Increase In Elastic Modulus Research Articles

Impact of Viscoelasticity on Sand-Carrying Ability of Viscous Slickwater and Its Sand-Carrying Threshold in Hydraulic Fractures

Viscous slickwater has a higher viscosity and better sand-carrying ability than conventional slickwater at the same concentration. At a concentration of 0.4 wt.%, the viscosity of the viscous slickwater is 4.7 times that of the conventional slickwater. It is generally believed that viscosity is one of the main influencing factors on the sand-carrying ability of the fluid. However, this study has shown that the good sand-carrying ability of the viscous slickwater is more attributed to its viscoelasticity. Through rheology and sand-carrying tests, it has been found that the viscoelastic properties vary when fluids have the same viscosity; this then leads to a significant difference in the settling rate of sand and the sand-carrying threshold of the fluid in a fracture at a certain flow rate. The routine method of characterizing the viscoelastic property of the slickwater was to observe the cross point of the elastic modulus (G′) and viscous modulus (G″) curves. The smaller the frequency of the cross point, the better the viscoelastic property of the fluid. However, it has been found in experiments that even when the cross point is the same, there is still a significant difference in the sand-carrying ability of fluids. Therefore, sand-carrying experiments are conducted under a similar cross point and different magnitudes of modulus, of which the results indicate that as the elastic modulus increases, the settling rate of sand decreases. The flow rate threshold occurring as sand settles obtained from laboratory experiments is compared with the field condition during hydraulic fracturing. From laboratory experiments, the threshold of inner-fracture flow rate that prevents the sand settling is found to be 8.02 m/min for 0.6 wt.% viscous slickwater with a sand ratio of 30%. In the field operation, the operation conditions meet the sand-carrying threshold obtained from laboratory experiments. Observations from the field test confirm the applicability of the threshold plot proposed according to laboratory measurements, which can provide guidance for optimizing the fracturing scheme in the field.

CAD-CAM resin composites: Effective components for further development

ObjectiveThis paper summarizes the effective components of computer-aided design and computer-aided manufacturing (CAD-CAM) resin composites that contribute to achieving greater mechanical properties and further development. MethodsIn silico multi-scale analysis, in silico nonlinear dynamic finite element analysis (FEA), and artificial intelligence (AI) were used to explore the effective components of CAD-CAM resin composites. The effects of the filler diameter and silane coupling ratio on the mechanical properties of CAD-CAM resin composites have been clarified through multi-scale analysis. The effects of the filler contents, and filler and monomer compositions have been investigated by AI algorithms. The fracture behavior of CAD-CAM composite crown was analyzed using in silico non-linear dynamic FEA. The longevity of CAD-CAM composite crown was assessed through step-stress accelerating life testing (SSALT). ResultsAs the filler diameter decreases, there is an increase in elastic moduli and compressive strengths at the macroscale. At the nanoscale, a decrease in the filler diameter results in a decrease in the maximum value of the maximum principal strain. When the silane coupling ratio decreases, there is a decrease in the elastic modulus and compressive strength. According to the exhaustive search and feature importance analysis based on the AI algorithm, the combination of certain components was narrowed down to achieve a flexural strength of 269.5 MPa. The in silico non-linear FEA successfully detected the sign of the initial crack of the CAD-CAM composite molar crown. The SSALT revealed that CAD-CAM resin composite molar crowns containing nanofillers with a high fraction of resin matrix demonstrated great longevity. SignificanceThis paper summarized the effective components of CAD-CAM resin composites for their further development. The integration of in vitro and in silico approaches will expedite the advancement of CAD-CAM resin composites, offering benefits such as time efficiency and reduction of material waste for researchers and manufacturers.

Numerical simulation on dynamic compression properties of sandstone under axial static preload

In this study, through a series of static mechanical tests and split Hopkinson pressure bar (SHPB) dynamic impact tests, the static and dynamic mechanical parameters of yellow sandstone are determined, and the Holmquist–Johnson–Cook model parameters of the rock are determined by the test data and theoretical calculation. The feasibility of a numerical model is verified, based on which the SHPB impact process under different axial pressure is subjected to numerical analysis. The results show that with increasing impact load, the degree of rock breakage increases, and the dynamic compressive strength and dynamic elastic modulus increase continuously. With the application and increase of axial pressure, the dynamic compressive strength and dynamic elastic modulus of the rock decrease gradually under the same impact load, and the maximum cumulative strain keeps increasing, indicating that under the influence of axial pressure, micro-cracks in the rock have initially developed and expanded. With increasing axial pressure, the rock is more vulnerable to breakage, and its weakening degree keeps increasing. The energy utilization rate of one-dimensional dynamic and static combined loading is affected by the axial compression ratio and impact load. At low axial compression ratio, the rock has high impact resistance but high energy utilization rate; at high axial compression ratio, the rock has low impact resistance but low energy utilization rate. Therefore, the combination of axial compression ratio and impact velocity can improve the crushing effect and energy utilization rate on the premise of clear crushing form requirements.

Experimental Investigation of the Size Effect on Roller-Compacted Hydraulic Asphalt Concrete under Different Strain Rates of Loading.

Asphalt concrete is widely used in hydraulic structure facilities as an impermeable structure in alpine cold regions, and its dynamic mechanical properties are influenced by the strain rate and specimen size. However, the specimen size has an important effect on mechanical properties; few systematic studies have investigated on the size effect of hydraulic asphalt concrete (HAC) under dynamic or static loading rates. In the present study, four sizes of cylindrical roller-compacted hydraulic asphalt concrete (RCHAC) specimens with heights of 50 mm, 100 mm, 150 mm, and 200 mm were prepared and tested under different loading rates ranging from 10-5 s-1 to 10-2 s-1 to investigate the size effects of mechanical properties and failure modes at the temperature of 5 °C. The effect of strain rate on the size effects of the compressive strength and the elastic modulus of RCHAC have also been explored. These tests indicate that when the specimen size increases, the compressive strength and failure degree decrease, while the elastic modulus increases. When the height increases from 50 mm to 200 mm, the compressive strength at different strain rates decreased by more than 50%. Furthermore, the elastic modulus increased by about 211.8% from 0.51 GPa to 1.59 GPa at a strain rate of 10-5 s-1, and increased by 150% from 5.08 GPa to 12.71 GPa at a strain rate of 10-2 s-1. As the strain rate increases, the variation trends with the size of the compressive strength, elastic modulus, and failure degree are distinctly intensified. A modified dynamic size effect law, which incorporates both the specimen size and strain rate, is proposed and verified to illustrate the dynamic size effect for the RCHAC under different loading rates.

Physical and Mechanical Properties and Damage Mechanism of Sandstone at High Temperatures

The physical and mechanical properties of rocks change significantly after being subjected to high temperatures, which poses safety hazards to underground projects such as coal underground gasification. In order to investigate the effect of temperature on the macroscopic and microscopic properties of rocks, this paper has taken sandstone as the research object and conducted uniaxial compression tests on sandstone specimens at different temperatures (20–1000 °C) and different heating rates (5–30 °C/min). At the same time, the acoustic emission (AE) test system was used to observe the acoustic emission characteristics of the rock damage process, and the microstructural changes after high temperature were analyzed with the help of a scanning electron microscope (SEM). The test results show that the effect of temperature on sandstone is mainly divided into three stages: Stage I (20–500 °C) is the strengthening zone, the evaporation of water and the contraction of primary fissures, and sandstone densification is enhanced. In particular, the compressive strength and elastic modulus increase, the macroscopic damage mode is dominated by shear damage, and the fracture micromorphology is mainly brittle fracture. Stage II (500–600 °C) is the transition zone, 500 °C is the threshold temperature for the compressive strength and modulus of elasticity, and the damage mode changes from shear to cleavage damage, and the sandstone undergoes brittle–ductile transition in this temperature interval. Stage III is the physicochemical deterioration stage. The changes in the physical and chemical properties make the sandstone compressive strength and modulus of elasticity continue to decline, the macroscopic damage mode is mainly dominated by cleavage damage, and the fracture microscopic morphology is of a more toughness fracture. The effect of different heating rates on the mechanical properties of sandstone was further studied, and it was found that the mechanical properties of the rock further deteriorated under higher heating rates.

Study on the effects of elastic modulus of constructions on heat and mass transfer of gas explosion

The factor of combustion and explosion remains one of the main constraints on coal mining and management. To clarify the impact of structural properties on the consequences of gas explosion disasters during coal mining, this article conducts a study on the impact of the elastic modulus of structures on gas explosion disasters. The research results indicate that in the case where structures with high elastic modulus must exist, the elastic modulus of the structure has minimal impact on the structure during the early stage of flame development. The area of flame front and the degree of deflagration also decrease with the increase of elastic modulus, but the disturbance degree of air-flow and flame in the pipe increases with the increase of elastic modulus. The peak flame velocity at elastic modulus of 0.7 GPa and 2.8 GPa increased by 3.56% and 7.47% compared to elastic modulus of 0.18 GPa, respectively. The upstream overpressure peak increased by 24.63% and 42.52%. The downstream overpressure peak increased by 11.19% and 20.62%. The peak values of flame velocity and overpressure increase with the increase of elastic modulus, while the explosion intensity and pressure rise rate increase with the increase of elastic modulus. The explosion intensity index at elastic modulus 2.8 GPa is approximately 1.45 times that at elastic modulus 0.18 GPa. Therefore, it is necessary to choose structures with smaller elastic modulus as much as possible to achieve the best fire and explosion suppression effect.

Transforming Wood into a High-Performance Engineering Material via Cellulose Nanocrystal Impregnation

Abstract The demand for wood in construction has led to shortages of strong wood types, causing a shift to costlier alternatives like concrete and nonbiodegradable materials, prompting the investigation of modifying softwoods for better engineering properties. This study investigates the optimization of a multistep impregnation process utilizing functionalized cellulose nanocrystals (f-CNCs) to enhance softwood properties. The process involves alkali delignification, ultrasonication, and vacuum pressure treatment to improve wood porosity and in turn improve CNC impregnation with uniform dispersion. Microstructural analyses through field emission scanning electron microscopy and atomic force microscopy (AFM) offer detailed insights into cell wall morphology and surface topography, whereas Fourier transform infrared spectroscopy highlights compositional shifts resulting from f-CNC impregnation. Mechanical testing demonstrates significant improvements for treated woods, particularly a 67 percent increase in modulus of elasticity for the 2 percent CNC-treated group compared with the control group; a 71 percent increase in modulus of rupture was observed for 2 percent CNC-, 3 percent NaOH-, and 2 percent acetic acid-treated group compared with the control sample. The sample delignified with 3 percent NaOH and impregnated by 2 percent f-CNC emerged as particularly effective. This research sets the stage for potential advancements in strengthening softwood using CNC, including a novel AFM method and alternative impregnation techniques like the Lowry method, inviting further exploration.

Molecular dynamics simulation of mechanical and thermal properties of nano-zinc oxide modified cellulose insulating paper

With the surge in electrical loads and increasing voltage levels, the mechanical performance and thermal stability of insulating paper are facing severe challenges. However, due to the lack of direct scientific theories or simulation guidance, traditional inefficient “trial-and-error” experiments are difficult to effectively develop new types of cellulose composite insulating papers. For solving this problem, in this work we are to enhance the effects of nanoscale zinc oxide (nano-ZnO) on the mechanical and thermal properties of cellulose through molecular dynamics simulations. Initially, we model the nano-ZnO/cellulose composite material , then carry out a microscopic analysis of the mechanical performance and thermal stability of modified cellulose with varying nano-ZnO content, thus determining the optimal ratio of nano-ZnO to cellulose. The results indicate that compared with the outcomes from the unmodified model, the mechanical performance, cohesive energy density, glass transition temperature, and thermal conductivity of the nano-ZnO-modified cellulose model are all improved, with the highest increase in elastic modulus reaching 45.31% and the highest increase in thermal conductivity attaining 41.49%. The addition of nano-ZnO effectively fills the gaps in the fiber network and enhances the interactions between cellulose chains and thermal conduction channels, thereby improving the thermodynamic performance of cellulose. This work provides valuable theoretical references for rapidly preparing modified cellulose insulating papers with excellent thermodynamic performance.

Anionic starch-based hybrid cryogel-embedded ZnO nanoparticles: tuning the elasticity and pH-functionality of biocomposites with dicarboxylic acid units.

Weakly anionic semi-interpenetrating polymer network (semi-IPN) biocomposites based on starch (ST)-incorporated poly(acrylamide-co-itaconic acid)/ZnO (ST-PAI/ZnO) were synthesized by a simple one-pot method via free radical aqueous polymerization. Hybrid biocomposites exhibited lower equilibrium swelling compared with neat copolymer gel. For both hydrogels and cryogels, swelling followed a decreasing order as copolymer PAI > starch-free PAI/ZnO > ST-PAI/ZnO gels. With the addition of 9% ST and ZnO, the swelling ratio of gels decreased from 898 to 68.3, resulting in a significant increase in elastic modulus. Compared with a fixed amount of ST, biocomposite cryogels exhibited significantly higher modulus than hydrogels. With the addition of 9% ST, the elastic modulus of cryogels reached 22.2 kPa while it was 2.7 kPa for the hydrogels. An equation expressing the effective cross-linking density of semi-IPNs presented by a cubic polynomial as a function of starch was obtained. As pH increased with the presence of dicarboxylic acid units, a gradual increase in swelling occurred at two different pH values. A gradually reproducible swelling change of semi-IPNs was depicted with pH ranging from 2.1 to 11.2. Biocomposite cryogels showed rapid swelling in a buffer solution of pH 11.2 and rapid shrinking in pH 2.1. Salt-induced swelling testing showed that the ability to reduce the degree of swelling and solubility of starch was Br- > Cl- > NO3- > SO42- for anions consistent with the Hofmeister series. Adsorption efficiency for the removal of methyl violet (MV) dye was analyzed using Langmuir, Freundlich, Dubinin-Radushkevich and Temkin isotherm models. The results confirmed that the Langmuir isotherm and pseudo-second-order model are suitable for describing MV adsorption on semi-IPN biocomposites. The synthesized biocomposites with good swelling/deswelling kinetics in different pH-buffer solutions, high saline absorbency, desirable adsorption efficiency, and acceptable pH-dependent swelling reversibility can be considered as smart hybrid materials for the adsorption of the dye in water purification tasks.

Mechanical behavior of high entropy ceramic (TiZrHfVNb)C₅ under extreme conditions: A first-principles density functional theory study

Multi-component high-entropy carbides (HECs) have garnered extensive attention owing to their excellent serviceability in harsh environments characterized by ultra-high temperatures and high pressures. However, the microstructure, electronic structure, and chemical bonding of materials are significantly influenced by high pressure. This study investigates the effects of high-pressure conditions on the stability and properties of (TiZrHfVNb)C₅ phases using the first-principles calculation. According to the judgment analysis in thermodynamics, mechanics, and kinetics, HECs can form a single solid-solution phase which is stable in 0–100 GPa. When pressure is applied, HECs undergo more significant property changes. With increasing pressure, there are some increases in lattice distortion, elastic modulus, mechanical anisotropy, sound velocity, and Debye temperature of (TiZrHfVNb)C₅ ceramic. It is worth noting that hardness has a perverse behavior at high pressures, and the hardness decreases with increasing pressure. At 40–50 GPa, HECs also experience a brittle–ductile transition. A shift in HECs' electronic structure under pressure is what essentially causes the changes in brittle–ductile transition and hardness. This work provides instructive insights for predicting and designing high-performance high-entropy carbide ceramics tailored for extreme environmental conditions.

Stress-strain characteristics of autoclaved aerated concrete masonry under varying displacement rates

Comprehending the impact of displacement rate on the mechanical properties of autoclaved aerated concrete (AAC) masonry is critical for predicting the response of structures to seismic and other natural dynamic loads. This study investigates the effect of varying displacement rates (0.1 mm/min, 1 mm/min, and 10 mm/min) on the mechanical properties of AAC masonry under uniaxial compression through systematic laboratory tests. Results indicate a substantial increase in elastic modulus (100 %) and compressive strength (200 %) as displacement rates rise from 0.1 mm/min to 10 mm/min. Finite element analysis using a micro-modelling strategy in Abaqus corroborates experimental findings, simulating crack propagation and identifying stress and strain distribution. The outcomes of this study would facilitate the accurate design and analysis of framed buildings infilled with AAC block masonry, especially under dynamic loading. These findings are expected to significantly contribute to the enhancement of structural engineering practices, enhancing the reliability and effectiveness of AAC block masonry for constructing resilient buildings.

Low thermal expansion of high-entropy (ZrMg1−xMnxAlFeCr)0.4Mo1.5W1.5O12 with enhanced mechanical properties

Low thermal expansion (LTE) ceramics are needed to relieve stress in fine devices. Here we adopt high entropy to realise LTE (ZrMgAlFeCr)0.4Mo1.5W1.5O12 with an orthorhombic structure, but presenting poor mechanical properties. To improve the mechanical properties, we increase the compactness of the lattice structure by replacing Mg2+ (ionic radius: 72 p.m.) with Mn2+, which has a larger ionic radius (81 p.m.). As the content of Mn in (ZrMg1−xMnxAlFeCr)0.4Mo1.5W1.5O12 increases, the elastic modulus and compressive strength increase notably owing to the dense microstructure. At x = 0.3, the sample crystallises in the monoclinic phase, and the monoclinic–orthorhombic phase transition temperature increases slightly with an additional increase in the Mn content. Beyond the monoclinic–orthorhombic phase transition, the samples present LTE. The investigation paves a way to realise LTE ceramics with enhanced mechanical properties.

The Cold-Brittleness Regularities of Low-Activation Ferritic-Martensitic Steel EK-181

The behavior of the EK-181 low-activation ferritic-martensitic reactor steel (Fe–12Cr–2W–V–Ta–B) in the states with different levels of strength and plastic properties after traditional heat treatment (THT) and after high-temperature thermomechanical treatment (HTMT) in the temperature range from −196 to 25 °C, including the range of its cold brittleness (ductile–brittle transition temperature, DBTT) is studied. The investigations are carried out using non-destructive acoustic methods (internal friction, elasticity) and transmission and scanning electron microscopy methods. It is found that the curves of temperature dependence of internal friction (the vibration decrement) of EK-181 steel after THT and HTMT are similar to those of its impact strength. Below the ductile–brittle transition temperature, it is characterized by a low level of dislocation internal friction. The temperature dependence curves of the steel elastic modulus increase monotonically with the decreasing temperature. In this case, the value of Young’s modulus is structure-sensitive. A modification of the microstructure of EK-181 steel as a result of HTMT causes its elastic modulus to increase, compared to that after THT, over the entire temperature range under study. The electron microscopic studies of the steel microstructure evolution near the fracture surface of the impact samples (in the region of dynamic crack propagation) in the temperature range from −196 to 100 °C reveal the traces of plastic deformation (increased dislocation density, fragmentation of the martensitic structure) at all of the temperatures under study, including those below the cold brittleness threshold of EK-181 steel.

The influence of substrate temperature on the structure and optical properties of NiO thin films deposited using the magnetron sputtering in the layer-by-layer growth regime

Vanadium oxide (VO x ) thin films are promising materials, exhibiting electrical, optical, and mechanical properties highly tunable by processing and structure. This work uniquely applying atomic force microscopy (AFM) nanoindentation correlated with X-ray diffractometry and Raman spectroscopy structural analysis to investigate the intricate connections between VO x post-annealing, phase composition, and resulting nanoscale mechanical functionality. Utilizing an ultra-sharp diamond tip as a nanoscale indenter, indentation is performed on VO x films with systematic variations in structure – from mixed insulating oxides to VO 2 -dominated films. Analytical modeling enables extraction of hardness and elastic modulus with nanoscale resolution. Dramatic mechanical property variations are observed between compositions, with order-of-magnitude increases in hardness and elastic modulus for the VO 2 -rich films versus insulating oxides. Ion implantation further enhances nanomechanical performance through targeted defect engineering. Correlating indentation-derived trends with detailed structural and morphological characterization elucidates explicit structure-property relationships inaccessible by other techniques. The approach provides critical mechanics-driven insights into links between VO x synthesis, structure evolution, and property development. Broader implementation will accelerate processing optimization for electronics and advanced fundamental understanding of nanoscale structure-functionality relationships

Nanomechanical properties of polycrystalline vanadium oxide thin films of different phase composition

Vanadium oxide (VO x ) thin films are promising materials, exhibiting electrical, optical, and mechanical properties highly tunable by processing and structure. This work uniquely applying atomic force microscopy (AFM) nanoindentation correlated with X-ray diffractometry and Raman spectroscopy structural analysis to investigate the intricate connections between VO x post-annealing, phase composition, and resulting nanoscale mechanical functionality. Utilizing an ultra-sharp diamond tip as a nanoscale indenter, indentation is performed on VO x films with systematic variations in structure – from mixed insulating oxides to VO 2 -dominated films. Analytical modeling enables extraction of hardness and elastic modulus with nanoscale resolution. Dramatic mechanical property variations are observed between compositions, with order-of-magnitude increases in hardness and elastic modulus for the VO 2 -rich films versus insulating oxides. Ion implantation further enhances nanomechanical performance through targeted defect engineering. Correlating indentation-derived trends with detailed structural and morphological characterization elucidates explicit structure-property relationships inaccessible by other techniques. The approach provides critical mechanics-driven insights into links between VO x synthesis, structure evolution, and property development. Broader implementation will accelerate processing optimization for electronics and advanced fundamental understanding of nanoscale structure-functionality relationships

Experimental investigation of the dynamic mechanical properties of concrete under different strain rates and cyclic loading

To investigate the effects of strain rate and cyclic loading on the mechanical parameters of concrete compressive strength, residual strain, peak strain and elastic modulus, a series of cyclic loading tests over concrete were conducted by setting different numbers of cycles, magnitude factors, and cycle frequencies/periods based on the FST-1000 alpine geotechnical dynamic and static triaxial test system. The quantitative relationships between the mechanical parameters of concrete and the parameters of cyclic loading as well as the strain rate were also proposed. The results show that as the strain rate increases, the concrete compressive strength and elastic modulus increase linearly, while the residual strength and peak strain show a decreasing trend. Under cyclic loading, the compressive strength was quadratically related to each cyclic loading parameter, and the elastic modulus was quadratically related to the cyclic number and magnitude factor. The trend of the concrete compressive strength rate sensitivity undergoes a change at the specific thresholds of 0.145 for the magnitude factor and 1.93 Hz for the frequency. The minimum value of the peak strain rate sensitivity corresponds to the specific thresholds of 6023 for the number of cycles, 0.14 for the magnitude factor, and 1.38 Hz for the frequency thresholds, respectively. Additionally, the enhancement of the elastic modulus rate sensitivity occurs when the number of cycles exceeds 918 or when the magnitude factor surpasses 0.33. The results can provide a theoretical basis for the design of concrete structures and seismic engineering.

Variación de las propiedades mecánicas del hueso inmaduro en las etapas más tempranas del desarrollo

IntroductionBone as a material varies its composition and mechanical properties throughout life. Although these variations are better understood in adulthood, there is little experimental information on the variation of these properties in early stages of development. The objective of this study is to analyze the mechanical behavior and chemical properties of cortical bone tissue from two animal species in these earliest stages. Material and methodologyTwenty specimens of cortical bone were manufactured from bovine and ovine species that were in different stages of development (feeding exclusively on breast milk, in the transition period to feed or pasture, and young animals but on a solid food diet). The specimens were subjected to tensile tests, recorded with a high-speed camera to obtain deformation maps. Measurements of the tensile force until the specimen broke were also carried out. A fractographic study was carried out with a scanning electron microscope to analyze the fracture surface and an analysis of the amount of calcium in each of the specimens using X-ray dispersion spectroscopy. ResultsA statistically significant and positive correlation was found between the elastic modulus of the specimens and their calcium content. A trend towards more rigid behavior with age was observed. ConclusionsYoung bone tissue tends to stiffen with age as the calcium content increases with an increase in elastic modulus.

Influence of Lateral Pressure on the Mechanical Performance of Bolted Specimens under Biaxial Compression

The influence of lateral pressure (σ2) on the stability of the surrounding rock of roadway increases after excavation. The rock bolt is usually used to improve the stability of the surrounding rock. Therefore, it is important to understand the biaxial compressive behaviors of the bolted samples influenced by lateral pressure. In this study, biaxial compression experiments are carried out to investigate the biaxial compressive properties of bolted rock samples influenced by lateral pressure. The results show that bolting can improve the peak strength, inhibit the post-peak strength attenuation and reduce the pre-peak brittleness of the bolted rock mass. With the increase of lateral pressure, the strength and elastic modulus of the bolted samples increases approximately parabolic and linearly, respectively. The failure modes of the bolted samples influenced by lateral pressure can be divided into splitting failure and compression-shear failure. A reinforcement mechanism of bolt is observed, namely axial action, axial and transverse action at the pre- and post-peak stages of the bolted samples. Based on a modified true triaxial Mohr-Coulomb strength criterion and this bolt reinforcement mechanism, a new method for calculating the equivalent cohesion and equivalent internal friction angle of the bolted specimens under biaxial compression is proposed. The research results of this paper have certain reference value for the stability control of roadway

Fluid-structure Interaction Study on Drag Characteristics of Flexible Ribbon

The flexible ribbon can be used as a projectile stabilizing device to provide a stable moment for the projectile, and the research on its drag characteristics is of great significance. This paper uses the arbitrary Lagrange-Euler (ALE) method to simulate the fluid-structure interaction process of the ribbon swinging in the airflow. The numerical method is validated by comparing it with wind tunnel experimental results from previous literature. This study utilized numerical simulation to investigate the impact of inflow velocity, ribbon material properties, and ribbon shape on drag characteristics. The research concluded that for a single ribbon, the drag value increases as the incoming flow velocity, ribbon material density, elastic modulus, and length-width ratio increase. In addition, the drag value of the annular ribbon is greater than that of the double ribbon. The drag values of the double ribbon and the annular ribbon are averaged to one side, the unilateral drag of the annular ribbon is greater than that of the single ribbon, and the unilateral drag of the double ribbon is smaller than that of the single ribbon. The conclusions can provide a reference for studying flexible ribbon stabilized projectiles.

Digital light processing of multi-walled carbon nanotubes-reinforced photosensitive resin composites: Effects on microstructures and mechanical properties

Owing to their great potential to enhance the structural, mechanical, and electrical properties of materials, numerous researchers have dedicated their efforts to manufacturing multi-walled carbon nanotubes (MWCNTs)-reinforced composites via additive manufacturing (AM) to leverage AM's ability to fabricate intricate structural components. However, there is currently limited research on MWCNTs in photosensitive resin (PR) systems processed via a type of vat photopolymerization AM technique - digital light processing (DLP). Additionally, the distribution pattern of MWCNTs in PR systems is still unknown. To address these research gaps, this investigation focuses on fabricating MWCNTs-reinforced PR (MWCNTs-PR) via DLP and studying the effects of MWCNTs content on microstructure characterizations and mechanical properties of MWCNTs-PR. These results show that PR with 0.05 wt% MWCNTs addition exhibits a 25 % increase in elastic modulus and a 2 % increase in bending strength compared to pure PR. To achieve a more uniform distribution of MWCNTs in the PR, a combination of an ultrasonic bath and mechanical stirring was adopted. To further investigate the mechanism behind MWCNTs-enhanced bending resistance, a multi-material layered 3D printing structure was developed. The experimental findings reveal that the 10001 structure yields the highest bending modulus, surpassing the control group by 14.9 %. To validate the bending resistance mechanism attributed to MWCNTs-PR, finite element analysis was conducted.