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Routes to failure in rotating MEMS devices experiencing sliding friction

Description: Gear systems rotating on hubs have been operated to failure using Sandia`s microengine as the actuation device. Conventional failure modes such as fatigue induced fracture did not occur, indicating that the devices are mechanically extremely robust. The generic route to failure observed for all rotating devices involves sticking of structures that are in sliding contact. This sticking evidently results from microscopic changes in the sliding surfaces during operation. The rate at which these changes occur is accelerated by excessive applied forces, which originate from non-optimized designs or inappropriate drive voltages. Precursors to failure are observed, enabling further understanding of the microscopic changes that occur in the sliding surfaces that ultimately lead to failure.
Date: August 1, 1997
Creator: Miller, S.L.; LaVigne, G.; Rodgers, M.S.; Sniegowski, J.J.; Waters, J.P. & McWhorter, P.J.
Partner: UNT Libraries Government Documents Department

Characterization of transfer layers on steel surfaces sliding against diamondlike carbon in dry nitrogen

Description: Transfer layers on sliding steel surfaces play important roles in tribological performance of diamondlike carbon films. This study investigated the nature of transfer layers formed on M50 balls during sliding against diamondlike carbon (DLC) films (1.5 {mu}m thick) prepared by ion-beam deposition. Long-duration sliding tests were performed with steel balls sliding against the DLC coatings in dry nitrogen at room temperature and zero humidity. Test results indicated that the friction coefficients of test pairs were initially 0.12 but decreased steadily with sliding distance to 0.02-0.03 and remained constant throughout the tests, which lasted for more than 250,000 sliding cycles (30 km). This low-friction regime appeared to coincide with the formation of a carbon-rich transfer layer on the sliding surfaces of M50 balls. Micro-laser-Raman spectroscopy and electron microscopy were used to elucidate the structure and chemistry of these transfer layers and to reveal their possible role in the wear and friction behavior of DLC-coated surfaces.
Date: March 1, 1995
Creator: Erdemir, A.; Bindal, C.; Pagan, J. & Wilbur, P.
Partner: UNT Libraries Government Documents Department

AN ANALYSIS OF THE MEASURED VALUES FOR THE STATE OF STRESS IN THEEARTH'S CRUST

Description: The state of stress in the crust of the earth is of great fundamental and practical significance. No totally satisfactory method for measuring the complete state of stress has been devised yet. Despite this, many efforts have been made to measure this state of stress at different locations. From a compilation of many of the results, fifty which yielded the complete state of stress and in which one of the principal stresses is vertical, have been selected for a statistical analysis in an endeavor to define the nature of the state of stress in the crust. These data have been analyzed as a whole, and divided into three groups depending upon whether the vertical stress is the maximum, minimum or intermediate principal stress. Linear regression analyses of the values of half the maximum stress difference as a function of half the sum of the maximum and minimum principal stresses have been made. The correlation coefficients for these fits are 0.786 for the data as a whole and 0.848, 0.790 and 0.383 for each of the groups. Values of the coefficient of sliding friction between blocks of rock comprising the crust, interpreted from the slopes of these lines, ranged from 0.625 (for those measurements where the vertical stress is the maximum principal stress) through 0.427 (for those cases where the vertical stress is the minimum principal stress), to 0.220 (for those cases where vertical stress is the intermediate principal stress). The 98 percent confidence limits for these values lie within +19.4 percent - 16.6 percent.
Date: August 1, 1978
Creator: Jamison, Dennis B. & Cook, Neville G.W.
Partner: UNT Libraries Government Documents Department

Material science experiments on the Atlas Facility

Description: Three material properties experiments that are to be performed on the Atlas pulsed power facility are described; friction at sliding metal interfaces, spallation and damage in convergent geomety, and plastic flow at high strain and high strain rate. Construction of this facility has been completed and experiments in high energy density hydrodynamics and material dynamics will begin in 2001.
Date: January 1, 2001
Creator: Keinigs, R. K. (Rhonald K.); Atchison, W. L. (Walter L.); Faehl, R. J. (Rickey J.); Lindemuth, I. R. (Irvin R.); Anderson, W. E. (Wallace E.); Bartsch, R. R. (Robert Richard) et al.
Partner: UNT Libraries Government Documents Department

Numerical simulation and experimental observations of initial friction transients

Description: Experiments were performed to better understand the sliding frictional behavior between metals under relatively high shear and normal forces. Microstructural analyses were done to estimate local near-surface stress and strain gradients. The numerical simulation of the observed frictional behavior was based on a constitutive model that uses a state variable approach.
Date: July 1, 1995
Creator: Hughes, D.A.; Weingarten, L.I. & Dawson, D.B.
Partner: UNT Libraries Government Documents Department

Tribological Characteristics of sputtered Au/Cr films on alumina substrates at elevated temperatures

Description: This paper describes research to evaluate the tribological properties of alumina pins sliding against thin sputtered gold films deposited on alumina disk substrates. A 250 {angstrom} thick chromium interlayer was first deposited onto the alumina test disks to enhance adhesion and high temperature wetting of the gold films. The Au/Cr films were tribotested in pure sliding in a pin-on-disk tribometer under a 4.9 N load at 1 m/s. The test atmosphere was room air at temperatures of 25, 500, and 800 C and the test duration varied from 60 to 540 min. The use of the Au/Cr films reduced friction by about a factor of two compared to the unlubricated alumina sliding couple. The coating prevented wear of the alumina substrate disks and reduced pin wear by one to two orders of magnitude. In addition, wear lives in excess of 200 000 sliding passes (9 hr) were observed during sliding at 800 C. Results suggest that these films show promise for the practical lubrication of many high temperature sliding components.
Date: December 31, 1993
Creator: Benoy, P.A. & DellaCorte, C.
Partner: UNT Libraries Government Documents Department

Force models for particle-dynamics simulations of granular materials

Description: Engineering-mechanics contact models are utilized to describe the inelastic, frictional interparticle forces acting in dry granular systems. Simple analyses based on one-dimensional chains are utilized to illustrate wave propagation phenomena in dense and dilute discrete particulates. The variation of restitution coefficient with impact velocity is illustrated for a variety of viscous and hysteretic normal force models. The effects of interparticle friction on material strength in discrete-particle simulations are much closer to measured values than are theories that do not allow article rotations.
Date: December 1, 1994
Creator: Walton, O.R.
Partner: UNT Libraries Government Documents Department

Frictional sliding in layered rock: laboratory-scale experiments

Description: The work is part of the rock mechanics effort for the Yucca Mountain Site Characterization Program. The laboratory-scale experiments are intended to provide high quality data on the mechanical behavior of jointed structures that can be used to validate complex numerical models for rock-mass behavior. Frictional sliding between simulated rock joints was studied using phase shifting moire interferometry. A model, constructed from stacks of machined and sandblasted granite plates, contained a central hole bore normal to the place so that frictional slip would be induced between the plates near the hole under compressive loading. Results show a clear evolution of slip with increasing load. Since the rock was not cycled through loading- unloading, the quantitative differences between the three data sets are probably due to a ``wearing-in`` effect. The highly variable spatial frequency of the data is probably due to the large grain size of the granite and the stochastic frictional processes. An unusual feature of the evolution of slip with increasing load is that as the load gets larger, some plates seem to return to a null position. Figs, 6 refs.
Date: September 1, 1996
Creator: Buescher, B.J.; Perry, K.E. Jr. & Epstein, J.S.
Partner: UNT Libraries Government Documents Department

HE friction sensitivity oblique impact sensitivity of explosives (the SKID test). Progress report, October 1971--December 1971

Description: The oblique impact test series on LX-10-0 Lot 710-2 was completed. Two instrumented oblique impact tests were done using RX-04-DW dropped at 45{degrees}, 5{prime} on a smooth steel surface. One additional oblique impact using RX-04-EB at 45{degrees} 3.5{prime} was done. An instrumented vertical drop and oblique impact series was begun on RX-04-EC (96/4 HMX/Viton).
Date: December 1998
Creator: Van Velkinburgh, J. H.
Partner: UNT Libraries Government Documents Department

Four great challenges confronting our understanding and modeling of sliding friction

Description: This paper addresses four challenges whose solutions may together enable significant progress in the predication and control of friction for energy conservation. Posed as questions these are: (1) how can materials with greatly different properties and compositions produce similar kinetic friction coefficients when tested under comparable conditions; (2) how is it possible that the kinetic friction coefficient for the same materials pair can differ greatly when it is slid in different tribosystems; (3) how can frictional phenomena at different size scales be reconciled; and (4) how can the effects of the machine, the materials (including lubricants) and the environment be successfully incorporated into quantitative and predictive friction models? Examples related to these four challenges are provided, as are possible approaches for attacking them in future research efforts.
Date: August 1, 1997
Creator: Blau, P.J.
Partner: UNT Libraries Government Documents Department

Tribological properties of hard carbon films on zirconia ceramics

Description: This study investigated the tribological properties of hard diamondlike carbon (DLC) films on magnesia-partially-stabilized zirconia (MgO-PSZ) substrates over a wide range of loads, speeds, temperatures, and counterface materials. The films were 2 {micro}m-thick and produced on by ion-beam deposition at room temperature. Tribological tests were conducted on a ball-on-disk machine in open air of 30 to 50% relative humidity under contact loads of 1 to 50 N, at sliding velocities of 0.1 to 6 m/s, and at temperatures to 400{degrees}C. A1{sub 2}O{sub 3} and Si{sub 3}N{sub 4} balls were also used and rubbed against the DLC-coated MgO-PSZ disks, primarily to assess and compare their friction and wear performance to that of MgO-PSZ balls. A series of long-duration lifetime tests was run at speeds of 1, 2, and 6 m/s under a 5-N load to assess the durability of these DLC films. Test results showed that the friction coefficients of MgO-PSZ balls sliding against MgO-PSZ disks were in the range of 0.5-0.8, and the average specific wear rates of MgO-PSZ balls ranged from 10{sup {minus}5} to 5 {times} 10{sup {minus}4} mm{sup 3}/N.m, depending on sliding velocity, contact load and ambient temperature. The friction coefficients of MgO-PSZ balls sliding against the DLC-coated-MgO-PSZ disks varied between 0.03 to 0.1. The average specific wear rates of MgO-PSZ balls were reduced by factors of three to four orders of magnitude when rubbed against the DLC coated disks. These DLC films could last 1.5 million to 4 million cycles, depending on sliding velocity. Scanning electron microscopy and micro-laser Raman Spectroscopy were used to elucidate the microstructural and chemical nature of DLC films and worn surfaces.
Date: December 31, 1995
Creator: Erdemir, A.; Bindal, C.; Fenske, G.R. & Wilbur, P.
Partner: UNT Libraries Government Documents Department

Friction and wear properties of smooth diamond films grown in fullerene-argon plasmas

Description: In this study, we describe the growth mechanism and the ultralow friction and wear properties of smooth (20-50 nm rms) diamond films grown in a microwave plasma consisting of Ar and fullerene (the carbon source). The sliding friction coefficients of these films against Si{sub 3}N{sub 4} balls are 0.04 and 0.1 in dry N{sub 2} and air, which are comparable to that of natural diamond sliding against the same pin material, but is lower by factors of 5 to 10 than that afforded by rough diamond films grown in conventional H{sub 2}-CH{sub 4} plasmas. Furthermore, the smooth diamond films produced in this work afforded wear rates to Si{sub 3}N{sub 4} balls that were two to three orders of magnitude lower than those of H{sub 2}-CH{sub 4} grown films. Mechanistically, the ultralow friction and wear properties of the fullerene-derived diamond films correlate well with their initially smooth surface finish and their ability to polish even further during sliding. The wear tracks reach an ultrasmooth (3-6 nm rms) surface finish that results in very little abrasion and ploughing. The nanocrystalline microstructure and exceptionally pure sp{sup 3} bonding in these smooth diamond films were verified by numerous surface and structure analytical methods, including x-ray diffraction, high-resolution AF-S, EELS, NEXAFS, SEM, and TEM. An AFM instrument was used to characterize the topography of the films and rubbing surfaces.
Date: August 1, 1995
Creator: Erdemir, A.; Fenske, G.R.; Bindal, C.; Zuiker, C.; Krauss, A.R. & Gruen, D.M.
Partner: UNT Libraries Government Documents Department

Characterizing the effects of friction liner materials on the performance of piezoelectric motors using finite element analysis

Description: A finite element model of a Panasonic USM-40D piezoelectric motor`s rotor was coupled with a finite element model of the motor`s friction liner/rotor so that the frictional interface could be further studied. Results from the model were used to study the affects of various friction liner material properties on motor stall torque. Statistical methods were used to determine the significant friction liner material properties and their interactions. An equation for predicting the stall torque as a function of the significant variables and their interactions was established.
Date: October 1, 1995
Creator: Gute, G.D. & Halter, S.L.
Partner: UNT Libraries Government Documents Department

Electrophoretically-deposited solid film lubricants

Description: An aqueous-based process that uses electrophoresis to attract powdered lubricant in suspension to a charged target was developed. The deposition process yields coatings with low friction, complies with environmental safety regulations, requires minimal equipment, and has several advantages over processes involving organic binders or vacuum techniques. This work focuses on development of the deposition process, includes an analysis of the friction coefficient of the material in sliding contact with stainless steel under a range of conditions, and a functional evaluation of coating performance in a precision mechanical device application. Results show that solid lubricant films with friction coefficients as low as 0.03 can be produced. A 0.03 friction coefficient is superior to solid lubricants with binder systems and is comparable to friction coefficients generated with more costly vacuum techniques.
Date: April 1, 1995
Creator: Dugger, M.T.; Panitz, J.K.J. & Vanecek, C.W.
Partner: UNT Libraries Government Documents Department

Wear-mechanism modelling. Final report

Description: Goals of the program are to calculate the surface temperatures in dry sliding, develop a soft wear tester for ceramics, survey the wear mechanisms in brittle solids, and couple the temperature calculations with models to give wear maps for brittle solids. (DLC)
Date: March 1, 1993
Creator: Ashby, M. F.
Partner: UNT Libraries Government Documents Department

Micro and Nano-structure Development and Multiscale Physics at Sliding Metal Interfaces

Description: This final report describes research on the response of ductile materials to extreme loading conditions and high strain rates during impact combined with sliding friction. The work has involved a collaboration among two groups at Los Alamos National Laboratory and a tribology research grouup at The Ohio State University. The project involved experimental work and computer simulations at both laboratories and continuum mechanics analysis at OSU, supplemented by testing at AWE, Harwell, UK. Results demonstrated the importance of vorticity and mechanical mixing near the sliding interface in the development of nanocrystalline tribomaterial that is far from equilibrium. The work also revealed that strain rate sensitivity is an important materials property for determining the development of the velocity profile during sliding. As such, it is a property that is key to understanding the evolution of sliding behavior.
Date: June 1, 2006
Creator: Rigney; David & A.
Partner: UNT Libraries Government Documents Department

An analytic solution to a driven interface problem

Description: The frictional properties of sliding metal interfaces at high velocities are not well known from either an experimental or theoretical point of view. The constitutive properties and macroscopic laws of frictional dynamics at high velocities necessary for materials continuum codes have only a qualitative validity and it is of interest to have analytic problems for sliding interfaces to enable separation of model from numerical effects. The authors present an exact solution for the space and time dependence of the plastic strain near a sliding interface in a planar semi-finite geometry. This solution is based on a particular form for the strain rate dependence of the flow stress and results in a hyperbolic telegrapher equation for the plastic strain. The form of the solutions and wave structure will be discussed.
Date: October 1, 1997
Creator: Hammerberg, J.E. & Pepin, J.
Partner: UNT Libraries Government Documents Department

SANTOS - a two-dimensional finite element program for the quasistatic, large deformation, inelastic response of solids

Description: SANTOS is a finite element program designed to compute the quasistatic, large deformation, inelastic response of two-dimensional planar or axisymmetric solids. The code is derived from the transient dynamic code PRONTO 2D. The solution strategy used to compute the equilibrium states is based on a self-adaptive dynamic relaxation solution scheme, which is based on explicit central difference pseudo-time integration and artificial mass proportional damping. The element used in SANTOS is a uniform strain 4-node quadrilateral element with an hourglass control scheme to control the spurious deformation modes. Finite strain constitutive models for many common engineering materials are included. A robust master-slave contact algorithm for modeling sliding contact is implemented. An interface for coupling to an external code is also provided. 43 refs., 22 figs.
Date: July 1, 1997
Creator: Stone, C.M.
Partner: UNT Libraries Government Documents Department

Integrated modeling and testing of a micro hinged structure for sliding friction measurement

Description: This paper summarizes the design, modeling, and initial evaluation of a hinged structure for friction measurement in surface micromachining technology. While the area requirements are small, the present structure allows a much larger velocity and pressure range to be evaluated as compared to comb drive structures. The device consists of a cantilevered driver beam connected to a friction pad through a strategically located hinge. AC excitation of the beam flexure forces axial sliding of the friction pad due to beam foreshortening. Normal force is controlled by DC voltage on wings adjacent to the friction pad. While the achievable slip is small (10--30 nm), it is sufficient to disengage contacting asperities and engage new points of contact, and thus should be representative of frictional processes. Furthermore, the design enables the friction pad contact area to remain relatively constant over the excitation cycle. Computer simulation results are provided to mimic on-going experimental work. Increased friction forces are shown to enhance the size of hysteresis loops relating beam deflection to driver voltage.
Date: August 1, 1998
Creator: Redmond, J.M.; Boer, M.P. de & Michalske, T.A.
Partner: UNT Libraries Government Documents Department

Physical and tribological properties of diamond films grown in argon-carbon plasmas

Description: Nanocrystalline diamond films have been deposited using a microwave plasma consisting of argon, 2--10% hydrogen and a carbon precursor such as C{sub 60} or CH{sub 4}. It was found that it is possible to grow the diamond phase with both carbon precursors, although the hydrogen concentration in the plasma was 1--2 orders of magnitude lower than normally required in the absence of the argon. Auger electron spectroscopy, x-ray diffraction measurements and transmission electron microscopy indicate the films are predominantly composed of diamond. Surface roughness, as determined by atomic force microscopy and scanning electron microscopy indicate the nanocrystalline films grown in low hydrogen content plasmas grow exceptionally smooth (30--50 nm) to thicknesses of 10 {mu}m. The smooth nanocrystalline films result in low friction coefficients ({mu}=0.04--0.06) and low average wear rates as determined by pin-on-disk measurements.
Date: June 1, 1995
Creator: Zuiker, C.; Krauss, A.R.; Gruen, D.M.; Pan, X.; Li, J.C.; Csencsits, R. et al.
Partner: UNT Libraries Government Documents Department

Tribological properties of nanocrystalline diamond films

Description: In this paper, the authors present the friction and wear properties of nanocrystalline diamond (NCD) films grown in A-fullerene (C{sub 60}) and Ar-CH{sub 4} microwave plasmas. Specifically, they address the fundamental tribological issues posed by these films during sliding against Si{sub 3}N{sub 4} counterfaces in ambient air and inert gases. Grain sizes of the films grown by the new method are very small (10--30 nm) and are much smoother (20-40 nm, root mean square) than those of films grown by the conventional H{sub 2}-CH{sub 4} microwave-assisted chemical-vapor-deposition (CVD) process. Transmission electron microscopy (TEM) revealed that the grain boundaries of these films are very sharp and free of nondiamond phases. The microcrystalline diamond (MCD) films grown by most conventional methods consist of large grains and a rough surface finish, which can cause severe abrasion during sliding against other materials. The friction coefficients of films grown by the new method (i.e., in Ar-C{sub 60} and Ar-CH{sub 4} plasmas) are comparable to those of natural diamond, and wear damage on counterface materials is minimal. Fundamental tribological studies indicate that these films may undergo phase transformation during long-duration, high-speed and/or high-load sliding tests and that the transformation products trapped at the sliding interfaces can intermittently dominate friction and wear performance. Using results from a combination of TEM, electron diffraction, Raman spectroscopy, and electron energy loss spectroscopy (EELS), they describe the structural chemistry of the debris particles trapped at the sliding interfaces and elucidate their possible effects on friction and wear of NCD films in dry N{sub 2}. Finally, they suggest a few potential applications in which NCD films can improve performance and service lives.
Date: January 26, 2000
Creator: Erdemir, A.; Fenske, G. R.; Kraus, A. R.; Gruen, D. M.; McCauley, T. & Csencsits, R. T.
Partner: UNT Libraries Government Documents Department

A hinged-pad test structure for sliding friction measurement in micromachining

Description: The authors describe the design, modeling, fabrication and initial testing of a new test structure for friction measurement in MEMS. The device consists of a cantilevered forked beam and a friction pad attached via a hinge. Compared to previous test structures, the proposed structure can measure friction over much larger pressure ranges, yet occupies one hundred times less area. The placement of the hinge is crucial to obtaining a well-known and constant pressure distribution in the device. Static deflections on the device were measured and modeled numerically, Preliminary results indicate that friction pad slip is sensitive to friction pad normal force.
Date: August 1, 1998
Creator: Boer, M.P. de; Redmond, J.M. & Michalske, T.A.
Partner: UNT Libraries Government Documents Department

Properties of a single asperity and the interface between molecular dynamics and continuum mechanics: A commentary

Description: The speakers in this session attempted to bridge the large spatial gap between the atomistic processes occurring at a sliding interface and the continuum description of such processes. This task is indeed formidable. One may ask why should we study such elementary processes at all if what we are really interested in is a global picture of friction. Real surfaces are uneven, impure, and may be covered by nasty things like lubricants specifically placed there to modify frictional behavior. Isn`t the real world of friction too ``dirty`` to be studied by surface science techniques? Indeed, even if we were to understand the interaction of every geometry of single asperity under every environment, how to average this information to produce a model of friction is unknown. Does this mean that we shouldn`t attempt to measure and calculate these simple processes? I think not. Understanding the response of a single asperity is an important essential element which will lead to a thorough predictive understanding of friction. But clearly our work cannot end with the study of single asperities. There are two critical phenomena which have to be added to a single asperity model: first the inclusion of a distribution in both size and location of single asperities and second the role of microstructure evolution. Clearly single asperities do not respond independently from each other. The proximity of two asperities changes both the local stress distribution as well as the contact area. I believe the greatest challenge that faces us is how to assemble the vast amount of single asperity data that we can generate and from it create useful engineering models.
Date: December 1, 1995
Creator: Baskes, M.I.
Partner: UNT Libraries Government Documents Department