A New Bilayer Continuum Model Based on Gurtin-Murdoch and Consistent Couple-Stress Theories for Stability Analysis of Beam-Type Nanotweezers

2016 ◽  
Vol 33 (2) ◽  
pp. 137-146 ◽  
Author(s):  
M. Keivani ◽  
A. Koochi ◽  
M. Abadyan

AbstractNano-scale beams might not be considered uniform isotropic since the energy of the surface layer and microstructure of the bulk part highly affect the mechanical characteristics of the beams. Herein, the impact of the energy of the surface layer and the microstructure of the bulk on the mechanical stability of beam-type nanotweezers are investigated. A new bilayer continuum model has been developed which incorporates the strain energy of the surface atoms as well as the microstructure-dependent strain energy of the bulk material. The recently-developed consistent couple stress elasticity (CCSE) in combination with the Gurtin-Murdoch surface theory is applied to derive the governing equation. The nonlinear governing equation was solved using numerical generalized differential quadrature (GDQ). Effects of various parameters including characteristics of the surface layer, microstructure of the bulk and external forces on the static and dynamic stability threshold of the nanostructure are demonstrated.

2011 ◽  
Vol 133 (3) ◽  
Author(s):  
Gang Ma ◽  
Xiang Ling

Ultrasonic impact treatment (UIT) can be used to create a thin nanostructured surface layer that plays a significant role in enhancing the overall strength, fatigue life, and corrosion resistance of the treated material. The hardness and elastic modulus of surface nanostructured 304 stainless steel treated by UIT have been investigated by nanoindentation and microhardness measurements. The hardness of the top nanostructured surface layer and its elastic modulus are about 38% and 30% higher, respectively, than those of the bulk material in the nanohardness testing. Also, the hardness is increased by about 23% in the Vickers microhardness testing. The nanohardness of the nanostructured surface layers decreases with depth and then trends to stable values. A hardened layer is found in the impact zone and the thickness is approximately 450–500 μm. All results demonstrated that the surface nanocrystallization can effectively enhance the mechanical properties of the 304 stainless steel.


2016 ◽  
Vol 23 (05) ◽  
pp. 1650043 ◽  
Author(s):  
MARYAM KEIVANI ◽  
ALI KOOCHI ◽  
ABOLFAZL KANANI ◽  
MOHAMADREZA ABADYAN

Nanoscale beams might not be considered uniform isotropic since the energy of the surface layer and microstructure of the bulk material highly affect the mechanical characteristics of the beams. Herein, the simultaneous effects of energy of the surface and microstructure of the bulk on the dynamic response and stability of beam-type electromechanical nanocantilevers are investigated. A bilayer model has been developed which incorporates the strain energy of the surface atoms as well as the microstructure-dependent strain energy of the bulk. The Gurtin–Murdoch surface elasticity in conjunction with the modified couple stress theory (MCST) is applied to derive the governing equation. Since the classical assumption for zero normal surface stresses is not consistent with the surface equilibrium assumption in Gurtin–Murdoch elasticity, the presence of normal surface stresses is incorporated. The von Karman nonlinear strain is employed to derive the governing equation. The presence of gas rarefaction at various Knudsen numbers is considered as well as the edge effect on the distribution of Coulomb and dispersion forces. The mode shapes of the nanobeam are determined as a function of the surface and microstructure parameter and the nonlinear governing equation is solved using Galerkin method. The dynamic response, phase plane and stability threshold of the nanocantilever are discussed.


2015 ◽  
Vol 10 (2) ◽  
pp. 82-86
Author(s):  
Тимолянов ◽  
Konstantin Timolyanov ◽  
Савенков ◽  
Dmitriy Savenkov

During the outflow of the bulk material from the hopper, the particles interact with each other, the walls of hopper, forming a so-called arches. Arching is a common phenomenon at the end of bulk materials. A large number of authors fight against arches, a lot of theories and models were designed. The use of arch destroyers is the most effective way to combat by arching process. The parameters of such devices are calculated on existing methods, where the frequency and impact on the bulk material is selected. Constructions for arch destroying are a large number, but each is present lack of expressed in constant maintenance and outer energy consumption. Therefore, an optimization of the hopper parameters, under arch creating conditions, at the design stage, is an urgent task for the theoretical description. In the analysis of the hopper with a side outlet, it was established, that the arches are formed in the least section, during the movement of bulk material. Such a section is called arch-making section. If arch-making section is too small, relative to the diameter of the bulk material, a static arch will formed, and the outflow will be terminated. To continue outflow can be only if you deduced an arch from the equilibrium state by external forces. This paper proposes a curved profile of the bottom profile so as to increase the height of arch-making section, retaining a predetermined pitch, thereby reducing the impact of the arch, keeping the specified feed of grain material. It was revealed that due to the new profile of the bottom at the lowest feeds of bulk material, more stable expiration is observed.


Author(s):  
И.В. Бачериков ◽  
Б.М. Локштанов

При проектировании открытых и закрытых хранилищ измельченных сыпучих материалов древесных материалов, таких как щепа и опилки, большое значение имеет угол естественного откоса (статический и динамический) этих материалов. В технической литературе приводятся противоречивые сведения о величине этих углов, что приводит к ошибкам при проектировании складов. В справочных данных не учитываются условия, в которых эксплуатируются емкости для хранения сыпучих материалов, свойства и состояние этих сыпучих материалов. В свою очередь, ошибки при проектировании приводят к проблемам (зависание, сводообразование, «затопление» и т. д.) и авариям при эксплуатации бункеров и силосов на производстве. В статье представлены сведения, посвященные влиянию влажности и температуры на угол естественного откоса сыпучих материалов. На основании лабораторных и натурных экспериментов, проведенных с помощью специально разработанных методик и установок, была скорректирована формула для определения углов естественного откоса (статического и динамического) для измельченных древесных материалов в зависимости от их фракционного и породного состава, влажности (абсолютной и относительной) и температуры. При помощи скорректированной формулы можно определить угол естественного откоса древесных сыпучих материалов со среднегеометрическим размером частицы от 0,5 мм до 15 мм (от древесной пыли до технологической щепы) в различных производственных условиях. Статья может быть полезна проектировщикам при расчете угла наклона граней выпускающей воронки бункеров и силосов предприятий лесной отрасли и целлюлозо-бумажной промышленности. In the design of open and closed storage warehouses chopped wood materials for bulk materials such as wood chips and sawdust, great importance has an angle of repose (static and dynamic) of these materials. In the technical literature are conflicting reports about the magnitude of these angles, which leads to errors in the design of warehouses. In the referencesdoes not take into account the conditions under which operated capacities for storage of bulk materials, and properties and condition of the bulk material. The design errors lead to problems (hanging, arching, «flooding», etc.) and accidents in the operation of hoppers and silos at the mills. The article provides information on the impact of humidity and temperature on the angle of repose of granular materials. On the basis of laboratory and field experiments, conducted with the help of specially developed techniques and facilities has been adjusted formula for determining the angle of repose (static and dynamic) for the shredded wood materials depending on their fractional and species composition, humidity (absolute and relative) and temperature. It is possible, by using the corrected formula, to determine the angle of repose of loose wood materials with average particle size of from 0.5 mm to 15 mm (wood dust to pulpchips) in various operating conditions. The article can be helpful to designers in the calculation of the angle of inclination of the funnel faces produces bunkers and silos forest industries and pulp and paper industry.


Minerals ◽  
2021 ◽  
Vol 11 (2) ◽  
pp. 213
Author(s):  
Hamid Ait Said ◽  
Hassan Noukrati ◽  
Hicham Ben Youcef ◽  
Ayoub Bayoussef ◽  
Hassane Oudadesse ◽  
...  

Three-dimensional hydroxyapatite-chitosan (HA-CS) composites were formulated via solid-liquid technic and freeze-drying. The prepared composites had an apatitic nature, which was demonstrated by X-ray diffraction and Infrared spectroscopy analyses. The impact of the solid/liquid (S/L) ratio and the content and the molecular weight of the polymer on the composite mechanical strength was investigated. An increase in the S/L ratio from 0.5 to 1 resulted in an increase in the compressive strength for HA-CSL (CS low molecular weight: CSL) from 0.08 ± 0.02 to 1.95 ± 0.39 MPa and from 0.3 ± 0.06 to 2.40 ± 0.51 MPa for the HA-CSM (CS medium molecular weight: CSM). Moreover, the increase in the amount (1 to 5 wt%) and the molecular weight of the polymer increased the mechanical strength of the composite. The highest compressive strength value (up to 2.40 ± 0.51 MPa) was obtained for HA-CSM (5 wt% of CS) formulated at an S/L of 1. The dissolution tests of the HA-CS composites confirmed their cohesion and mechanical stability in an aqueous solution. Both polymer and apatite are assumed to work together, giving the synergism needed to make effective cylindrical composites, and could serve as a promising candidate for bone repair in the orthopedic field.


2021 ◽  
Vol 6 (6) ◽  
pp. 79
Author(s):  
Nuno M. M. Ramos ◽  
Joana Maia ◽  
Andrea R. Souza ◽  
Ricardo M. S. F. Almeida ◽  
Luís Silva

Near-infrared (NIR) reflective materials are being developed for mitigating building cooling needs. Their use contributes to broadening the range of colours, responding to the urban aesthetic demand without compromising the building performance. Despite the increase in NIR reflective pigments investigation, there is still a knowledge gap in their applicability, impact, and durability in multilayer finishing coatings of External Thermal Insulation Composite Systems (ETICS). Hence, the main goal of this work consists of evaluating the impact of incorporating NIR reflective pigments (NRP) in the solar reflectance of the surface layer of ETICS, without affecting the colour perception, as well as their influence on the colour durability and surface temperature. As such, colour, solar reflectance, and surface temperature were monitored for 2 years in dark-coloured specimens of ETICS, with and without NRP and a primer layer. It was confirmed that the main contribution of NRP is the increase of solar reflectance and, consequently, the decrease in surface temperature, especially for high exterior temperatures (around 30 ºC). Moreover, these pigments highly increase the NIR reflectance without affecting the visible colour. In addition, they contribute to maintaining the colour characteristics. The application of primer increased the surface temperature, especially for higher exterior temperatures. However, it contributes to a lower colour difference and solar reflectance variation, which is an important achievement for durability purposes.


2021 ◽  
Vol 104 (2) ◽  
pp. 003685042110136
Author(s):  
Safia Akram ◽  
Najma Saleem ◽  
Mir Yasir Umair ◽  
Sufian Munawar

The impact of lateral walls and partial slip with different waveforms on peristaltic pumping of couple stress fluid in a rectangular duct with different waveforms has been discussed in the current article. By means of a wave frame of reference the flow is explored travelling away from a fixed frame with velocity c. Peristaltic waves generated on horizontal surface walls of rectangular duct are considered using lubrication technique. Mathematical modelling of couple fluid for three-dimensional flow are first discussed in detail. Lubrication approaches are used to simplify the proposed problem. Exact solutions of pressure gradient, pressure rise, velocity and stream function have been calculated. Numerical and graphical descriptions are displayed to look at the behaviour of diverse emerging parameters.


2020 ◽  
Vol 12 (22) ◽  
pp. 3777
Author(s):  
Yuhui Li ◽  
Yun Qiu ◽  
Jianyu Hu ◽  
Cherry Aung ◽  
Xinyu Lin ◽  
...  

Multisource satellite remote sensing data and the World Ocean Atlas 2018 (WOA18) temperature and salinity dataset have been used to analyze the spatial distribution, variability and possible forcing mechanisms of the upwelling off Manaung Island, Myanmar. Signals of upwelling exist off the coasts of Manaung Island, in western Myanmar during spring. It appears in February, reaches its peak in March and decays in May. Low-temperature (<28.3 °C) and high-salinity (>31.8 psu) water at the surface of this upwelling zone is caused by the upwelling of seawater from a depth below 100 m. The impact of the upwelling on temperature is more significant in the subsurface layer than that in the surface layer. In contrast, the impact of the upwelling on salinity in the surface layer is more significant. Further research reveals that the remote forcing from the equator predominantly induces the evolution of the upwelling, while the local wind forcing also contributes to strengthen the intensity of the upwelling during spring.


1998 ◽  
Vol 31 ◽  
pp. 26
Author(s):  
L. Labey ◽  
H. Van Campenhout ◽  
J. Vander Sloten ◽  
R. Van Audekercke ◽  
G. Van der Perre ◽  
...  

SPE Journal ◽  
2022 ◽  
pp. 1-18
Author(s):  
Marat Sagyndikov ◽  
Randall Seright ◽  
Sarkyt Kudaibergenov ◽  
Evgeni Ogay

Summary During a polymer flood, the field operator must be convinced that the large chemical investment is not compromised during polymer injection. Furthermore, injectivity associated with the viscous polymer solutions must not be reduced to where fluid throughput in the reservoir and oil production rates become uneconomic. Fractures with limited length and proper orientation have been theoretically argued to dramatically increase polymer injectivity and eliminate polymer mechanical degradation. This paper confirms these predictions through a combination of calculations, laboratory measurements, and field observations (including step-rate tests, pressure transient analysis, and analysis of fluid samples flowed back from injection wells and produced from offset production wells) associated with the Kalamkas oil field in Western Kazakhstan. A novel method was developed to collect samples of fluids that were back-produced from injection wells using the natural energy of a reservoir at the wellhead. This method included a special procedure and surface-equipment scheme to protect samples from oxidative degradation. Rheological measurements of back-produced polymer solutions revealed no polymer mechanical degradation for conditions at the Kalamkas oil field. An injection well pressure falloff test and a step-rate test confirmed that polymer injection occurred above the formation parting pressure. The open fracture area was high enough to ensure low flow velocity for the polymer solution (and consequently, the mechanical stability of the polymer). Compared to other laboratory and field procedures, this new method is quick, simple, cheap, and reliable. Tests also confirmed that contact with the formation rapidly depleted dissolved oxygen from the fluids—thereby promoting polymer chemical stability.


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