Search results for "Shear"
showing 10 items of 804 documents
Cross-stream migration of a Brownian droplet in a polymer solution under Poiseuille flow
2018
The migration of a Brownian fluid droplet in a parallel-plate microchannel was investigated using dissipative particle dynamics computer simulations. In a Newtonian solvent, the droplet migrated toward the channel walls due to inertial effects at the studied flow conditions, in agreement with theoretical predictions and recent simulations. However, the droplet focused onto the channel centerline when polymer chains were added to the solvent. Focusing was typically enhanced for longer polymers and higher polymer concentrations with a nontrivial flow-rate dependence due to droplet and polymer deformability. Brownian motion caused the droplet position to fluctuate with a distribution that prim…
Friction stir welding of lap joints: Influence of process parameters on the metallurgical and mechanical properties
2009
Abstract Aluminum alloys are widely used in the aircraft industries even if such materials present lower ductility with respect to steels, anisotropy phenomena and, more important, they are often “difficult” to be welded or even “non-weldable”. In the last years the friction stir welding process (FSW) was proposed and applied in order to get good mechanical and technological performances of the joints. In this paper, an experimental and numerical investigation on the lap joining of AA2198-T4 aluminum alloy blanks by FSW is presented. In particular the joints strength and metallurgical properties are investigated by varying the joint configuration and the tool geometry and rotational speed. …
Experimental and Theoretical Study of the Field Induced Phase Separation in Electro- and Magnetorheological Suspensions
1999
We present here the study of field induced phase separation in E.R. and M.R. fluids. Two thermodynamic models — one for the formation of chais of particles and the other for phase separation are presented and compared with experimental results obtained with two kinds of suspensions. One was made of silica particles in silicone oil and the other was made of magnetic polystyrene particles in water. In the presence of a flow the phase separation occurs with the dense phase forming a regular pattern of stripes. The dependence of the period of these stripes on the intensity of the magnetic field is well reproduced by the same kind of thermodynamic model if we add the effect of normal stresses i…
The effect of different force magnitudes for placement of orthodontic brackets on shear bond strength, in three adhesive systems.
2018
Background: Amount of pressure exerting on orthodontic brackets during bonding can create different thickness of adhesive and affect shear bonding strength(SBS) in different adhesive systems. The purpose of this study was to evaluate the effect of different force magnitudes for placement of brackets on SBS. Material and Methods: In an in vitro study, 420 brackets were placed on the bovine teeth, using three types of adhesives, Concise (chemically cured two-paste mix), Unite (chemically cured no mix), and Transbond XT( light cured), with the application of seven force magnitudes of 50, 100, 200, 300, 400, 600 and 1000 grams in twenty-one groups of twenty samples each. SBS means (using two-wa…
From equilibrium to steady state: The transient dynamics of colloidal liquids under shear
2008
We investigate stresses and particle motion during the start up of flow in a colloidal dispersion close to arrest into a glassy state. A combination of molecular dynamics simulation, mode coupling theory and confocal microscopy experiment is used to investigate the origins of the widely observed stress overshoot and (previously not reported) super-diffusive motion in the transient dynamics. A link between the macro-rheological stress versus strain curves and the microscopic particle motion is established. Negative correlations in the transient auto-correlation function of the potential stresses are found responsible for both phenomena, and arise even for homogeneous flows and almost Gaussia…
Time dependent viscoelastic rheological response of pure, modified and synthetic bituminous binders
2016
Bitumen is a viscoelastic material that exhibits both elastic and viscous components of response and displays both a temperature and time dependent relationship between applied stresses and resultant strains. In addition, as bitumen is responsible for the viscoelastic behaviour of all bituminous materials, it plays a dominant role in defining many of the aspects of asphalt road performance, such as strength and stiffness, permanent deformation and cracking. Although conventional bituminous materials perform satisfactorily in most highway pavement applications, there are situations that require the modification of the binder to enhance the properties of existing asphalt material. The best kn…
Comparison between a Uniaxial Compaction Tester and a Shear Tester for the Characterization of Powder Flowability
2014
The complete characterization of powder flow properties with shear cells is a long and time-consuming process that requires specially trained operators or costly automated instruments. For these reasons, in industrial practice, the use of simpler and less extensive measurement by uniaxial compaction testers is often preferred. However, previous studies in the literature indicate that the results of the two techniques are not directly comparable due to the different stress state conditions achieved in the two testers.In this study, an experimental campaign to measure the flow function of five different powders with a ring shear tester (RST) and a uniaxial compaction tester (UCT) was performe…
Polymer-brush lubricated surfaces with colloidal inclusions under shear inversion.
2011
We characterize the response of compressed, sheared polymer-brush bilayers with colloidal inclusions to highly nonstationary inversion processes by means of molecular dynamics simulations and scaling theory. Bilayers with a simple (dimeric) solvent reveal an overshoot for the shear stress, while simulations of dry brushes without explicit solvent molecules fail to display this effect. We demonstrate that mechanical instabilities can be controlled by the inclusion of macromolecular structures, such as colloids of varying softness. Based on a recently developed theory, we suggest a scaling approach to determine a characteristic time for conformational and collective responses.
Discontinuous FRP-Confinement of Masonry Columns
2020
Recent seismic events, all over the world, demonstrated that masonry constructions are prone to brittle collapses when shear or compression capacity is reached. It is clear that, in many real cases, masonry columns need to be strengthened for enhancing their load-carrying capacity and to develop a more ductile response. The Fiber Reinforced Polymers (FRPs) confinement of masonry columns is a well-known technique that may produce these advantages. Unfortunately, full-wrapping insulates the column from the environment; so interstitial humidity can easily occur and cause the acceleration of the masonry's decay. In order to prevent it, partial-confinement is commonly assessed instead of total-j…
Lessons Learned on the Tensile and Bond Behavior of Fabric Reinforced Cementitious Matrix (FRCM) Composites
2020
Fabric Reinforced Cementitious Matrix (FRCM) composites represent an effective, compatible and cost-efficient solution for strengthening and retrofitting existing structures. A strong research effort was done to investigate the tensile and bond properties of these materials, as well as the overall behaviour of strengthened members. A Round Robin Test was organized by Rilem TC 250-CSM on 28 FRCM composites comprising basalt, carbon, glass, PBO, aramid and steel textiles, embedded in either cement, lime or geopolymer mortars, to collect an experimental dataset and define test protocols. This paper collects the outcomes of this study to highlight fundamental properties of FRCM and to investiga…