutive model for rock considering characteristics of the void compaction stage based on normal distribution

A statistical thermal damage constitutive model for rock considering characteristics of the void compaction stage based on normal distribution

Regional Division and Its Criteria of Mining Fractures Based on Overburden Critical Failure

Mining fracture is the key factor in realizing water-conservation mining, stability evaluation of coal mining subsidence areas, and accurate restoration of the surface eco-environment. To clarify, the evolution and distribution of mining fractures, based on the key strata theory and the mining degree of overburden failure, the contact state of rock stratum after overburden critical failure was analyzed, the formation mechanism of “saddle shaped” water conducting fracture zone was revealed, and the permanent mining fractures were determined to be primarily concentrated in the overburden structure at the boundary of the working face. According to the shear test of sandstone in the fracture zone, the damage degree of the rock sample was positively correlated with shear stress, and the overburden structure exhibited no instability. Based on the distribution of mining fractures, the fracture zone was divided into the original fracture, tensile fracture, structural void, and void compaction areas in the horizontal direction. The structural void area had the largest residual deformation in the goaf. A regional division method based on overburden critical failure was proposed and applied in engineering by using surface movement monitoring. The results showed that the surface subsidence near the boundary of working face was greater than that in the middle, and the residual surface deformation in the goaf was closely related to the mining time, which has long-term characteristics. The rationality of the regional division method of mining fractures was also verified.

Statistical Damage Model of Rock Structural Plane Considering Void Compaction and Failure Modes

The shear behavior of rock structural planes contains various symmetry laws, and the shear failure can be considered as an asymmetric state of the rock and rock mass. The study of shear deformation and the failure of rock structural planes plays a vital role in ensuring the safety and stability of engineered rock masses. In view of the inability of traditional shear constitutive models to describe the non-linear characteristics of the dilatancy stage and the single applicable failure form, firstly, we discuss, in depth, the law and mechanism of shear deformation and failure of structural planes, and introduce the compaction index α to measure the non-linear characteristics of shear stress–shear displacement caused by compaction of microcracks and internal pores of structural planes, and the structural plane damage model, considering the void compaction and failure mode, was established. Then, the statistical damage theory was introduced, and the strength and failure of the microunits of the rock structural plane were assumed to obey the Weibull distribution. Based on the Mohr-Coulomb strength criterion to measure the strength of the microunits of the rock structure surface, a statistical damage model of structural planes, which can describe void compaction and failure modes, was established. Finally, a comparative analysis was carried out with the test curve, and the results showed that: the calculation curve of the structural plane statistical damage model established, considering the void compaction and failure modes, has the same trend as the structural plane shear test curve, which can better describe the shear stress– shear displacement at the dilatancy stage, as well as the shearing stage and sliding stage in different failure modes. The changing law of shear displacement reflects the rationality and accuracy of the constructed constitutive model. The research results can provide a theoretical basis for the shear deformation and failure of rock structural planes.

Constitutive modeling of rock materials considering the void compaction characteristics

Constitutive modeling of rock materials considering the void compaction characteristics

Acoustic emission behavior and damage evaluation of recycled aggregate concrete under compression

Application of recycled coarse aggregate concrete (RAC) will generate considerable environmental benefits. However, the properties of RAC must be studied before being adopted in structures. In this research, the failure process and damage assessment of RAC under compression were investigated by applying acoustic emission (AE) technology. The variables include loading rates, maximum coarse aggregate sizes, and water–cement ratios (w/c). Meanwhile, an innovative approach called stage cumulative proportion (SCP) analysis of AE result was put forward. Subsequently, the damage of RAC under compression was evaluated based on the rate process theory. The results demonstrated that void compaction and original crack expansion occurred first in the test and then the stable microcracking in interfacial transition zone (ITZ) and unstable cracking in mortar, and finally, there is the macrocrack expansion followed by the fracture. It was found that AE counts and energy were mainly produced before the peak stress was reached. The increase in loading rate caused the AE counts and energy to increase in stable microcracking of ITZ but decreased in unstable cracking of mortar. Increasing the w/c would also affect the AE results in these stages, but the effect was the opposite to the loading rate. Besides, an increase in coarse aggregate sizes would increase the AE counts and energy in unstable cracking of mortar and decrease in macrocrack expansion. In addition, a polynomial expression of the relationship between AE parameters and stress level was established. Then, an evaluation criterion was proposed based on the expressions and the rate process theory.

Study on the mechanical properties and damage constitutive model of frozen weakly cemented red sandstone

The freezing method is an effective method for shaft construction in water-rich strata. To determine the mechanical properties of frozen walls that contain ice, study the fracture and instability of frozen rock walls, and solve ice-rock coupling problems, it is necessary to research frozen rock masses under triaxial compressive stress. In this paper, using X-ray diffraction and mesostructure observation, the microstructural characteristics and deformation mechanism of frozen red sandstone specimens taken from the Shilawusu coal mine at a depth of 300 m in the Ordos Basin were studied. A series of tests were performed on frozen red sandstone samples under triaxial compression at 4 temperatures and 4 confining pressures using self-developed DRTS−500 subzero rock triaxial test system. The strength and deformation characteristics of the frozen red sandstone under three-dimensional loading were examined. Test results showed that the bonding water formed by charge adsorption on the surface of the mineral particles and the freezing of pore gravity water enhance the cementation of the mineral particles and the flow plasticity under high stress. At constant temperature, the peak strength and elastic modulus of the frozen red sandstone increase with increasing confining pressure. At constant confining pressure, the peak strength and elastic modulus of the frozen red sandstone increase with decreasing temperature, but temperature has little effect on the peak strain. The internal friction angle of the frozen red sandstone is between 28° and 35° and decreases linearly with decreasing temperature. The cohesion is between 4 and 9 MPa and increases linearly with decreasing temperature. At high freezing temperatures, with an increase in confining pressure, the main factors controlling of the triaxial strength of the rock samples change from the cohesive force to the biting force caused by the mineral particles and ice crystals and the friction between them, and the failure mode of the rock samples changes from tension to shear failure. When the temperature is low, the main controlling factors for sample failure are the cohesive force and friction bite force, and the swelling failure and tension-shear composite failure are the main factors. Based on the parabolic strength criterion and the statistical damage theory derived from the strain equivalence principle, a statistical damage constitutive model that considers the void compaction stage and residual strength deformation stage is established, and the analytical expressions for the model parameters are given, which verify the rationality and validity of the model.

The effect of loading duration on damage initiation in high-strength concrete

The rate sensitivity of the failure strength of concrete and other brittle materials is well documented. However, the underlying mechanism(s) that gives rise to this phenomenon remains a topic of debate. Experimental results suggest that the time-dependent failure process plays a significant role in the observed strength increase. This study investigates the failure process in high-strength concrete (HSC) specimens under uniaxial compression loading. This is accomplished through the use of a modified Kolsky compression bar to apply controlled and repeatable mechanical loading in combination with the non-destructive observation capability of high-resolution X-ray computed-microtomography (micro-CT). The evolution of specimen damage morphology is observed as a result of intermittent short-duration uniaxial stress loadings. Experimental results show that HSC specimens are capable of supporting the applied stress above their quasi-static failure strength for short durations. This duration is found to be a function of the overload stress level. Additionally, micro-CT results reveal that specimens undergo a brief period of void compaction followed by the coalescence and propagation of cracks before completely losing load bearing capability.

Prediction of process-induced void formation in anisotropic Fiber-reinforced autoclave composite parts

A numerical methodology is proposed to predict void content and evolution during autoclave processing of thermoset prepregs. Starting with the initial prepreg void content, the void evolution model implements mechanisms for void compaction under the effect of the applied pressure, including Ideal Gas law compaction, and squeeze flow for single curvature geometries. Pressure variability in the prepreg stack due to interactions between applied autoclave pressure and anisotropic material response are considered and implemented. A parametric study is conducted to investigate the role of material anisotropy, initial void content, and applied autoclave pressure on void evolution during consolidation of prepregs on a tool with single curvatures. The ability of the model to predict pressure gradient through the thickness of the laminate and its impact on void evolution is discussed.

Computational models for simulations of lithium-ion battery cells under constrained compression tests

In this paper, computational models are developed for simulations of representative volume element (RVE) specimens of lithium-ion battery cells under in-plane constrained compression tests. For cell components in the finite element analyses, the effective compressive moduli are obtained from in-plane constrained compressive tests, the Poisson's ratios are based on the rule of mixture, and the stress–plastic strain curves are obtained from the tensile tests and the rule of mixture. The Gurson's material model is adopted to account for the effect of porosity in separator and electrode sheets. The computational results show that the computational models can be used to examine the micro buckling of the component sheets, the macro buckling of the cell RVE specimens, and the formation of the kinks and shear bands observed in experiments, and to simulate the load–displacement curves of the cell RVE specimens. The initial micro buckling mode of the cover sheets in general agrees with that of an approximate elastic buckling solution. Based on the computational models, the effects of the friction on the deformation pattern and void compaction are identified. Finally, the effects of the initial clearance and biaxial compression on the deformation patterns of the cell RVE specimens are demonstrated.

A new material model for concrete in high-dynamic hydrocode simulations

The development of material laws for concrete subjected to highly dynamic loadings is a topic of current research. Explosive charges or high-velocity impacts produce high pressures in the kilobar region within microseconds. Hydrocode simulations by coupling of Lagrangian with Eulerian grids have been carried out, considering the interaction between explosive loading and the structure. Concrete is a composite material with a variety of inhomogenities. By homogenization of the microstructure, a macroscopic approach in the framework of continuum mechanics has been adopted. Appropriate constitutive laws that enable the nonlinear rate-dependent as well as the local damage behaviour to be modelled had to be introduced. A new damage law that describes void compaction as well as the classical theory of plasticity had been taken into account. An equation of state had to be provided to ensure the compliance with conservation laws on which hydrocodes are based. To obtain the necessary material data, experimental investigations were indispensable. Therefore, a series of field tests with specimens which were concrete slabs exposed to explosive contact charges has been conducted.

The influence of a glassy phase on the high strain rate response of a ceramic

Results of pressure-shear plate impact experiments on an alumina ceramic (AD85) containing a significant amount of an oxide glass phase are presented. Under high strain-rate loading, the ceramic shows low shear strength and a strong strain softening behavior. This behavior is attributed to the response of the intergranular glassy phase. The ceramic is modeled by using an atomistic constitutive model for the response of the glass. This model utilizes the concept of free volume. Computations performed using this constitutive model predict a localization of the deformation near the impact end of the specimen and show that the increase in free volume that occurs in the glass during the deformation is responsible for the observed softening response. Void compaction in the AD85 during the compressive loading is also modeled.

Dynamic failure in ductile porous materials

In this paper, a mathematical model of dynamic fracture in porous ductile materials under intense dynamic general loading is developed. The mathematical model includes the influence of inertial effects and material rate sensitivity, as well as the contribution of surface energy of a void and material work-hardening. In addition, the condition of the void compaction is considered as well. The threshold stresses for the void growth and compaction are obtained. A simple criterion for ductile fracture which is associated with material distention and plastic deformation is adopted. As an application of the theoretical model, the processes of two-dimensional spallation in LY12 aluminum alloy are successfully simulated by means of two-dimensional finite-difference Lagrangian code.

Addendum: On the influence of void compaction and material non-uniformity on the propagation of one-dimensional acceleration waves in granular materials

Addendum: On the influence of void compaction and material non-uniformity on the propagation of one-dimensional acceleration waves in granular materials

On the influence of void compaction and material non-uniformity on the propagation of one-dimensional acceleration waves in granular materials

On the influence of void compaction and material non-uniformity on the propagation of one-dimensional acceleration waves in granular materials