A Study of the Contact of an Elastic Layer-Substrate System Indented by a Long Rigid Cylinder Incorporating Surface Effects

Contact problem of a layer-substrate system comprising of an elastic layer and an elastic substrate perfectly bonded to each other with surface effects based on Gurtin-Murdoch (GM) model indented by a long rigid cylinder is solved. The requisite Green's function relating surface displacement to surface load is obtained semi-analytically through the combination of the Airy stress function and Fourier transforms under the plane-strain condition. The contact solution is analyzed to study the influence of layer thickness, modulus mismatch between the layer and substrate, and surface parameters on contact size and contact pressure during indentation of a layer-substrate system. A map is presented which indicates whether during indentation by a rigid cylinder, a layer-substrate system is required or a homogeneous system based on layer properties is enough for a given shear modulus mismatch ratio and layer thickness. The map and the related analysis clearly indicate that whenever the contact size or layer thickness approaches intrinsic length scale based on the ratio of surface parameter and bulk elastic properties, surface effects should be considered

DESIGN OF OPTIMAL PUMPING SCHEDULES TO ENHANCE OIL AND GAS PRODUCTION FROM UNCONVENTIONAL RESERVOIRS

Hydraulic fracturing is a technique extensively used in the oil and gas industry, where water, proppant (sand) and additives are injected into unconventional reservoirs to enhance the recovery of shale hydrocarbon. Because of complex fracture growth in naturally fractured unconventional reservoirs, the ultimate goal of hydraulic fracturing operation should be changed from achieving a desired fracture geometry to maximizing the total fracture surface area (TFSA) for given fracturing resources, as it will allow more drainage area available for oil recovery. Unfortunately, there are no such techniques available to develop pumping schedules to maximize the TFSA for given fracturing resources in naturally fractured unconventional reservoirs. Motivated by this, we developed a model-based pumping schedule by utilizing a recently developed unconventional complex fracture propagation model called Mangrove describing complex fracture networks by accounting for interaction between hydraulic fractures and natural fractures. We demonstrated that by using the proposed control scheme, the TFSA can be greatly enhanced which will increase the cumulative shale oil production volume, compared to the existing pumping schedules. Although some previous studies have developed pumping schedules that maximize gas production for a single-size proppant, there are very few studies that consider the effect of varying proppant diameters across pumping stages on shale gas production. Motivated by this, we conducted a sensitivity analysis and extended the previous pumping schedule by considering multi-size proppant for simultaneously propagating multiple fractures to maximize shale gas production from unconventional reservoirs. Since the size of injected proppant particles determines the average propped surface area (PSA) and average fracture conductivity (FC), we developed a framework called Sequentially Interlinked Modeling Structure (SIMS) to predict the average PSA, average FC and cumulative shale gas production volume for a given pumping schedule. Then, we used the SIMS framework to obtain a multi-size proppant pumping schedule that maximizes shale gas production. Finally, we demonstrated that obtained pumping schedule gives a gas production volume greater than the values obtained from the existing pumping schedules which consider only single size proppant

Plane strain cylindrical indentation of functionally graded half-plane with exponentially varying shear modulus in the presence of residual surface tension

A functionally graded half-plane with shear modulus varying exponentially along the direction normal to the surface and surface effects accounted through Gurtin Murdoch model, indented by long rigid smooth cylindrical indenter is solved to understand the effect of material inhomogeneity and surface effects on indentation response. The Green's function relating surface load to surface displacement under plane strain condition is obtained semi analytically through the combination of Airy stress function approach and Fourier transforms and utilized to solve the contact problem. The solution is used to study the effect of inhomogeneity through grading parameter and surface effects through residual surface tension based intrinsic length scale on the contact pressure, contact size and in-plane normal stress on the surface responsible for cracks during indentation. (C) 2017 Elsevier Ltd. All rights reserved

Analytical Investigation of Binder's Role on the Diffusion Induced Stresses in Lithium Ion Battery through a Representative System of Spherical Isolated Electrode Particle Enclosed by Binder

Binder which serves to maintain mechanical and electrical integrity of Lithium ion batteries and occupies as much as 50% of battery weight is rather relatively less explored in terms of its effect on electrode and binder stresses during charging-discharging operation and hence motivates the present work. Closed form solution of diffusion induced stresses in an isolated spherical linear elastic, perfectly plastic electrode particle encapsulated by a linear viscoelastic binder during galvanostatic charging-discharging cycle under two sets of boundary conditions for the binder surface viz. traction free and fully constrained are developed. It is proved that the stresses in binder are unchanged even if electrode deforms elastically or plastically and whether diffusion in electrode is driven by concentration gradient or combination of concentration gradient and hydrostatic stress. The analysis identifies that current density not only directly controls the diffusion induced stress in electrode but affects it indirectly through change in stiffness of the binder depending upon the cycle time. Furthermore analysis reveals lower viscosity, lower stiffness and faster relaxation behavior as the recommended binder properties for lower diffusion induced stresses in electrode and binder. (C) 2017 The Electrochemical Society. All rights reserved

Plane strain indentation on finite thickness bonded layer in couple stress elasticity

Contact of flat, cylindrical and wedge indenter on a finite thickness layer obeying couple stress elasticity and bonded to a rigid base under plane strain conditions is solved. The method of stress functions and Fourier transforms is employed to reduce the mixed boundary value contact problem to a singular integral equation in terms of the unknown contact pressure and contact size. For a given load on the indenter, the solution is obtained iteratively through numerical inversion of the integral equation and the effect of layer thickness and intrinsic length inherent in couple stress elastic material on the contact pressure and contact size is studied. Finally a map described in terms of the intrinsic length and layer thickness is proposed which can be used as a guiding tool to decide appropriate combination of geometry i.e. layer or half space and material behavior i.e. classical elasticity or couple stress elasticity to obtain accurate indentation response for a given system.(C) 2016 Elsevier Ltd. All rights reserved

Stress enhanced calcium kinetics in a neuron

Accurate modeling of the mechanobiological response of a Traumatic Brain Injury is beneficial toward its effective clinical examination, treatment and prevention. Here, we present a stress history-dependent non-spatial kinetic model to predict the microscale phenomena of secondary insults due to accumulation of excess calcium ions (Ca) induced by the macroscale primary injuries. The model is able to capture the experimentally observed increase and subsequent partial recovery of intracellular Ca concentration in response to various types of mechanical impulses. We further establish the accuracy of the model by comparing our predictions with key experimental observations

<span style="font-size: 22.5pt;mso-bidi-font-size:15.5pt;font-family:"Times New Roman","serif"; mso-bidi-font-weight:bold">Ultrasonic study of molecular interactions in binary liquid mixtures: acrolien <span style="font-size:21.5pt;mso-bidi-font-size: 14.5pt;font-family:"Arial","sans-serif";mso-bidi-font-weight:bold">& <span style="font-size:22.5pt;mso-bidi-font-size:15.5pt;font-family:"Times New Roman","serif"; mso-bidi-font-weight:bold">cinnanlaldehyde in methanol, cyclohexane <span style="font-size:21.5pt;mso-bidi-font-size:14.5pt;font-family:"Arial","sans-serif"; mso-bidi-font-weight:bold">& <i style="mso-bidi-font-style:normal"><span style="font-size:22.5pt;mso-bidi-font-size:15.5pt;font-family:"Times New Roman","serif"; mso-bidi-font-weight:bold">p</span></i><span style="font-size:22.5pt; mso-bidi-font-size:15.5pt;font-family:"Times New Roman","serif";mso-bidi-font-weight: bold">-dioxane </span></span></span></span></span>

849-854<span style="font-size: 15.5pt;mso-bidi-font-size:8.5pt;font-family:" times="" new="" roman","serif""="">The velocity of ultrasonic waves (10 MHz) for different compositions of mixtures or methanol, cyclohexane and <span style="font-size:14.5pt;mso-bidi-font-size: 7.5pt;font-family:" arial","sans-serif""="">p-<span style="font-size: 15.5pt;mso-bidi-font-size:8.5pt;font-family:" times="" new="" roman","serif""="">dioxane with acrolein and cinnamaldehyde has been measured in the temperature range 10-40°C. The excess compressibility <span style="font-size:18.0pt;mso-bidi-font-size: 11.0pt;font-family:" arial","sans-serif""="">βaE and excess molar volume VE<span style="font-size:18.0pt; mso-bidi-font-size:11.0pt;font-family:" times="" new="" roman","serif""=""> parameters have been discussed in the light of inter-molecular AB interaction s and resulting disorder in these mixtures. It is observed that excess parameters βaEand <span style="font-size:17.5pt;mso-bidi-font-size:10.5pt;font-family: " arial","sans-serif""="">VE <span style="font-size:15.5pt; mso-bidi-font-size:8.5pt;font-family:" times="" new="" roman","serif""="">can be used for classification or all types or molecular interactions in binary liquid mixtures. </span