Relationship between Fractal Dimension of Fragmentation Degree and Energy Dissipation of Rock-Like Materials under Initial Stress

In order to obtain the relationship between fractal dimension and energy dissipation of rock-like materials under initial stress state, a variable cross-section split Hopkinson pressure bar (SHPB) test system with active confining pressure loading device was used to carry out impact compression and splitting tests on cemented sand specimens. The impact test results show that (1) the prediction value on the fragmentation degree of cemented sand specimens by using the fractal model is basically consistent with the screening results of actual test, which verifies the applicability of the fractal calculation model given in this study; (2) the more the fracture energy dissipated in the crushing process of cemented sand specimens, the more serious the fragmentation degree is, and accordingly the larger the fractal dimension is, that is, the fracture energy is positively correlated with the fractal dimension; (3) there is an exponential relationship between the fractal dimension and energy dissipation of cemented sand specimens under initial stress, which is so different from that under no initial stress. The experimental results in this study can be used to modify the fractal damage model for rock blasting considering the initial stress.

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Experimental Study on Dynamic Compression Characteristics of Red Sandstone under Wetting-Drying Cycles

Advances in Civil Engineering ◽

10.1155/2020/6688202 ◽

2020 ◽

Vol 2020 ◽

pp. 1-10

Author(s):

Bin Du ◽

Haibo Bai ◽

Minglei Zhai ◽

Shixin He

Keyword(s):

Compressive Strength ◽

Fractal Dimension ◽

Strain Rate ◽

Split Hopkinson Pressure Bar ◽

Dynamic Compression ◽

Degradation Mechanism ◽

Impact Compression ◽

Red Sandstone ◽

Dynamic Compressive Strength ◽

The Impact

To study the influence of wetting-drying cycles on dynamic mechanical properties of rock masses, the impact compression tests of red sandstone samples were carried out by using a split Hopkinson pressure bar (SHPB) apparatus with a diameter of 50 mm. The results showed that under the same number of wetting-drying cycles, the dynamic compressive strength of red sandstone increased exponentially with the strain rate, and the sensitivity of the strain rate decreased with the increase of wetting-drying cycles. The deterioration effect of wetting-drying cycles was significant, and the dynamic and static compressive strength decreased with the increase of wetting-drying cycles; the higher the strain rate, the stronger the sensitivity to wetting-drying cycles. Besides, the influence of wetting-drying cycles and strain rate was comprehensively studied, and the equation of dynamic compressive strength of red sandstone was obtained. After different wetting-drying cycles, the fractal characteristics of red sandstone dynamic fragmentation were obvious, and the fractal dimension was 2.02–2.80, and the fractal dimension increased logarithmically with the strain rate. Finally, the internal microstructure of red sandstone after different wetting-drying cycles was analyzed, and the degradation mechanism of the rock by the cycles was discussed.

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Dynamic Compression Damage Energy Consumption and Fractal Characteristics of Shale

Shock and Vibration ◽

10.1155/2019/5792841 ◽

2019 ◽

Vol 2019 ◽

pp. 1-7

Author(s):

Guoliang Yang ◽

Jingjiu Bi ◽

Linian Ma

Keyword(s):

Fractal Dimension ◽

Energy Consumption ◽

Energy Dissipation ◽

Strain Rate ◽

Split Hopkinson Pressure Bar ◽

Dynamic Compression ◽

Fractal Theory ◽

Dissipated Energy ◽

Impact Tests ◽

The Impact

Studying the relationship between energy consumption and crushed size of shale under different loading conditions is the key to efficient shale cracking. The split Hopkinson pressure bar system was used to study the dynamic mechanical properties of shale under parallel- and vertical-bedding loading, and energy dissipation in the impact tests was calculated. Relationships between the average crushed size of shale fracture products and energy dissipation and between the fractal dimension and dissipated energy were studied using fractal theory. The experimental results showed that the dynamic compressive strength of shale under parallel- and vertical-bedding conditions had an obvious positive correlation with the strain rate. Dissipative energy of the shale samples under loading in both directions increased with the increase of strain rate. The increase of the strain rate enhanced crushing of the sample. The vertical-bedding shale samples had stronger ability to absorb energy and more internal crack propagation. Dissipative energies of the shale samples in the parallel- and vertical-bedding impact tests were positively related to the fractal dimension. The fractal dimension increased with the increase of dissipative energy during sample failure; with further increase in the dissipative energy, its effect on the change of fractal dimension gradually weakened.

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Breakage Characterization of Magnetite under Impact Loads and Cyclic Impact Loading

Energies ◽

10.3390/en13205459 ◽

2020 ◽

Vol 13 (20) ◽

pp. 5459

Author(s):

Liang Si ◽

Yijun Cao ◽

Guixia Fan

Keyword(s):

Fractal Dimension ◽

Strain Rate ◽

Intergranular Fracture ◽

Split Hopkinson Pressure Bar ◽

Fractal Theory ◽

Fracture Morphology ◽

Impact Loads ◽

Impact Compression ◽

Cyclic Impact ◽

The Impact

A series of impact compression tests were conducted to study the breakage characteristics of magnetite, as well as the impact pressure on its strain rate and dynamic compressive strength. The dynamic mechanical properties and fragmentation size distribution of magnetite under diverse impact loads and cyclic impact were investigated, with fractal theory as a basis and split Hopkinson pressure bar (SHPB). Breakage methods were also employed to analyze the fracture morphology of magnetite. According to the result, the fractal dimension can reflect the distribution of fragments in various sizes. If the strain rate increases, the fractal dimension will be larger, the fragment size will be finer, and the fragmentation degree will be more influential. A micro-analysis of SEM images demonstrates that the fracture morphology is determined by mineral properties. Under low load cyclic impact, intergranular fracture is the main fractography. Besides, the intergranular fracture will be changed to a transgranular one as the impact load increases.

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Research on Fractal Characteristics and Energy Dissipation of Concrete Suffered Freeze-Thaw Cycle Action and Impact Loading

Materials ◽

10.3390/ma12162585 ◽

2019 ◽

Vol 12 (16) ◽

pp. 2585 ◽

Cited By ~ 3

Author(s):

Yan Li ◽

Yue Zhai ◽

Xuyang Liu ◽

Wenbiao Liang

Keyword(s):

Fractal Dimension ◽

Energy Consumption ◽

Energy Dissipation ◽

Impact Loading ◽

Physical Parameters ◽

Impact Compression ◽

Freeze Thaw ◽

Thaw Cycle ◽

Freeze Thaw Cycle ◽

Fractal Characteristics

In order to study the fractal characteristics and energy dissipation of concrete suffered freeze-thaw cycle actions and impact loading, C35 concrete was taken as the research object in this paper, and freeze-thaw cycle tests were carried out with a freeze-thaw range of −20 °C~20 °C and a freeze-thaw frequency of 0~50 times. The degradation characteristics of concrete material and the variation rules of basic physical parameters under various freeze-thaw cycle conditions were obtained consequently. By using the SHPB (separated Hopkinson pressure bar) test device, impact compression tests of concrete specimens under different freeze-thaw cycle actions were developed, then the process of impact crushing and the mechanism of damage evolution were analyzed. Based on the screening statistical method and the fractal theory, the scale-mass distribution rules and fractal dimension characteristics of crushing blocks are investigated. Furthermore, the absorption energy, fracture energy and block kinetic energy of concrete under different conditions were calculated according to the energy dissipation principle of SHPB test. The relationship between the energy consumption density and the fractal dimension of fragments was established, and the coupling effect mechanism of freeze-thaw cycle action and strain rate effect on the fractal characteristics and energy consumption was revealed additionally. The research results show that the concrete under different freeze-thaw cycle conditions and impact loading speeds has fractal properties from the microscopic damage to the macroscopic fracture. The energy dissipation is intrinsically related to the fractal characteristics, and the energy consumption density increases with the increase of the fractal dimension under a certain freeze-thaw cycle condition. When at a certain loading speed, with the growth of freeze-thaw cycles, the energy consumption density reduces under the same fractal dimension, while the fractal dimension improves under the same energy consumption density.

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The impact of traditional plants and their secondary metabolites in the discovery of COVID-19 treatment

Current Pharmaceutical Design ◽

10.2174/1381612826666201118103416 ◽

2020 ◽

Vol 26 ◽

Author(s):

Shabana Bibi ◽

Ayesha Sarfraz ◽

Ghazala Mustafa ◽

Zeeshan Ahmed ◽

Muhammad Aurang Zeb ◽

...

Keyword(s):

Secondary Metabolites ◽

Test System ◽

Chemical Information ◽

System Type ◽

The Family ◽

Comprehensive Search ◽

Coronavirus Infection ◽

The Impact ◽

First Time ◽

Plant Sources

Background: Coronavirus Disease-2019 belongs to the family of viruses which cause a serious pneumonia along with fever, breathing issues and infection of lungs for the first time in China and later spread worldwide. Objective: Several studies and clinical trials have been conducted to identify potential drugs and vaccines for Coronavirus Disease-2019. The present study listed natural secondary metabolites identified from plant sources with antiviral properties and could be safer and tolerable treatment for Coronavirus Disease-2019. Methods: A comprehensive search on the reported studies was conducted using different search engine such as Google scholar, SciFinder, Sciencedirect, Medline PubMed, and Scopus for the collection of research articles based on plantderived secondary metabolites, herbal extracts, and traditional medicine for coronavirus infections. Results: Status of COVID-19 worldwide and information of important molecular targets involved in COVID-19 is described and through literature search, is highlighted that numerous plant species and their extracts possess antiviral properties and studied with respect to Coronavirus treatments. Chemical information, plant source, test system type with mechanism of action for each secondary metabolite is also mentioned in this review paper. Conclusion: The present review has listed plants that have presented antiviral potential in the previous coronavirus pandemics and their secondary metabolites which could be significant for the development of novel and a safer drug which could prevent and cure coronavirus infection worldwide.

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Lightweight Cement Conglomerates Based on End-of-Life Tire Rubber: Effect of the Grain Size, Dosage and Addition of Perlite on the Physical and Mechanical Properties

Materials ◽

10.3390/ma14010225 ◽

2021 ◽

Vol 14 (1) ◽

pp. 225

Author(s):

Andrea Petrella ◽

Michele Notarnicola

Keyword(s):

Grain Size ◽

End Of Life ◽

Compression Tests ◽

Tire Rubber ◽

Impact Compression ◽

Weight Percentage ◽

Deep Groove ◽

Mechanical Strengths ◽

The Impact ◽

Thermal Conductivities

Lightweight cement mortars containing end-of-life tire rubber (TR) as aggregate were prepared and characterized by rheological, thermal, mechanical, microstructural, and wetting tests. The mixtures were obtained after total replacement of the conventional sand aggregate with untreated TR with different grain sizes (0–2 mm and 2–4 mm) and distributions (25%, 32%, and 40% by weight). The mortars showed lower thermal conductivities (≈90%) with respect to the sand reference due to the differences in the conductivities of the two phases associated with the low density of the aggregates and, to a minor extent, to the lack of adhesion of tire to the cement paste (evidenced by microstructural detection). In this respect, a decrease of the thermal conductivities was observed with the increase of the TR weight percentage together with a decrease of fluidity of the fresh mixture and a decrease of the mechanical strengths. The addition of expanded perlite (P, 0–1 mm grain size) to the mixture allowed us to obtain mortars with an improvement of the mechanical strengths and negligible modification of the thermal properties. Moreover, in this case, a decrease of the thermal conductivities was observed with the increase of the P/TR dosage together with a decrease of fluidity and of the mechanical strengths. TR mortars showed discrete cracks after failure without separation of the two parts of the specimens, and similar results were observed in the case of the perlite/TR samples thanks to the rubber particles bridging the crack faces. The super-elastic properties of the specimens were also observed in the impact compression tests in which the best performances of the tire and P/TR composites were evidenced by a deep groove before complete failure. Moreover, these mortars showed very low water penetration through the surface and also through the bulk of the samples thanks to the hydrophobic nature of the end-of-life aggregate, which makes these environmentally sustainable materials suitable for indoor and outdoor elements.

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Application and Development of an Environmentally Friendly Blast Hole Plug for Underground Coal Mines

Shock and Vibration ◽

10.1155/2018/6964386 ◽

2018 ◽

Vol 2018 ◽

pp. 1-12

Author(s):

Donghui Yang ◽

Yixin Zhao ◽

Zhangxuan Ning ◽

Zhaoheng Lv ◽

Huafeng Luo

Keyword(s):

Split Hopkinson Pressure Bar ◽

Low Cost ◽

Blast Hole ◽

Environmentally Friendly ◽

Test System ◽

Industrial Test ◽

Labor Intensity ◽

Rock Blasting ◽

Hopkinson Pressure Bar ◽

The Impact

Drilling and blasting technology is one of the main methods for pressure relief in deep mining. The traditional method for blasting hole blockage with clay stemming has many problems, which include a large volume of transportation, excess loading time, and high labor intensity. An environmentally friendly blast hole plug was designed and developed. This method is cheap, closely blocks the hole, is quickly loaded, and is convenient for transportation. The impact test on the plug was carried out using an improved split Hopkinson pressure bar test system, and the industrial test was carried out in underground tunnel of coal mine. The tests results showed that, compared with clay stemming, the new method proposed in this paper could prolong the action time of the detonation gas, prevent premature detonation gas emissions, reduce the unit consumption of explosives, improve the utilization ratio, reduce the labor intensity of workers, and improve the effect of rock blasting with low cost of rock breaking.

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Sensitivity Based Approach for Transmission Congestion Management Utilizing Bids for Generation Rescheduling and Load Curtailment

International Journal of Emerging Electric Power Systems ◽

10.2202/1553-779x.1357 ◽

2006 ◽

Vol 7 (4) ◽

Cited By ~ 4

Author(s):

Himanshu Kumar Singh ◽

S.C. Srivastava ◽

Ashwani Kumar Sharma

Keyword(s):

Electricity Markets ◽

Power Flow ◽

Reactive Power ◽

Congestion Management ◽

Test System ◽

Hyperbolic Function ◽

Flow Sensitivity ◽

Fair Competition ◽

Load Curtailment ◽

The Impact

One of the most important tasks of System Operator (SO) is to manage congestion as it threatens system security and may cause rise in electricity price resulting in market inefficiency. In corrective action congestion management schemes, it is crucial for SO to select the most sensitive generators to re-schedule their real and reactive powers and the loads to curtail in extreme congestion management. This paper proposed the selection of most sensitive generators and loads to re-schedule their generation and load curtailment based on the improved line flow sensitivity indices to manage congestion. The impact of slack bus on power flow sensitivity factors has been determined to encourage fair competition in the electricity markets. Effect of bilateral and multilateral transactions, and impact of multi-line congestion on congestion cost has also been studied. The generators reactive power bid has been modeled by a continuous differentiable tangent hyperbolic function. The proposed concept of congestion management has been tested on a practical 75-bus Indian system and IEEE-118-bus test system.

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Green Preparation, Spheroidal, and Superior Property of Nano-1,3,5,7-Tetranittro-1,3,5,7-Tetrazocane

Journal of Nanomaterials ◽

10.1155/2018/5839037 ◽

2018 ◽

Vol 2018 ◽

pp. 1-8 ◽

Cited By ~ 5

Author(s):

Xinlei Jia ◽

Jingyu Wang ◽

Conghua Hou ◽

Yingxin Tan

Keyword(s):

Activation Energy ◽

Particle Size ◽

Fractal Dimension ◽

Particle Size Distribution ◽

Size Distribution ◽

Fractal Theory ◽

Crystal Form ◽

Decomposition Temperature ◽

Scanning Calorimetry ◽

The Impact

Herein, a green process for preparing nano-HMX, mechanical demulsification shearing (MDS) technology, was developed. Nano-HMX was successfully fabricated via MDS technology without using any chemical reagents, and the fabrication mechanism was proposed. Based on the “fractal theory,” the optimal shearing time for mechanical emulsification was deduced by calculating the fractal dimension of the particle size distribution. The as-prepared nano-HMX was characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), and differential scanning calorimetry (DSC). And the impact sensitivities of HMX particles were contrastively investigated. The raw HMX had a lower fractal dimension of 1.9273. The ideal shearing time was 7 h. The resultant nano-HMX possessed a particle size distribution ranging from 203.3 nm to 509.1 nm as compared to raw HMX. Nano-HMX particles were dense spherical, maintaining β-HMX crystal form. In addition, they had much lower impact sensitivity. However, the apparent activation energy as well as thermal decomposition temperature of nano-HMX particles was decreased, attributing to the reduced probability for hotspot generation. Especially when the shearing time was 7 h, the activation energy was markedly decreased.

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Eco-friendly technology of manufacturing complex products made of composites

E3S Web of Conferences ◽

10.1051/e3sconf/201914002004 ◽

2019 ◽

Vol 140 ◽

pp. 02004

Author(s):

Aleksey Ignatov ◽

Rustam Subkhankulov

Keyword(s):

Composite Materials ◽

Cross Section ◽

Manufacturing Process ◽

Volume Fraction ◽

Turbine Blades ◽

Variable Cross Section ◽

Variable Cross ◽

Technological Parameters ◽

Technological Support ◽

The Impact

Numerous studies in application of modern composite materials show that their advantages can be successfully implemented in manufacturing «smart» products. This study proposes an improved technological method of manufacturing multilayer environmentally friendly products with a variable cross section, which allows us to expand the possibilities of using modern polymer composite materials (PCM). The technology allows manufacturing products of the most complex geometric shapes, such as wind turbine blades. The aim of the study is the technological support of engineering production in the manufacture of multilayer products of variable cross section made from PCM. Scientific novelty consists in identifying the patterns of implementation and management of the manufacturing process of multilayer products of variable cross-section, and establishing the influence of structural and technological parameters of the manufacturing process on their operational characteristics. The relationship between the pressure of a hot directed air stream and the volume fraction of pores in the hardened material of a multilayer composite product with a variable cross section during layer-by-layer application is investigated. During the study, fundamental and applied principles of mechanical engineering technology, material resistance, adhesion theory, mathematical statistics tools and software were used to process the results of the experiment. Based on the results of laboratory studies, a methodology has been developed for effective prediction of pore content in the manufacturing of composite products. The introduction of the presented technology and the corresponding original methodology into production will reduce the complexity and energy costs of manufacturing composite products, improve their quality and reduce the impact of toxic components from composite materials on workers.

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