Addition Of Shear Research Articles

Experimental study of dewetting instability in polymer multilayer shear flow

<h2>Abstract</h2> The interfacial stability of multilayer Couette flow is investigated experimentally. A better understanding of this flow is critical for the processing of multilayer polymeric structures, such as multilayer coextrusion. We first look at the liquid film rupture predictions from numerical simulations of the thin film equation that considers capillary and van der Waals forces. With the addition of shear, three regimes have then been evidenced as a function of the shear rate. In the regime of low shear rates the rupture is delayed when compared to the no-shear problem, while at higher shear rates it is suppressed. Then, experiments investigating the effect of shear on the dewetting of thin polymer films at different temperatures by using an optical microscope coupled with a shearing hotstage will be presented. The dewetting dynamics, i.e. the growth of dewetting holes is monitored over time at various shear rates. It is observed that their circularity is modified by shear and that for all temperatures and thicknesses studied, the growth speed of the formed holes rapidly increases with increasing shear rate. A model balancing capillary forces and viscous dissipation while taking into account shear-thinning is then proposed and captures the main features of the experimental data, such as the ellipsoid shape of the holes and the faster dynamics in the direction parallel to the shear.

Dewetting of a thin polymer film under shear

The objective of this work is to give new insight into the stability of thin polymer films under shear, in order to pave the way to a better control of the nanolayer coextrusion process. To do so, a finite-difference numerical scheme for the resolution of the thin film equation was set up taking into account capillary and van der Waals (vdW) forces. This method was validated by comparing the dynamics obtained from an initial harmonic perturbation to established theoretical predictions. With the addition of shear, three regimes have then been evidenced as a function of the shear rate. In the case of low shear rates the rupture is delayed when compared to the no-shear problem, while at higher shear rates it is even suppressed: the perturbed interface goes back to its unperturbed state over time. In between these two limiting regimes, a transient one in which shear and vdW forces balance each other, leading to a non-monotonic temporal evolution of the perturbed interface, has been identified. While a linear analysis is sufficient to describe the rupture time in the absence of shear, the nonlinearities appear to be essential otherwise.

Design of Testing Device for Mechanical Property Testing System of Tai Lake Shield

According to the requirements of testing the mechanical properties of water s hield from Tai Lake the corresponding testing system was designed by adopting the id ea of open structure. The test system includes the detection device, the upper computer operation unit and the connected control unit. The testing device adopts a vertical fram e suitable for testing materials in water, USES a stepper motor to drive the lead screw t o achieve the basic tensile movement, and can achieve other testing functions through the addition of shear, friction and other expansion modules. The upper computer USES Kingview7.5 to develop the test interface corresponding to each test function, which c an carry out manual debugging and automatic test operations, and input the measurem ent data and process parameters into the MySQL database to provide real-time display and historical query functions. The main controller is realized by Arduino Mega2560 c ircuit board, which communicates with the HX711 conversion module through the sin gle bus protocol to collect the stress data of materials. By monitoring the running proc ess of stepping motor, the material deformation data is calculated. Through communic ation with Modbus RTU protocol of upper computer, operation command and test data transmission are realized.

Energy flow in thermostatted non-equilibrium molecular dynamics simulations

Energy transfers between internal kinetic and potential energy reservoirs in a simple liquid are studied by setting the temperature of one energy reservoir to a different value from that of the others and computing the resultant energy flows. In the first set of simulations, the x-directional kinetic temperature was artificially raised above the other five, and in the second, the x-directional configurational temperature was artificially raised above the other five. In both cases, external energy flows balanced, but unexpected energy flows between different directional components of the potential energy were observed. Additional simulations showed that these energy flows occurred regardless of the arrangement of thermostats imposed on the six degrees of freedom and the addition of shear. Heat flow between degrees of freedom that were ostensibly at the same temperature was anomalously observed. It was concluded that a different breakdown of the contributions to the configurational energy that is consistent with the definition of the directional configurational temperatures is required.

Quiescent and flow-induced crystallization in polyamide 12/cellulose nanocrystal composites

Understanding the crystallization kinetics and microstructure that result after an imposed shear flow in an additive-containing polymeric system is imperative for the development of robust polymer composites suitable for advanced engineering applications. Both nucleating agents and flow accelerate the crystallization kinetics as well as alter the ultimate polymer microstructure. During melt processing, polymers are subject to shear flow prior to the solidification of the melt. As an unsheared baseline in this study, the addition of 5 wt % cellulose nanocrystals (CNC) into quiescent polyamide 12 (PA 12) revealed that CNCs act as a natural nucleating agent to the quiescent PA 12 during slow cooling and at high temperatures, as measured by standard differential scanning calorimetry. To evaluate the role of shear work in promoting flow-induced crystallization, both neat and PA 12/CNC composite were subjected to known amounts of shear work. Then fast scanning calorimetry was used to differentiate the nucleation activity from both flow-induced precursors and CNC particles during isothermal crystallization across a wide temperature range. It was found that the addition of the CNC accelerated crystallization in the heterogeneous nucleation regime (T > 100 °C) in the quiescent material. With the addition of shear, the neat system displayed a reduced crystallization peak time with increasing shear history. In the nanocomposite system, the CNCs are an extremely efficient nucleating agent, achieving a saturating limit for nucleation of crystallization, such that shear was only a factor at low supercooling, specifically at temperatures greater than 140 °C.

Compression and shear on lead in a rotational diamond anvil cell

ABSTRACTBy application of large plastic shear on a lead sample in a rotational diamond anvil cell, we studied the pressure self-multiplication and the stress deviation phenomena, along with the consequential effects on a phase transformation of lead. It is indicated that pressure can be promoted by the gradual addition of shear. The stress deviation in the sample along different Chi angles is minimal and within the systematic error range. It is thus specified that a quasi-hydrostatic condition is generated in the sample chamber. Moreover surprisingly, under such shear-controlled pressure elevation, the lead fcc-to-hcp phase transformation pressure is found to initiate and complete, respectively, at 12.8 and 18.5 GPa, which is identical to those observed in hydrostatic compressions. The phenomena of the so-launched quasi-hydrostatic pressure, the self-multiplication, along with the consequential effects on the phase transformation properties by shear at pressures are expected to lead to further understanding of materials as well as to potential new technologies at extremes.

Technological Improvements in Three-Piece Inflatable Penile Prosthesis Design over the Past 40 Years.

The advent of the penile prosthesis revolutionized the treatment of erectile dysfunction (ED), resulting in near-complete treatment efficacy and high patient satisfaction rates. While several types of penile prosthesis are available, the inflatable penile prosthesis (IPP) is the most commonly used device in the United States. To describe the key modifications to IPPs from the two major manufacturers-American Medical Systems (AMS) and Coloplast-since the invention of the IPP, and to relate these changes to improvements in prosthesis function and patient outcomes based on available literature. Review and evaluation of the literature between 1973 and present describing modifications in IPP design and the influence of these modifications on IPP durability and patient-related factors. Data describing the impact of iterative improvements in three-piece IPP design on device function, durability, and patient outcomes. There were progressive improvements in IPP technology from both major manufacturers not only on the durability of the prosthesis but also on patient outcomes, with fewer device failures and lower infection rates. Notable improvements include incorporation of kink-resistant tubing, changes in the weave or addition of shear- and infection-resistant coatings to cylinder layers, pump and tubing connection modifications, the addition of rear tip extenders, and the incorporation of lockout valves to prevent autoinflation. Numerous incremental modifications to the IPP from both major manufacturers since its invention have increased its durability and improved patient outcomes.

Ice flow relations for stress and strain-rate components from combined shear and compression laboratory experiments

AbstractThe generalized (Glen) flow relation for ice, involving the second invariants of the stress deviator and strain-rate tensors, is only expected to hold for isotropic polycrystalline ice. Previous single-stress experiments have shown that for the steady-state flow, which develops at large strains, the tertiary strain rate is greater than the minimum (secondary creep) value by an enhancement factor which is larger for shear than compression. Previous experiments combining shear with compression normal to the shear plane have shown that enhancement of the tertiary octahedral strain rate increases monotonically from compression alone to shear alone. Additional experiments and analyses presented here were conducted to further investigate how the separate tertiary shear and compression strain-rate components are related in combined stress situations. It is found that tertiary compression rates are more strongly influenced by the addition of shear than is given by a Glen-type flow relation, whereas shear is less influenced by additional compression. A scalar function formulation of the flow relation is proposed, which fits the tertiary creep data well and is readily adapted to a generalized form that can be extended to other stress configurations and applied in ice mass modelling.

Behavior of Curved I-Girder Webs Subjected to Combined Bending and Shear

Two previous papers by the writers described the buckling and finite-displacement behavior of curved I-girder web panels subjected to pure bending, presented a theoretically pure analytical model, and presented equations that describe the reduction in strength due to curvature. This paper describes the buckling and finite-displacement behavior of curved web panels under combined bending and shear. Unlike straight girder web panels, the addition of shear in curved panels is shown to increase the transverse “bulging” displacement of the web prior to buckling. The accompanying decrease in moment carrying capacity is analyzed in a manner similar to that used for the combined bending and shear nominal strength interaction for straight girder design. Preliminary recommendations are made toward forming design criteria for curved webs.