Frontiers in Mechanical Engineering最新文献_第9页

Role of Interfacial Water and Applied Potential on Friction at Au(111) Surfaces 界面水和外加电位在Au(111)表面摩擦中的作用

IF 2.3

Frontiers in Mechanical Engineering Pub Date : 2019-06-21 DOI: 10.3389/fmech.2019.00039

Leila Pashazanusi, K. Kristiansen, Shaowei Li, Yu Tian, N. Pesika

{"title":"Role of Interfacial Water and Applied Potential on Friction at Au(111) Surfaces","authors":"Leila Pashazanusi, K. Kristiansen, Shaowei Li, Yu Tian, N. Pesika","doi":"10.3389/fmech.2019.00039","DOIUrl":"https://doi.org/10.3389/fmech.2019.00039","url":null,"abstract":"The tribological properties between an AFM tip and a Au(111) surface in an aqueous environment is influenced by an applied electrical potential. Using lateral force microscopy, we measure the resulting friction force, while simultaneously applying a predetermined electrical potential on the Au surface via a three-electrode setup. Applying a positive potential to the Au surface forms an interfacial water layer at the Au/electrolyte interface, which sharply increases friction. However, when an anodic potential is applied, lower friction forces are measured. The potential dependent friction is observed on ultra-smooth gold surfaces as well as Au surfaces with larger roughness. An increase in the ionic strength of the electrolyte is found to lower friction. The use of an aqueous NaOH solution is found to lower the critical potential at which the friction sharply increases. Normal force curves are also measured as a function of approach velocity. The normal force linearly increases as the approach velocity increases in agreement with a drainage model. These results provide valuable insight into the effect of applied electrical potentials on the properties of water at charged surfaces and can potentially impact a wide range of fields including tribology, micro-electro-mechanical systems (MEMS), energy storage devices, fuel cells and catalysis.","PeriodicalId":53220,"journal":{"name":"Frontiers in Mechanical Engineering","volume":"1 1","pages":""},"PeriodicalIF":2.3,"publicationDate":"2019-06-21","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"83136030","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

引用次数: 5

An Experimental Study of Intermittent Heating Frequencies From Wind-Driven Flames 风动火焰间歇加热频率的实验研究

IF 2.3

Frontiers in Mechanical Engineering Pub Date : 2019-06-20 DOI: 10.3389/fmech.2019.00034

Wei Tang, M. Finney, S. McAllister, M. Gollner

{"title":"An Experimental Study of Intermittent Heating Frequencies From Wind-Driven Flames","authors":"Wei Tang, M. Finney, S. McAllister, M. Gollner","doi":"10.3389/fmech.2019.00034","DOIUrl":"https://doi.org/10.3389/fmech.2019.00034","url":null,"abstract":"An experimental study was conducted to understand the intermittent heating behavior downstream of a gaseous line burner under forced flow conditions. While previous studies have addressed time-averaged properties, here measurements of the flame location and intermittent heat flux profile help to give a time-dependent picture of downstream heating from the flame, useful for understanding wind-driven flame spread. Two frequencies are extracted from experiments, the maximum flame forward pulsation frequency in the direction of the wind, which helps describe the motion of the flame, and the local flame-fuel contact frequency in the flame region, which is useful in calculating the actual heat flux that can be received by the unburnt fuel via direct flame contact. The forward pulsation frequency is obtained through video analysis using a variable interval time average (VITA) method. Scaling analysis indicates that the flame forward pulsation frequency varies as a power-law function of the Froude number and fire heat-release rate, . For the local flame-fuel contact frequency, it is found that the non-dimensional flame-fuel contact frequency remains approximately constant before the local Rix reaches 1, e.g., attached flames. When Rix>1, decreases with local as Rix flames lift up. A piece-wise function was proposed to predict the local flame-fuel contact frequency including the two Rix scenarios. Information from this study helps to shed light on the intermittent behavior of flames under wind, which may be a critical factor in explaining the mechanisms of forward flame spread in wildland and other similar wind-driven fires.","PeriodicalId":53220,"journal":{"name":"Frontiers in Mechanical Engineering","volume":"4 1","pages":""},"PeriodicalIF":2.3,"publicationDate":"2019-06-20","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"78423437","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

引用次数: 5

Influence of MHD Lubrication and Textured Surface in EHL Line Contact MHD润滑和织构表面对EHL线接触的影响

IF 2.3

Frontiers in Mechanical Engineering Pub Date : 2019-06-20 DOI: 10.3389/fmech.2019.00033

Suresh Jadhav, G. D. Thakre, Satish C. Sharma

引用次数: 3

Passive and Active Control on 3D Convective Flow of Viscoelastic Nanofluid With Heat Generation and Convective Heating 热生成与对流加热粘弹性纳米流体三维对流的被动与主动控制

IF 2.3

Frontiers in Mechanical Engineering Pub Date : 2019-06-20 DOI: 10.3389/fmech.2019.00036

S. Eswaramoorthi, M. Bhuvaneswari

引用次数: 4

Firebrand Generation From Thermally-Degraded Cylindrical Wooden Dowels 由热降解圆柱木销子产生的火种

IF 2.3

Frontiers in Mechanical Engineering Pub Date : 2019-06-14 DOI: 10.3389/fmech.2019.00032

Sara E. Caton-Kerr, A. Tohidi, M. Gollner

{"title":"Firebrand Generation From Thermally-Degraded Cylindrical Wooden Dowels","authors":"Sara E. Caton-Kerr, A. Tohidi, M. Gollner","doi":"10.3389/fmech.2019.00032","DOIUrl":"https://doi.org/10.3389/fmech.2019.00032","url":null,"abstract":"During wildland fires, firebrands form once they break off of burning vegetation or structures. Many are then lofted into the fire plume where they are transported long distances ahead of the fire front, igniting new “spot” fires as they land. To date, very few studies have been conducted on the breakage mechanism of thermally-degraded vegetative elements. Knowledge of these mechanisms is needed to feed mathematical models of firebrand transport from traditional wildfires as well as those that spread into communities. First, a framework to understand the behavior of thermally-degraded wooden elements under simultaneous external loading is presented. A set of experiments were designed such that cylindrical wooden dowels of different species are exposed to different heating conditions similar to wildland fires, in order to model the breakage mechanisms of these elements in the absence of wind. The thermally-degraded elements are subjected to the three-point bending test to obtain the mechanical response of the materials after combustion. Assuming Hookean Orthotropic behavior for combusted dowels, dimensional analysis of the results reveals that the ultimate strength of the dowels is affected by the recoverable elastic strain during loading, which is found to occur under two distinct regimes. These results are not only important for better understanding of the breakage mechanisms but also are advantageous for developing a failure theory of thermally degrading wooden elements under simultaneous wind loading conditions.","PeriodicalId":53220,"journal":{"name":"Frontiers in Mechanical Engineering","volume":"6 1","pages":""},"PeriodicalIF":2.3,"publicationDate":"2019-06-14","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"80005873","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

引用次数: 17

A Concept of the Effective Surface Profile to Predict the Roughness Parameters of Worn Surface 预测磨损表面粗糙度参数的有效表面轮廓概念

IF 2.3

Frontiers in Mechanical Engineering Pub Date : 2019-06-06 DOI: 10.3389/fmech.2019.00031

A. Kovalev, Yazhao Zhang, Cao Hui, Y. Meng

引用次数: 9

Ragone Relations for Thermal Energy Storage Technologies 热储能技术的Ragone关系

IF 2.3

Frontiers in Mechanical Engineering Pub Date : 2019-06-04 DOI: 10.3389/fmech.2019.00029

K. Yazawa, P. Shamberger, T. Fisher

{"title":"Ragone Relations for Thermal Energy Storage Technologies","authors":"K. Yazawa, P. Shamberger, T. Fisher","doi":"10.3389/fmech.2019.00029","DOIUrl":"https://doi.org/10.3389/fmech.2019.00029","url":null,"abstract":"The Ragone relation is a facile approach to assess and compare electro-chemical battery performance in terms of two critical performance parameters: power density and energy density. This power and energy nexus is equally relevant for thermal energy storage materials for thermal management applications that require a balance between energy storage capacity and on-demand cooling or heating rates. Here, thermal energy storage is evaluated for sensible heating and for phase-change materials (PCMs). We propose an analytic expression using a lumped mass model for thermal storage through an analogy with heat diffusion that allows for intuitive mapping of materials and components in power-energy space. In addition, a previously proposed figure-of-merit, $eta_q$, describing the intrinsic capability of PCMs to rapidly absorb or discharge heat is placed in the context of the thermal Ragone (power-energy) relation. This figure of merit serves as a proxy for the cooling power of PCMs and single-phase materials to store thermal energy. Thus, $eta_q$ plotted against energy density can serve graphically to illustrate performance tradeoffs between different thermal storage materials, as well as composites composed of different materials.","PeriodicalId":53220,"journal":{"name":"Frontiers in Mechanical Engineering","volume":"1 1","pages":""},"PeriodicalIF":2.3,"publicationDate":"2019-06-04","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"83668243","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

引用次数: 13

Artificial Neural Networks (ANNs) as a Novel Modeling Technique in Tribology 人工神经网络(ANNs)作为一种新的摩擦学建模技术

IF 2.3

Frontiers in Mechanical Engineering Pub Date : 2019-05-29 DOI: 10.3389/fmech.2019.00030

I. Argatov

引用次数: 49

Are There Limits to Superlubricity of Graphene in Hard, Rough Contacts? 石墨烯在坚硬粗糙接触中的超润滑性是否存在限制?

IF 2.3

Frontiers in Mechanical Engineering Pub Date : 2019-05-22 DOI: 10.3389/fmech.2019.00028

M. Müser

引用次数: 3

Controlling Friction With External Electric or Magnetic Fields: 25 Examples 用外部电场或磁场控制摩擦:25个例子

IF 2.3

Frontiers in Mechanical Engineering Pub Date : 2019-05-21 DOI: 10.3389/fmech.2019.00022

J. Krim

{"title":"Controlling Friction With External Electric or Magnetic Fields: 25 Examples","authors":"J. Krim","doi":"10.3389/fmech.2019.00022","DOIUrl":"https://doi.org/10.3389/fmech.2019.00022","url":null,"abstract":"Studies of the fundamental origins of friction have undergone rapid progress in recent years, providing valuable information on the relative contributions of electronic, magnetic, electrostatic and phononic dissipative mechanisms. They are now evolving into methods that allow active control of nano and/or meso scale friction through tuning of magnetic and electric fields external to the contact. These methods constitute an area of rapidly growing interest, as they address one of tribology’s present day grand challenges: achieving in situ control of friction levels without removing and replacing lubricant materials situated within inaccessible confines of a contact. In this minireview, 25 examples of electromagnetic tuning of friction are overviewed, with examples spanning atomic to macro scale systems to demonstrate the variety and versatility of approaches that have been reported in the literature. Applications include, but are not limited to triboelectric generators, geological drilling, automotive braking and efficiency, spacecraft systems, biological systems and magnetic spintronics. Experimental methods for measuring the impact of electric or magnetic fields on friction include AFM, SFA, QCM, pin-on-disk, hard disk head- substrate, MEMS and NEMS based tribometers, and optical spectroscopies. Computational and theoretical approaches include analytic, equilibrium and nonequilbrium Monte Carlo simulations.","PeriodicalId":53220,"journal":{"name":"Frontiers in Mechanical Engineering","volume":"1 1","pages":""},"PeriodicalIF":2.3,"publicationDate":"2019-05-21","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"80161350","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

引用次数: 31