Plastic Yield Research Articles

Thixotropic characterisation of slag modified 3D printable metakaolin based geopolymer composite

Geopolymer concrete (GPC) is a substitute for ordinary Portland cement (OPC) in 3D concrete printing for sustainable construction. However, poor structural build-up arising from a slow chemical reaction rate of a two-part GPC is a limitation to buildability. Therefore, slag (0, 5, 10, and 15% by weight of metakaolin), and fibre (0.5% by volume of mix) inclusion in metakaolin (MK)-based GPC composite could improve structural build-up and enhance buildability. This paper presents the rheological thixotropic characterisation of static and dynamic yield stresses, Rthix (re-flocculation rate), and Athix (structuration rate), of slag-modified fibre-reinforced MK-based geopolymer for 3D printing of concrete using an ICAR rheometer at selected resting times of 0 to 2700 s depending on mix behaviour. The printability of the GPC is validated with a 3D concrete print of a 250 mm diameter column for each mix. The results show that the reference, M1, with 0% slag content is more workable than M2 with 5% slag; however, M2 exhibits better thixotropic properties. Slag inclusion in M2 improved the buildability of validated 3D prints by 36% compared to M1. The 3D prints of M1 and M2 columns are buildable up to 27 and 42 layers, respectively, before plastic yield and collapse. Slag inclusion beyond 5% had too little open time than required for printing, leading to a significant and early increase in stiffness and clogging of the printer hose.

Influence of various admixtures on energy absorption characteristics of foam concrete measured using one dimensional strain analysis test

Foam concrete (FC) (a light weight cellular concrete) has recently clutched the interest of military engineering due to its special attributes such as cushioning behavior and energy absorption. However, only a very few investigations on the mechanical performance of FC and its energy absorption characteristics are reported in the literature. This study examines the effects of the addition of polypropylene fibres, fly ash (as filler replacement), and silica fume (as binder replacement) on fresh state features (stability and consistency), mechanical properties, and energy absorption characteristics. The individual and combination effects of various admixtures are studied experimentally. Hingot surfactant was used to produce FC mixes of target density 1000 kg/m3 with water to solid ratio of 0.3. Comparative analysis of various mixes showed that the fiber-reinforced fly ash mix showed the highest mechanical strength due to the bonding of fibres with the matrix, thus demonstrating synergistic behavior. Further, one-dimensional compression strain testing methodology was employed to study the energy absorption characteristics of FC. Experimental outcomes showed that the energy absorption values depend on two important components which are resistance against plastic yield, referred to as ductility, and resistance against damage referred to as the strength of the material. The incorporation of fibres enhanced the ductility of the specimen by acting as a toughening agent, whereas fly ash substitution contributed to enhancement of strength of the specimen due to pozzolanic and filler effects. Hence the combination mix with FA and PP (CMFP) showed significant improvement of 34.6% in energy absorption when compared to control mix.

Enhancement of rheological properties and cutting carrying capacity of water based drilling fluid using Al2O3 nanoparticles

Drilling mud is a necessary component of drilling operations. There have been notable attempts to enhance the filtration and rheological properties and increase the cutting carrying capacity of water-based mud (WBM) using nanoparticles (NPs). This study investigates how varying Al2O3 concentrations affect the rheological properties and cutting carrying capacity of drilling fluids. In this study, different drilling muds were produced using bentonite (2.8g) without nanoparticle, 50% bentonite (1.4g) and 50% Al2O3(1.4) and 0% bentonite(0g) and 100% Al2O3 (2.8g). Testing and comparisons were done on the formed mud samples' physiochemical properties, rheology, filtration properties, and cutting carry index (CCI). The Power Law Model was used to define the rheological behavior of the manufactured mud samples, and results showed that all the mud samples were pseudoplastic fluids and remain a preference for drilling fluids because their flow behavior index (n) was less than 1. It was observed that the addition of Al2O3 is directly proportional to the plastic viscosity, apparent viscosity and yield point and inversely proportional to the gel strength of the drilling fluid. The study also shows that the addition of Al2O3 nanoparticle influences the cutting carrying index CCI as the calculated cutting carrying index gives a high cutting carrying index CCI which means that the hole cleaning potential of the drilling mud is good. The study shows that Al2O3 nanoparticles are feasible for use in drilling fluid formulation.

Evolution of slip partitioning in a major continental margin strike-slip fault system during a transition to oblique plate-margin tectonics: Insight into the evolution of the Garlock fault zone, California (USA)

Abstract The Walker Lane belt and Eastern California shear zone of California, USA, are active, plate boundary–related dextral systems with transtensional and transpressional deformation, respectively. They are separated by the sinistral Garlock fault, creating a complex system without an overall integrated formation and evolution model. We examine the deformation within the eastern segment of the Garlock fault zone over geologic timescales by determining the slip history of faults. We assess the progression of faulting and associated deformation along the WSW-striking Garlock fault zone and how it applies to the overall NNW-directed dextral system. Previous studies found that large synthetic fault strands take up 30% of the slip of the Garlock fault zone and have proposed multiple mechanisms to explore how to accommodate regional NNW-directed shear across the Garlock fault without cutting its trace. We analyze an unstudied section of faulting in one of the more complex areas of regional deformation via compiled and reinterpreted published geologic data for an analysis of total and incremental slip on the main faults of the eastern Garlock fault zone. We identify geologic offset features to interpret total slip, timing, and deformation evolution. We find that 30% of the total slip of the Garlock zone occurs on strands other than the Garlock fault sensu stricto, with the locus of main slip sidestepping during the evolution of accommodation of throughgoing, regional dextral shear. Our results support ideas of the creation and evolution of the regional dextral system via stress concentration on a sub-Garlock lithospheric anisotropy with a resulting lowering of the plastic yield stress. Our results also show an eastward increase in fault system complexity, which may imply an underappreciated seismic hazard of the eastern Garlock fault zone.

Numerical simulation of failure properties of interbedded hydrate-bearing sediment and their implications on field exploitation

Marine natural gas hydrate is widely accepted as a promising substitute energy resource, whereas geotechnical responses of hydrate-bearing sediments (HBS) are crucial for the safe development of natural gas hydrate. The hydrate spatial distribution in sediments is multitype and present different coalescence degrees, its distribution pattern significantly influences the failure behavior of HBS, but the mechanics behind this influence is unclear. Numerical simulations are of great importance in revealing such mechanics. In this paper, a series of numerical simulations, using a modified Mohr–Coulomb (MC) model, were performed to analyze the deformation mechanisms of HBS when the hydrate was laminarly distributed in its host sediment. Considering the vertical heterogeneity of the hydrate distribution, the vertical-laminar hydrate distribution samples were simplified as interbedded samples. The interbedded HBS specimens consisted of three layers: the middle layer with relatively lower hydrate saturation; and the upper and lower layers with relatively high hydrate saturation. Interbedded samples with different hydrate saturations, depressurization ratios, and thickness ratios were designed to analyze their mechanical behaviors. The results indicated that in both the hydrate saturation and thickness ratio of the interbedded samples, the plastic yield area first occurred in the lower hydrate saturation layer; the failure mechanism was mainly determined by the strength of the lower hydrate saturation layer. In addition, the shear failure behavior of the HBS was controlled by the hydrate saturation difference between the middle and upper layers. With a smaller hydrate saturation difference between the middle and upper layers, the samples were more likely to experience shear failure. In the thickness ratio samples, the HBS changed from brittle to ductile failure with an increase in the thickness of the lower hydrate saturation layer. Under different depressurization amplitudes, the larger compression and shear yield zones were mainly confined in the upper layer. This study provides a theoretical framework for controlling the strength-weakening mechanism during natural gas development, which can be used to guide reservoirs characterization, the selection of depressurization schemes, and decomposition zones monitoring.

Determination of ecological plasticity and stability for female components of maize hybrids

Topicality. In Ukraine, a sharp manifestation of unfavorable climate elements for growing hybrid maize seeds, brought to the fore the tolerance of the female components of hybrids to environmental factors limiting the formation of potential yield. Therefore, the study and evaluation of the ecological plasticity and stability of female components are an urgent issue of the modern seed production of maize hybrids. Purpose. To determine the requirements of the female components of maize hybrids to environmental conditions. Materials and Methods. During the research, 20 female components of maize hybrids bred by the SE Institute of Grain Crops of NAAS were used. The female components were single cross sterile hybrids. The methodology of S. A. Eberhart, V. A. Russell, edited by A. Zykin and others, was used. The methodology is based on the calculation of two parameters: the linear regression coefficient bi (ecological plasticity) and the dispersion σd² (ecological stability). Results. The grain yield of the female components was determined in five years of the research. The influence of environmental conditions on the yield of female components of maize hybrids was determined. The female components were distributed according to the requirements for growing conditions. Conclusions. The most valuable, highly intensive female components include sister hybrids Kros253C, Kros256C, Kros247C and Kros238C with high environmental plasticity and stability. To realize the potential yield, they need a high agricultural background under favorable weather conditions. Female components Kros364M and Kros368M with high regression coefficient and root mean square deviation are less valuable because their high plasticity is combined with low yield stability. It is desirable to grow these female components only on a high agricultural background under favorable climatic conditions to get the maximum yield. Hybrids Kros254M, Kros255M, Kros266S, Kros277M, Kros301M, etc., have low environmental plasticity and high yield stability. These hybrids will give maximum returns for minimum costs in extensive cultivation. Keywords: female component, yield, hybrid, adaptation, regression coefficient, root mean square deviation, stability, plasticity

Rubber aggregates' effect on the rheological and mechanical behavior of self-compacting concrete

This research work aims to study the effect of the incorporation of aggregates from the recycling of used tires on the rheological and mechanical behavior of self-compacting concrete (SCC). In this regard, rubber particles with diameters of 0–4 mm were used in the SCC mixture as a partial substitution at 10, 20, 25, and 30% of the volume of sand.The rheological behavior of SCCs based on rubber aggregates is characterized by empirical tests (namely, slump flow, L-box, and V-Funnel) and by measuring the plastic viscosity and yield stress using a concrete rheometer. Furthermore, mechanical behavior is characterized by measuring the compressive strength and the density in the hardened state.Based on the experimental and statistical data, adding more rubber to SCCs makes it more likely that the mixtures will get stuck, making them harder to work with and less resistant to being compressed. Based on this analysis, a suggestion has been made for the best amount of rubber to use so that the mixtures meet the requirements to be called SCC.

Experimental Recognition of Plastic Domain in Contact Problem Based on Full Field Metrology and Neural Network

Contact usually results in stress concentration which can easily cause the yield of materials and structures. The classic elastic–plastic yield criterion needs to utilize stress or strain field for calculation. However, most advanced full-field measurement methods output the displacement as the original data, and the fitting from displacement to strain will induce error accumulation in applications. In this paper, a plastic domain characterization method is developed that can directly judge the elastic–plastic state of materials based on the full-field displacement and neural network. By establishing and training a three-layer-based neural network, the relationship between the displacement and the elastic/plastic stage of the sampling points is modeled. A physical model is formulated based on the yield criterion and embedded in the layer of the network, which can increase the convergence rate and accuracy. Only the displacements of the contact member are required in this method, which can be easily measured by the optical metrologies. The performances of the developed method are carefully discussed through simulated data and real-world tests. Results show that the method can accurately identify the plastic domain during the tests.

Micromechanical controls on the brittle-plastic transition in rocks

SUMMARYThe rheology of rocks transitions from a cataclastic brittle behaviour to plastic flow with increasing pressure and temperature. This brittle-plastic transition is empirically observed to occur when the material strength becomes lower than the confining stress, which is termed Goetze’s criterion. Such a criterion works well for most silicates but is not universal for all materials. We aim to determine the microphysical controls and stress–strain behaviour of rocks in the brittle-plastic transition. We use a micromechanical approach due to Horii and Nemat-Nasser, and consider representative volume elements containing sliding wing-cracks and plastic zones. We find solutions for frictional slip, plastic deformation and crack opening at constant confining pressure, and obtain stress–strain evolution. We show that the brittle-plastic transition depends on the confining stress, fracture toughness and plastic yield stress but also critically on the friction coefficient on pre-existing defects. Materials with low friction are expected to be more brittle, and experience transition to fully plastic flow at higher pressure than anticipated from Goetze’s criterion. The overall success of Goetze’s criterion for the brittle-plastic transition in rocks is likely arising from the low toughness, high strength and medium friction coefficient character of most rock forming minerals.

A three-dimensional constitutive model for shape memory alloy considering transformation-induced plasticity, two-way shape memory effect, plastic yield and tension-compression asymmetry

In this paper, a three-dimensional phenomenological constitutive model for shape memory alloys (SMA) is proposed with consideration given to various thermomechanical mechanisms. This model includes, for the first time in literature, the major mechanisms influencing the behaviors of SMA actuators in a unified thermodynamics framework: transformation-induced plasticity (TRIP), two-way shape memory effect (TWSME), plastic yield as well as tension-compression asymmetry. Furthermore, a new method to address the characteristics of transformation strain varying with stress levels was proposed. Moreover, a new transformation hardening function was proposed which can give a more accurate prediction of the transformation process. The three-dimensional constitutive model is solved using return mapping algorithm for an increment in a material point in the form of strain and temperature increment. The complete algorithm is proposed and the user-defined material subroutine (UMATs) for finite element problem is established. To validate the proposed SMA constitutive model, the parameters of the SMA material are determined through uniaxial tensile tests. The SMA tubes of the same material are used to conduct both experiments and simulation, with tension-compression asymmetry considered. Training experiments and simulations have been carried out on the SMA tubes, with evident TWSME observed. The typical loading conditions to trigger simultaneous transformation and plastic yield were designed, with experiments and simulations performed. According to the results, the SMA constitutive model is effective in capturing the thermomechanical response of SMA structures under various loading conditions.

The Mechanical Characteristics of High-Strength Self-Compacting Concrete with Toughening Materials Based on Digital Image Correlation Technology.

Brittle fracture is a typical mechanical characteristic of high-strength self-compacting concrete, and the research on its toughening modification remains the highlight in the engineering field. To understand the effect of toughening materials (including polymer latex powders, rubber particles, and polyethylene fibers) on the mechanical behavior of C80 high-strength self-compacting concrete under static loading, the failure mode, mechanical strength, strain field, and crack opening displacement (COD) of prepared high-strength self-compacting concrete under compressive, splitting, and flexural loads were studied based on digital image technology (DIC). The corresponding mechanism is also discussed. The results show that the hybrid of polymer latex powders, rubber particles, and polyethylene fibers can increase the crack path and inhibit the development of macrocracks in concrete, thus turning the fracture behavior of concrete from brittle to ductile. The addition of toughening materials reduced the compressive and flexural strengths of high-strength self-compacting concrete, but it increased the splitting strength. DIC showed that the incorporation of toughening materials promoted the redistribution of strain and reduced the degree of strain concentration in high-strength self-compacting concrete. The evolution of COD in high-strength self-compacting concrete can be divided into two stages, including the linear growth stage and the plastic yield stage. The linear growth stage can be extended by incorporating toughening materials. The COD and energy absorption capacity of concrete were enhanced with the addition of toughening materials, and the best enhancement was observed with the hybrid of polymer latex powders, rubber particles, and polyethylene fibers. Overall, this research provides a reference for exploring effective technical measures to improve the toughness of high-strength self-compacting concrete.

Study on the Influence of Gas Hydrate Reservoir Creep on Borehole Wall Deformation

Hydrate decomposition caused by long-time drilling operations will reduce the strength of the reservoir and increase the risk of borehole wall damage. At the same time, the creep characteristics of the hydrate reservoir may also lead to engineering problems such as borehole shrinkage and sticking in the later stage of drilling, which seriously affects the drilling safety. The creep parameters are introduced to explore the influence mechanism of hydrate decomposition, and hydrate-bearing sediment creeps characteristics on wellbore mechanical behavior. The influence law of sediment shale content and hydrate saturation on wellbore stability during hydrate reservoir drilling is analyzed. The result shows the hydrate-bearing sediments creep characteristics will lead to the homogenization of stress distribution in different directions of the hydrate reservoir around the well, make theplastic yield zone shape around the well to circular, and may lead to the overall collapse of the well wall. Drilling for a long time will lead to a greater hydrate decomposition range and plastic yield zone around the well. Lower initial hydrate saturation, smaller sediment strength, and larger initial plastic strain and yield range of the formation. Increase of shale content will enhance the creep characteristics of sediments and aggravate yield degree of formation.

Optimisation of Rheological Properties of Water-Based Mud (WBM) with Natural Additives by Using Response Surface Methodology (RSM)

The rheological properties of drilling muds are critical for achieving optimal performances during drilling operations. In this study, bentonite, tannin, and xanthan gum were utilised as water-based drilling mud additives to enhance the rheological properties. The Response Surface Methodology (RSM) with Box-Behnken Design (BBD) was used to investigate the additive's effect on the rheological properties of the drilling muds. The concentration of bentonite, tannin and xanthan gum were considered as the independent variables, while plastic viscosity (PV), apparent viscosity (AV), and yield point (YP) as the responses in the design of experiment (DOE). The YP, AV and PV were determined using 9.0 ppg of drilling mud according to the API standard procedures. Response surface plots (3D) were used to analyse the effect of the independent factors on the rheological properties and resulting in R2 values of 0.9753 for PV, 0.9582 for AV and 0.9513 for YP, which indicates that the interaction between elements in the system were statistically significant as these R2 values were close to 1.0. Bentonite was observed to significantly increased the PV, AV, and YP, whereas it decreased as tannin concentration increased. The optimal rheological properties required for low PV and AV with a high YP could be achieved using WBM formulation of bentonite at 4.02 g, 7.29 g of tannin, and 0.53 g of xanthan gum. Meanwhile, xanthan gum had an insignificant effect on the PV, AV, and YP. This finding demonstrates that the RSM model is accurate and relevant tool; hence it may be utilised to optimise the experimental conditions of mud formulation and accurately predict the rheology parameters of drilling muds.

Making a Case for Hybrid GFRP-Steel Reinforcement System in Concrete Beams: An Overview

Ageing concrete infrastructures are known to be facing deterioration, especially regarding the corrosion of their reinforcing steel. As a solution, glass fibre-reinforced plastic (GFRP) bars are now considered a reinforcement alternative to conventional steel, and design codes now exist for designing GFRP-RC structures. However, there is a need to improve on addressing the limited plastic yield in GFRPs. Consequently, it is suggested that a hybrid steel–GFRP RC system can enhance the mechanical performance of flexure beams up to the required standard and, at the same time, address the durability concerns of steel-only RC beams. This overview presents the studies conducted to enhance the performance of hybrid GFRP–steel RC beams by reviewing the analytical models proposed to improve the various aspects of reinforcement design. The models consider mechanical effects such as ductility, crack width, flexure and shear, and the physical effects such as thermal stability when exposed to the temperature. Though the evidence reviewed supports the viability of the hybrid GFRP–steel reinforcing system to address ductility, much is still required in the area of research, as highlighted in the future outlook.

Enhancing drilling mud performance through CMITS-modified formulations: rheological insights and performance optimization.

In the context of deep well drilling, the addition of functionalized additives into mud systems becomes imperative due to the adverse impact of elevated borehole temperatures and salts on conventional additives, causing them to compromise their intrinsic functionalities. Numerous biomaterials have undergone modifications and have been evaluated in drilling muds. However, the addition of dually modified tapioca starch in bentonite-free mud systems remains a notable gap within the existing literature. This study aims to examine the performance of dually modified carboxymethyl irradiated tapioca starch (CMITS) under high temperature and salt-containing conditions employing central composite design approach; the study evaluates the modified starch's impact on mud rheology, thermal stability, and salt resistance. The findings indicated that higher DS (0.66) and CMITS concentrations (8 ppb) improved plastic viscosity (PV), yield point (YP) and gel strength (GS), while increased salt and temperature decreased it, demonstrating the complex interplay of these factors on mud rheology. The developed empirical models suggested that DS 0.66 starch addition enhanced rheology, especially at elevated temperatures, demonstrating improved borehole cleaning potential, supported by quadratic model performance indicators in line with American Petroleum Institute (API) ranges. The optimized samples showed a non-Newtonian behavior, and Power-law model fitting yields promising results for improved cuttings transportation with starch additives.

Effect of Raw and Delignified Banana Stem (Musa Cavendish) On the Rheological and Filtration Loss Properties of Water Based Mud

In compliance with environmental laws and safety rules, oil and gas companies have taken necessary steps to eradicate the use of toxic chemicals conventionally used in drilling muds, thereby promoting biodegradable alternatives. This research was carried out to investigate the effect of two banana stem samples; Raw Banana Stem (RBS) and Delignified Banana Stem (DBS) as potential and proficient viscosifiers and fluid loss control agents in water based mud. The rheological properties evaluated include plastic viscosity (cP), apparent viscosity (cP), yield point (Ib/100ft2) and gel strength (Ib/100ft2) at 10 seconds and 10 minutes. Filtration loss properties evaluated include filter cake thickness (mm) and fluid loss volume (ml). Each drilling mud sample was prepared using 350 ml, 20 g bentonite and varying contents (g) of carboxyl methyl cellulose (CMC), RBS and DBS. A mixer was used to mix the mud homogenously; the rheological properties were calculated using a viscometer while the filtration loss properties were calculated using a filter press. The results and analysis were compared to the effects of commercially available carboxymethyl cellulose to validate its properties. RBS and DBS improved the rheological properties of the mud sample contents of 3 g, 5 g, 7 g and 9 g. At contents of 5 g, 10 g, 15 g and 20 g, RBS and DBS samples provide significant fluid loss control and their results are similar to the results of CMC. RBS has a fluid loss volume increase of 6.84 %, 5.69 %, 17.12 % and 8.06 % from CMC’s results at slightly similar filter cake thickness while DBS has a fluid loss volume increase of 15.59 %, 15.09 %, 27.55 % and 15.35 % from CMC’s result. The data obtained from the experiments showed both banana samples can be used as environmentally friendly viscosifiers and fluid loss control agents.

Optimization of Water-Based Drilling Muds Using Dioscorea Villosa Starch: A Response Surface Methodology Approach

The need for environmentally friendly alternatives to water-based drilling fluids has prompted an investigation into the effects of Dioscorea villosa starch as a natural additive in the petroleum and gas industry. In this study, a design of experiments approach utilizing Response Surface Methodology (RSM) through Box-Behnken design (BBD) was employed to optimize the extraction of starch from wild yam (Dioscorea villosa) and formulate drilling muds. The regression model was used to determine the optimized parameters for starch extraction and the results showed a close agreement between the experimental and predicted values with a difference of only 1.295%. The responses considered in the design were plastic viscosity, yield point, apparent viscosity, filtrate volume, and filtercake thickness, with three factors being considered: bentonite, Dioscorea villosa starch, and temperature. The properties of the formulated water-based drilling muds enhanced with Dioscorea villosa starch were analyzed using ANOVA, and linear models were selected based on their significance. The findings suggest that the addition of Dioscorea villosa starch improves the filtration and rheological properties of the drilling muds, with optimal concentrations of 16.92g of bentonite, 3.85g of Dioscorea villosa starch, and a temperature of 81.90°F. Overall, the study demonstrates the potential of Dioscorea villosa starch as a natural additive in water-based drilling fluids, providing an eco-friendly alternative to chemical additives and offering potential environmental benefits.

Deformation and fracture of Cr – Mn – C – N steel in as-cast condition

The paper studies the influence of boundary conditions and the loading rate on the strain behavior and fracture of Cr – Mn – C – N austenitic steel in the cast state without additional heat treatment. Regularities of steel strain and fracture were analyzed on the basis of three-point bending test data of square-section samples with and without a notch, placed with a rib on supports. In addition to the initial stage of the steel elastic strain, this unconventional arrangement of the sample on supports enabled the detection of two more stages of strain development under the effect of an external applied force: the stage of nonlinear strain and the stage of discontinuous strain preceding the moment of sample failure. As the loading rate increases, it was demonstrated that the fracture resistance and the extent of the nonlin-ear strain stage of the sample with a notch increases, and the extent of the discontinuous strain stage decreases. The sample without a notch has a prolonged nonlinear strain stage and exhibits maximum strength in the absence of the discontinuous stage. The end of the nonlinear strain stage corresponds to the moment of sample failure. A characteristic property of cast steel under the given loading conditions is that the fracture of the sample is brittle, despite the prolonged stage of non-linear strain. Structural metallographic and diffractometric studies have shown that in all tests the steel fracture is brittle with-out traces of plastic yield. The nonlinear strain stage of steel is determined not by dislocation plastic yield, but by the mechanism of γ → αʹ transformation in austenitic interlayers between nitride and car-bide particles under the effect of an external applied force. The discontinuous strain stage of steel is associated with the process of stable crack propagation across the sample.

A Study on the Healing Performance of Mortar with Microcapsules Using Silicate-Based Inorganic Materials.

Advancements in material science have led to the development of various self-healing concrete technologies. Among these is the use of microcapsule-based self-healing materials. This study evaluated the effects of self-healing microcapsules on the quality and healing properties of mortar. A silicate-based inorganic material mixture was used as the healing material tested with ordinary Portland cement. Accordingly, the effects of microcapsules (MCs) on the rheological, mechanical, and healing properties of mortar were determined. The mixing of MCs reduced the plastic viscosity and yield stress of the cement composite material owing to the particle properties of the MCs. The reduction was in proportion to the mixing ratio. The evaluation results show that the unit water permeability decreased owing to the healing reaction immediately after crack initiation. The healing rate was more than 95% at 7 days of healing age when more than 3% of MCs was mixed. This study provides a reference for the optimal mixing rate of MCs to achieve an ideal concrete healing rate.

Experimental Investigation and Micromechanical Modeling of Hard Rock in Protective Seam Considering Damage–Friction Coupling Effect

The hard rock in the protective coal seam of the Pingdingshan Mine in China is a typical quasi-brittle material exhibiting complex mechanical characteristics. According to available research on the mechanical property, the inelastic deformation and development of damage are considered related with crack initiation and propagation, which are main causes of the material degradation. In the present study, an original experimental investigation on the rock sample of the Pingdingshan coal mine is firstly carried out to obtain the basic mechanical responses in a conventional triaxial compression test. Based on the homogenization method and thermodynamic theory, a damage–friction coupled model is proposed to simulate the non-linear mechanical behavior. In the framework of micromechanics, the hard rock in a protective coal seam is viewed as a heterogeneous material composed of a homogeneous solid matrix and a large number of randomly distributed microcracks, leading to a Representative Elementary Volume (REV), i.e., the matrix–cracks system. By the use of the Mori–Tanaka homogenization scheme, the effective elastic properties of cracked material are obtained within the framework of micromechanics. The expression of free energy on the characteristic unitary is derived by homogenization methods and the pairwise thermodynamic forces associated with the inelastic strain and damage variables. The local stress tensor is decomposed to hydrostatic and deviatoric parts, and the effective tangent stiffness tensor is derived by considering both the plastic yield law and a specific damage criterion. The associated generalized Coulomb friction criterion and damage criterion are introduced to describe the evolution of inelastic strain and damage, respectively. Prepeak and postpeak triaxial response analysis is carried out by coupled damage–friction analysis to obtain analytical expressions for rock strength and to clarify the basic characteristics of the damage resistance function. Finally, by the use of the returning mapping procedure, the proposed damage–friction constitutive model is applied to simulate the deformation of Pingdingshan hard rock in triaxial compression with respect to different confining pressures. It is observed that the numerical results are in good agreement with the experimental data, which can verify the accuracy and show the obvious advantages of the micromechanic-based model.