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In this study, a novel micromechanics-based damage model is proposed for the damage evolution of a two-component microencapsulated-based self-healing polymer composite. In this way, a representative volume element (RVE) including an epoxy matrix with randomly distributed poly(methyl methacrylate) (PMMA) microcapsules is modeled in DigimatTM software and analyzed in Abaqus®. A new technique is developed to investigate the progressive damage by pre-inserted cohesive elements along all element boundaries of the epoxy matrix, PMMA shell, and capsule-matrix interfaces with the bilinear traction–separation law. Moreover, the impact of interface bonding strength, interface fracture energy, and PMMA microcapsules volume fraction on the load-carrying capacity of the RVEs under uniaxial tension loading was studied. The results indicated that the tensile strength of the self-healing polymer composite increased as the interfacial strength and fracture energy increased from 10 to 60 MPa and 100 to 1000 J/m2, respectively. Furthermore, the higher volume fraction of 5% PMMA microcapsules results in a lower load-carrying capacity of self-healing polymer composite with a strength of 4.9 N. A similar trend of Young's modulus was observed for microcapsule-loaded epoxy composite compared to the pristine epoxy matrix. The micromechanical model has proper accuracy in predicting the tension behavior of self-healing composite in comparison to experimental results. Finally, two healing strategies are considered for the damaged RVE. [ABSTRACT FROM AUTHOR]

Continuous fibre reinforced ceramic matrix composites (CMCs) are increasingly being employed in safety critical applications. As a result, their use in these applications requires the adoption of appropriate design methodologies that are able to consider their complex non-linear mechanical behaviour. In this paper, a simple but robust formulation for continuum damage model, thermodynamically consistent and written under plane stress condition, is proposed for a laminated 2D woven composite material. This model is implemented via the Classical Laminate Theory (CLT) extended to non-linear behaviour to predict the behaviour of different stacking sequences. In-plane tensile tests were performed on an oxide/oxide composite up to 1000 °C to fully identify the model. The procedure is described and used on tests at room temperature before being extended higher temperature tests. Finally, the law and its coupling with the CLT are validated by means of tests on quasi-isotropic and cross-ply laminates at different temperatures. [ABSTRACT FROM AUTHOR]

Peeling wheat yields higher-quality flour. During processing in a flaking machine, wheat kernels undergo continuous compression within the machine's chamber. As this compression persists, damage to the kernels intensifies and accumulates, eventually leading to kernel breakage. To study the damage characteristics of wheat kernels during peeling, this study established a continuous damage model based on Hertzian contact theory and continuous damage theory. The model's accuracy was validated through experiments, culminating in the calculation of critical parameters for wheat peeling. This study focused on different wheat varieties (Ningmai 22 and Jichun 1) and kernel sizes (the thicknesses of the small, medium, and large kernels were standardized as follows: Ningmai 22—2.67 ± 0.07 mm, 2.81 ± 0.07 mm, and 2.95 ± 0.07 mm; Jichun 1—2.98 ± 0.11 mm, 3.20 ± 0.11 mm, and 3.42 ± 0.11 mm). Continuous compression tests were conducted using a mass spectrometer, and critical damage parameters were analyzed and calculated by integrating the theoretical model with experimental data. The test results showed that the average maximum crushing force (Fc) for small, medium, and large-sized kernels of Ningmai 22 was 96.71 ± 2.27 N, 110.17 ± 2.68 N, and 128.41 ± 2.85 N, respectively. The average maximum crushing deformation (αc) was 0.65 ± 0.08 mm, 0.68 ± 0.13 mm, and 0.77 ± 0.17 mm, respectively. The average elastic–plastic critical pressure (Fs) was 50.21 N, 60.13 N, and 59.08 N, respectively, and the average critical values of elastic–plastic deformation (αs) were 0.37 mm, 0.38 mm, and 0.39 mm, respectively. For Jichun 1, the average maximum crushing force (Fc) for small-, medium-, and large-sized kernels was 113.34 ± 3.15 N, 125.28 ± 3.64 N, and 136.15 ± 3.29 N, respectively. The average maximum crushing deformation (αc) was 0.75 ± 0.11 mm, 0.83 ± 0.15 mm, and 0.88 ± 0.18 mm, respectively. The average elastic–plastic critical pressure (Fs) was 58.11 N, 64.17 N, and 85.05 N, respectively, and the average critical values of elastic–plastic deformation (αs) were 0.45 mm, 0.47 mm, and 0.52 mm, respectively. The test results indicated that during mechanical compression, if the deformation is less than αs, the continued application of the compression load will not result in kernel crushing. However, if the deformation exceeds αs, continued compression will lead to kernel crushing, with the required number of compressions decreasing as the deformation increases. If the deformation surpasses αc, a single compression load is sufficient to cause kernel crushing. Since smaller wheat kernels are more susceptible to breakage during processing, the peeling pressure (F) within the chamber should be controlled to remain below the average elastic–plastic critical pressure (Fs) of small-sized wheat kernels. Additionally, the kernel deformation (α) induced by the flow rate and loading in the chamber should be kept below the average elastic–plastic critical deformation (αs) of small-sized wheat kernels. This paper provides a theoretical foundation for the structural design and optimization of processing parameters for wheat peeling machines. [ABSTRACT FROM AUTHOR]

AbstractWhen the stress field in a reinforced concrete element remains homogeneous until cracking occurs, as for example in a tie-rod or a cylindrical vessel under pressure, cracking prediction related to the location of the cracks, remains an open problem. The numerical difficulties involved in arriving at an objective prediction remain problematic. In this paper, we propose a simplified approach to this problem, with the aim of predicting cracking indicators (spacing, opening) on average. The approach is based on a dialogue between a classical calculation leading to a situation of diffuse damage and that of localised cracking described on the basis of the concepts of limit analysis. Applied to the simple case of elements in tension or bending, the procedure works. But above all, it is shown that on the basis of adapted models, certain specific situations such as the gusset between the raft and containment of a nuclear power plant, which is subject to strong expansion-shrinkage effects as the concrete matures, the proposed procedure leads to relevant results. [ABSTRACT FROM AUTHOR]

Background: The formation of stem cell clones enables close contact of stem cells inside. The gap junctions in such clone spheres establish a microenvironment that allows frequent intercellular communication to maintain self-renewal and functions of stem cells. Nevertheless, the essential gap junction protein for molecular signaling in clones is poorly known. Methods: Primary human airway basal cells (hBCs) were isolated from brushing samples through bronchoscopy and then cultured. A tightly focused femtosecond laser was used to excite the local Ca2+ in an individual cell to initiate an internal Ca2+ wave in a clone to screen gap junction proteins. Immunoflourescence staining and clonogenicity assay were used to evaluate self-renewal and functions. RNA and protein levels were assessed by PCR and Western blot. Air–liquid interface assay was conducted to evaluate the differentiation potential. A Naphthalene injury mouse model was used to assess the regeneration potential. Results: Herein, we identify Connexin 25 (Cx25) dominates intercellular Ca2+ communications in clones of hBCs in vitro to maintain the self-renewal and pluripotency of them. The self-renewal and in vitro differentiation functions and in vivo regeneration potential of hBCs in an airway damage model are both regulated by Cx25. The abnormal expression of Cx25 is validated in several diseases including IPF, Covid-19 and bronchiectasis. Conclusion: Cx25 is essential for hBC clones in maintaining self-renewal and functions of hBCs via gap junctions. [ABSTRACT FROM AUTHOR]

AbstractThe traction force of the tracked miner is primarily determined by the shear characteristics of deep-sea sediments. The influence of different parameters on the shear characteristics of deep-sea sediments and the particles change law of the soil–track interface are discussed. By constructing the relationship between the particles horizontal displacement and residual shear strength, a novel shear rheological damage model of deep-sea sediments considering the influence of grounding pressure is proposed, and the microscopic mechanism of shear displacement of deep-sea sediments is explained. The results show that the peak shear strength and residual shear strength increase significantly with the increase of grounding pressure, track length, grouser height and shear speed. Moreover, the particles within the soil–track interface move along the lower right of the vehicle operating direction during the shearing process under different working conditions, the change of particle spacing shows a non-linear trend, and a quantitative equation for the horizontal deformation of soil–track interface under the experimental conditions is constructed. Additionally, the new shear model has a high level of accuracy in fitting with the experimental data, the internal particle migration changes on the soil–track interface can be divided into four characteristics: compaction, failure, deformation and translation. [ABSTRACT FROM AUTHOR]

This study develops a sophisticated three-dimensional elastoplastic progressive damage finite element analysis (FEA) model for stiffened composite materials under axial compression. The model integrates the Hashin and Ye criteria to capture the inception of damage within the composite and introduces a cohesive zone model (CZM) to simulate debonding between stiffeners and panels. Furthermore, damage evolution based on energy release rate and plastic flow rules grounded in Hill’s criteria are employed to thoroughly explore the progressive failure behavior of stiffened composite materials. Implemented within Abaqus/Explicit through user-defined ‘VUMAT’ subroutines, the model ensures computational accuracy and reliability. Comparative evaluations against standard linear elastic progressive damage models demonstrate a statistically significant improvement of at least 5% in predicting ultimate load capacities. Additionally, this model accurately captures different failure modes, providing a nuanced understanding of stiffened composite material failure under compressive loads. [ABSTRACT FROM AUTHOR]

Currently, research on the dynamic damage characteristics of sintered NdFeB is still in its early stages. Previous dynamic mechanical experiments on sintered NdFeB have shown that it is a strain rate-sensitive material. So, it is necessary to establish an appropriate damage constitutive model to describe the dynamic mechanical behavior of sintered NdFeB, with the aim of expanding its practical application range. This paper first establishes a damage evolution model by combining the Weibull distribution with a wing crack propagation model that considers crack spacing. Then, the damage model is integrated with the Zhu-Wang-Tang (ZWT) constitutive model to create the ZWT damage constitutive model. The model is fitted against previous experimental data to determine the specific parameters. Finally, to verify the accuracy of the newly established damage constitutive model, it is compared with the damage constitutive model proposed by Li. The comparison results fully affirmed the accuracy of the newly established ZWT damage constitutive model. [ABSTRACT FROM AUTHOR]

Coal and gas outbursts are complex dynamic disasters closely associated with gas pressure dynamics and coal damage. An experimental system was established to investigate the effects of water injection on coal particles. The experiments utilized helium (He) and carbon dioxide (CO2) gases, at initial pressures ranging from 0.25 to 1.0 MPa and water injection periods ranging from 0 to 12 days, to measure gas pressure variation, particle size distribution, equivalent diameter, and newly generated surface area. The results indicated that outburst gas pressure follows a power-law decay, with He decaying more rapidly than CO2. Elevated gas pressure and adsorptivity intensified coal particle damage: each 0.25 MPa rise in pressure increased the new surface area by 1.02 times for He and 1.28 times for CO2, with the CO2's surface area being 5.03–5.20 times larger than that of He. Water injection mitigated the damage caused by adsorptive gases; as the injection time increased, the new surface area initially decreased and then increased, with the least damage at 6 days. For every 3 day increase in the water injection time, the average surface area of He-fractured coal increases by 0.69 times. A gas pressure decay model and a coal damage model considering pressure differential tension, gas adsorption expansion, and adsorption-induced strain were developed and validated against experimental results. These findings provide theoretical insights into coal and gas outbursts. [ABSTRACT FROM AUTHOR]

The appropriate understanding and formulation of rock discontinuities via FEM is still challenging for rock engineering, as continuous algorithms cannot handle the discontinuities in rock mass. Also, different failure modes of rock samples, containing tensile and shear failure, need to be computed separately. In this study, a novel double-phase field damage model was introduced with two independent phase field damage variables. The construction of the proposed model follows the thermodynamics framework from the overall Helmholtz free energy, with elastic, plastic and surface damage components. The proposed model is calibrated via traditional damage variables, based on ultrasonic wave velocity measurement and acoustic emission monitoring, and both show great consistency between simulation results and laboratory observations. Then the double-phase field damage model is applied to COMSOL software to simulate microcrack propagation in a pre-fractured rock sample. Both lateral and wing cracks are observed in this study, manifested as shear- and tensile-dominated cracks. We also observed different microcracking mechanisms in the proposed numerical models, such as tensile and shear cracking, the influence of plastic strain and the percolation between tensile and shear microcracks. Overall, this study provides valuable insights into the mechanics of microcracking in rocks, and the proposed model shows promising results in simulating crack propagation. Highlights: Developed an elastoplastic double-phase field damage model with separate tensile and shear phase field damage variables. Calibrated the proposed model using ultrasonic wave velocity measurement and acoustic emission monitoring. Simulated microcrack propagation numerically and observed the occurrence of both tensile and shear cracking in rock materials. Investigated the percolation phenomenon between tensile and shear microcracks, considering the influence of plastic strain. [ABSTRACT FROM AUTHOR]

Constant amplitude loading fatigue tests were carried out for 7075/2A12 dissimilar aluminum alloy friction stir welding (FSW) lap joints, and the fatigue fracture characteristics were observed accordingly. Experimental observation suggested that the effective lap sheet thickness had a salient effect on the fatigue strength of the specimen. Specimens tend to fail at the lower sheet thickness under low relatively loading, while fail at the hook root at higher loading. There exists a competition between the two failure cases, and the fracture site changes with loading levels. The stress/strain at the periphery of the weld nugget were discerned by elastic and elasto–plastic finite element analyses respectively, which were then utilized to evaluate the fatigue life by local life prediction approaches and notch stress methods. Two widely used local stress approaches, the Morrow's modified Manson-Coffin (MMC) damage model and the Smith-Watson-Topper (SWT) damage model both could give reasonable results relatively close to experimental lives within the low cycle life regime. The notch stress method could give relatively closer life in the high cycle life regime. [ABSTRACT FROM AUTHOR]

The cortical bone is a hierarchical composite material that, at the microscale, is segmented in an interstitial matrix, cement line, osteons, and Haversian canals. The cracking of the structure at this scale directly influences the macro behavior, and, in this context, the cement line has a protagonist role. In this sense, this work aims to simulate the crack initiation and propagation processes via cortical bone microstructure modeling with a two-dimensional mesh fragmentation technique that captures the mechanical relevance of its constituents. In this approach, high aspect ratio elements are inserted between the regular constant strain triangle finite elements to define potential crack paths a priori. The crack behavior is described using a composed damage model with two scalar damage variables, which is integrated by an implicit-explicit (Impl-Ex) scheme to avoid convergence problems usually found in numerical simulations involving multiple cracks. The approach's capability of modeling the failure process in cortical bone microstructure is investigated by simulating four conceptual problems and one example based on a digital image of an experimental test. The results obtained in terms of crack pattern and failure mechanisms agree with those described in the literature, demonstrating that the numerical tool is promising to simulate the complex failure mechanisms in cortical bone, considering the properties of its distinct phases. [ABSTRACT FROM AUTHOR]

Providing any accurate fracture criteria for composite materials requires consideration of energy dissipation effects at the crack tip due to its quasi-brittle nature. In this paper, a non-local damage model is incorporated into the reinforced isotropic solid (RIS) model for mixed mode I/II fracture assessment of orthotropic materials. In contrast with the local stress, in the non-local stress approach the effects of the fracture process zone (FPZ) can be included into the criterion with defined coefficients. After choosing an appropriate criterion to investigate the growth of micro-cracks, the concept of non-local stress (NLS) is used for developing the mentioned criterion. Due to the formation of the fracture process zone in the matrix of the damaged material, the RIS concept is used as a superior material model to simulate the fracture behavior of orthotropic materials. In RIS model, fibers take part as matrix reinforcements, and their effects are considered as stress reduction coefficients in theoretical investigation. Initial cracks are considered along and perpendicular to the fibers. The concept of crack kinking and growth along the fibers is utilized to develop fracture criterion for cracks perpendicular to the fibers. In comparison with available criteria, this criterion can consider different crack–fiber angles. Combination of the RIS theory with this defined damage coefficient presents a new model for prediction of the properties of damage zone for the cracked orthotropic materials. Fracture envelop curves in comparison with the available experimental results show the capability of the presented criterion in predicting the moment of failure of orthotropic materials. [ABSTRACT FROM AUTHOR]

Tri(1,3-dichloro-2-propyl)phosphate (TDCPP) is one of the most widely used organophosphorus flame retardants in consumer products. TDCPP has been confirmed to be neurotoxic, but its mechanism has not been clarified and may be related to mitophagy. AMBRA1 can promote neurological autophagy, but whether AMBRA1 is involved in the mechanism of TDCPP-induced neurotoxicity has not been elucidated. In this study, the optimal neuronal damage model was established by exposing mice hippocampal neurons to TDCPP. Furthermore, on the basis of this model, siRNA was used to knock down AMBRA1. Combined with qRT-PCR and Western blot techniques, we identified AMBRA1-mediated mitophagy-induced neuronal damage in vitro mechanism. The experimental results indicated that TDCPP treatment for 24 h led to a decrease in the cell viability of mouse hippocampal neurons, causing neuronal damage. Meanwhile, TDCPP exposure increased autophagy marker proteins p62 and LC3B, and down-regulated mitochondrial DNA ND1 damage and TOMM20 protein, suggesting that TDCPP exposure promoted mitophagy. In addition, TDCPP exposure led to changes in the expression of AMBRA1 and the key factors of mitophagy, FUNDC1, PINK1, and PARKIN, whereas mitophagy was inhibited after knockdown of AMBRA1. The research results indicated that exposure to TDCPP induced neuronal damage and promoted mitophagy. The mechanism may be that AMBRA1 promoted mitophagy in neuronal cells through the PARKIN-dependent/non-dependent pathway. This study revealed the toxic effects of TDCPP on the nervous system and its potential molecular mechanisms, which provided important clues for further understanding the mechanism of action of AMBAR1-mediated mitophagy. [ABSTRACT FROM AUTHOR]

We investigate a bivariate replacement policy for a system under shocks effect. A system including two units experiences to one of two types of shocks. Whenever a type I shock arrives, unit 1 has a minor failure which can be removed through a minimal repair; while a type II shock leads to a catastrophic failure of the system. The occurrence probabilities of shock types depend on the number of shocks since the last replacement. Whenever unit 1 suffers a minor failure, it causes some additive damage to unit 2. Once cumulative damage of unit 2 reaches a threshold level L, unit 2 will fail, which will also cause unit 1 to fail at the same time, causing a catastrophic failure of the system. Furthermore, unit 2 whose cumulative damage is x may fail minorly with probability π(x) at the instant of minor failure of unit 1, and requires minimal repair when it fails. It is assumed that the system implements preventive replacement as the system's age reaches T, or the mth type I shock occurs, or corrective replacement as a type II shock occurs or the cumulative damage to unit 2 reaches a threshold level L, whichever comes first. For this model, we derive the formula for the mean cost rate and determine analytically and numerically the corresponding optimal policy. Finally, it is also shown that the policy can be regarded as a generalization of existing policies. This generalization makes our policy more flexible and applicable in real situations than existing policies. [ABSTRACT FROM AUTHOR]

The clearance flow in dry-running vacuum pumps is the main loss mechanism. To reduce the clearance mass flow rate in rarefied gas flows, sawtooth structures transversing to the direction of flow can be utilized. However, due to the sawtooth's structure size, micro-machining is necessary, whereby burr formation is a central challenge. First, the effectiveness of non-idealized sawtooth structures is investigated, demonstrating a high sensibility of the performance regarding the geometry of the tip. Therefore, burr formation in the cutting process must be minimized. For this reason, a 3D finite element (FE) chip formation model capable of predicting the burr formation is developed. An analysis of the burr formation zone showed positive triaxialities; thus, the triaxiality-dependent Johnson–Cook damage model is utilized. To minimize the mesh-induced error, a convergence analysis is conducted, showing no convergence of the maximum burr height. This is caused by the pathological mesh size dependence of local continuum damage models. A comparison of the cutting experiments and simulations revealed a reasonable prediction of cutting forces. In contrast, the passive force is predicted poorly, which is attributed to the underestimation of the ploughing force for non-elastic simulations. The prediction quality regarding the maximum burr height differs for the investigated cutting speeds, which can be explained by a built-up edge and a change in the machine tool compliance. Thereby, an analysis of the burr formation revealed that the burr height is captured by a non-physical remeshing algorithm and that the burr volume might be a more appropriate characteristic. [ABSTRACT FROM AUTHOR]

This paper presents the mathematical derivation and numerical implementation of a novel regularized density-driven damage mechanics (D3M) model for simulating failure in concrete members. The novel idea behind the derivation of the approach is that damage is described as a function of the local change in material density. This choice is justified by the fact that the development of local damage directly corresponds to a reduction in local density since undamaged cementitious composites inherently have a higher density than the fluid or gas that occupies damaged regions. For this reason, devising numerical approaches that can predict the material behavior as a function of density could open up new possibilities for the prediction of the nonlinear behavior of concrete structures, as well as the derivation of novel testing procedures for the evaluation of strength by means of direct and indirect measures of density. In this context, a three-phase mesoscopic representation of concrete material is used, where coarse aggregate, mortar, and the interfacial transition zone are explicitly modeled to obtain a realistic representation of the material internal structure. The manuscript first presents the mathematical derivation of the model, with emphasis devoted to the regularization of the computational implementation. This paper then proceeds to demonstrate that the novel regularized D3M is insensitive to the mesh size chosen to represent the three material phases while also predicting realistic compression-to-tension strength ratios and damage patterns at failure. In addition, a parametric study is carried out to illustrate the effect of the relevant mechanical parameters on the observed response. Finally, the proposed model is validated by comparison with experimental results of 3-point bending tests on plain concrete beams of various sizes, also demonstrating that the regularized D3M is capable of predicting size effect in concrete members. [ABSTRACT FROM AUTHOR]

The prediction accuracy of ductile damage models is subject to a sound calibration strategy, which normally involves the execution of complex multiaxial tests and requires dedicated facilities. In addition, finite element (FE) analysis is mandatory to retrieve the stress and strain states at the critical point, which cannot be directly measured from experiments. To overcome this complexity, a minimal set of simple multiaxial tests is selected, and an analytical‐numerical approach is proposed to evaluate, without resorting to FE, both the stress evolution with plastic deformation and the fracture strain, under any different loading condition of each test. This is achieved from the sole knowledge of the material bilinear stress–strain relation and of the applied test displacement at fracture. The obtained results are compared with a traditional testing and calibration methodology, and the robustness of the approach is proved on a 17‐4PH steel, an X65 steel, and a Ti6Al4V alloy. Highlights: Ductile damage models are calibrated by an analytical approach based on multiaxial tests.Local stress and strain in tests can be calculated from experiments without resort to FEM.Uniaxial and different shear‐tension stress states are investigated.The method works on a wide range of alloys; only test displacement at failure is required. [ABSTRACT FROM AUTHOR]

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Copyright of Acta Materiae Compositae Sinica is the property of Acta Materiea Compositae Sinica Editorial Department and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

This laboratory study employed synthesized urea-formaldehyde (UF) microcapsules and polyvinyl alcohol (PVA) microfibers as a self-healing system to improve the durability of concrete in cold climates. The resistance of concrete specimens to rapid freezingand- thawing (F/T) cycles was evaluated by measuring the change of relative dynamic modulus of elasticity (RDM) with respect to the number of F/T cycles. The control specimens (either with or without PVA microfibers) approached the failure state with a reduction of 38% in RDM after being subjected to 54 F/T cycles, whereas the self-healing specimens (either with or without PVA microfibers) remained in a good state with a reduction of approximately 10 to 15% in RDM after 732 F/T cycles. A polynomial regression model was developed to establish the relationship between the RDM and number of F/T cycles, and a three-parameter Weibull distribution model was employed to conduct the probabilistic damage analysis and characterize the relationship between the number of F/T cycles (N) and the damage level (D) with various reliabilities. The results revealed that the benefits of UF microcapsules and PVA microfibers to the frost durability of concrete diminish once the damage level exceeds a certain high level. Based on the Weibull distribution model, the relationships were established and validated between N and D by comparing the experimental data, the predicted data based on the nonlinear polynomial regression model, and the predicted data based on N-D relationships. The field service life of the self-healing concrete was then predictable at any given reliability. [ABSTRACT FROM AUTHOR]

Silty mudstone distributed in southern China subjected to wet–dry cycling exacerbates the rock deterioration, posing significant challenges to slope stability. This study aims to investigate the damage characteristics and degradation mechanisms of silty mudstone after undergoing multiple wet–dry cycles. The specimen variation was simulated in laboratory under repeated cycles and the degree of specimen degradation across various cycle numbers (N) was evaluated using a combination of geotechnical tests (uniaxial compressive and split tensile tests) and microscopic observations via Scanning Electron Microscopy. Further, the fractal feature was characterized by Box-counting Dimension method implemented in MATLAB, and the damage evolution equation was obtained based on the damage theory. The findings reveal a pronounced decline in mechanical properties and a transition from brittle to shear failure modes with an increase in N, alongside an enhancement in cross-sectional integrity post-damage. Porosity changes notably, with an increased proportion of larger pores post-erosion. The fractal dimension escalates with rising N, with the damage variable and strength degradation rate initially increasing followed by stabilizing. A developed quadratic polynomial damage model exhibits universality for silty mudstone submitted to wet–dry cycling. The degradation mechanism is identified as resulting from cement dissolution and recrystallization, mineral surface hydration, and particle softening and disintegration. [ABSTRACT FROM AUTHOR]

Due to its significant non-linear softening characteristics and its wide variety of use cases, concrete has received considerable attention for the modeling of its mechanical behavior. The non-linear simulation of linear concrete structures is often associated with mesh dependency, the resolution of which requires some form of regularization. While most of the past research has focused on tension energy regularization for better mesh-objectivity, the compression behavior has been partly left out, even though it may have a significant impact for particular applications. By starting from the failed attempt to simulate a pushout test from the literature, this paper focuses on the enhancements brought by the energetic regularization in compression to an isotropic damage model based on Mazars' equivalent strain. The resulting model is applied in three representative case studies where the enhanced mesh-objectivity is shown relative to the load–displacement behaviors and the damage patterns that are produced, and compared to those obtained by the classical model. [ABSTRACT FROM AUTHOR]

This work aims to reveal the effect of rock bridge length (RBL), i.e., 10, 20, 30, or 40 mm, on the fatigue mechanical responses and fracture evolution of marble samples containing stepped fissures under multilevel cyclic loading paths. Comprehensive investigations were conducted on fatigue strength, deformation, damping evolution, and damage propagation. The test results demonstrate that fatigue strength, volumetric deformation, and fatigue lifetime increase as rock bridge length increases. The energy dissipation reflected by the damping ratio indicates that much energy is consumed to drive crack propagation, especially for rock with larger rock bridge segments at the final cyclic loading stage (CLS). An index of strain incremental rate is proposed to predict rock failure development. It is found that volumetric strain rate is a better early warning sign than axial strain rate. Warning time decreases with increasing rock bridge length; it is suggested that rock with large segments has good ability to resist external fatigue loading. [ABSTRACT FROM AUTHOR]

The traditional finite element method (FEM) has limitations in accurately modeling crack propagation. Peridynamics, a nonlocal extension of the classical continuum theory, provides an alternative approach to remedy the limitations of the FEM but with a higher computational cost. In this paper, a peridynamic bond-based fatigue damage model is developed and incorporated into a commercial finite-element software (ABAQUS 2017) via user subroutines. Model-predicted results including the crack path spatial position and the damage accumulation rate were validated against empirical data. The predicted crack growth as a function of loading cycle and crack trajectory showed good agreement with the experimental data over 200,000 loading cycles. Therefore, the integration of the peridynamic bond-based fatigue damage model into existing FEM software provides an economical means to simulate complex fracture behaviors, such as crack growth, in a compact tension specimen examined in this paper. [ABSTRACT FROM AUTHOR]

Researching the mechanical characteristics of concrete subjected to the freeze–thaw cycle is crucial for building engineering in cold climates. As a result, uniaxial compression tests were performed on concrete samples exposed to various freeze–thaw (F–T) cycles, and the measurements of the pore size distribution, porosity, and P-wave velocity of the saturated concrete samples were obtained, both before and after being exposed to the F–T cycles. Concrete's F–T damage mechanism and damage evolution model were thoroughly examined. Using rock structure and moisture analysis test equipment to observe the T2 spectrum, the results showed that the F–T cycles can cause the internal structure of the samples to deteriorate. Porosity and F–T cycles have a positive correlation, although P-wave velocity has a negative correlation with the F–T cycles. As the F–T cycles increased, the specimens' peak strength and elastic modulus steadily declined, while the peak strain clearly exhibited an increasing trend. A microscopic F–T damage model that takes into account the pore size distribution was developed, based on the relative changes in the pore structure distribution (PSD), before and after the F–T cycles. The concrete sample damage evolution law under various F–T cycles was examined using the following metrics: total energy, pore size distribution, static and dynamic elastic moduli, porosity, and P-wave velocity. Uniaxial compressive strength (UCS) and peak strain tests were used to evaluate the accuracy of the pore size distribution damage model, as well as that of five other widely used damage models. [ABSTRACT FROM AUTHOR]

According to wastewater concrete (WWC) specimens of different sizes (L = 40 mm, L = 100 mm, L = 150 mm, L = 200 mm) and different freeze–thaw cycles (FTCs) (N = 0, N = 10, N = 20, N = 30, N = 40, N = 50), the compressive strength (CS) and splitting tensile strength (STS) of specimens with different sizes under different FTCs were tested. After 50 FTCs, the maximum and minimum loss rates of CS of cube specimens were 60.07% and 24.11%, respectively. The maximum and minimum loss rates of STS were 54.76% and 17.42%, respectively. The relationship between the number of FTCs and the size of the specimen on the CS of concrete was obtained, and the damage model of WWC based on damage mechanics theory with the number of FTCs for different specimen sizes was established. Using the fitting method, the strength model of CS and STS for different specimen sizes under FTCs was established. The R2 is 0.9709 and 0.9627, the fitting performance is good, and the freeze–thaw damage (FTD) models can accurately predict the freeze–thaw damage degree of concrete under the coupling effect of FTCs and specimen sizes. [ABSTRACT FROM AUTHOR]

To investigate the impact of freeze–thaw damage on the mechanical properties of concrete, this study utilized Python in combination with ABAQUS 2016 to generate a two-dimensional meso-scale model of concrete. Uniaxial compression tests were conducted on the concrete after freeze–thaw cycles to study the evolution of its mechanical properties. Using "relative compressive strength" as a variable, the relationships between this variable and the parameters of the freeze–thaw damage model were determined, leading to the establishment of the freeze–thaw damage model and the simulation of compressive tests on concrete after freeze–thaw cycles. This study also explored the changes in the mechanical properties of concrete with variations in ITZ parameters and coarse aggregate content. The conclusions drawn are as follows: A comparison with experimental data showed that the model ensures that the relative error of each mechanical property parameter does not exceed 7%, verifying the model's rationality. Increasing the ratio of ITZ parameters improved the mechanical properties of the ITZ, enhancing the overall mechanical performance, but had almost no effect on the elastic modulus. Compared to ratios of 0.7 and 0.8, concrete with a ratio of 0.9 showed slower rates of decrease in compressive strength and elastic modulus and slower rates of increase in peak compressive strain after freeze–thaw cycles. The increase in coarse aggregate content had a similar effect on the strength and freeze–thaw resistance of concrete as the ratio of ITZ parameters. Concrete with a coarse aggregate content of 60% exhibited slower rates of change in mechanical properties after freeze–thaw cycles. [ABSTRACT FROM AUTHOR]

The largest normal stress excursion during contiguous turn time instants of the maximum torsional stress is presented as an innovative path-independent fatigue damage quantity upon the critical plane, which is further employed for characterizing fatigue damage under multiaxial loading. Via using the von Mises equivalent stress formula, an axial stress amplitude with equivalent value is proposed, incorporating the largest torsional stress range and largest normal stress excursion upon the critical plane. The influence of non-proportional cyclic hardening is considered within the presented axial equivalent stress range. Moreover, according to proposed axial equivalent stress amplitude, an energy-based damage model is presented to estimate multiaxial fatigue lifetime upon the critical plane. In order to verify the availability of the proposed approach, the empirical results of a 7050-T7451 aluminum alloy and En15R steel are used, and the predictions indicated that estimated fatigue lives correlate with the experimentally observed fatigue results well for variable amplitude multiaxial loadings. [ABSTRACT FROM AUTHOR]

The use of high-pressure water injection technology in gas-bearing coal seams is an important method for effectively addressing coalbed methane issues. To explore the mechanisms and influencing factors of water injection and permeability enhancement, a model was established based on the theories of unstable seepage and elastic damage in coal and rock mass. Additionally, a mechanical model of elastic damage-based beams was established, taking into account rheological damage, and the mechanical property variation of the surrounding rock in the working face was analyzed. The study included numerical simulations and verification with practical examples. The results suggested that high-pressure water injection could cause damage to the coal body and deformation of the roof, resulting in changes in ground stress, which was a significant contributor to the increase in coal seam permeability. The study showed positive correlations between rheological effects, injection time, injection flow rate, coal seam depth, and the influence range of water injection. Case studies indicated that the long-term influence range of water injection was approximately 60 m, which aligned with field results. The paper introduces a mechanical model for calculating variations in ground stress. This model can help assess the impact of water injection and permeability enhancement, providing valuable insights for related engineering projects. [ABSTRACT FROM AUTHOR]

Firstly, the proposed static test was carried out on eight fly ash foamed concrete walls with different axial compression ratios µ and steel ratios ρ. Secondly, the quantitative analysis method of wall damage was proposed based on the crack development theory, and the real damage index was proposed. Then, through theoretical analysis and curve fitting, two kinds of seismic damage models-- energy method and Park-Ang-W--were proposed, and the damage values were calculated to compare with the real damage values. Finally, the Park-Ang-W model was used to analyze the parameter expansion of 16 Abaqus wall models with different axial compression ratios µ and steel ratios ρ. The results show that the damage evaluation index based on crack development theory can effectively reflect the damage of fly ash foamed concrete walls. The accuracy of the energy method model is not high at the low number of cycles, and the error is less than 20% at the high number of cycles. The Park-Ang-W model has an error of approximately 10% at a high number of cycles, which better reflects the true damage of the specimen. The axial compression ratio µ has little effect on the wall damage, with a maximum effect range of 6.7%. Increasing the reinforcement ratio can effectively reduce the wall damage, with a maximum effect range of 12.6%. The results of the study provide a theoretical basis for the future application of fly ash foamed concrete in construction projects. [ABSTRACT FROM AUTHOR]

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We present a corrosion internal state variable (ISV) damage model based upon the integrated computational materials engineering (ICME) hierarchical multiscale paradigm. Structure–property experiments for magnesium alloys were used where the only inputs were the volume fractions of each element of the periodic table. This macroscale ISV corrosion model finds its basis in Horstemeyer's mechanical damage model, which includes three separate ISVs for damage nucleation, growth, and coalescence, as well as Walton's inclusion of corrosion, which introduces five new ISVs for pit nucleation, growth, and coalescence, along with general corrosion and intergranular corrosion. While Walton's corrosion ISVs are phenomenological in nature, herein we develop a multiscale physical basis for the corrosion ISVs. The parameters for the macroscale corrosion ISVs were garnered from the mesoscale Butler–Volmer equations. Pure magnesium with differing amounts of aluminum were used in corrosion tests to exemplify the different pitting, general corrosion, and intergranular corrosion rates, and the macroscale ISV model was calibrated with said data, in which the only inputs to the model are the volume percentages of the elements magnesium and aluminum. Although magnesium alloys were used to motivate and calibrate the model, the model is abstract enough to possibly capture other material systems as well. [ABSTRACT FROM AUTHOR]

A hierarchical coupled multiscale method is developed to capture the onset and propagation of damage within the three-dimensional four-directional (3D4D) braided composites subjected to bending loading. Using a directly two-scale coupled scheme, the macroscopic nonlinear behavior at the structural dangerous region could be iteratively solved, combined with the progressive damage response of the realistic mesoscale architecture. The continuum damage model is merely defined at the mesoscale and considers failure in each of constituents with the well-established Hashin failure criteria and the Bažant crack band damage model. To accelerate finite element computation in two scales, a parallel numerical implementation is presented alongside the commercial software ABAQUS/Standard. Besides the good agreement between the experimental and the predicted values, the results also show a significant effect of the braiding angle on the bending performance of 3D4D braided composites. With the increase of braiding angle, the bending stiffness and strength of 3D4D braided composites decreases, but the fracture toughness increases. This phenomenon was numerically investigated by identifying the different fundamental failure mechanism and damage development process at both the scales. [ABSTRACT FROM AUTHOR]

To investigate the protective effect of selenated Acanthopanax polysaccharide (Se-ASPS) against D-galactose-induced (D-gal) oxidative damage in mice. The oxidative damage model of mice was established by intrabitoneal injection of D-gal. The mice in the high, medium and low dose groups were supplemented with 200, 100 and 50 mg/kg·bw of selenated Acanthopanax polysaccharide, respectively. The mice were gavaged continuous intragastric administration for 28 days. Changes in body weight and feed intake and organ indices of mice in each group were compared, and HE staining was used to observe liver lesions in mice. Serum, heart, liver, spleen and kidney tissues were analyzed for SOD, CAT, GSH-Px, MDA, AST, ALT using the kit. Compared with the D-gal model group, both selenated Acanthopanax polysaccharide groups significantly increased the body weights of mice (P<0.05), and the selenated Acanthopanax polysaccharide highdose group significantly increased the organ index of mice (P<0.05). HE staining revealed that selenated Acanthopanax polysaccharide could repair the damage caused by D-galactose to mouse liver tissue. The high-dose group of selenated Acanthopanax polysaccharides significantly increased the activities of SOD, GSH-Px, and CAT enzymes in serum, heart, liver, spleen, and kidney tissues of mice (P<0.05), and significantly decreased the contents of MDA, AST, and ALT (P<0.05), with the high-dose group showing the most prominent performance (P<0.01). Se-ASPS can significantly protect the organism against oxidative damage caused by D-gal. [ABSTRACT FROM AUTHOR]

To accurately characterize the damage of rock-like materials under simultaneous or alternating tensile and compressive loading, a dynamic damage constitutive model for rock-like materials based on elastic tensile strain is developed by integrating the classical compressive plastic damage model and the tensile elastic damage model. The model is based on the Holmquist–Johnson–Cook (HJC) and Kuszmaul (KUS) models, categorizing the element stress state into tensile and compressive states through positive and negative elastic volumetric strain. It utilizes elastic tensile strain to enhance the calculation method for tensile cracks, determining the tensile strength of the principal direction based on the contribution rate of tensile principal stress for uniaxial/multiaxial loading. Additionally, it establishes a maximum elastic tensile strain rate function to rectify the model's effect on the tensile strain rate. Through the LS-DYNA subroutine development, the model proficiently delineates the distribution of ring-shaped cracks on the frontal side and strip-shaped cracks on the rear side of the reinforced concrete slab subjected to impact loading. Numerical simulations demonstrate that the model provides more accurate damage prediction results for stress conditions involving simultaneous or alternating compression and tension, offering valuable insights for damage analysis in engineering blasting or impact penetration. [ABSTRACT FROM AUTHOR]

In this study, a constitutive model applied to predict the tensile properties and fracture behavior of well‐bonded multilayered metal composites is extended. The equivalent single‐layer model, as a convenient method, is introduced into finite‐element simulations by combining it with an improved Xue–Wierzbicki damage plasticity model that considers material anisotropy. The steel use stainless (SUS) 430/Al1050/SUS430 laminated sheet fabricated by cold rolling is selected as the research material. The quasistatic uniaxial tests and Nakazima tests are operated to verify the accuracy of the proposed method. The mean errors in tensile stress and fracture forming limit strains are 2% and 3%, respectively. A load‐sharing mixture rule is proposed to assess the effects of the volume fraction, strength coefficient, and hardening exponent of the constituent materials on the mechanical properties of the laminates. In the results, it is indicated that the laminate exhibits sufficient elongation and remains markedly enhanced in tensile strength, reaching 470 Mpa when the ductile Al layer is combined with the higher strength and hardenability steel layer. In this research, it is aimed to clarify the formability characteristics in laminated composites for optimal sheet configuration design and development. [ABSTRACT FROM AUTHOR]

This study reports a novel, eco-friendly; fast and cost-effective microwave method for synthesizing carboxymethylated graphene oxide (CMGO) from sugarcane residues. Fourier-transform infrared spectroscopy (FTIR) confirmed successful CMGO synthesis through the presence of characteristic peaks at 1567.93 and 1639.29 cm−1 (COONa vibrations) and increased CH2 intensity compared to unmodified graphene oxide (GO). Furthermore, CMGO derived from sugarcane residues demonstrated potential in mitigating the side effects of toxic materials like carbon tetrachloride (CCl4). Treatment with CMGO partially reduced elevated levels of liver enzymes (ALT and AST) and nitrogenous waste products (urea and uric acid) in CCl4-induced liver damage models, suggesting an improvement in liver function despite ongoing cellular damage.This work paves the way for a sustainable and economical approach to produce functionalized graphene oxide with promising biomedical applications in alleviating toxin-induced liver injury. [ABSTRACT FROM AUTHOR]

Summary: Near‐field ground motions with fling‐step and forward‐directivity characteristics contain large‐amplitude pulses in velocity history, causing severe damage to stilted buildings in mountainous areas. In this study, three groups of 20 near‐field ground motions with fling‐step and forward‐directivity characteristics and 10 far‐field ground motions were selected as seismic inputs. Nonlinear response history analysis (NLRHA) was performed on plane finite element models of two seven‐story stilted frame structures, one with steel braces in the stilted story and the other without steel braces in the slope direction. Structural seismic response obtained from NLRHA was discussed in terms of inter‐story drift ratio (IDR) and peak floor acceleration (PFA). In addition, damage to two structures was assessed using the modified Park–Huang damage model. The results show that stilted structures exhibit greater inter‐story ratios and damage index values under near‐field ground motions with fling‐step characteristics and forward‐directivity characteristics than far‐field ground motions, where the stilted story has the highest amplification ratio in both IDR and damage index among floors. Designers should pay sufficient attention to the influence of ground motions with fling‐step and forward‐directivity characteristics on seismic demands and damage to stilted structures. The peak inter‐story ratio and damage index of stilted structures with steel braces were significantly lower than that of stilted structures without braces, proving the validation of setting steel braces on reducing the seismic demands of stilted structures and improving structural seismic safety. Additional NLRHA performed using artificial pulses shows that the seismic response of stilted buildings is related to pulse periods of near‐field ground motions and the greatest seismic demands and damage are obtained when the pulse period is 1.5–1.6 times the fundamental period of the stilted building. [ABSTRACT FROM AUTHOR]

In instances of impact, the preeminent load-bearing framework for on-board hydrogen storage cylinders manifests in the carbon fiber reinforced polymer (CFRP) composite layer. Investigating the morphology of impact and elucidating the mechanism governing damage evolution in CFRP is crucial for optimizing the impact resistance of the cylinder. In this work, impact tests were performed on CFRP laminates with six types of interlaminar mismatch angles, under varying impact energies. The impact damage of laminates was characterized using an extended depth-of-field 3D microscopy. A numerical model, implemented in ABAQUS/Explicit, was devised to scrutinize the mechanical properties and damage mechanisms in laminates. A subroutine (VUMAT) was crafted to effectively predict intralaminar damage, while the application of a bilinear cohesive model served to capture interlaminar damage. In addition, this study delves into the ramifications of impact energy and interlaminar mismatch angles. The results reveal that the increase of impact energy leads to more irreversible damage and energy dissipation within laminates. Compared to damage depth (D) and cross-sectional area (A c), the assessment of damage volume (V) and surface area (A s) are more reflective of energy dissipation in laminates. The laminates with mismatch angle of 0° and "helicoidal" lay-up sequence exhibit the worst impact resistance. Within the range of 24°–90°, laminates with a smaller interlaminar mismatch angle demonstrate better impact resistance. These findings lay the groundwork for optimizing the composite layer to enhance the impact resistance of hydrogen storage cylinders. [Display omitted] • The damage surface area and volume were used as new characterization parameters. • A user-defined subroutine VUMAT involving intralaminar damage model was developed. • The mechanical response and damage mechanism of CFRP laminates were studied. • Effects of impact energy and interlaminar mismatch angle were investigated. [ABSTRACT FROM AUTHOR]

Simple Summary: Diabetic male reproductive damage is a prevalent complication of type II diabetes, prompting a multitude of experimental investigations. However, the use of mammalian models for studying diabetic reproductive damage is expensive and raises ethical concerns. Hence, the identification of alternative animal models is imperative. The scientific community is increasingly recognizing the use of silkworms Bombyx mori as animal models, primarily because of their numerous advantages, including low cost and fewer ethical concerns. This study established a type II diabetic silkworm model via a high-glucose diet. The impact of diabetes on the reproductive system of male silkworms was observed, confirming the potential for using silkworms to create a model for diabetic reproductive damage. The increasing prevalence of diabetic reproductive complications has prompted the development of innovative animal models. The use of the silkworm Bombyx mori as a model for diabetic reproductive damage shows potential as a valuable research tool. This study employed silkworms as a novel model to investigate diabetic reproductive damage. The silkworms were fed a high-glucose diet containing 10% glucose to induce a diabetic model. Subsequently, the study concentrated on assessing the influence of diabetes on the reproductive system of male silkworms. The results indicate that diabetes resulted in reduced luteinizing hormone (LH) and testosterone (T) levels, as well as elevated triglyceride (TG) levels in male silkworms. Moreover, diabetes mellitus was associated with pathological testicular damage in male silkworms, accompanied by decreased glutathione peroxidase (GSH-Px) and superoxide dismutase (SOD) levels, along with increased malondialdehyde (MDA) levels in the testis. Additionally, diabetes mellitus reduced the expression of siwi1 and siwi2 genes in the testis of male silkworms. Overall, these results support using silkworms as a valuable model for studying diabetic reproductive damage. [ABSTRACT FROM AUTHOR]

Exhaust manifolds in diesel engines undergo continuous thermal cycle loading of varying thermal cycles with different mean, amplitude, and rate of temperature change created by application duty cycles. This makes analysis and testing of the exhaust manifold to meet the thermal mechanical fatigue life expectation of different applications challenging. In this paper, a simulation-based product development approach, which uses application duty cycles, simulation models of different capabilities, including three-dimensional Finite element simulation model, one-dimensional (1D) physis-based damage model to develop an abusive thermal cycle engine test for validating exhaust manifold, is presented. [ABSTRACT FROM AUTHOR]

In the present study, the fatigue crack growth life of standard and smooth notched specimens containing residual stresses are evaluated based on the continuum damage and fracture mechanics approaches. It is indicated that fatigue crack growth lives assessed by the continuum damage model are closer to the experimental results, with a difference of <10% in the specimens containing residual stresses. The total stress intensity factor range is used to consider the effects of residual stresses in the estimation of fatigue crack growth life based on the fracture mechanics. It is found that in existing residual stresses, the stress intensity factor K is not a proper parameter to evaluate crack tip zone. Fatigue crack initiation life is experimentally obtained based on assessing variations of the slope of unloading curve in the force-displacement diagram of fatigue experiments. The cycle including a change in the slope is considered as fatigue crack initiation event. Isotropic and kinematic hardening parameters of ASTM A516 pressure vessel steel are considered in finite element analyses. Tensile residual stresses are introduced into the notched specimens by employing four-point-bending with a magnitude of around 90% of the yield stress of the material. The results indicate that at least 65% of the fatigue life of the specimens is decreased due to the presence of tensile residual stresses. Tensile residual stresses are measured using the hole-drilling technique. [ABSTRACT FROM AUTHOR]

In practical applications, TiNi shape memory alloys (SMAs) exhibit behavior that can pose a challenge with current constitutive models and their implementations in finite element method (FEM) software. TiNi SMA devices typically operate in the forward or reverse martensitic transformation regime, which is known as subloop loading. During such cyclic loading–unloading, the hysteresis stress–strain loop changes because of material damage, which can be considered the fatigue of TiNi SMAs. During both the loading and unloading processes, the stress plateau decreases. At the same time, the accumulated (residual) martensitic transformation strain increases. In this study, the experimental investigation results and observations of the aforementioned phenomena are presented. Next, the phase-field damage model is employed, along with a modified Lagoudas constitutive model, to simulate the change in stress–strain hysteresis. Furthermore, a fatigue function is used to simulate the accumulation of martensitic transformation strain. The experimental stress–strain response is compared with the simulation results, and good quantitative and qualitative agreement is obtained. The damage and martensitic volume fraction with respect to strain are discussed for full-loop and subloop loading. The observations and conclusions, as well as open questions, are presented. Possible directions for future research are provided. [ABSTRACT FROM AUTHOR]

Liquid nitrogen (LN2) can be utilized in the development of enhanced geothermal systems, as well as for deep/ultra-deep hydrocarbon reservoir stimulation, fire suppression, and other high-temperature geological projects. It is a crucial issue in the utilization of LN2 to investigate the pore structure evolution, permeability, and damage characteristics of high-temperature rocks under the influence of LN2 cooling shock. These rocks were first slowly heated to 150∼600°C and held for 2 h, followed by LN2 or natural cooling. The evolution of pore volume in high-temperature rocks affected by liquid nitrogen cooling was quantified. T 2 cutoff values were determined through centrifugal tests, while the contents of irreducible and mobile fluids were estimated. Based on the aforementioned analysis as well as changes in irreducible fluid saturation, pore throat, tortuosity, and permeability, this study examines the closure and development of pores along with permeability behavior. The findings suggest that, despite a more pronounced decrease in porosity at lower heating temperatures, LN2 cooling specimens exhibit superior pore connectivity and permeability compared to those cooled naturally. LN2 stimulation not only induces crack initiation and propagation but also results in further cooling induced densification based on heating densification. 225°C is considered to be the optimal temperature for cooling contraction induced densification in this study. At higher heating temperatures, the damage to rock cooled with LN2 is more severe than that of naturally cooled. This results in a greater increase in porosity, movable fluid content and proportion, and permeability of LN2 cooled specimens compared to naturally cooled specimens. The damage mechanism can be better understood by the constructed damage model that coordinates the pore increase/decrease and mutual pore transformation from the perspective of pore evolution. [ABSTRACT FROM AUTHOR]

We applied physics-informed neural networks to solve the constitutive relations for nonlinear, path-dependent material behavior. As a result, the trained network not only satisfies all thermodynamic constraints but also instantly provides information about the current material state (i.e., free energy, stress, and the evolution of internal variables) under any given loading scenario without requiring initial data. One advantage of this work is that it bypasses the repetitive Newton iterations needed to solve nonlinear equations in complex material models. Furthermore, after training, the proposed approach requires significantly less effort in terms of implementation and computing time compared to the traditional methods. The trained model can be directly used in any finite element package (or other numerical methods) as a user-defined material model. We tested this methodology on rate-independent processes such as the classical von Mises plasticity model with a nonlinear hardening law, as well as local damage models for interface cracking behavior with a nonlinear softening law. In order to demonstrate the applicability of the methodology in handling complex path dependency in a three-dimensional (3D) scenario, we tested the approach using the equations governing a damage model for a three-dimensional interface model. Such models are frequently employed for intergranular fracture at grain boundaries. However, challenges remain in the proper definition of collocation points and in integrating several non-equality constraints that become active or non-active simultaneously. As long as we are in the training regime, we have observed a perfect agreement between the results obtained through the proposed methodology and those obtained using the classical approach. Finally, we compare this new approach against available standard methods and discuss the potential and remaining challenges for future developments. [ABSTRACT FROM AUTHOR]

The deterioration of the mechanical properties of gypsum due to water–rock reactions has attracted extensive attention in the areas of structural geology and civil engineering, and accurately predicting variations in the mechanical behavior of gypsum under different engineering conditions presents a challenging yet intriguing endeavor. In our study, we conducted experimental investigations of the influence of water–rock reactions on the mechanical behavior and mechanisms of gypsum-bearing mudstone. Subsequently, we constructed a mechanical damage model to predict the behavior under varying dissolution times. During the water–rock reaction, water dissolves substances along crystal interfaces and mineral joint surfaces, changing the way particles contact each other, weakening the contact strength, creating intergranular solubility pores, and causing an increase in porosity, all of which lead to a decrease in the mechanical strength of gypsum–containing rocks. The experimental results showed that the maximum decrease in peak strength and cohesion of the samples with the increase in porosity was 69.68% and 79.02% after the water–rock reaction, respectively, and the internal friction angle showed a small fluctuation change with increasing porosity. The maximum increase in elastic modulus and peak strength with increase in confining pressure was 34.21% and 37.10%, respectively. In addition, for samples with different shapes and spatial locations of weak zones due to water–rock reactions, there is no clear relationship between the change of elastic modulus and the porosity of the samples. By constraining the peak strength and peak deformation, the established gypsum-bearing mudstone constitutive model was accurate and flexible. Comparing the established damage constitutive model with measurements, we found that the developed damage constitutive model is compatible with the measured data during the damage evolution process of water–rock reactions over long periods and can play a predictive role. This study has laid an important foundation for research on the evolution of gypsum mechanical properties and model construction under water–rock reactions. Highlights: Extensive indoor dissolution tests and mechanical tests are conducted. The damage mechanism of gypsum-bearing mudstone under water–rock reactions is explored. The variation of rock mechanical parameters under water–rock reactions is obtained. A widely applicable constitutive model is developed [ABSTRACT FROM AUTHOR]

Electric impulse drilling (EID) technology has great industrialization potential since it has unique advantages in crushing hard rocks of deep formation. To study the mechanism of dielectric breakdown is of great significance for accelerating the practical application of EID technology. In this paper, the dielectric breakdown damage model (DBDM) is established based on the heterogeneous granite model. On the basis of DBDM, the whole process of absolute dielectric breakdown (ADB) is studied, including the formation of the plasma channel and the variation of the electric field. Then, the mechanism of regional dielectric breakdown (RDB) development to ADB is studied, and the influence of peak voltage, electrode spacing and the parameters of a high-voltage electric pulse (HVEP) is discussed. Besides, the efficiency of two dielectric breakdown modes is evaluated. It is found that dielectric breakdown will only occur in the domain where the strength of the local electric field formed by HVEP exceeds the critical breakdown field strength of rock. RDB will occur when the pulse duration is too short or the peak voltage is too low. It is worth noting that RDB can be developed into ADB under multi-HVEPs. Moreover, under the same voltage, there is almost no difference between the failure volume caused by RDB under multi-HVEPs and ADB under a single HVEP. However, the energy consumption of the RDB under multi-HVEPs decreases exponentially with increasing voltage and is always higher than that of the ADB under a single HVEP. When designing the supporting tools and bits of EID technology, the life of insulation, the characteristics of formation, and energy utilization should be fully considered. The related research in this paper aims to provide reference and guidance for the application of EID technology in drilling engineering. Highlights: The variation of the electric field, the change of minerals and the generation of plasma channel in granite during dielectric breakdown is studied. The effect of the characteristics of high-voltage electric pulse (HVEP) on the dielectric breakdown in granite is studied. The mechanism and rock-breaking efficiency of absolute dielectric breakdown (ADB) and regional dielectric breakdown (RDB) are explored. [ABSTRACT FROM AUTHOR]