Mechanical Strength Characteristics Research Articles

Seepage Characteristics and Influencing Factors of Weakly Consolidated Rocks in Triaxial Compression Test under Mining-Induced Stress Path

The rock of weakly consolidated coal measure strata has the characteristics of low mechanical strength and strong water sensitivity. Under the stress and seepage disturbance caused by coal seam mining, the surrounding rock structure is prone to instability, which leads to mine safety accidents and water resources loss. In order to master the mechanical response and permeability evolution law of weakly consolidated rock under the disturbance of coal seam mining, the specimens of Jurassic mudstone, sandy mudstone, and sandstone in the Ili mining area of China were collected, and a triaxial compression seepage test was carried out. A comprehensive analysis was carried out on the mineral composition and microstructure characteristics of the rock. The results show the following: (1) Compared to the constant confining pressure condition, mining-induced stress promotes the fracture development rate of weakly consolidated rocks. The ratios of strain at the yield point of mudstone, sandy mudstone, and sandstone under mining-induced stress and constant confining pressure are 0.33, 0.43, and 0.79, respectively, and the ratios of strain at the failure point were 0.48, 0.52, and 0.72, respectively. (2) Under the condition of mining-induced stress, the permeability change range and the permeability recovery rate of the three types of rocks were different, which decreased in the order of mudstone, sandy mudstone, and sandstone. (3) In the process of the triaxial compression test, there was a strong hysteresis in the permeability change of the mudstone, and the permeability and hysteresis of the three types of rocks decreased with the increase in the clay mineral content. (4) Combined with the analysis of the rock mineral composition and microstructure characteristics, it is believed that the clay minerals in the rock after water mud and swelling are the main reasons for the hysteresis of the permeability change of weakly consolidated rock, and the content of clay minerals is the main factor affecting the permeability characteristics of the weakly consolidated rock.

Investigation of mechanical strength and permeability characteristics of pervious concrete mixed with coral aggregate and seawater

The availability of the conventional raw materials required to produce pervious concrete on sea islands remote from the mainland is lacking, which could be alleviated by utilizing marine resources. This study aimed to develop seawater coral aggregate pervious concrete (SCAPC) by utilizing coral waste and seawater and assess the potential application of this method to sea islands. The SCAPC specimens were designed with different coral aggregate sizes (2.36–4.75 mm, 4.75–9.5 mm) and aggregate/binder ratios (2, 2.5, 3), and the addition of 10 % of sea sand. The physical properties (hardened density and porosity), mechanical strengths (compressive and splitting tensile strengths), water permeability, and sulfate attack resistance were investigated. The failure surface under mechanical loading and the microtopography between matrix and coral aggregate of SCAPC samples were also characterized. The results showed that the compressive strength and water permeability coefficient of the resulting SCAPCs at 28 days with a porosity ranging from 16.9 % to 33.5 % could reach 6.2–18.5 MPa and 12.9–26.5 mm/s, respectively. This not only satisfied the ACI 522R-recommended values for pervious concrete applicable to pedestrian road areas, but the samples demonstrated excellent permeability. The SCAPC specimens manufactured with aggregate/binder ratios of 2.5 incorporating 10 % sea sand were found to achieve the required balance between compressive strength (11.8–12.5 MPa) and water permeability coefficient (19.6–20.9 mm/s). The failure patterns of the SCAPC samples presented a markedly different complete fracture of coral aggregate point from that of traditional aggregate pervious concrete, ascribing this variation to the characterized fragility of coral aggregate and intensified interfacial adhesion.

Mechanical Strength and Energy Absorption Optimization of Biomimetic Honeycomb Anti-Collision Pier

The anti-collision pier plays an irreplaceable role in road traffic protection due to its significance. In this research, the biomimetic honeycomb structure was applied to internal anti-collision pier interior structures. The enhancement of mechanical strength and energy absorption characteristics was explored and optimized by five anti-collision pier honeycomb structures. Finite elements of the piers are designated as 650 mm in diameter and 850 mm in height. Polypropylene Acetate (PLA) material is utilized in this research due to its environment-friendly characteristics. Displacement loading in finite element simulation is 50 mm to the middle region of the model at YOZ direction. The energy-absorbing properties of five optimized honeycomb anti-collision piers at the same force position will be carefully compared. Moreover, the influence of internal hexagon direction-quantity configuration upon loading resistance under displacement loading is outlined. The results determined the best biomimetic structure to be three honeycomb shapes with a central triangle area, with maximum stress of 503.8 MPa and fracture displacement of 58.02 mm. Furthermore, the numerical simulation shows that the number of nest increases has a negative relationship with the effect upon force and deformation of the model. Moreover, the triangular central area is superior to the Y-shape central area in both mechanical strength and energy absorption performance.

Computational insights into the superior efficiency of Cs2AgGa(Cl,Br)6 double halide perovskite solar cells

Owing to their ecological integrity, non-toxicity, and outstanding performances, Double-Halide perovskites have been vigorously promoted as sustainable alternatives for thermoelectric and photovoltaic applications. In this context, we have systematically explored the structural and mechanical strength characteristics of Cs2AgGa(Cl,Br)6 materials through the tolerance factor analyses and Born stability criteria. Subsequently, a detailed study of their electronic, optical, and thermoelectric properties has been performed. As results, both Cs2AgGaCl6 and Cs2AgGaBr6 show semiconducting nature with a direct bandgap of about 2.57 eV and 1.42 eV, respectively. Additionally, with such desirable band gaps, the optical properties were examined based on the complex dielectric function. It has been derived that both materials exhibit a very high absorption spectrum in the order of 105 cm−1 and a low reflectivity not exceeding more than 18% in the visible and UV region. Furthermore, the Cs2AgGaBr6 has been taken into account as absorber to construct the planar p-intrinsic-n structure (FTO/TiO2/Cs2AgGaBr6/Spiro-OMeTAD/Au) and a high-record efficiency of 32.57% has been reached. The thermoelectric performance was also studied and revealed a very high Seebeck coefficient (thermo-power) and a sufficient figure of merit (ZT). Based on these results, we believe that the studied double-halide perovskites present outstanding performance for both optoelectronic and thermoelectric engineering devices.

Efficient photodegradation of disulfine blue dye and Tetracycline over Robust and Green g-CN/Ag3VO4/PAN nanofibers: Experimental design, RSM, RBF-NN and ANFIS modeling

The g-CN/Ag3VO4/PAN nanofibers (NFs) is prominent from various nanophotocatalysts (NPCs) due to their higher surface to volume ratio, mechanical strength and recyclable characteristics. In this study, g-CN/Ag3VO4/PAN NFs were obtained through in situ method by immobilizing Ag3VO4 on g-CN/PAN NFs. Compared to g-CN/PAN and Ag3VO4/PAN, the g-CN/Ag3VO4/PAN NFs revealed excellent photocatalytic performance toward disulfine blue dye (DB). Also, the g-CN/Ag3VO4/PAN NFs showed highly activity over some interference of inorganic cations/anions and excellent cycling stability. Furthermore, the batch experiments designed by central composite design (CCD) were employed for remove of tetracycline (TC). Afterward, response surface methodology (RSM), Radial basis function artificial neural network (RBF ANN) and an adaptive neuro-fuzzy inference system (ANFIS) have been used for modeling of photocatalyst dose, concentration of TC and irradiation time. Due to strong influence of pH on the photocatalytic degradation, the pH was optimized as one at a time variable. For all three models, the values of the statistical parameters were calculated. The obtained results reveal that the ANFIS models is more accurate to predict the degradation of TC. Furthermore, the effective factors were optimized by employing the Desirability function (DF) and genetic algorithm (GA) approach and then used for real water samples. At this optimum condition, the removal percentage was obtained ∼97% by DF and GA approach, respectively. At the end, the LC-Mass method was employed to detect the intermediates of photodegradation of TC molecules.

Designing new halide double perovskite materials Rb2AgGaX6 (X: Br, Cl) with direct band gaps and high power conversion efficiency

The development of lead-free inorganic halide perovskites has revolutionized photovoltaic and optoelectronic research in recent years. In this study, ab-initio methods have been implemented to predict the mechanical, optical, structural, and electronic properties of Rb2AgGaX6(X ​= ​Cl, Br). Through tolerance factor and third-order elastic constant analyses, we systematically probed the structural and mechanical strength characteristics of Rb2AgGaBr6 and Rb2AgGaCl6. These analyses provide both structural and mechanical stability. Additionally, thermodynamic stability tests were undertaken using formation energies. The calculated direct bandgaps by mBJ with spin-orbit-coupling are 2.53 ​eV and 1.28 ​eV for Rb2AgGaCl6 and Rb2AgGaBr6 respectively. The appropriate narrow electronic bandgaps provide visible-light absorption. Consequently, the optical properties revealed a high absorption coefficients (α(ω) ​≈ ​1.9 ​× ​105 ​cm−1 for Rb2AgGaBr6 and 2.1 ​× ​105 ​cm−1 for Rb2AgGaCl6), high conductivity and low reflectivity (R(ω) ​< ​10 %), which make the Rb2AgGaBr6 and Rb2AgGaCl6 attractive semiconductors for optoelectronic application. The theoretical maximum light conversion efficiency was calculated under AM1.5G solar illumination based on the variable thickness. The outcome is that bromine-based perovskite provides a superior efficiency of approximately 32.20 % and chlorine-based perovskite demonstrates an efficiency of 12.0 %. By virtue of extremely favorable bandgaps, low reflectivity and impressive efficiency, the eco-friendly halide perovskites appear to be auspicious clean renewable energy materials. Our results provide the scientific community with new insights and lead to the design of future solar cell devices.

Metal salts assisted thermoplastic polymer NIPAM in-situ carbonization on porous silica microspheres surface

The preparation of different carbon-shell morphology microspheres and controllable surface area via using thermoplastic polymers as carbon source was still a challenge. In addition, the unique structure of porous Silica@Carbon (Sil@C) microspheres not only can provide larger surface area and active site, but also have the characteristics of high mechanical strength and easy modification. Herein, we report a simple method to in-situ fixation a series of different morphology graphitized carbon shell (rosa roxburghii, bulk, and carbon sphere shapes) on porous silica microspheres surface. Metal salt assisted polymer carbonization will not only prepare graphitized carbon with different morphology on silica surface, but also facilitate the in-situ carbonization of thermoplastic polymer on the silica microspheres surface instead of internal pores; the more heat of metal salt released during carbonization, the larger the specific surface area of Sil@C.

Investigation of distinct welding parameters on mechanical and corrosion properties of dissimilar welded joints between stainless steel and low carbon steel.

The tensile strength and corrosion behavior of dissimilar welded joints are currently a subject of concern. In this work, gas metal arc welding (GMAW) and distinct welding parameters (welding current, arc voltage, and welding speed) were used to join 304 stainless steel (SUS304) and SS400 low carbon steel, and the ultimate tensile strength (UTS) of the dissimilar welded joints was investigated. A corrosion test was conducted by immersion in 3.5 wt.% sodium chloride (NaCl) solution for 7, 14, and 21 days. Based on tensile strength and Tafel testing, the welding parameters "Item 4" (welding current: 170 A, arc voltage: 20 V, welding speed: 40 cm/min) yielded good mechanical strength and low corrosion characteristics. The microstructure characterization showed that the area around the welded joints and SUS304 had more granular corrosion and corrosion tubercles with increasing immersion time. The chromium content gradually decreased. When exposed to the chloride environment, these welded joints easily underwent corrosion due to the loss of passivity. However, high-velocity oxygen-fuel (HVOF) spray used on the welded joints reduced the corrosion current density. Compared with the non-thermal spray sample (corrosion current density:7.49e - 05 A/cm2) while the corrosion current density (7.89e - 10 A/cm2) is five orders of magnitude lower. This spray effectively slowed down the corrosion rate of the welded joints and gave the structural objects good protection in the sodium chloride solution.

Experimental substantiation of kidney sutures

Introduction. Partial nephrectomy occupies a rightful priority position in the treatment of localized renal cell carcinoma. It not only provides high oncological results but also allows you to save the renal parenchyma. This reduces the risk of chronic kidney disease and cardiovascular accidents, which is especially important in young patients. The main technical problem is the closure of the renal wound with reliable hemostasis and low risk of urine leakage, especially in patients with large endophytic lesions.Objective. To study the mechanical properties of the renal parenchyma and to establish ways to prevent suture eruption under an experimental model.Materials and methods. The studies were carried out using the equipment of the Center for Collective Use "Technologies and Materials of the Belgorod State National Research University". Mechanical tests of the strength characteristics of the layers of the renal parenchyma were performed on 60 cadaveric kidneys. The tensile strength and tension of tissues during the application of various surgical sutures, as well as variants of the latter with the use of spacers made of materials that prevent thread eruption, were studied using a tensile machine.Results. During mechanical tests, the medulla was found to have the highest strength (23.58 ± 9.17 load (L)) between the layers of the renal parenchyma. The mechanical strength (8.40 ± 2.89 L) of the cortical substance in the absence of the capsule was minimal. When replacing the vertical suture through all layers by tied a knot along the resection line with a similar horizontal mattress suture, it significantly increased tensile strength (27.35 ± 12.04 L) to levels comparable to the tensile strength of the medulla. The use of a hemostatic mesh (SurgicelÒ) as a lining did not significantly affect the ultimate strength (23.58 ± 9.17 L) of the horizontal mattress suture. The use of a prolene mesh (LintexÒ mesh) for this purpose significantly prevented suture eruption (31.48 ± 9.98 L) compared to the native suture and the SurgicelÒ mesh. The maximum tensile strength (45.61 ± 6.1 L) of a horizontal mattress suture was obtained for a tape made of a polytetrafluoroethylene vascular prosthesis.Conclusion. The study of the mechanical strength of the layers of the renal parenchyma showed the inexpediency of performing a cortical suture. The use of a horizontal mattress suture significantly increases the tensile strength compared to a vertical one. Maximum mechanical strength characteristics were obtained using polytetrafluoroethylene inserts.

Experimental study on strength characteristics and internal mineral changes of Lime-stabilized loess under High-Temperature

• Effect of lime treatment on compression and shear strength of loess were studied. • Tests were carried out at a wide temperature range (30 ∼ 300 °C) and 5 lime contents. • Treatment with lime improved the strength of loess at high-temperatures. • Multiple methods XRD, TGA, DSC reveal the mechanisms of the lime-loess reactions. In this study, lime-stabilized loess with five lime contents (0 %, 3.5 %, 7 %, 10.5 %, and 14 %) treated at four temperature levels (30 °C, 100 °C, 200 °C, and 300 °C) were tested for 48 h in a series of laboratory experiments to investigate the mechanical strength characteristics and internal mineral changes of lime-stabilized loess under high temperature. The unconfined compressive strength (UCS) tests and shear box test results show that the compressive and shear strengths of lime-stabilized loess are larger than those of plain loess, not only at room temperature but also at high temperatures. Under the same lime content, the mechanical strength of each sample was greatly improved after high-temperature treatment. As the heat-treatment temperature increased within the test temperature range, the compressive and shear strengths gradually improved. These mechanical strength test results prove that adopting lime-stabilized loess as the building material for structures vulnerable to high temperatures is feasible. When compressive and shear strengths were selected as the evaluation criteria for determining the lime content, the optimal lime content in this study was 7 %. X-ray diffraction and thermal analysis test results revealed that the strength enhancement of lime-stabilized loess is mainly derived from the lime slaking reaction, pozzolanic reaction, and crystallization reaction. High-temperature treatments can promote the reaction rates of these processes.

Experimental study on the effect of prefabricated fissures on the creep mechanical properties and acoustic emission characteristics of sandstone under uniaxial compression

This study investigates the effect of prefabricated fissures on the creep mechanical strength and acoustic emission (AE) characteristics of sandstone. Under the same test conditions, indoor uniaxial compression creep AE tests were performed on intact and artificially fissured sandstone specimens using a rock rheometer and a PCI-Ⅱ AE tester controlled with an RLJW-2000 microcomputer. The variation characteristics of strain, long-term strength, number of AE events, AE ringing count, AE energy, and RA value of the two specimens were then analyzed to determine the effect of prefabricated fissures on the creep mechanical properties and AE characteristics of sandstone. The results show that under the same stress level, the instantaneous strain, creep strain, and total strain of the prefabricated fissures specimen was larger than the corresponding values of the intact specimen. The prefabricated fissures exhibited the most significant influence on the creep strain of the specimen, followed by the total strain. The fissures showed the least influence on the instantaneous strain of the specimen. Furthermore, the long-term strength of the prefabricated fissures specimen was only 37.5% of that of the intact specimen. Owing to the influence of the prefabricated fissures, the long-term strength of the sandstone was significantly reduced. In engineering practice, fissures should be noted and analyzed for the potential failure of a formation. Moreover, as the stress level increases, the number of AE events of the specimen also increases. The number of AE events and cumulative AE events generated by the prefabricated fissures specimen at various stress levels is significantly higher than the corresponding values of the intact specimen. The maximum ringing count of the prefabricated fissures specimen was 7.3 times that of the intact specimen, and the maximum AE energy was 3.8 times that of the intact specimen. The cumulative AE ringing count was 1.5 times that of the intact specimen, and the cumulative energy was 4.5 times that of the intact specimen. The prefabricated fissures significantly affect the maximum AE ringing count, maximum AE energy, cumulative AE ringing count, and cumulative AE energy of the specimen. Finally, tensile fissures were the main microcracks generated inside the intact specimen during creep, and shear cracks were secondary. The microcracks generated inside the prefabricated fissures specimen consisted of mixed tension-shear cracks, but mainly consisted of shear cracks with fewer tension cracks. The RA value correlates well with the observed internal microcracks, indicating that the RA value can be used to characterize fractures in sandstone specimens. The RA value has a guiding significance for characterizing the type of internal microcracks in the process of rock creep.

Fabrication of high aspect ratio ceramic micro-channel in diamond wire sawing as catalyst support used in micro-reactor for hydrogen production

Ceramic is an ideal material for preparing micro-channel catalyst supports with their characteristics of high temperature resistance, corrosion resistance and mechanical strength. High aspect ratio micro-channel structure has the advantages of large specific surface area, strong mass and heat transfer performance and high material utilization. However, ceramic materials are hard and brittle, and it is difficult to fabricate micro-channel structures with aspect ratio more than 1.5:1 by traditional processing methods. In this paper, a cutting method of large diameter diamond wire sawing was proposed. The micro-channels with width of 520 μm and aspect ratio of more than 4:1 was successfully fabricated by this method. Furthermore, the integrity of the micro-channel structure processed by diamond wire sawing was analyzed. And than the effect of surface morphology in different processing parameters on the catalyst loading performance were studied. The catalyst loading strength of ceramic slices with different surface morphology was tested. Finally, the ceramic micro-channel array was used as the catalyst support in micro-reactor for hydrogen production via methanol steam reforming (MSR). The methanol conversion rate and H2 production rate could reach 87.8% and 74.6 mmol/h, respectively under GHSV 12600 ml/g·h at 300 °C. The experimental results show that the large-diameter diamond wire sawing technology can be used to process ceramic microchannels with high aspect ratio; using ceramic microchannel arrays as catalyst supports in hydrogen production can obtain better reaction performance; the feasibility of ceramic materials were broadened as microchannel catalyst supports.

Frost resistance and mechanical degradation characteristics of cement-stabilized macadam under the long-term freezing–thawing cycles

• Three different cement contents and removal of two different fine particle sizes of cement-stabilized macadam (CSM) were tested. • The mechanical strength characteristics were degraded by long-term freezing−thawing cycles. • The removal size of larger fine particles had adverse effects on the strength and degradation rate of CSM. • The increase in the cement content led to an increase in the frost resistance and strain energy density of CSM. • The initial elastic modulus determined using unconfined compressive strength tests could be applied to characterize the stiffness of CSM for high-speed railway lines. The high-speed railway subgrade in seasonal frozen soil regions should be able to resist long-term freezing and thawing cycles. In consideration of cement-stabilized macadam (CSM) as the subgrade surface material needs to have resistant to freeze–thaw strength deterioration. This study aimed to evaluate the mechanical degradation characteristics of CSM under the long-term freezing-thawing cycles by the unconfined compressive strength tests. Three different cement contents (3 %, 5 %, and 7 %) and removal of two different fine particle sizes (0.1 and 0.25 mm) of CSM were studied and analyzed. The number of freezing–thawing cycles was set to 0, 1, 3, 5, 7, 10, 15, 20, 30, 40, and 50, respectively. Based on the unified calculation model of strength deterioration, evaluation index of frost resistance, and analysis of strain energy density failure, C 5 P 0.1 could be used in seasonal frozen soil regions. If the subgrade bed had requirements for permeability, fine particles with larger sizes could be removed. The results indicated that, first, the strength of fine particles with larger size removal was smaller and the strength deterioration was faster under the same cement content. Second, when the cement content was higher, CSM showed better resistance to freezing–thawing strength degradation. Further, when the cement content increased, the increase in the amplitude of strain energy density varied significantly; the increasing effect was the best when the cement content increased from 3 % to 5 %. Finally, the initial elastic modulus of the Duncan-Chang hyperbolic model was used to characterize the stiffness of CSM in the high-speed railway subgrade bed. This study revealed the mechanical degradation characteristics of CSM under the long-term freezing–thawing cycles with different cement contents and removal sizes of fine particles. The findings were useful for understanding the mechanical behavior of CSM under the long-term freezing–thawing cycles.

A comprehensive review on geotechnical properties of alkali activated binder treated expansive soil

Geopolymer based soil stabilization is an emerging research field as shown by recent research studies which indicate strong potential of their wide use for sustainable ground treatment. This paper comprehensively reviews the literature on expansive soil stabilization using alkali activated binders, focusing on the stabilization mechanism and geotechnical characteristics of treated soil inclusive of mechanical strength and durability characteristics. The stabilization mechanism is governed by the cation exchange process and the geopolymer/hydration products formation. The reported highest unconfined compressive strength (UCS) and California bearing ratio (CBR) of the geopolymer treated expansive soil cured at room temperature are 15 MPa and 81%, respectively and these values satisfy the strength criteria of most of the standards used for road base materials. The findings of the review revealed that incorporation of precursors in the range of 15–20%, alkaline molarities between 5 and 10 M, along with strong alkalis (NaOH or KOH), Ca rich additives, and discrete fibers could enhance the stabilization performance with respect to strength, swell, and durability. Alkaline activation treatment is expensive compared to the conventional Portland cement based stabilization methods, and yet the cost can be significantly reduced by employing cost effective silicates for alkaline activation. Overall, alkali activated binders (AAB) can be sustainable stabilizers to treat expansive soils for satisfactory geotechnical performance (compaction, strength and durability), however, as recommended in this review, further research should be advanced to realize the utmost viability of this promising approach in successful field application.

Experimental and numerical investigation of mechanical strength characteristics of natural fiber retrofitted rammed earth walls

Unreinforced earthen houses offer manifold environmental and economic advantages. However, such houses are inadmissible in today's era due to their poor performance during earthquakes. Recent Jan 3, 2017 moderate Tripura earthquake (Mw=5.7) has evidenced a sizable stock of damages to non-engineered adobe/rammed earth houses which primarily act as the motivation behind the present study. In this context, the present study is an attempt to propose a novel seismic encasing retrofitting technique by providing natural and artificial fiber with a key focus on the economy, sustainability, and utilizing locally available material. In this regard, static mechanical strength characteristics (i.e., shear, compressive and flexural strength) of unreinforced and retrofitted rammed earth wall units are investigated through model-scale experiments in the laboratory considering parametric variations as well as numerical analysis of prototype wall. Further, multiple linear regression analysis is performed to develop empirical relationships for predicting shear and compressive strength of retrofitted rammed earth walls. The study highlights the significant improvement in mechanical strength of retrofitted rammed earth walls by treated natural fiber retrofitting strips as well as artificial waste PP strips. Besides, the sanctity of proposed regression-based empirical equations is well verified through a numerical case study on a prototype rammed earth wall.

Experimental and numerical study on failure characteristics and mechanism of coal under different quasi-static loading rates

In mining engineering, mining rate is a significant factor for determining mining efficiency and safety. In the present work, uniaxial compression tests under different quasi-static loading rates (varying from 0.0005 mm/s to 0.01 mm/s), combined with high-speed digital image correlation (DIC) technique and numerical simulation, were conducted to study the mechanical strength and failure characteristics of coal samples. Experimental results show that strength parameters (including compressive strength, peak strain, elastic strain energy, and elastic modulus) initially increase rapidly, then the rate of increase slows as the loading rate continues to increase. Besides,with increasing loading rate, the failure mode of the coal samples gradually transitions from tension-shear to spalling-ejection failure, while full-field strain transitions from inclined shearing to vertical tensile strain distribution. Furthermore, the particle flow code (PFC) numerical simulation results indicate that the accumulative microcrack number increases and the microcracks inclination angle distribution range decreases approximately from 60° (60° − 120°) to 20° (80° − 100°) with increasing loading rate. Moreover, the micro damage and number of microcracks increase and macrocracks are more difficult to initiate as loading rate increases. As a result, the accumulated energy is less likely to be released and a more severe block ejection will occur for a sample under a high loading rate.

Self-Healing, Anti-Freezing Hydrogels and Its Application in Diversified Skin-Like Electronic Sensors

Flexible, wearable and stretchable artificial electronic skin is essential for realizing applications in many fields such as remote medical monitoring, soft robotics, human health monitoring, and artificial intelligence. However, the key lies in the development of wearable electronic products with excellent stretchability, high sensitivity, good mechanical strength and multifunctional characteristics. In this work, an antifreeze conductive hydrogel sensor based on polyvinyl alcohol (PVA), silk fibroin (SF) and polypyrrole (PPy) is prepared. The hydrogel has good electrical conductivity, considerable stretchability (860%) and compressibility. It can achieve good self-healing performance under environmental conditions. Moreover, it could be accurately capture the changes for temperatu rerange of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$- 10^{\circ }\text{C}$ </tex-math></inline-formula> to <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$50^{\circ }\text{C}$ </tex-math></inline-formula> , and could be further developed as a flexible temperature sensor. In addition, this work applies 3D printing method to prepare of wearable strain/pressure sensor. The resulting strain/pressure sensor has a wide sensing range (strain, 10%-706%; pressure, 0.5-124.75 kPa) and high sensitivity. The sensor is capable detect human movements, such as small finger movements and bending, pulse and so on. Due to the multifunctional properties and 3D printability of PVA/SF/PPy hydrogels, which is further reveals that hydrogels has fascinating potential applications in various fields such as human-machine interfaces, biosensors and wearable devices.

THE EVALUATION OF CURRENT RESEARCH ON THE STRENGTH OF DENTAL RESTORATIVE COMPOSITE MATERIALS

The aim of the study: to analyze the sources of scientific and metric information on the state of research on the strength of dental composites for tooth restoration.&#x0D; It has been determined that the range of composite materials available on the dental market is very wide. They differ significantly in chemical, mechanical, physical, and biological characteristics, operating properties, techniques of their usage. All this requires special training to use the composites effectively and to get high quality restoration results. The optimal choice of material and suitable technique taking into account a particular clinical situation can increase the durability of restorations and prevent the development of complications that largely depends on the strength characteristics of composites.&#x0D; At present, the problem of selecting and creating the perfect filling material has not been completely solved that is confirmed by the large number of new developments in materials science. At the same time, composite polymers are gaining ground in dental practice. The new concept of adhesive preparation of dental tissues before inserting filling material and improving the properties of the composite materials themselves contribute to the maximum preservation of healthy dental tissues, increase the aesthetics, durability and functionality of dental restorations.&#x0D; It has been determined that the mechanical strength characteristics of composite materials play a significant role in the longevity/durability of restorations depending on different chewing force and occlusal loading. It is important to investigate factors, which may cause the destruction of dental composites during the functional loading.&#x0D; The physical and mechanical properties of dental composites are impacted by a number of factors, including the type of polymer matrix, the amount of material takes, size and distribution of the filler, the state of the bond between the filler and the matrix, the degree of polymerization. The choice of a material also depends on a number of characteristics in terms of the combination of main components. Since the material parameters set by the material manufacturers can not be changes, the deep understanding of its properties will help to choose the best material in each clinical situation.&#x0D; The main physical properties of dental composites include compressive and tensile strength, modulus of elasticity, coefficient of thermal expansion, wear resistance, polymerization shrinkage, X-ray contrast, density and thixotropy, optical effects (transparency, fluorescence, etc.).&#x0D; The AE method based on the registration of elastic waves arising from the formation, change and destruction of the structure of various materials, is currently the most effective for studying the processes and stages of development of material defects. It enables in detecting initial changes in the material structure, the initial location of defects, the direction of their spreading and determining the maximum strength of the material. The advantages of this method include the ability to obtain information about the destruction in the early stages, its high accuracy and sensitivitys.&#x0D; The AE method is commonly used to study the resistance to destruction of various composite materials, the study of the tooth / composite interface, the analysis of polymerization stresses and the degree of shrinkage.

Potential of Waste Marble Sludge for Repressing Alkali-Silica Reaction in Concrete with Reactive Aggregates.

The continuous development of the marble industry has led to an increase in the accumulation of waste marble sludge causing landfilling and health-associated issues. The intention of the current study is to explore the potential of waste marble sludge powder (MS) utilization as a means of controlling alkali-silica reaction (ASR) in concrete. Specimen (cubes, prisms, and mortar bars) were prepared to incorporate reactive aggregates and various proportions of MS ranging from 5% to 40% as a replacement for aggregates. Expansion and mechanical strength characteristics were determined to investigate the effectiveness of MS to control ASRfor up to 150 days. Results revealed that on replacing aggregates in the control specimen with 25% MS, the ASR expansion at 14 days reduced from 0.23% to 0.17%, and the expansion at 28 days reduced from 0.28% to 0.17% which is within limits as per American Standard for Testing of Materials (ASTM) C1260. Furthermore, specimens incorporating MS exhibited improved compressive and flexural strength as compared to the identical specimen without MS. Microstructural analysis using Scanning electron microscopy (SEM) revealed micro-cracks in the control specimen while the specimen incorporating MS was found intact. Thus, it can be foreseen that the use of MS as a partial replacement of aggregates can control ASR in concrete as well as reduce the dumping and harmful emissions issue.

Fabrication of Bipolar Plates from Thermoplastic Elastomer Composites for Vanadium Redox Flow Battery.

A vanadium redox flow battery (VRFB) is a promising large-scale energy storage device, due to its safety, durability, and scalability. The utilization of bipolar plates (BPs), made of thermoplastic vulcanizates (TPVs), synthetic graphite, woven-carbon-fiber fabric (WCFF), and a very thin pyrolytic graphite sheet (GS), is investigated in this study. To boost volumetric electrical conductivity, WCFF was introduced into the TPV composite, and the plate was covered with GS to increase surface electrical conductivity. Created composite BPs acquire the desired electrical conductivity, mechanical strength, and deformation characteristics. Those properties were assessed by a series of characterization experiments, and the morphology was examined using an optical microscope, a scanning electron microscope, and atomic force microscopy. Electrochemical testing was used to confirm the possibility of using the suggested BP in a working VRFB. The laminated BP was utilized in a flow cell to electrolytically convert V(IV) to V(V) and V(II), which achieved comparable results to a commercial graphite bipolar plate. Following these experiments, the laminated bipolar plates’ surfaces were examined using X-ray photoelectron spectroscopy, and no evidence of corrosion was found, indicating good durability in the hostile acidic environment.