Compressions of magnetorheological fluids under instantaneous magnetic field and constant area

Compressions of magnetorheological (MR) fluids have been carried out under instantaneous magnetic fields. The yield strength of the MR fluid in compressive mode has been derived by assuming that it was a transformed shear flow in Bi-visous model. The compressive stresses have experimentally studied under different magnetic fields, different initial gap distances and different compressive velocities. The nominal yield shear stresses of the compressed MR fluid under different influential factors have been calculated. The compressive stress increased in a power law as the applied magnetic field increased, while it decreased as the initial gap distance and the compressive velocity increased. With the increase of magnetic field, the difference between the nominal yield shear stress curves increased, and the exponents of the power law increased with the increase of the magnetic field strengths. A larger initial gap distance and a lower compressive velocity resulted in a higher nominal yield shear stress under the same instantaneous magnetic field. The achieved results of the nominal yield shear stress with magnetic field seemed to deviate from the prediction of dipole model, and the chain structure aggregation effect, the sealing effect and the friction effect by compression should be considered.

Fundamental Process Mechanics Common to Machining and Grinding Operations

All different production processes have one thing in common: in each case a workpiece with characteristic material behavior, stress, strain, self-hardening and temperature will be produced by a tool with special geometry and individual kinematic conditions, with a wide range of energy in a designed machine tool which is working along programmed lines. For the workpiece material, it is not important from which machine the energy is coming. To be able to predict more accurate values of the production process, it will be necessary to focus more on the complex and difficult process mechanics. The result must have a strong physical base and be in good agreement with practical results To solve these problems, we have to uncover all previous simplification assumptions for the existing models. This leads in a first step to a new fundament in process mechanics, which is only based on mathematics, physics and material behavior with friction conditions, and resulting temperatures during metal plastic flow. The new mathematical equations developed for yield shear stress and strain rate will be presented and discussed in this paper. The plastic deformation is the only parameter that will not disappear after completing the operation. Therefore, this will be the base to compare the developed theoretical deformation with the experimental results for two operations: cutting and grinding. In addition, it could be shown that yield shear stress and corresponding strain rate versus temperatures have an interdependent relationship, which creates the opportunity to determine the temperatures during metal plastic flow.

Simulations of Frictional Losses in a Turbulent Blood Flow Using Three Rheological Models

Blood flow rate is a crucial factor in transporting an oxygen and depends on several parameters like heart pressure, blood properties like density and viscosity, frictional loss and diameter and shape of vein. Frictional loss is a main challenge of current engineering. Therefore, simulation of dependence of blood properties on frictional loss is very important. When blood properties are considered the first step is to find proper rheological model. It is well known that human blood demonstrates a yield shear stress. Therefore, the research is focused on simulating frictional losses in a turbulent flow of human blood, which demonstrates a yield stress. Three arbitrarily chosen rheological models were considered, namely Bingham, Casson and Herschel-Bulkley. Governing equations describing turbulent blood flow were developed to axially symmetrical an aorta. The mathematical model constitutes three partial differential equations, namely momentum equation, kinetic energy of turbulence and its dissipation rate. The main objective of the research is examining influence of the yield shear stress on frictional losses in a human blood in an aorta when flow becomes turbulent. Simulation of blood flow confirmed marginal influence of a yield shear stress on frictional losses when flow becomes turbulent. Results of simulations are discussed and final conclusions are stated.

Effect of Specimen Dimensions on Yield Shear Stress in Torsion Testing by using Taguchi Method and GRA

In this paper, investigated the effect of Al 6061 T6 solid specimen dimensions on torsional tests on yield shear stress. Torsion experiments were conducted at various levels of solid aluminum samples using key sample dimensions such as outer diameter, effective length, total length and fillet radius. Taguchi parameter design and optimization approaches are used to design experiments, and then predict the optimal set of parameters. Multi-objective optimization was done using the Grey Relational Analysis (GRA) method. In the GRA method, a grey relational grade is found to determine a set of parameters for multi-objective optimization of parameters. It is found that the outer diameter has a greater effect on the yield shear stress.

Mechanical and Optical Properties Characterization of C-Plane (0001) and M-Plane (10−10) GaN by Nanoindentation and Luminescence

ABSTRACTYield shear stress dependence on dislocation density and crystal orientation was studied in bulk GaN crystals by nanoindentation examination. The yield shear stress decreased with increasing dislocation density which is estimated by dark spot density in cathodoluminescence, and it decreased with decreasing nanoindentation strain-rate. It reached and coincided at 11.5 GPa for both quasi-static deformed c-plane (0001) and m-plane (10-10) GaN. Taking into account theoretical Peierls–Nabarro stress and yield stress for each slip system, these phenomena were concluded to be an evidence of heterogeneous mechanism associated plastic deformation in GaN crystal. Transmission electron microscopy and molecular dynamics simulation also supported the mechanism with obtained r-plane (-1012) slip line right after plastic deformation, so called pop-in event. The agreement of the experimentally obtained atomic shuffle energy with the calculated twin boundary energy suggested that the nucleation of the local metastable twin boundary along the r-plane concentrated the indentation stress, leading to an r-plane slip. This nanoindentation examination is useful for the characterization of crystalline quality because the wafer mapping of the yield shear stress coincided the photoluminescence mapping which shows increase of emission efficiency due to reduction of non-radiative recombination process by dislocation.