Recent experiments have shown the 'size effects' in micro/nano scale. But the classical plasticity theories can not predict these size dependent deformation behaviors because their constitutive models have no characteristic material length scale. The Mechanism - based Strain Gradient(MSG) plasticity is proposed to analyze the non-uniform deformation behavior in micro/nano scale. The MSG plasticity is a multi-scale analysis connecting macro-scale deformation of the Statistically Stored Dislocation(SSD) and Geometrically Necessary Dislocation(GND) to the meso-scale deformation using the strain gradient. In this research we present a study of nano-indentation by the MSG plasticity. Using W. D. Nix and H. Gao’s model, the analytic solution(including depth dependence of hardness) is obtained for the nano indentation , and furthermore it validated by the experiments.

Mechanism-based Strain Gradient Plasticity 를 이용한 나노 인덴테이션의 해석

A Review of Elastic–Plastic Contact Mechanics

Innovations in relevant micro-contact areas are highlighted, these include, design, contact resistance modeling, contact materials, performance and reliability. For each area the basic theory and relevant innovations are explored. A brief comparison of actuation methods is provided to show why electrostatic actuation is most commonly used by radio frequency microelectromechanical systems designers. An examination of the important characteristics of the contact interface such as modeling and material choice is discussed. Micro-contact resistance models based on plastic, elastic-plastic and elastic deformations are reviewed. Much of the modeling for metal contact micro-switches centers around contact area and surface roughness. Surface roughness and its effect on contact area is stressed when considering micro-contact resistance modeling. Finite element models and various approaches for describing surface roughness are compared. Different contact materials to include gold, gold alloys, carbon nanotubes, composite gold-carbon nanotubes, ruthenium, ruthenium oxide, as well as tungsten have been shown to enhance contact performance and reliability with distinct trade offs for each. Finally, a review of physical and electrical failure modes witnessed by researchers are detailed and examined.

/pdf/a-review-of-micro-contact-physics-for-microelectromechanical-4z1vzxhmv2.pdf

A review of micro-contact physics for microelectromechanical systems (MEMS) metal contact switches

The contact force and the real contact area between rough surfaces are important in the prediction of friction, wear, adhesion, and electrical and thermal contact resistance. Over the last four decades various mathematical models have been developed. Built on very different assumptions and underlying mathematical frameworks, model agreement or effectiveness has never been thoroughly investigated. This work uses several measured profiles of real surfaces having vastly different roughness characteristics to predict contact areas and forces from various elastic contact models and contrast them to a deterministic fast Fourier transform (FFT)-based contact model. The latter is considered “exact” because surfaces are analyzed as they are measured, accounting for all peaks and valleys without compromise. Though measurement uncertainties and resolution issues prevail, the same surfaces are kept constant (i.e., are identical) for all models considered. Nonetheless, the effect of the data resolution of measured sur...

/pdf/on-the-modeling-of-elastic-contact-between-rough-surfaces-2id07w7mep.pdf

On the Modeling of Elastic Contact between Rough Surfaces

Although nanoparticle additives have been the topic of multiple studies recently, very little work has attempted to explicitly model the third body contact of nanoparticles. This work presents and uses a novel methodology to model nanoparticles in contact between rough surfaces. The model uses two submodels to handle different scales of contact, namely the nano-sized particles and micrometer-sized roughness features. Silicon nanoparticles suspended in conventional lubricant are modeled in contact between steel rough surfaces. The effect of the particles on contact force and real area of contact has been modeled. The model makes predictions of the coefficient of friction and wear using fundamental models. The results suggest that particles would reduce the real area of contact and, therefore, decrease the friction force. Also, particles could induce abrasive wear by scratching the surfaces. The implications of the model are also discussed, and the arguments and results have been linked to available experimental data. This work finds that particle size and distribution are playing a key role in tribology characteristics of the nanolubricants. [DOI: 10.1115/1.4024297]

The Effect of Nanoparticles on the Real Area of Contact, Friction, and Wear

https://www.eng.auburn.edu/~jacksr7/Wilson-ECRsurfaceseperation-2009.pdf

Surface separation and contact resistance considering sinusoidal elastic–plastic multi-scale rough surface contact

Reliability and life study of hydraulic solenoid valve. Part 1: A multi-physics finite element model

Reliability and life study of hydraulic solenoid valve. Part 2: Experimental study

Any engineering component possesses roughness on its surface when it is observed microscopically, including electrical connectors Electrical connectors usually consist of a spring and a pin In this study, the spring part is in the shape of a compliant curved beam whereas the pin one is of a flat form and these two parts are in contact during operation This work presents a multi-physics (structural, electrical and thermal) finite element model of the bulk region of an electrical connector The rough surfaces of the spring and pin parts are considered using a multi-scale sinusoidal rough surface (MSRS) contact model The resulting coupled multi-physics connector model is used to analyze the performance of the connector while the applied current is incremented from 5 to 20 A As expected, this produced a proportional rise in voltage drop and temperature across the bulk regions of the connector parts The coupled multi-physics model together with the MSRS model should provide greater accuracy in the prediction of contact forces, electrical contact resistance (ECR) and thermal contact resistance (TCR) The present work also provides valuable information on stresses and strains distributions, current flow and temperature variations in the bulk regions of the electrical connector

A Multi-Physics Finite Element Model of an Electrical Connector Considering Rough Surface Contact

A comprehensive multi-physics theoretical model of a solenoid valve used in an automobile transmission is constructed using the finite element method. The multi-physics model includes the coupled effects of electromagnetic, thermodynamics and solid mechanics. The resulting finite element model of the solenoid valve provides useful information on the temperature distribution, mechanical and thermal deformations, and stresses. The model results predict that the solenoid valve is susceptible to a coupled electrical–thermo-mechanical failure mechanism. The coil can generate heat which can cause compressive stress and high temperatures that in turn could fail the insulation between the coil wires. The model facilitates the characterization of the solenoid valve performance, life and reliability and can be used as a predictive tool in future solenoid design.

S.V. Angadi

Papers

Surface separation and contact resistance considering sinusoidal elastic–plastic multi-scale rough surface contact

Reliability and life study of hydraulic solenoid valve. Part 1: A multi-physics finite element model

Reliability and life study of hydraulic solenoid valve. Part 2: Experimental study

A Multi-Physics Finite Element Model of an Electrical Connector Considering Rough Surface Contact

Reliability and Life Study of Hydraulic Solenoid Valve - Part 1 - A Multi-physics Finite Element Model