scholarly journals Strength Deterioration Mechanism of Bentonite Modified Loess After Wetting-Drying Cycles

2021 ◽  
Author(s):  
Zelin Niu ◽  
Jian Xu ◽  
Yanfeng Li ◽  
Zefeng Wang ◽  
Bao Wang
Keyword(s):  
Fractal Dimension ◽  
Friction Angle ◽  
Damage Mechanism ◽  
Regression Equations ◽  
Strength Deterioration ◽  
Damage Degree ◽  
Before And After ◽  
Lower Porosity ◽  
Deterioration Mechanism ◽  
Loess Region

Abstract The employment of bentonite modified loess (BML) is a common method of constructing the anti-seepage lining of landfills in the loess region of China, and its long-term secure performance is threatened by wetting-drying (W-D) cycles. Taking the remolded loess (RL) and BML with 15% in mass of bentonite as research objects, the W-D cycles test, scanning electron microscope (SEM) test and direct shear test were carried out to analyze the effects of W-D cycles on the microstructure and shear strength of samples. The regression equations between strength and micro-pore structure parameters were established by multivariate linear stepwise regression method. The damage mechanism of BML after W-D cycles was studied by establishing damage degree models based on porosity and cohesion. Results indicate that clay minerals such as montmorillonite in BML absorb water and expand to fill the macropores, resulting in more medium and small pores and more pronounced surface contact of particles. After W-D cycles, the particle arrangement of samples before and after bentonite modification tends to be loose. Both the porosity and fractal dimension increase and tend to stabilize after five cycles. The BML exhibits lower porosity and greater fractal dimension while its cohesion and internal friction angle show more significant decrease after W-D cycles than those of RL. The damage variables based on porosity and cohesion well describe the W-D induced damage of loess before and after modification from macro- and micro-scale perspectives. The damage degree of samples increases with W-D cycles, but the increment decreases.

scholarly journals Strength Deterioration Mechanism of Bentonite Modified Loess After Wetting- Drying Cycles

2021 ◽  
Author(s):  
Ze-Lin Niu ◽  
Jian Xu ◽  
Yan-Feng Li ◽  
Ze-Feng Wang ◽  
Bao Wang
Keyword(s):  
Fractal Dimension ◽  
Friction Angle ◽  
Damage Mechanism ◽  
Area Ratio ◽  
Regression Equations ◽  
Strength Deterioration ◽  
Damage Degree ◽  
Pore Area ◽  
Before And After ◽  
Loess Region

Abstract The employment of bentonite modified loess (BML) is a common method of constructing the anti-seepage lining of landfills in the loess region of China, and its long-term secure performance is threatened by wetting-drying (W-D) cycles. Taking the remolded loess (RL) and BML with 15% in mass of bentonite as research objects, the W-D cycles test, scanning electron microscope (SEM) test and direct shear test were carried out to analyze the effects of W-D cycles on the microstructure and shear strength of samples. The regression equations between strength and micro-pore structure parameters were established by the multivariate linear stepwise regression method. The damage mechanism of BML after W-D cycles was studied by establishing damage degree models based on pore area ratio and cohesion. Results indicate that the water absorption and expansion of bentonite effectively block the intergranular pores, resulting in more medium and small pores and more pronounced surface contact of particles. After W-D cycles, the particle arrangement of samples before and after bentonite modification tends to be loose. Both the pore area ratio and fractal dimension increase and tend to stabilize after five cycles. The BML exhibits lower pore area ratio and greater fractal dimension while its cohesion and internal friction angle show more significant decrease after W-D cycles than those of RL. The damage variables based on pore area ratio and cohesion well describe the W-D induced damage of loess before and after modification from macro- and micro-scale perspectives. The damage degree of samples increases with W-D cycles, but the increment decreases.

Comparison of corrosion resistance properties of Ni-P and Ni-W-P coatings obtained by electroless deposition

2020 ◽  
Vol 25 (2) ◽  
pp. 66-71
Author(s):  
A.B. Drovosekov
Keyword(s):  
Corrosion Resistance ◽  
Sulfuric Acid ◽  
Electroless Deposition ◽  
Corrosion Damage ◽  
Electrochemical Activity ◽  
High Porosity ◽  
Environment Analysis ◽  
Damage Degree ◽  
Lower Porosity ◽  
Electroless Coatings

Corrosion resistance properties, such as porosity, stability in the atmosphere of NaCl mist, and anodic electrochemical activity in a sulfuric acid solution are studied and compared for Ni-W-P and Ni-P coatings obtained by electroless deposition. The studied coatings were obtained from solutions with glycine as the main ligand and contained 10.2 to 15.6 at.% of phosphorus and up to 3.3 at.% of tungsten. It is shown that Ni-W-P coatings with a tungsten content of 2.3 to 3.3 at.% and a thickness of 15 μm have a significantly lower porosity as compared with nickel-phosphorus coatings of the same thickness. Also, significantly better stability of Ni-W-P coatings in a NaCl mist atmosphere was observed, their corrosion damage degree is less than that of Ni-P coatings, and relatively little depends on the duration of exposure in a corrosive environment. Analysis of anodic polarization curves showed an almost similar electrochemical activity upon dissolution of Ni-P and Ni-W-P coatings in sulfuric acid. Both these types of electroless coatings showed a markedly better tendency to anodic dissolution than pure nickel. Taking into account the obtained experimental data, a conclusion is made as to the better protective characteristics of Ni-W-P coatings in comparison with nickel-phosphorus coatings. The main reason of the inferior protective properties of Ni-P coatings is their relatively high porosity.

Heat Power Determination of Dv-290 Refrigerator’s Evaporator on the Basis of Thermodynamic Parameters of Inlet Air / Określenie Mocy Cieplnej Parownika Chłodziarki Dv-290 Na Podstawie Parametrów Termodynamicznych Powietrza Wlotowego

2012 ◽  
Vol 57 (4) ◽  
pp. 911-920
Author(s):  
Bernard Nowak ◽  
Zbigniew Kuczera
Keyword(s):  
Thermodynamic Parameters ◽  
Thermal Power ◽  
Correlation Coefficients ◽  
Specific Humidity ◽  
Physical Parameters ◽  
Air Cooling ◽  
Regression Equations ◽  
Evaporation And Condensation ◽  
Before And After ◽  
The Given

Abstract The present paper introduces a method for calculating the thermal power of DV-290 mining air cooler’s evaporator. The power usually differs from the nominal power given by the manufacturer. The thermodynamic parameters of cooled air are not obtained as a result of in situ measurements, but in indirect manner that is by determining the evaporation and condensation’s pressure values of R407C refrigerant. The pressure dependencies formulated as a function of air enthalpy at the evaporator’s inlet were obtained using calculations of a computer program which solves the system of equations describing heat and mass transfer in the refrigerator’s compressor on the basis of previous measurements of air performed before and after its cooling. The obtained dependencies are demonstrated in a graphical (fig. 2 and fig. 3) and analytical (the regression equations (19) and (20)) manner, the values of correlation coefficients are also presented. For the known evaporation and condensation pressure values of the refrigerant, and thus for its basic physical parameters the complete thermal power of the evaporator was determined, that is its: air cooling overt power, dehumidification occult power, temperature, relative humidity and specific humidity of air after its cooling. In addition, using the mentioned method, the capacity of DV-290 refrigerator’s evaporator is provided for the given thermodynamic parameters of air before cooling, along with air thermodynamic parameters after cooling.

Damage Assessment of the Attacked Airports Based on Image Analysis

2013 ◽  
Vol 321-324 ◽  
pp. 1168-1171
Author(s):  
Xiao Nan Zhang ◽  
Jun Feng Yang ◽  
Si Liang Du ◽  
Jun Zhi
Keyword(s):  
Damage Assessment ◽  
Automatic Method ◽  
Analysis Method ◽  
Image Information ◽  
Damage Degree ◽  
Before And After ◽  
Battle Damage Assessment ◽  
Damage Extent ◽  
Modern War ◽  
Assessment Result

Battle Damage Assessment (BDA) is to assess the damage degree of enemy’s target after being attacked. In modern war, combat commanders always make decision on the basis of BDA. In this paper, an automatic method for assessing the damage extent of an attacked airport based on the image taken before and after a strike is described. Firstly, the airport blockade condition is analyzed and damage assessment criteria of airport are proposed. Secondly, three steps of the image information pretreatment are carried out and a reliability analysis method of image information is proposed. Lastly, damage assessment result is calculated to verify the validity and availability of the proposed method.

scholarly journals Shear Strength Deterioration Effect and Slope Reliability Analysis Under Extreme Ice-snow Melting Conditions 

2021 ◽  
Author(s):  
Tongqiang Xiong ◽  
Jianlin Li ◽  
Lehua Wang ◽  
Huafeng Deng ◽  
Xiaoliang Xu
Keyword(s):  
Shear Strength ◽  
Friction Angle ◽  
Soil Samples ◽  
Creep Model ◽  
Shear Strength Parameters ◽  
Snow Melting ◽  
Strength Deterioration ◽  
Melting Cycle ◽  
Deformation Stability ◽  
Deterioration Effect

Abstract Extreme ice-snow melting in winter affects the infiltration process of snow water on the slope surface significantly, and plays an important role in the deformation stability of landslide. The fluctuation trend of slope stability under ice-snow melting is the same as that of soil volume water content. The deterioration effect of mechanical parameters will directly affect the deformation stability of bank slope. Based on this, the ice-snow melting cycle model test of slope soil was designed and carried out. The results are showed.(1) We were established an ice-snow melting model based on physical process. In the process of ice-snow melting, the soil cohesion and internal friction Angle have obvious deterioration effect .The deterioration of cohesion is obviously larger than that of internal friction Angle. In the early part of the ice-snow melting cycle, the deterioration of shear strength parameters is very obvious. Among them, the deterioration of shear strength parameters caused by the first four ice-snow melting cycles accounted for about 70% of the total deterioration. After the G2/T2 ice-snow melting cycle, the degree of phase deterioration gradually decreases. The deterioration trend of shear parameters of soil samples gradually tends to be gentle. (2) In the ice-snow melting cycle, the inside of the soil samples have micro-cracks, fissures repeatedly opened and closed, gradually developed and converged. The result is that the soil samples change from dense state to loose state where internal cracks develop. The internal damage of soil samples is the fundamental reason for the gradual deterioration of shear strength.（3）We are keep to the relative independence principle of creep model and unsaturated seepage equation. We are studied and improved the parameter solving method of creep model. The modified model is reasonable and effective. The creep trend and main characteristics of the unsaturated soil can be described well. Shear strength deterioration effect and slope reliability analysis under extreme ice-snow melting conditions .It has important reference significance to the protection of extreme snow and ice disaster on the bank slope.

Megan’s Law 20 Years Later: An Empirical Analysis and Policy Review

2018 ◽  
Vol 45 (7) ◽  
pp. 1028-1046 ◽  
Author(s):  
Kristen M. Zgoba ◽  
Wesley G. Jennings ◽  
Laura M. Salerno
Keyword(s):  
Sex Offenders ◽  
Sex Offender ◽  
Risk Group ◽  
High Risk Group ◽  
Regression Equations ◽  
Megan's Law ◽  
Multivariate Logistic Regression ◽  
Recidivism Rates ◽  
Before And After ◽  
General Recidivism

This present study examines the sexual and general recidivism rates of 547 convicted sex offenders released before and after the enactment of Megan’s Law in New Jersey. Presenting the longest Megan’s Law evaluation, participants were followed for an average of 15 years after release (range = 10-29 years). Bivariate and multivariate logistic regression equations were estimated to identify covariates significantly associated with both sexual and general recidivism. Group-based trajectories of general recidivism within the 10 years post–prison release were also estimated and compared according to pre–Megan’s Law and post–Megan’s Law release status. No differences in recidivism rates were noted between the cohorts, but differences emerged in the offending trajectories of the high-risk group of offenders within 10 years of release. These results highlight the lack of impact that sex offender registration and notification (SORN) laws have on sexual and general reoffending rates postrelease.

scholarly journals Evolution Rules of Fractures for Mudstone under Compression Shear Load and the Fractal Characteristics of Broken Blocks

2019 ◽  
Vol 2019 ◽  
pp. 1-7 ◽  
Author(s):  
Zhaoyun Chai ◽  
Jinbo Bai ◽  
Haiyang Zhang ◽  
Pan Yang
Keyword(s):  
Fractal Dimension ◽  
Compression Test ◽  
Shear Fracture ◽  
Fractal Theory ◽  
Friction Angle ◽  
Shear Loading ◽  
Shear Load ◽  
Deformation And Failure ◽  
Fractal Characteristics ◽  
Logarithmic Relationship

Failure of rocks is commonly induced by compressive and shear coupling loading. Knowledge of the mechanism and process of deformation and failure of rocks under compressive shear loading condition is an important basis for the study of stability in rock engineering. Based on the nonlinear fractal theory, it is possible to examine the evolution rules of fractures in mudstone under compression shear load and the fractal characteristics of broken blocks using the shear compression test with variable angles of mudstone specimens in natural conditions. This research shows that the cohesion and friction angle parameters of rock samples are achieved by draw Mohr’s strength envelope according to the test date of variable-angle shear compression test. It also shows that the shape of load-displacement curves of rocks can be divided into four stages: compaction, elastic, plastic, and fracture, and the curve can accurately represent the transformation and breakage characteristics of rock during shear fracture. And the distribution of broken blocks shows a strong statistical resemblance to the fractal distribution, and the fractal dimension is able to reflect the distribution characteristics of broken blocks. With increasing the shear angle, the fractal dimension of broken blocks decreases in a logarithmic relationship.

Curvature and Strength of Ni-YSZ Solid Oxide Half-Cells After Redox Treatments

2010 ◽  
Vol 7 (5) ◽  
Author(s):  
Antonin Faes ◽  
Henrik Lund Frandsen ◽  
Mikko Pihlatie ◽  
Andreas Kaiser ◽  
Darlene R. Goldstein
Keyword(s):  
Thermal Stresses ◽  
Solid Oxide ◽  
Stabilized Zirconia ◽  
Half Cell ◽  
Redox Cycles ◽  
Before And After ◽  
Lower Porosity ◽  
Ring Method ◽  
Anode Supported Cell ◽  
Cell Strength

One of the main drawbacks of anode-supported solid oxide fuel cell technology is the limited capability to withstand reduction and oxidation (“RedOx”) of the Ni phase. This study compares the effect of RedOx cycles on curvature and strength of half-cells, composed of a nickel-yttria-stabilized-zirconia (Ni-YSZ) support, a Ni-YSZ anode, and an 8YSZ electrolyte. Five different treatments are studied: (i) reduction at 600°C, (ii) reduction at 1000°C, (iii) 1RedOx cycle at 750°C, (iv) 5RedOx cycles at 750°C, and (v) 5RedOx cycles at 600°C. The strength is measured by the ball-on-ring method, where it is calculated analytically from the force. In this calculation the thermal stresses are estimated from the curvature of the half-cell. For each treatment, more than 30 samples are tested. About 20 ball-on-ring samples are laser cut from one original 12×12 cm2 half-cell. Curvature and porosity are measured for each sample before and after RedOx treatments. The first observations show that increasing the reduction temperature enhance strength but does not influence the curvature, whereas 1RedOx cycle at 750°C increases the curvature without changing the strength. Consecutive RedOx cycles seem to decrease anode-supported cell strength but this is coupled to lower porosity of the tested samples.

Ice-Formation Expansion of Salt Solution and its Effect on Frost Damage of Concrete

2014 ◽  
Vol 633 ◽  
pp. 281-285
Author(s):  
Zu Quan Jin ◽  
Tie Jun Zhao ◽  
Song Gao ◽  
Su Yuan Zhang
Keyword(s):  
Frost Damage ◽  
Corrosion Products ◽  
Ice Formation ◽  
Chloride Salt ◽  
Nacl Solution ◽  
Damage Degree ◽  
Salt Corrosion ◽  
Deterioration Mechanism ◽  
Composite Solution ◽  
Air Entrained Concrete

In order to explain the deterioration mechanism of air entrained concrete subjected to freeze-thaw cycles in water, NaCl, Na2SO4 and composite solution, The damage of concrete and ice-formation expansion of salt corrosion solution are tested. The experimental results show that the damage degree of concrete under salt frost is NaCl solution>composite solution>water>Na2SO4 solution. Considering the chloride penetrated into concrete and following 2nd Fick’s Law, the ice-formation expansion resulted by NaCl solution in surface layer of concrete is higher than that in inner, and the expansion stress at outer layer is 1.73 times of that at inner layer according to the proposed function. The expansion stress difference between the internal and external layer causes spalling damage of concrete in chloride salt frost. The ice-formation expansion of Na2SO4 solution increases with its raising concentration and it is higher than that of NaCl solution at the same temperature. However, the corrosion products are ettringite and gypsum after sulfate salt frost, and the volume of solid corrosion products is barely change, or even reducible.

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