Modulus Peak Research Articles

Nonlinear viscoelasticity of filamentous fungal biofilms of Neurospora discreta

The picture of bacterial biofilms as a colloidal gel composed of rigid bacterial cells protected by extracellular crosslinked polymer matrix has been pivotal in understanding their ability to adapt their microstructure and viscoelasticity to environmental assaults. This work explores if an analogous perspective exists in fungal biofilms with long filamentous cells. To this end, we consider biofilms of the fungus Neurospora discreta formed on the air-liquid interface, which has shown an ability to remove excess nitrogen and phosphorous from wastewater effectively. We investigated the changes to the viscoelasticity and the microstructure of these biofilms when the biofilms uptake varying concentrations of nitrogen and phosphorous, using large amplitude oscillatory shear flow rheology (LAOS) and field-emission scanning electron microscopy (FESEM), respectively. A distinctive peak in the loss modulus (G″) at 30–50 % shear strain is observed, indicating the transition from an elastic to plastic deformation state. Though a peak in G″ has been observed in several soft materials, including bacterial biofilms, it has eluded interpretation in terms of quantifiable microstructural features. The central finding of this work is that the intensity of the G″ peak, signifying resistance to large deformations, correlates directly with the protein and polysaccharide concentrations per unit biomass in the extracellular matrix and inversely with the shear-induced changes in filament orientation in the hyphal network. These correlations have implications for the rational design of fungal biofilms with tuneable mechanical properties.

Mechanical properties and regulatory strategy of twinned tetrahedral lattice structures

Given the outstanding mechanical performance of lattice metamaterials, novel structural forms and performance modulation strategies have garnered considerable attention. Herein, we develop a twined tetrahedral lattice structure (TTL) with a bending defect inside the unit cell. Mechanical properties before and after the introduction of defects in TTLs were studied using experiments and numerical simulations. The developed structure exhibits strictly stretching-dominated properties in the absence of bending defects. Whereas, the bending-dominant component of TTLs is elevated with increasing bending angle that can increase energy absorption efficiency. Moreover, the relative elastic modulus and initial peak stress can be reduced by even more than 70 % and 50 %, respectively, as the bending angle increases. Besides, a theoretical model for the relative elastic modulus of TTL at θ = 0° was established based on the displacement method on the Representative Volume Element (RVE), including both Euler-Bernoulli beam theory and Timoshenko beam theory. However, the two solutions show consistent results for strictly stretching-dominated structures. The accuracy of solutions is verified by experiments and simulations. The plateau stress theoretical model for TTLs was derived from the deformation process of the RVE based on plastic hinge theory. The theoretical solutions under different θ align well with numerical and experimental results. Overall, TTLs have superior relative elastic modulus, relative yield strength, and specific energy absorption compared to common lattice structures. The developed TTLs provide a new perspective on the property regulation of mechanical metamaterials.

Stress stress-strain behavior of hydraulic filled coral sand subjected to internal erosion

Coral sand foundations lose fine particles under the action of groundwater infiltration. As the soil skeleton structure deteriorates, the foundation becomes uneven and may even collapse. In this study, a triaxial drainage shear test of coral sand is used as a quantitative control method for the loss of fine particulate soil, and the effect of internal erosion on the mechanical behavior of coral sand is evaluated. An experiment is used to demonstrate that erosion leads to a decrease in the peak shear strength and residual strength of coral sand. Erosion has different effects on coral sand with different fine particle contents, and the effects on the friction angles of coral and terrestrial sand are also different. The secant modulus E50 and peak secant modulus Ep gradually decrease as the loss of fine particles increases. The effect of fine particle loss on the peak secant modulus Ep is significant at fine-particle losses exceeding 10% for a fine-particle content of 20%. The loss of fine particles creates new pore spaces in the coral sand, which, in turn, affects the stability of the original soil skeleton. Erosion has been shown to have an effect on the gradational features of coral sand, leading to the phenomenon that the dilatancy effect increases as a function of the amount of erosion that takes place. To prevent uneven foundation settlement caused by subsurface erosion in engineering designs, it is important to consider the gradation characteristics and fine particulate content of coral sand, which affect the stability of coral reef foundations.

Mechanical behavior of carbon/glass polypropylene hybrid composites

AbstractThis research investigates the influence of graphene and some additives on the mechanical behavior of polypropylene (PP). Anhydride maleic coupling agent (MAPP), graphene nanoplatelets (GNPs), and glass fiber (GF) were incorporated into the polymer matrix. The incorporation of MAPP and/or GNP significantly improved the affinity between the PP matrix and fibers while altering the surface morphology. More than 60% of the fibers showed a dimension lower than 0.5 mm. The tensile strength increased from 27.45 to 41 MPa for the neat PP compared to one of the composites. The strength modulus varied from 0.5 to 0.9 GPa. Mechanical tests showed that the addition of MAPP improved the tensile toughness (from 27.45 to 41 N mm mm−2) by 49%, while the GF increased tensile strength, albeit reducing elongation at break. The dynamic mechanical thermal analysis uncovered distinct behavioral variations among fiber‐reinforced samples, particularly in modulus peak differences. In rheological assessment, the presence of GF notably increased viscosity within certain shear rate ranges (at 100 [1/s], the viscosity goes from 200 to 300 Pa s to neat PP for some composites). This research highlights how chosen additives can influence a PP homopolymer's properties, offering useful insights for practical material processing and design.Highlights MAPP and GNP can increase PP and glass fiber interfacial bonding. Glass fiber raises tensile strength and decreases elongation. Sample with just GNP has a rougher surface, implying better energy dissipation. Glass fiber raises viscosity in the observed shear rate ranges. DMA demonstrates that MAPP and GNP have an influence on energy dissipation.

Impact of Diverse Rainfall Patterns and Their Interaction on Soil and Water Loss in a Small Watershed within a Typical Low Hilly Region

Assessing the impact of varied rainfall patterns on soil and water loss within a hilly watershed over an extended temporal scope holds paramount importance in comprehending regional runoff and sediment traits. This study utilized continuous rainfall and sediment data spanning from 2013 to 2021, and the K-means clustering method was employed to analyze rainfall types. Subsequently, the rain-type characteristics underwent further analysis through LSD, and a multiple linear regression equation was formulated. The result showed that: within the Qiaotou small basin, rainfall, maximum rainfall intensity within 30 min (I30), and rainfall erosivity exhibited notable effects on sediment yield and loss. The water-sediment attributes of 305 rainfall events were characterized by rainfall below 100 mm, I30 of less than 35 mm/h, a runoff coefficient below 0.5, and sediment content under 0.6 g/L. According to the characteristics of different rainfall types and the degree of influence on water and sediment in small watersheds, 305 rainfall events in the basin were divided into three types by the K-means clustering analysis method: A (heavy rainfall, moderate rain), B (small rainfall, light rain), and C (medium rainfall, heavy rain). The most frequent rain type observed was B, followed by C, while A had the lowest frequency. Despite the lower intensity of B-type rainfall, it holds significant regional importance. Conversely, C-type rainfall, although intense and short, serves as the primary source of sediment production. The multiple regression equation effectively models both sediment yield modulus and flood peak discharge, exhibiting an R2 coefficient exceeding 0.80, signifying significance. This equation enables the quantitative calculation of pertinent indicators. Sediment yield modulus primarily relies on sediment concentration, runoff depth, and rainfall, while peak discharge is significantly influenced by runoff depth, sediment concentration, and I30. Furthermore, the efficacy of various soil and water conservation measures for flow and sediment reduction correlates with I30. Overall, the impact of different measures on reducing flow and sediment increases with a higher I30, accompanied by a reduced fluctuation range.

Investigation of optical, dielectric, and conduction mechanism in lead-free perovskite CsMnBr3.

Metallic perovskites have advantageous optical and electrical properties, making them a valuable class of semiconductors for the manufacturing of solar cells. CsMnBr3 is notable among them due to its important optical characteristics. The electrical and dielectric characteristics as a semiconductor are examined in this study. Direct transitions with a 3.29 eV bandgap and an Urbach energy of 0.96 eV are revealed by the results. Through AC conductivity, it demonstrated semiconductor characteristics at 443 K. The dielectric loss varied with frequency and peaked at high frequencies. Furthermore, as temperature rose, a relaxation peak in the electrical modulus was seen to migrate to higher frequencies. Ac conductivity is described by the double power law expression. The conduction in our compound is governed by small polaron tunneling. Based on the optical results reported in the bibliography for this sample, we realize the importance of examining the electrical characteristics to comprehend the semiconductor behavior of CsMnBr3.

Influence of Zn-substitution on structural, magnetic, dielectric, and electric properties of Li–Ni–Cu ferrites

The polycrystalline Li0.15Ni0.6-xZnxCu0.1Fe2.15O4 ferrites are fabricated by the method of conventional solid-state reaction technique. The X-ray diffraction (XRD) confirms that the structure of the composition is a single-phase cubic spinel structure for all samples. The particle size of the compositions is varied from 36 to 52 nm. The lattice parameter and densities are found to increase with enhancing Zn content, as the ionic radius and atomic weight of Zn are greater than Ni. The porosity exhibits a decreasing trend. The average grain size determined using Field Emission Scanning Microscopy (FESEM) increases until x = 0.40, then declines. The Energy-Dispersive Spectroscopy (EDS) examination revealed that the percentage of obtained elements is well matched with the stoichiometric elements. The addition of Zn content acts as an accelerator for enhancing the value of the real part of initial permeability and the highest value is obtained (μiʹ = 276) for the x = 0.40 sample, as well as the highest relative quality factor (RQF) of around 3000. The loss factor for the Zn substituted composition is nine times lower than for the parent composition. The optimum saturation magnetization of around 77.49 emu/g is found for the x = 0.40 sample. The maximum dielectric constant (εʹ = 2.85 × 103) is found for x = 0.10 samples at 10 kHz. Further, from impedance studies, the non-Debye type dielectric relaxation is seen for the Zn-substituted samples. The observed region of the imaginary electric modulus peak signifies the transition of charge carrier mobility from a larger range to a short-range distance. The phenomenon of ac conductivity is attributed to the process of the small polaron hopping mechanism.

Effect of Cobalt Doping on Structural, Morphological, Magnetic, Electrical, and Optical Properties of (Ba0.7Sr0.3)0.98Ca0.02Ti1−XCoxO3 Ceramics for Device Applications

Considering the multifunctional performance, the (Ba0.7Sr0.3)0.98Ca0.02Ti1−xCoxO3 (x = 0.00–0.2) ceramics are successfully synthesized using the traditional solid‐phase reaction method. The effect of cobalt doping on the samples’ structural, morphological, magnetic, electrical, and optical characteristics is elucidated. Raman spectroscopy and X‐ray diffraction data confirm the dopants’ integration into the cubic perovskite microstructure. At room temperature, the magnetization–magnetic field intensity hysteresis loops from vibrating sample magnetometer reveal the samples’ ferromagnetic character, with a maximum magnetization of 0.091 emu g−1 achieved for x = 15%. The real part of the initial permeability demonstrates that the replacement of Co2+ causes a shift in resonance toward higher frequencies above 85 MHz, indicating the potential of the synthesized ceramics for high‐frequency magnetic applications. The variation in dielectric characteristics from 100 Hz to 10 MHz is explained using electron hopping on octahedral sites and Maxwell–Wagner's model. The increase of AC conductivity in the high‐frequency region is consistent with the strengthening of the grain effect on the conduction mechanism, which supports the small‐range polaron‐hopping theory. The complex electric modulus's peak (M′′) shifts toward a higher‐frequency region with cobalt content, suggesting a reduction in the relaxation rate. The optical bandgap is observed to decrease from 3.08 to 2.96 eV with cobalt content.

Anisotropic structure-property relations of FDM printed short glass fiber reinforced polyamide TPMS structures under quasi-static compression

Triply minimal surface structures of short glass fiber reinforced polyamide with different relative densities were prepared and the effects of induced anisotropy, cell topology, and relative density on the compressive properties were evaluated. Schwarz Diamond, Schoen Gyroid, and Schwarz Primitive structures were 3D printed with relative densities ranging from 0.2 to 0.4, and compression properties along the axial and lateral build directions were determined. Gipson-Ashby numerical parameters required to establish a relation between the cell topology and the compressive properties of the lattice structures were estimated. The plastic deformation and failure mechanisms were analyzed. Results revealed that the compression properties are dominated by the cell topology rather than the relative density. Besides, the present work confirmed that the compressive properties of the lattice structures fabricated with short fiber reinforcement are significantly affected by anisotropy. These structures exhibited a higher compressive modulus and lower peak compressive stress in the lateral direction, which can be attributed to the inline orientation of the short glass fibers. Schwarz Diamond proved to be the stiffest structure, followed by Schoen Gyroid and Schwarz Primitive under axial and lateral compression. Likewise, Schwarz Primitive generated low stresses compared to Schoen Gyroid and Schwarz Diamond. All cell topologies deformed in a controlled manner layer by layer, minimizing undulations in the load-bearing capacity of the structures. D and G structures compressed in the axial direction exhibited significant strain hardening and identical structures compressed in the lateral direction exhibited stable post-yield behavior with negligible undulations which is highly preferred for crashworthiness applications.

Angle-Domain Common-Image Gathers for Imaging of Multiples Using Poynting Vectors

As a complementary to imaging of primaries, multiples can be used for imaging and produce additional angular illumination. These additional illumination angles can improve imaging resolution. There are several methods to calculate angle gathers from imaging of primaries, among which the directional vector methods are matured and have been implemented in practice. For conventional directional vector algorithms using common-shot reverse time migration, usually only one angle with the main contribution to each imaging point is collected, which is referred to as one-shot, one-position, and one-angle mapping strategy. This strategy is appropriate for imaging of primaries. However, the principle fails in imaging of multiples, where more than one angle exists at an imaging point even using a shot gather. Therefore, conventional directional vector approaches cannot separate different imaging angles produced by imaging of multiples. In this paper, we introduce the Poynting vector method to calculate angle gathers for imaging of multiples. Based on the one-shot, one-position, and one-angle mapping strategy, we search for the peak of modulus of Poynting vectors in a time window to differentiate imaging angles at an imaging point. The ray-path diagrams and angle-gather imaging conditions are used to demonstrate the improved angular illumination from imaging of multiples. Then, the arrival-time equation is derived mathematically to demonstrate wavefield arrival-time differences for different imaging angles from imaging of multiples. Based on the arrival-time differences, a Poynting vector algorithm is proposed to compute more than one angle at one subsurface location for imaging of multiples. Data examples are used to validate our approach.

Elucidation of segmental relaxations of silica‐filled cis‐polybutadiene rubber composites

AbstractThere has been a lot of interest in characterizing polymer chain dynamics of rubber compounds because it is thought to underpin the exceptional mechanical properties of composites. We studied the effect of precipitated silica on segmental mobility of cis‐polybutadiene rubber by using differential scanning calorimetry (DSC) and dynamic mechanical analysis (DMA). It was found that the calorimetric glass and melting transitions of silica‐filled master batch materials were essentially identical to those of the gum rubber, showing no dependence of silica loading and silane treatment. And, we observed in calorimetric measurement a change in the melting transition step for the vulcanizates. The results were correlated to the change of chemical crosslinks caused by various factors filler agglomeration and adsorption effect that tended to decrease chemical crosslink density and silane modification increased it. The DMA results demonstrated that the second peak in loss modulus versus temperature curve for the quenched vulcanizates was assigned to melting peak, and this peak disappeared at a slow cooling rate, which coincided well with DSC results. Moreover, crystalline parts constrained amorphous regions such that the glass transition temperature was raised for the cooled vulcanizates with high chemical crosslinks.

Influence of pretreated sugarcane bagasse fiber by steam explosion, soaking with caustic soda, and addition of coupling agent into polylactic acid biocomposites

Biocomposites containing natural fibers waste have gained the attention of researchers due to their biodegradability and suitability for several applications in different industries. In this study, sugarcane bagasse fibers waste was treated by digestion with NaOH and steam explosion to the previous soaking with NaOH, and their impregnation with 1% maleated polyethylene was used as reinforcement in poly (lactic acid) matrix composites. Surface morphological changes were observed with scanning electron microscopy due to fiber treatment/MAPE in the PLA matrix. The biocomposites with MAPE improved Young’s modulus, but the strength tensile was reduced. Flexural modulus of biocomposites shows a considerable increase with MAPE, for biocomposites of 10% and 20% of bagasse the values are circa 8000 MPa regarding the 3500 MPa from PLA. These increases in the properties are ascribed to the improved interfacial interaction of the modified sugarcane bagasse fibers into the PLA. The analysis of TGA shows that incorporation of fiber with and without treatment and MAPE improved the thermal stability. By adding fiber into the biocomposites, the loss modulus peak becomes wider, this means that adhesion of the matrix and the fiber were improved. The X-ray diffraction graph shows an increase in the crystallinity of the biocomposites after the treatment and the addition of MAPE compared to the matrix of PLA.

Three-dimensional grain-based model study on triaxial mechanical behavior and fracturing mechanism of granite containing a single fissure

In order to investigate the mechanical behavior and failure mechanism of fissured granite under triaxial compression, a three-dimensional grain-based model (GBM3D) was established in particle flow code (PFC) for simulating the triaxial compression of granite specimens with various fissure inclinations (α = 0°, 30°, 45°, 60° and 90°) under different confining pressures (0, 5, 10 and 20 MPa). First, a group of micro-parameters used in GBM3D was calibrated based on the experimental triaxial compression results of intact specimens, the simulation results of fissured specimens based on these parameters are in good agreement with the experimental results. Compared with intact granite, the fissured granite has smaller peak strength, crack damage threshold, elastic modulus and axial peak strain. Confining pressure can improve the mechanical properties of granite at the same fissure angle, and under the same confining pressure, the mechanical properties increase with the increase of fracture angle. With the increase of axial stress, the cracks first emerge from the crack apices and propagate toward the ends of the specimen along the direction of the principal stress, and the cracks penetrate each other and eventually lead to the failure of the specimens. The displacement field shows that the main cracks are all generated at the interfacial locations where large relative displacements occur between the particles. The three-dimensional spatial crack distribution characteristics of the damaged specimens are not only influenced by the confining pressure, but also related to the fissure angle. The confining pressure not only complicates the crack distribution characteristics, but also increases the total count of cracks. As the fissure angle increases, anti-tensile wing crack is more likely to appear in the specimen.

Upper bound of fragility from spatial fluctuations of shear modulus and boson peak in glasses.

It is shown that the normalized rms fluctuation of the shear modulus on the medium-range order scale in glasses correlates with fragility: the higher fragility, the smaller the fluctuation amplitude. The latter is calculated within the heterogeneous elasticity theory using the data on the boson peak in glasses. On a smaller scale corresponding to cooperative structural relaxation, the normalized rms fluctuation of the infinite-frequency shear modulus was estimated using the data on the decoupling of viscosity and diffusion in supercooled liquids. These fluctuations are much smaller in amplitude, and, in contrast, they increase with increasing fragility. Extrapolation predicts intersection of both rms fluctuations and disappearing of the boson peak at the upper limit to fragility ≈180.

Graphene nanoplatelets reinforced cement as a solution to leaky wellbores reinforcing weak points in hydrated Portland cement with graphene nanoparticles improves mechanical and chemical durability of wellbore cements

To improve the performance of wellbore cement under subsurface environments, graphene nanoplatelets (GNPs) were added in various percentages to Class-H cement slurry. Microstructural characterization of cement slurries cured at 90 °C and 95% RH indicates that GNP modifies the microstructure of hydrated cement by reinforcing pore spaces. As a result, the mechanical properties, such as Young's modulus and axial peak stress, obtained from high temperature triaxial compression tests are significantly improved based on different percentages of added GNPs. Furthermore, the hydrated 1 × 2inch GNP- Portland cement cores tested under simulated deep wellbore conditions of high-temperature and high pressure (HTHP), appear to have a ductile-like behavior, when compared to a typical brittle nature of Portland cement pastes. From our observations and published data on graphene resistance to fracture, GNP addition to cement is evidently enhancing the flexibility of cement. These improvements would reduce the risks associated with wellbore cement deterioration and a consequent leakage in fossil fuel production, geothermal energy production, CO2 storage as well as long-term sealing materials in plugging and abandonment of all wellbores at the end of their service life.

Rheological and Mechanical Properties of Thermoplastic Crystallizable Polyimide-Based Nanocomposites Filled with Carbon Nanotubes: Computer Simulations and Experiments.

Recently, a strong structural ordering of thermoplastic semi-crystalline polyimides near single-walled carbon nanotubes (SWCNTs) was found that can enhance their mechanical properties. In this study, a comparative analysis of the results of microsecond-scale all-atom computer simulations and experimental measurements of thermoplastic semi-crystalline polyimide R-BAPB synthesized on the basis of dianhydride R (1,3-bis-(3′,4-dicarboxyphenoxy) benzene) and diamine BAPB (4,4′-bis-(4″-aminophenoxy) biphenyl) near the SWCNTs on the rheological properties of nanocomposites was performed. We observe the viscosity increase in the SWCNT-filled R-BAPB in the melt state both in computer simulations and experiments. For the first time, it is proven by computer simulation that this viscosity change is related to the structural ordering of the R-BAPB in the vicinity of SWCNT but not to the formation of interchain linkage. Additionally, strong anisotropy of the rheological properties of the R-BAPB near the SWCNT surface was detected due to the polyimide chain orientation. The increase in the viscosity of the polymer in the viscous-flow state and an increase in the values of the mechanical characteristics (Young’s modulus and yield peak) of the SWCNT-R-BAPB nanocomposites in the glassy state are stronger in the directions along the ordering of polymer chains close to the carbon nanofiller surface. Thus, the new experimental data obtained on the R-BAPB-based nanocomposites filled with SWCNT, being extensively compared with simulation results, confirm the idea of the influence of macromolecular ordering near the carbon nanotube on the mechanical characteristics of the composite material.

Destructive testing and simulation for newly designed full-scale high-speed railway box girder

Destructive testing and numerical simulation of a full-scale box girder were conducted to understand the mechanical behaviour of a newly designed pre-stressed concrete box girder for high-speed railways. In the destructive testing, load values close to 2.5 times the designed bending moment were applied to the investigated box girder in 26 steps. The global displacement behaviour, local strain variation, and crack development throughout the destructive process were measured. During the numerical simulation, this study proposes a concrete constitutive relation considering the reinforcement effect of steel bars on the elastic modulus and failure peak stress of concrete for high-speed railway box girders. A refined and simplified finite element model (FEM) were established, and the mechanical behaviour under entire loading process was simulated using ABAQUS software, which agreed well with the testing results to a certain extent. The testing and simulation results show that the newly designed pre-stressed concrete box girder did not collapse under 2.5 times the designed bending moment, verifying the safety margin and providing guidelines for the subsequent structural design optimisation of high-speed railway box girders.

Modeling Payne effect on basis of linearization of a visco-hyperelastic model

The present work concerns the modeling of the Payne effect in nonlinear viscoelasticity. This effect is a characteristic property of filled elastomers. Indeed, under cyclic loading of increasing amplitude, a decrease is shown in the storage modulus and a peak in the loss modulus. In this study, the Payne effect is assumed to arise from a change of the material microstructure, i.e. the thixotropy. The so-called intrinsic time or shift time was inferred from solving a differential equation that represents the evolution of a material’s microstructure. Then, the physical time is replaced by the shift time in the framework of a recent fractional visco-hyperelastic model, which was linearized in the neighborhood of a static pre-deformation. As a result, we have investigated the effects of static pre-deformation, frequency, and magnitude of dynamic strain on storage and loss moduli in the steady state. Thereafter, the same set of parameters identified from the complex Young’s modulus was used to predict the stress in the pre-deformed configuration. Finally, it is demonstrated that the proposed model is reasonably accurate in predicting Payne effect.

Investigation on the evaluation method and influencing factors of cross-scale mechanical properties of shale based on indentation experiment

Low-cost, fast and accurate acquisition of multi-scale mechanical properties of shale is essential to realize the complex hydraulic fracture network and the optimization of multi-scale fracture efficiency of bottom hole rock. The macro-scale indentation test is used to study the mechanical parameters of the meso-scale across the scales. The rapid evaluation method of the shale mechanical parameters across the scales is established, which can be used as a method to obtain the mechanical parameters of shale quickly and accurately. The macro-indentation test experiment is carried out through the elastic contact hypothesis, the macro-micro mechanics theory, and the grid indentation experiment method. Considering the coupling effects of peak indentation fluctuations, contact stiffness(S), and the ratio of elastic work to total work (Wu/Wt), the cross-scale distribution characteristics of shale hardness(H) and elastic modulus(E) are studied. The results showed that the elastic modulus and hardness showed a normal distribution on the whole, and the macroscopic indentation process of the rock was accompanied by the meso-scale indentation. For Longmaxi shale, the elastic modulus and hardness have large discreteness and heterogeneity. The kernel density values of elastic modulus and hardness were studied by using kernel density analysis method. Different factors have different effects on the fluctuation amplitude of elastic modulus and hardness. The fluctuation range of the S is the largest, and the fluctuation range of Wu/Wt is the smallest. At the meso-scale, the dispersion of hardness peak value is larger, and the dispersion of elastic modulus peak value is smaller than that of valley value. The S-Wu/Wt-E-H coupling response law presents a “striped” characteristic. The S-Fm-E-H coupling response law presents a “multi-point” distribution. The Fm-Wu/Wt-E-H coupling response law shows a “wave-like” distribution. The hardness of vertical bedding indentation is greater than that of parallel bedding. There is a good linear correlation between the elastic modulus and hardness. With the increase of the elastic modulus, the hardness increases. The research results are helpful to determine the parameters in the actual design of hydraulic fracturing and improving the rock breaking efficiency.

Dynamic flexural behavior of AR-glass textile reinforced concrete under low-velocity impact loading

Textile reinforced concrete (TRC) has a higher sustainable potential than conventional reinforced concrete, with a significantly lower CO2 footprint. To study the dynamic flexural behavior of TRC composites, the Alkali Resistant (AR)-glass textile reinforced concrete (TRC) plate specimens was investigated with the three-point bending test under low-velocity impact. This study examined the influences of the textile layer number (1, 2, and 3 layers) and the impact velocity (1.29–4.04 m/s) on the dynamic behavior of TRC composites, and compared that with the quasi-static test results. The results show that the Young’s modulus and initial peak impact stress of the AR-glass TRC generally increase with the impact velocity, while its influence on the ultimate flexural stress is insignificant. It is found that the ultimate flexural stress can better represent the dynamic flexural capacity of AR-glass TRC materials than the initial peak stress. The failure modes were also analyzed in terms of crack patterns and crack widths, which were measured through the digital image correlation (DIC) method. It was found that rebound and rupture are the two main failure scenarios of the AR-glass TRC under low-velocity impact loading. The cracks of AR-glass TRC specimens could be mainly categorized into flexural crack, shear-flexural crack, and interfacial debonding crack. The study of stress-crack width relationship is helpful to determine the design strength of TRC material to meet the requirement on crack width.