Influence Of Surface Irregularities Research Articles

Behaviour of conical porous hybrid journal bearing operated with MHD lubricant considering influence of surface irregularities

This study concerns with the numerical simulation of a conical porous hybrid journal bearing (CPHJBS) considering the synergistic effect of three-dimensional (3D) surface irregularities and magnetohydrodynamic (MHD) lubricant. The study analyzes the interactive effects of permeability parameter, MHD lubricant behaviour, semi cone angle and 3D surface irregularities on the performance of CPHJBS. FEM is used to solve the governing Reynolds equation for an irregular surfaced CPHJBS configuration lubricated with MHD lubricant. The findings of the study shows that the CPHJBS operating with MHD lubricant provide enhanced values of fluid film thickness and damping coefficients.

Performance of a Spherical Hybrid Thrust Bearing Considering the Influence of Surface Irregularities and MR Lubricant Behavior

This article describes the finite element modeling of a spherical hybrid thrust bearing (SHTB), taking into account the influence of three-dimensional surface irregularities and magnetorheological (MR) lubricant behavior. The rheological behavior of MR lubricant was described using the Herschel–Bulkley model, and the yield shear stress relationship of MR fluid was expressed using the asymmetrical sigmoidal function. The finite-element method (FEM) is used to solve the governing Reynolds equation for an irregular surfaced SHTB configuration along with the orifice restrictor equation. The findings of the study indicate that the performance of the SHTB is improved by considering the three-dimensional (3-D) surface irregularities and operating with MR fluid at the expense of power loss due viscous friction. The percentage increase in the value of dynamic coefficients () and () due to the coupled effect of MR fluid and three-dimensional surface irregularity () on the spherical hybrid thrust bearing is of the order of 52.37% and 71.22%, respectively, at and

Evaluation of material properties of 3D printed carbon steel for material modelling

AbstractA procedure and material properties of tensile coupon specimens are presented. The coupon specimens were cut from the plates printed by ArcelorMittal Global R&D Bars & Wires. For this, a welding robot based on Wire Arc Additive Manufacturing (WAAM) procedure and welding wire AWS 5.18 ER70S‐6 Böhler K56 were used. The specimens were cut in different directions to the printing direction, to investigate possible material anisotropy. Surface milled and as printed specimens were investigated focusing on the influence of surface irregularities on the material behaviour. 2D Digital Image Correlation (DIC) was used for evaluating engineering stress‐strain diagrams, E‐modules and Poisson ratios for each specimen.Obtained results clearly indicate that 3D printing technology was appropriate, showing material properties rather close to the rolled mild steel and minor anisotropy, E=200GPa, fracture strain above 25%, strength/yield stress beyond 1,3, for fy=420 MPa. Roughness of the surface was just 0,2mm for the thickness of 3,7mm, obtained using the wire diameter of 3mm.Finite Element Method (FEM) was used to validate the experimental results and to calibrate damage material properties. Results of uniaxial coupon specimens, the stress‐strain curve, is divided in 3 stages: the elastic stage, the plastic stage and the coupled plastic stage. The coupled plastic‐damage stage is further decomposed into the plastic‐dominated zone and the damage‐dominated zone. The true stress‐strain curve after necking is calibrated by FEM.

Non-destructive strength characterization of concrete using surface waves

The paper presents a description of non-destructive strength characterization of concrete, using ultrasonic probes, and of measuring surface wave velocity. Probes work at frequencies of 40 and 100 kHz, and they are equipped with an exponential waveguide, the end of which has a surface of ca. 1 mm 2. A short characteristic of this type of probe is shown with an analysis of the influence of the inclination angle between the vertical and the examined surface as well as the influence of surface irregularities on ultrasonic wave propagation. The results of laboratory examination are described and examples of application of this measurement method in practice are given. It has been proved that this method has a number of advantages that are very useful in engineering practice.

Threshold between Smooth and Wavy Laminar Sheet Flow

A numerical and experimental investigation of roughness effects on thin laminar fluid films is described. The flow considered is pressure driven in an essentially two-dimensional channel between a flat wall and a wavy one. Conclusions, based on finite-element method solutions of the applicable equations of motion and substantiated by experimental findings, lead to the definition of a comprehensive friction index. This generalized friction coefficient appears to properly sense the microinertial influence of surface irregularities on the flow and allows the design of a “sensitivity parameter” for quantifying the threshold between hydrodynamically smooth and hydrodynamically wavy laminar sheet flow. Among relevant technical areas, this matter is of importance in hydrodynamic lubrication where it may determine the limit of the applicability of the classical Reynolds equation.

Progress in the knowledge of irregular solid electrode surfaces

Modern approaches to solid surface disorder provide a more rigourous way of defining roughness at solid surfaces, a crucial concept in electrocatalysis. The study of this type of surface comprises growth kinetics, geometric description, relaxation kinetics and influence of surface irregularities on different reactions. Continuous rough columnar structured metal surfaces constitute a good model system for the investigation of a number of processes which are of special interest in heterogeneous catalysis, including electrocatalysis. The topography of these metal surfaces can be determined by scanning tunneling microscopy (STM) at different scales and can be described by means of the dynamic scaling theory applied to STM imaging. Roughness relaxation kinetics followed by electrochemical techniques can be interpreted through a coalescence-type mechanism. Typical examples of adsorption and diffusion controlled electrochemical reactions on this type of electrodes are presented.

Mechanics of Elastic Dislocations in Strained Layer Structures

AbstractApplication of the elastic continuum theory of dislocations to modeling of phenomena associated with elastic strain relaxation in strained layer epitaxial heterostructures is discussed. The concept of critical thickness for onset of strain relaxation in a strained epitaxial layer is first reviewed, and some extensions to periodic arrays of dislocations and to multiple layers are described. Then, two issues are addressed that arise when the assumptions underlying the critical thickness concept are not met. One issue concerns the nucleation of dislocations at the growth surface of an epitaxial film, particularly the influence of surface irregularities on the activation energy for surface nucleation. A second issue concerns the kinetics of glide of a threading dislocation as it lays down an interface misfit dislocation when the layer thickness exceeds the critical thickness. A generalized driving force for the glide process is defined, and a relationship between this force and the glide speed is proposed.

Surface Activation for Wear Investigation of Precise Elements

Application of the surface activation method to wear investigation of precise elements forms some specific problems. Parameters affecting the activity distribution in the active layer, the influence of surface irregularities on local changes in a specific activity, as well as the methods of measurement of very low activities are discussed in this paper. An example of wear investigation in a precise couple is presented, including description of some technical approaches. The main thesis of this paper were presented in a lecture titled: “Selected problems of radioisotope technique for wear investigation of precise elements”, delivered in Leipzig.

The influence of surface irregularities upon the Van der Waals forces between macroscopic bodies

An expression is derived for the Van der Waals force between two semi-infinite bodies with small surface irregularities. Calculations are given both for the plane-plane and the plane-sphere configuration. The value of the correction from the surface irregularities upon the Van der Waals force is shown to amount easily to 10–50%.

Influence of surface irregularities on the optical properties of thin layers

Influence of surface irregularities on the optical properties of thin layers