The authors would like to acknowledge Tim Krantz from NASA Glenn and Duane Detwiler from Honda R&#38;D for their technical support and in-kind contributions. Financial support for this research was provided by the member organizations of the Smart Vehicle Concepts Center (www.SmartVehicleCenter.org), a National Science Foundation Industry/University Cooperative Research Center (I/UCRC). S.D. is supported by a Smart Vehicle Concepts Graduate Fellowship and a University Fellowship from The Ohio State University Graduate School.

1. Development of the Modified Tribometer
<ol>
	<li>Install chuck-motor subsystem.
	<ol>
		<li>Level vibration isolation table. Place DC motor on the table; level the motor with shims and fix it with struts and bolts. Place support frame around the motor.</li>
		<li>Connect splined shaft to the motor shaft using a key. Put support plate on the frame with the splined shaft going through the hole in the plate. Set thrust needle-roller bearing on the support plate and around the splined shaft. Lubricate the bearing with cutting fluids.</li>
		<li>Connect the splined shaft to the chuck through an adapter plate, which has a splined shaft coupling on one side and the chuck&#8217;s bolt pattern on the other side. At this point, the chuck is supported by the frame through the thrust bearing and connected to the motor through the adapter plate.</li>
	</ol>
	</li>
	<li>Install the gymbal assembly.
	<ol>
		<li>Build the support frame using U-channel struts, brackets, and bolts. Use four long struts as pillars, and use three shorter ones as cross beams.</li>
		<li>Secure the four pillars to the vibration isolation table using brackets and bolts. Connect the gymbal assembly to the middle cross beam using bolts and nuts.</li>
		<li>Install a horizontally-oriented load cell in the gymbal assembly; rigidly connect one side of the load cell to the gymbal assembly&#8217;s frame, while connecting the other side to the gymbal arm with a wire.</li>
	</ol>
	</li>
	<li>Assemble the piezoelectric actuator.
	<ol>
		<li>Insert 3 in long, fully-threaded rod through the hole of the piezoelectric stack; put one washer and one nut at each end of the stack; leave about 1/8 in of thread protruding from the end of one nut.</li>
		<li>Tighten the nuts at both ends to create a preload in the stack. Connect the long, exposed threads to the gymbal arm using nuts and washers. Thread acorn nut onto the other end of the piezo-actuator and insert disc in the chuck (this acorn nut and disc are used for set-up purposes, not for testing).</li>
		<li>Adjust the height of the gymbal assembly so that the acorn nut is in contact with the top of the disc and the gymbal arm is level.</li>
		<li>Adjust the position of the gymbal assembly so that the contact point between the acorn nut and disc is about 25 mm away from the rotational center of the disc. Tighten all bolts in the set-up to ensure stability.</li>
	</ol>
	</li>
	<li>Set up signal generation, signal amplification, and data acquisition subsystems.
	<ol>
		<li>Connect data acquisition system to a lab computer. Connect the output of signal generator to the input of an electrical amplifier. Connect the amplifier output with the input wires of the piezoelectric stack. Connect the amplifier monitors to the data acquisition system.</li>
		<li>Connect the load cell to a signal conditioner, and then connect the output of the signal conditioner to the data acquisition system.</li>
	</ol>
	</li>
	<li>Additional set-up.
	<ol>
		<li>Connect air hose to shop air. Fix the end of the hose to the frame such that its outlet points at the piezo-actuator. Tape the tip of thermocouple to the piezo-actuator. Connect the thermocouple leads to reader; hang the reader on the frame.</li>
	</ol>
	</li>
</ol>
2. Pre-test Preparation
<ol>
	<li>Calibrate the rotational speed of the motor.
	<ol>
		<li>Attach magnet to the rim of the chuck. Place Hall-effect probe close to the chuck. Connect the output of the Hall-effect probe to gaussmeter that is connected to the data acquisition system.</li>
		<li>Open the data acquisition software and start data acquisition. Turn on the motor; turn the speed knob of the motor controller to 10 (the lowest rotational speed the motor provides). After the motor rotates for 10 revolutions, turn off the motor. End data acquisition.</li>
		<li>Analyze the saved data; the time between two peaks of the output signal from the gaussmeter is the time for the motor to rotate one full revolution.</li>
		<li>Turn the knob from 10 to 100 (the highest rotational speed the motor provides) in increments of 10; repeat steps 2.1.2 to 2.1.3.</li>
	</ol>
	</li>
	<li>Place load sensor pad between the acorn nut and the disc to measure the normal force at the interface. Finely machine the surface of testing discs using a lathe.</li>
	<li>Clean the acorn nut and disc to be tested immediately before test.
	<ol>
		<li>Put on plastic gloves and face mask.Prepare pieces of lab wipes; fold them into 1 inch squares. Spray ethanol on the tissue squares; gently wipe the surface of the acorn nut and disc with them.</li>
	</ol>
	</li>
	<li>Install the clean acorn nut and disc.
	<ol>
		<li>Thread the acorn nut onto the piezo-actuator, tighten it with an open-end wrench. Insert the disc in the chuck; adjust the position to make sure the tip of the acorn nut is in contact with the disc surface.</li>
		<li>Align the top surface of the disc and the gymbal arm. Tighten the chuck so that the disc is held firmly.</li>
	</ol>
	</li>
	<li>Measure the runout of the disc rotation.
	<ol>
		<li>Install laser displacement sensor in a fixture, and place the fixture next to the tribometer. Adjust the height and angle of the sensor so that the disc is within the sensor&#8217;s range and the laser beam is normal to the disc.</li>
		<li>Connect the sensor&#8217;s output to the data acquisition system. Start the data acquisition. Turn on the motor and rotate the disc for 10 revolutions; turn off the motor. End data acquisition.</li>
	</ol>
	</li>
</ol>
3. Perform Testing
<ol>
	<li>Tests with ultrasonic vibrations.
	<ol>
		<li>Hang 2 N weight on one hook that connects to the gymbal arm through wire and two pulleys. The weight is used to apply a normal load between the acorn nut and the disc.</li>
		<li>Hang another 2 N weight on the other hook that connects to the gymbal arm to provide a horizontal pretension to the load cell.</li>
		<li>Set the signal generator to provide a continuous sinusoidal signal with DC offset of 3 V, amplitude of 3 V, and frequency of 22 kHz (the resonance frequency of the piezo-actuator). Note that the 3 V offset is used to prevent tension in the piezo-actuator.</li>
		<li>Start data acquisition (reduced friction force). Turn on the amplifier and turn the gain knob to 15, which corresponds to an actual gain of 4.67 (the numbers on the gain knob are arbitrary).</li>
		<li>Turn on the motor; set the rotational speed to 6.67 rpm to provide a linear velocity of 20.3 mm/sec. Run the test for 4 hr.</li>
		<li>Turn off the motor and amplifier, and then stop the data acquisition. Remove the tested acorn nut and disc from the set-up; Repeat steps 2.3 to 2.5 to install new acorn nut and disc.</li>
		<li>Repeat steps 3.1.1&#160;to 3.1.6. In step 3.1.5, set the rotational speed to 13.3 rpm and 28.7 rpm to provide linear velocities of 40.6 mm/sec and 87 mm/sec, respectively; run the tests for 2 and 0.94 hr&#160;correspondingly.</li>
	</ol>
	</li>
	<li>Tests without ultrasonic vibrations.
	<ol>
		<li>Repeat step 3.1.6 to change acorn nuts and discs. Repeat steps 3.1.1&#160;to 3.1.6 with the signal generator and signal amplifier off (the friction measured is intrinsic friction ).</li>
	</ol>
	</li>
</ol>
4. Optical Profilometer Measurements
<ol>
	<li>Measurement preparation
	<ol>
		<li>Clean the discs immediately before measurements using step 2.3. Make eight evenly distributed marks around the rim of the disc. Open the profilometer software.</li>
		<li>Raise the lens so that there is sufficient clearance between the lens and sample platform. Level the sample platform. Place a piece of lab wipe on the platform.</li>
		<li>Gently place the sample on top of the tissue with one of the eight marks facing the front of the profilometer.</li>
	</ol>
	</li>
	<li>Measurement settings.
	<ol>
		<li>Choose VSI (Vertical-Scanning Interferometry) as the processing type. Select 5X lens for large field of view and overall shape. Pick 0.55X magnification for a scan area of 1.8 mm by 2.4 mm.</li>
		<li>Choose 1X scan speed. Set scan range to -100 m to 100 m. Bring the lens downward toward the sample until there is a blurry image on the screen. Adjust the height of the lens until the image is clear.</li>
		<li>Choose 2 as the number of scans to average for each measurement. Click the measurement button.</li>
	</ol>
	</li>
	<li>Post-measurement procedures.
	<ol>
		<li>Use the vision recipe that defined in the software to correct the raw image for tilt of the whole sample. Open the analysis toolbox in the software.</li>
		<li>Obtain the measured roughness values from the &#8220;Basic Stats&#8221; item. Obtain the measured volume loss of the wear scar within the scan area from the &#8220;Volume&#8221; item.</li>
		<li>Save the images of 1D profiles in x and y directions, the 2D profile, the 3D profile, as well as the table of roughness values. Turn the sample clockwise until the next mark faces the front of the profilometer.</li>
	</ol>
	</li>
	<li>Repeat steps 4.2&#160;to 4.3&#160;for the remaining 7 marks.</li>
	<li>Repeat steps 4.1.&#160;to 4.4 on all six discs.</li>
</ol>

<ol>
	<li>Bhushan, B. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=.">.</a> Introduction to tribology. , (2002).</li><li>Severdenko, V., Klubovich, V., Stepanenko, A. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=.">.</a> Ultrasonic rolling and drawing of metals. , (1972).</li><li>Taylor, R., Coy, R. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Improved+fuel+efficiency+by+lubricant+design:+a+review.">Improved fuel efficiency by lubricant design: a review.</a> Proc. Instit. Mech. Eng., Part J: J Eng. Tribol. 214 (1), 1-15 (2000).</li><li>Littmann, W., Storck, H., Wallaschek, J. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Sliding+friction+in+the+presence+of+ultrasonic+oscillations:+superposition+of+longitudinal+oscillations.">Sliding friction in the presence of ultrasonic oscillations: superposition of longitudinal oscillations.</a> Arch. Appl. Mech. 71 (8), 549-554 (2001).</li><li>Littmann, W., Storck, H., Wallaschek, J. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Reduction+in+friction+using+piezoelectrically+excited+ultrasonic+vibrations.">Reduction in friction using piezoelectrically excited ultrasonic vibrations.</a> Proc. SPIE. 4331, (2001).</li><li>Bharadwaj, S., Dapino, M. J. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Friction+control+in+automotive+seat+belt+systems+by+piezoelectrically+generated+ultrasonic+vibrations.">Friction control in automotive seat belt systems by piezoelectrically generated ultrasonic vibrations.</a> Proc. SPIE. 7645, 7645E (2010).</li><li>Bharadwaj, S., Dapino, M. J. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Effect+of+load+on+active+friction+control+using+ultrasonic+vibrations.">Effect of load on active friction control using ultrasonic vibrations.</a> Proc. SPIE. 7290, 7290G (2010).</li><li>Kumar, V., Hutchings, I. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Reduction+of+the+sliding+friction+of+metals+by+the+application+of+longitudinal+or+transverse+ultrasonic+vibration.">Reduction of the sliding friction of metals by the application of longitudinal or transverse ultrasonic vibration.</a> Tribol. Int. 37 (10), 833-840 (2004).</li><li>Pohlman, R., Lehfeldt, E. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Influence+of+ultrasonic+vibration+on+metallic+friction.">Influence of ultrasonic vibration on metallic friction.</a> Ultrasonics. 4 (4), 178-185 (1966).</li><li>Popov, V., Starcevic, J., Filippov, A. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Influence+of+Ultrasonic+In-Plane+Oscillations+on+Static+and+Sliding+Friction+and+Intrinsic+Length+Scale+of+Dry+Friction+Processes.">Influence of Ultrasonic In-Plane Oscillations on Static and Sliding Friction and Intrinsic Length Scale of Dry Friction Processes.</a> Tribol. Lett. 39 (1), 25-30 (2010).</li><li>Dong, S., Dapino, M. J. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Piezoelectrically-induced+ultrasonic+lubrication+by+way+of+Poisson+effect.">Piezoelectrically-induced ultrasonic lubrication by way of Poisson effect.</a> Proc. SPIE. 8343, 83430L (2012).</li><li>Dong, S., Dapino, M. J. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Elastic-plastic+cube+model+for+ultrasonic+friction+reduction+via+Poisson+effect.">Elastic-plastic cube model for ultrasonic friction reduction via Poisson effect.</a> Ultrasonics. 54 (1), 343-350 (2014).</li><li>Dong, S., Dapino, M. J. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Wear+Reduction+Through+Piezoelectrically-Assisted+Ultrasonic+Lubrication.">Wear Reduction Through Piezoelectrically-Assisted Ultrasonic Lubrication.</a> Smart. Mater. Struct. 23 (10), 104005 (2014).</li><li>Chowdhury, M., Helali, M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=The+effect+of+frequency+of+vibration+and+humidity+on+the+wear+rate.">The effect of frequency of vibration and humidity on the wear rate.</a> Wear. 262 (1-2), 198-203 (2014).</li><li>Bryant, M., Tewari, A., York, D. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Effect+of+Micro+(rocking)+vibrations+and+surface+waviness+on+wear+and+wear+debris.">Effect of Micro (rocking) vibrations and surface waviness on wear and wear debris.</a> Wear. 216 (1), 60-69 (1998).</li><li>Bryant, M., York, D. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Measurements+and+correlations+of+slider+vibrations+and+wear.">Measurements and correlations of slider vibrations and wear.</a> J. Tribol. 122 (1), 374-380 (2000).</li><li>Goto, H., Ashida, M., Terauchi, Y. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Effect+of+ultrasonic+vibration+on+the+wear+characteristics+of+a+carbon+steel:+analysis+of+the+wear+mechanism.">Effect of ultrasonic vibration on the wear characteristics of a carbon steel: analysis of the wear mechanism.</a> Wear. 94, 13-27 (1984).</li><li>Goto, H., Ashida, M., Terauchi, Y. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Wear+behaviour+of+a+carbon+steel+subjected+to+an+ultrasonic+vibration+effect+superimposed+on+a+static+contact+load.">Wear behaviour of a carbon steel subjected to an ultrasonic vibration effect superimposed on a static contact load.</a> Wear. 110 (2), 169-181 (1986).</li><li>Robinowicz, E. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=.">.</a> The friction and wear of materials. , (1965).</li><li>Bowden, F., Freitag, E. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=The+friction+of+solids+at+very+high+speeds.">The friction of solids at very high speeds.</a> Proc. R. Soc. A. 248 (1254), 350-367 (1985).</li><li>Burwell, J., Rabinowicz, E. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=The+nature+of+the+coefficient+of+friction.">The nature of the coefficient of friction.</a> J. Appl. Phys. 24 (2), 136-139 (1953).</li><li>Cocks, M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Interaction+of+sliding+metal+surfaces.">Interaction of sliding metal surfaces.</a> J. Appl. Phys. 33 (7), 2152-2161 (1962).</li><li>Rusinko, A. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=.">.</a> Ultrasound and Irrecoverable Deformation in Metals. , (2012).</li></ol>

The authors have nothing to disclose.

Experiments were conducted using this protocol to study the effect of linear speed on ultrasonic friction and wear reduction. The measurements show that ultrasonic vibrations effectively reduce friction and wear at three linear speeds.&#160;Consistent with prior observations, the amount of friction reduction decreases from 62.2% at 20.3 mm/sec to 29.3% at 87 mm/sec. Wear reduction is negligible with changing linear speed (45.8% to 48.6%).
Material properties such as Young&#8217;s modulus and y...

Friction exists at the interface of two contacting surfaces when they slide or roll relative to each other. Friction usually occurs along with abrasive or adhesive wear.1 Ultrasonics is the science behind high frequency phenomena, that is, waves traveling at frequencies above the acoustic range (20 kHz). The field of ultrasonics encompasses two fundamentally different regimes. One regime involves low intensity waves like those utilized in imaging processes such as medical ultrasound or non-destructive inspection of structures. The other is a high power regime in which high-energy waves are utilized to execute or assist engineering processes such as welding of plastics and metals. It has been shown that application of the latter kind of ultrasonic vibrations at the interface of two surfaces in sliding contact reduces the effective friction force at the interface. This phenomenon is known as ultrasonic lubrication.
To achieve ultrasonic lubrication between two sliding objects, relative vibration at ultrasonic frequencies must be established between them. Vibrations are typically applied to one of the two objects, either in the longitudinal, transverse, or perpendicular direction relative to the sliding velocity. In this study, a tribometer&#8217;s pin is fitted with a piezoelectric actuator so that its tip vibrates in the direction perpendicular to the tribometer&#8217;s rotating disc. Piezoelectric materials are a class of &#8220;smart&#8221; materials that deform when exposed to electric fields, vibrating at the same frequency as the excitation field. Piezoelectric materials can vibrate at frequencies well into the MHz range. Being superimposed to the macroscopic velocity, ultrasonic vibrations have the effect of alternating the direction of the instantaneous friction force and the contact between the surfaces, which in combination leads to a reduction of the effective friction force and surface wear.
Ultrasonic friction reduction has been demonstrated in practical manufacturing systems. For example, this technology has been utilized to reduce the force between tool and work piece in metal machining and forming processes such as drilling, pressing, sheet rolling, and wire drawing. Benefits include improved surface finish2 and a reduced need for expensive and environmentally harmful detergents to remove lubricants from the final product. There are potential applications of ultrasonic lubrication in other areas as well. For example, ultrasonic lubrication can substantially enhance the user experience in personal health care products by eliminating the need for lubricants or coatings. In automobile applications, friction modulation can improve the performance of ball joints whereas friction reduction between vehicle seats and rails facilitates seat movement, saving space and mass that would otherwise be occupied by traditional components and mechanisms. Ultrasonic lubrication can also help to improve fuel efficiency by reducing friction in powertrain and suspension systems.3 In space applications, where traditional lubricants cannot be used, ultrasonic lubrication can be employed to reduce wear and dramatically extend the life of critical components.
Laboratory demonstrations of friction reduction through ultrasonic lubrication are numerous. Friction reduction is quantified as the difference between the friction force measured without ultrasonic lubrication and the friction force with ultrasonic vibrations applied. In either case, the friction force is directly measured with force sensors. Littmann et al. 4-5 connected a piezoelectrically-driven actuator to a slider, on which a force sensor and a frame were installed for measuring friction forces and applying normal loads. A pneumatic actuator was employed to push the slider together with the actuator along a guide rail. Ultrasonic vibrations were applied in the direction longitudinal to the sliding velocity. Bharadwaj and Dapino6-7 conducted similar experiments using a piezoelectric stack actuator connected to a conical waveguide at either end of the stack. Contacts took place between the spherical edges of the cones and the surface of the guide rail. The effects of system parameters such as contact stiffness, normal load, and global stiffness were studied. Kumar and Hutchings8 installed a pin on a sonotrode which was energized by an ultrasonic transducer. Ultrasonic vibrations were generated and transmitted to the pin, which was placed in contact with a tool steel surface. Normal force was applied by a pneumatic cylinder and measured by a load cell. The relative motion between the pin and the disc was created by a reciprocating table.
Pohlman and Lehfeldt9 also implemented a pin-on-disc experiment. Unlike other studies, they employed a magnetostrictive transducer to generate ultrasonic vibrations. To study the optimum direction for ultrasonic friction reduction, the transducer was carefully aligned so that the vibrational direction was longitudinal, transverse, and vertical to the macroscopic velocity. They studied ultrasonic friction reduction on both dry and lubricated surfaces. Popov et al.10 utilized an actuator with conical waveguides. The actuator was placed in contact with a rotating base plate. Cones made of nine materials with various hardnesses were adopted to study the influence of material hardness on ultrasonic friction reduction. Dong and Dapino11-13 used a piezoelectric transducer to generate and transmit ultrasonic vibrations to a prismatic waveguide with rounded edges. The longitudinal vibration causes vertical vibration due to Poisson&#8217;s effect. A slider with a curved top was placed under and in contact the waveguide. A frame was built to apply normal forces at the contact interface. The slider was pulled manually around the center area of the waveguide; the friction force was measured by a load cell that was connected to the slider.
Ultrasonically-induced wear reduction was also investigated and demonstrated. Volume loss, weight loss, and surface roughness changes are employed to quantify the severity of wear.Chowdhury and Helali14 vibrated a rotating disc in a pin-on-disc setup. The vibrations were generated by a support structure of two parallel plates located under the rotating disc. The top plate has a spherical ball installed off-center on the bottom surface, which slides in a slot that was engraved at the top surface of the bottom plate. The slot was machined with a periodically variable depth so that the top plate moves vertically during rotation. The frequencies ranged around 100 Hz according to the rotational speed.
Bryant and York15-16 studied the effect of micro-vibrations on wear reduction. They inserted a carbon cylinder through a holder with one end rested on a spinning steel disc and the other end connected to a coil spring. In one case, the cylinder was snug fitted in the holder so that there was no space for vibration. In other cases, clearances were left to allow micro-vibrations of the cylinder while the cylinder was in contact with the spinning disc. The weight loss of the cylinder was measured to calculate the wear rate. It was shown that the self-generated micro-vibrations helped reduce wear by up to 50%.
Goto and Ashida17-18 also adopted a pin-on-disc experiment. They connected pin samples with a transducer via a tapered cone and a horn. The pin vibrated in the direction perpendicular to the disc surface. A mass was connected to the transducer on its top for applying normal loads. Friction forces were translated from the torque that was applied to rotate the disc. Wear was identified as adhesive because both pin and disc were made of carbon steel. Wear rates were calculated from volume loss measurements.
It has been shown that linear speed plays an important role in ultrasonic lubrication. The experimental component of this research focuses on the dependence of friction and wear reduction on linear speed.

<table><tbody><tr><td>DC Motor&amp;nbsp;</td><td>Minarik&amp;nbsp;</td><td>SL14</td><td></td></tr><tr><td>Electrical amplifier</td><td>AE Techron</td><td>LVC5050</td><td></td></tr><tr><td>Signal conditioner&amp;nbsp;</td><td>Vishay Measurements Group</td><td>2310</td><td></td></tr><tr><td>Signal generator</td><td>Agilent&amp;nbsp;</td><td>33120A</td><td></td></tr><tr><td>Piezoelectric stack</td><td>EDO corporation</td><td>EP200-62</td><td></td></tr><tr><td>Load cell</td><td>Transducer Techniques</td><td>MLP-50</td><td></td></tr><tr><td>Load sensor pad</td><td>FlexiForce</td><td>A201</td><td></td></tr><tr><td>Laser meter</td><td>Keyence corporation&amp;nbsp;</td><td>LK-G32</td><td></td></tr><tr><td>Hall-effect probe and gaussmeter</td><td>Walker Scientific, Inc.</td><td>MG-4D</td><td></td></tr><tr><td>Data acquisition module</td><td>Data Physics</td><td>Quattro</td><td></td></tr><tr><td>Data acquisition software</td><td>Data Physics</td><td>SignalCalc Ace</td><td></td></tr><tr><td>Thermocouple reader</td><td>Omega</td><td>HH22</td><td></td></tr><tr><td>Optical profilometer</td><td>Bruker</td><td>Contour GT</td><td></td></tr><tr><td>Profilometer operation software</td><td>Bruker&amp;nbsp;</td><td>Vision 64</td><td></td></tr></tbody></table>

experiments on ultrasonic lubrication using a piezoelectrically-assisted tribometer and optical profilometer

Friction and wear are detrimental to engineered systems. Ultrasonic lubrication is achieved when the interface between two sliding surfaces is vibrated at a frequency above the acoustic range (20 kHz). As a solid-state technology, ultrasonic lubrication can be used where conventional lubricants are unfeasible or undesirable. Further, ultrasonic lubrication allows for electrical modulation of the effective friction coefficient between two sliding surfaces. This property enables adaptive systems that modify their frictional state and associated dynamic response as the operating conditions change. Surface wear can also be reduced through ultrasonic lubrication. We developed a protocol to investigate the dependence of friction force reduction and wear reduction on the linear sliding velocity between ultrasonically lubricated surfaces. A pin-on-disc tribometer was built which differs from commercial units in that a piezoelectric stack is used to vibrate the pin at 22 kHz normal to the rotating disc surface. Friction and wear metrics including effective friction force, volume loss, and surface roughness are measured without and with ultrasonic vibrations at a constant pressure of 1 to 4 MPa and three different sliding velocities: 20.3, 40.6, and 87 mm/sec. An optical profilometer is utilized to characterize the wear surfaces. The effective friction force is reduced by 62% at 20.3 mm/sec. Consistently with existing theories for ultrasonic lubrication, the percent reduction in friction force diminishes with increasing speed, down to 29% friction force reduction at 87 mm/sec. Wear reduction remains essentially constant (49%) at the three speeds considered.

The representative measurements presented here were obtained from the modified tribometer shown in Figure 1. The piezoelectric actuator generates vibrations with amplitude of 2.5 &#956;m at a frequency of 22 kHz. To study the dependence of friction and wear reduction on linear velocity, three different speeds (20.3, 40.6, and 87 mm/sec) were applied to the disc by changing the rotational speed of the motor. For all three groups, the number of disc revolutions and the travel distance of the pin were chose...

Watch this Scientific Journal Video about Experiments on Ultrasonic Lubrication Using a Piezoelectrically-assisted Tribometer and Optical Profilometer at JoVE.com

Experiments on Ultrasonic Lubrication Using a Piezoelectrically-assisted Tribometer and Optical Profilometer

We present a protocol for using a piezoelectrically-assisted tribometer and optical profilometer to investigate the dependence of ultrasonic wear and friction reduction on linear velocity, contact pressure, and surface properties.

Friction and wear are detrimental to engineered systems. Ultrasonic lubrication is achieved when the interface between two sliding surfaces is vibrated at ...

experiments-on-ultrasonic-lubrication-using-piezoelectrically

Research

JoVE Journal

Engineering

12.5K Views.  The Ohio State University. We present a protocol for using a piezoelectrically-assisted tribometer and optical profilometer to investigate the dependence of ultrasonic wear and friction reduction on linear velocity, contact pressure, and surface properties. 

Video: Experiments on Ultrasonic Lubrication Using a Piezoelectrically-assisted Tribometer and Optical Profilometer

Characterization of Surface Modifications by White Light Interferometry: Applications in Ion Sputtering, Laser Ablation, and Tribology Experiments

In materials science and engineering it is often necessary to obtain quantitative measurements of surface topography with micrometer lateral resolution. From the measured surface, 3D topographic maps can be subsequently analyzed using a variety of software packages to extract the information that is needed.
In this article we describe how white light interferometry, and optical profilometry (OP) in general, combined with generic surface analysis software, can be used for materials science and engineering tasks. In this article, a number of applications of white light interferometry for investigation of surface modifications in mass spectrometry, and wear phenomena in tribology and lubrication are demonstrated. We characterize the products of the interaction of semiconductors and metals with energetic ions (sputtering), and laser irradiation (ablation), as well as ex situ measurements of wear of tribological test specimens.
Specifically, we will discuss:
<ol class="lroman">
	<li>Aspects of traditional ion sputtering-based mass spectrometry such as sputtering rates/yields measurements on Si and Cu and subsequent time-to-depth conversion.</li>
	<li>Results of quantitative characterization of the interaction of femtosecond laser irradiation with a semiconductor surface. These results are important for applications such as ablation mass spectrometry, where the quantities of evaporated material can be studied and controlled via pulse duration and energy per pulse. Thus, by determining the crater geometry one can define depth and lateral resolution versus experimental setup conditions.</li>
	<li>Measurements of surface roughness parameters in two dimensions, and quantitative measurements of the surface wear that occur as a result of friction and wear tests.</li>
</ol>
Some inherent drawbacks, possible artifacts, and uncertainty assessments of the white light interferometry approach will be discussed and explained.

White light microscope interferometry is an optical, noncontact and quick method for measuring the topography of surfaces. It is shown how the method can be applied toward mechanical wear analysis, where wear scars on tribological test samples are analyzed; and in materials science to determine ion beam sputtering or laser ablation volumes and depths.

In materials science and engineering it is often necessary to obtain quantitative measurements of surface topography with micrometer lateral resolution. ...

Measurement of Vibration Detection Threshold and Tactile Spatial Acuity in Human Subjects

Tests that allow the precise determination of psychophysical thresholds for vibration and grating orientation provide valuable information about mechanosensory function that are relevant for clinical diagnosis as well as for basic research. Here, we describe two psychophysical tests designed to determine the vibration detection threshold (automated system) and tactile spatial acuity (handheld device). Both procedures implement a two-interval forced-choice and a transformed-rule up and down experimental paradigm. These tests have been used to obtain mechanosensory profiles for individuals from distinct human cohorts such as twins or people with sensorineural deafness.

Here, we present protocols to determine vibration detection thresholds and tactile acuity using psychophysical methods in man.

Tests that allow the precise determination of psychophysical thresholds for vibration and grating orientation provide valuable information about ...

Behavior

Characterization of Full Set Material Constants and Their Temperature Dependence for Piezoelectric Materials Using Resonant Ultrasound Spectroscopy

During the operation of high power electromechanical devices, a temperature rise is unavoidable due to mechanical and electrical losses, causing the degradation of device performance. In order to evaluate such degradations using computer simulations, full matrix material properties at elevated temperatures are needed as inputs. It is extremely difficult to measure such data for ferroelectric materials due to their strong anisotropic nature and property variation among samples of different geometries. Because the degree of depolarization is boundary condition dependent, data obtained by the IEEE (Institute of Electrical and Electronics Engineers) impedance resonance technique, which requires several samples with drastically different geometries, usually lack self-consistency. The resonant ultrasound spectroscopy (RUS) technique allows the full set material constants to be measured using only one sample, which can eliminate errors caused by sample to sample variation. A detailed RUS procedure is demonstrated here using a lead zirconate titanate (PZT-4) piezoceramic sample. In the example, the complete set of material constants was measured from room temperature to 120 &#176;C. Measured free dielectric constants <img alt="Equation 1" src="/files/ftp_upload/53461/image001.jpg" /> and&#160;<img alt="Equation 2" src="/files/ftp_upload/53461/image002.jpg" /> were compared with calculated ones based on the measured full set data, and piezoelectric constants d15 and d33 were also calculated using different formulas. Excellent agreement was found in the entire range of temperatures, which confirmed the self-consistency of the data set obtained by the RUS.

This protocol describes the procedure of measuring the temperature dependence of the full set material constants of piezoelectric materials using resonant ultrasound spectroscopy (RUS).

During the operation of high power electromechanical devices, a temperature rise is unavoidable due to mechanical and electrical losses, causing the ...

Ultrasonic Welding of Thermoplastic Composite Coupons for Mechanical Characterization of Welded Joints through Single Lap Shear Testing

This paper presents a novel straightforward method for ultrasonic welding of thermoplastic-composite coupons in optimum processing conditions. The ultrasonic welding process described in this paper is based on three main pillars. Firstly, flat energy directors are used for preferential heat generation at the joining interface during the welding process. A flat energy director is a neat thermoplastic resin film that is placed between the parts to be joined prior to the welding process and heats up preferentially owing to its lower compressive stiffness relative to the composite substrates. Consequently, flat energy directors provide a simple solution that does not require molding of resin protrusions on the surfaces of the composite substrates, as opposed to ultrasonic welding of unreinforced plastics. Secondly, the process data provided by the ultrasonic welder is used to rapidly define the optimum welding parameters for any thermoplastic composite material combination. Thirdly, displacement control is used in the welding process to ensure consistent quality of the welded joints. According to this method, thermoplastic-composite flat coupons are individually welded in a single lap configuration. Mechanical testing of the welded coupons allows determining the apparent lap shear strength of the joints, which is one of the properties most commonly used to quantify the strength of thermoplastic composite welded joints.

A straightforward procedure for ultrasonic welding of thermoplastic composite coupons for basic mechanical testing is described. Key characteristics of this ultrasonic welding process are the use of flat energy directors for simplified process preparation and the use of process data for the fast definition of optimum processing conditions.

This paper presents a novel straightforward method for ultrasonic welding of thermoplastic-composite coupons in optimum processing conditions. The ...

Measurement of Tension Release During Laser Induced Axon Lesion to Evaluate Axonal Adhesion to the Substrate at Piconewton and Millisecond Resolution

The formation of functional connections in a developing neuronal network is influenced by extrinsic cues. The neurite growth of developing neurons is subject to chemical and mechanical signals, and the mechanisms by which it senses and responds to mechanical signals are poorly understood. Elucidating the role of forces in cell maturation will enable the design of scaffolds that can promote cell adhesion and cytoskeletal coupling to the substrate, and therefore improve the capacity of different neuronal types to regenerate after injury.
Here, we describe a method to apply simultaneous force spectroscopy measurements during laser induced cell lesion. We measure tension release in the partially lesioned axon by simultaneous interferometric tracking of an optically trapped probe adhered to the membrane of the axon. Our experimental protocol detects the tension release with piconewton sensitivity, and the dynamic of the tension release at millisecond time resolution. Therefore, it offers a high-resolution method to study how the mechanical coupling between cells and substrates can be modulated by pharmacological treatment and/or by distinct mechanical properties of the substrate.

We measured the tension release in an axon that was partially lesioned with a laser dissector by simultaneous force spectroscopy measurement performed on an optically-trapped probe adhered to the membrane of the axon. The developed experimental protocol evaluates the axon adhesion to the culture substrate.

The formation of functional connections in a developing neuronal network is influenced by extrinsic cues. The neurite growth of developing neurons is ...

Bioengineering

In Situ High Pressure Hydrogen Tribological Testing of Common Polymer Materials Used in the Hydrogen Delivery Infrastructure

High pressure hydrogen gas is known to adversely affect metallic components of compressors, valves, hoses, and actuators. However, relatively little is known about the effects of high pressure hydrogen on the polymer sealing and barrier materials also found within these components. More study is required in order to determine the compatibility of common polymer materials found in the components of the hydrogen fuel delivery infrastructure with high pressure hydrogen. As a result, it is important to consider the changes in physical properties such as friction and wear in situ while the polymer is exposed to high pressure hydrogen. In this protocol, we present a method for testing the friction and wear properties of ethylene propylene diene monomer (EPDM) elastomer samples in a 28 MPa high pressure hydrogen environment using a custom-built in situ pin-on-flat linear reciprocating tribometer. Representative results from this testing are presented which indicate that the coefficient of friction between the EPDM sample coupon and steel counter surface is increased in high pressure hydrogen as compared to the coefficient of friction similarly measured in ambient air.

In Situ High Pressure Hydrogen Tribological Testing of Common Polymer Materials Used in the Hydrogen Delivery Infrastructure

A test methodology for quantifying tribological properties of polymers used in hydrogen infrastructure service is demonstrated and characteristic results for a common elastomer are discussed.

High pressure hydrogen gas is known to adversely affect metallic components of compressors, valves, hoses, and actuators. However, relatively little is ...

Ultrasonic Fatigue Testing in the Tension-Compression Mode

Ultrasonic fatigue testing is one of a few methods which allow investigating fatigue properties in the ultra-high cycle region. The method is based on exposing the specimen to longitudinal vibrations on its resonance frequency close to 20 kHz. With use of this method, it is possible to significantly decrease the time required for the test, when compared to conventional testing devices usually working at frequencies under 200 Hz. It is also used to simulate loading of material during operation in high speed conditions, such as those experienced by components of jet engines or car turbo pumps. It is necessary to operate only in the high and ultra-high cycle region, due to the possibility of extremely high deformation rates, which can have a significant influence on the test results. Specimen shape and dimensions have to be carefully selected and calculated to fulfill the resonance condition of the ultrasonic system; thus, it is not possible to test the full components or specimens of arbitrary shape. Before each test, it is necessary to harmonize the specimen with the frequency of the ultrasonic system to compensate for deviations of the real shape from the ideal one. It is not possible to run a test until a total fracture of the specimen, since the test is automatically terminated after initiation and propagation of the crack to a certain length, when the stiffness of the system changes enough to shift the system out of the resonance frequency. This manuscript describes the process of evaluation of materials' fatigue properties at high-frequency ultrasonic fatigue loading with use of mechanical resonance at a frequency close to 20 kHz. The protocol includes a detailed description of all steps required for a correct test, including specimen design, stress calculation, harmonizing with the resonance frequency, performing the test, and final static fracture.

A protocol for ultrasonic fatigue testing in the high and ultra-high cycle region in axial tension-compression loading mode.

Ultrasonic fatigue testing is one of a few methods which allow investigating fatigue properties in the ultra-high cycle region. The method is based on ...

Rapid and Non-Destructive Characterization of Biofilm Elastic Properties

Quantifying Elastic Properties of Environmental Biofilms using Optical Coherence Elastography

Biofilms are complex biomaterials comprising a well-organized network of microbial cells encased in self-produced extracellular polymeric substances (EPS). This paper presents a detailed account of the implementation of optical coherence elastography (OCE) measurements tailored for the elastic characterization of biofilms. OCE is a non-destructive optical technique that enables the local mapping of the microstructure, morphology, and viscoelastic properties of partially transparent soft materials with high spatial and temporal resolution. We provide a comprehensive guide detailing the essential procedures for the correct implementation of this technique, along with a methodology to estimate the bulk Young's modulus of granular biofilms from the collected measurements. These consist of the system setup, data acquisition, and postprocessing. In the discussion, we delve into the underlying physics of the sensors used in OCE and explore the fundamental limitations regarding the spatial and temporal scales of OCE measurements. We conclude with potential future directions for advancing the OCE technique to facilitate elastic measurements of environmental biofilms.

Author Spotlight: Characterizing Environmental Biofilm Mechanics Using Optical Coherence Elastography and its Applications in Wastewater Treatment

This paper highlights the optical coherence elastography (OCE) technique's efficacy in rapidly and non-destructively characterizing biofilm elastic properties. We elucidate critical OCE implementation procedures for accurate measurements and present Young's modulus values for two granular biofilms.

Biofilms are complex biomaterials comprising a well-organized network of microbial cells encased in self-produced extracellular polymeric substances ...

Environment

Fabrication and Characterization of Thickness Mode Piezoelectric Devices for Atomization and Acoustofluidics

We present a technique to fabricate simple thickness mode piezoelectric devices using lithium niobate (LN). Such devices have been shown to atomize liquid more efficiently, in terms of &#64258;ow rate per power input, than those that rely on Rayleigh waves and other modes of vibration in LN or lead zirconate titanate (PZT). The complete device is composed of a transducer, a transducer holder, and a &#64258;uid supply system. The fundamentals of acoustic liquid atomization are not well known, so techniques to characterize the devices and to study the phenomena are also described. Laser Doppler vibrometry (LDV) provides vibration information essential in comparing acoustic transducers and, in this case, indicates whether a device will perform well in thickness vibration. It can also be used to &#64257;nd the resonance frequency of the device, though this information is obtained more quickly via impedance analysis. Continuous &#64258;uid atomization, as an example application, requires careful &#64258;uid flow control, and we present such a method with high-speed imaging and droplet size distribution measurements via laser scattering.

Fabrication of piezoelectric thickness mode transducers via direct current sputtering of plate electrodes on lithium niobate is described. Additionally, reliable operation is achieved with a transducer holder and &#64258;uid supply system and characterization is demonstrated via impedance analysis, laser doppler vibrometry, high-speed imaging, and droplet size distribution using laser scattering.

We present a technique to fabricate simple thickness mode piezoelectric devices using lithium niobate (LN). Such devices have been shown to atomize liquid ...

Roughness Impact of Piezoelectric Dental Scaler on Two Distinct Flowable Composite Filling Materials

Dental ultrasonic scalers are commonly employed in periodontal treatment; however, their ability to roughen tooth surfaces is a worry since roughness may increase plaque production, a key cause of periodontal disease. This research studied the influence of a piezoelectric ultrasonic scaler on the roughness of two distinct flowable composite filling materials. To do this, 10 disc-shaped samples were generated from each of the two flowable composite materials. After standardized polishing, samples were submerged in water for 24 h before the first surface examination using electron microscopy and profilometry. The ultrasonic scaler was applied to a specified location of each sample for 60 s under water cooling and regulated force. Post-scaler surface parameters were again examined. Following the application of the scaler, both composite materials exhibited a notable increase in surface roughness, as determined by profilometry (p &lt; 0.01). Additionally, the observed surface roughness was also qualitatively visualized with scanning electron microscopy. While initial roughness levels were comparable across the two composites (p = 0.143) after scaler application, no substantial discrepancy in surface texture was noticed between them (p = 0.684). The use of a high-power piezoelectric ultrasonic scaler on routinely used flowable composite restorations might generate considerable surface roughness, possibly leading to increased plaque accumulation. Nevertheless, it might be postulated that nanohybrid flowable composite materials having conventional monomer ingredients may demonstrate comparable surface alterations within the limitations of this experiment.

This methodology allows applying a dental appliance on any specimen at any angle with standardized force and stability. This approach might be extensively used in health sciences to standardize the impacts of dental equipment with hand-holding elements such as micromotors, turbines, and ultrasonic scalers on varied surfaces.

Dental ultrasonic scalers are commonly employed in periodontal treatment; however, their ability to roughen tooth surfaces is a worry since roughness may ...

Experiments on Ultrasonic Lubrication Using a Piezoelectrically-assisted Tribometer and Optical Profilometer

Summary

Explore More Videos

Chapters in this video

Characterization of Surface Modifications by White Light Interferometry: Applications in Ion Sputtering, Laser Ablation, and Tribology Experiments

Measurement of Vibration Detection Threshold and Tactile Spatial Acuity in Human Subjects

Characterization of Full Set Material Constants and Their Temperature Dependence for Piezoelectric Materials Using Resonant Ultrasound Spectroscopy

Ultrasonic Welding of Thermoplastic Composite Coupons for Mechanical Characterization of Welded Joints through Single Lap Shear Testing

Measurement of Tension Release During Laser Induced Axon Lesion to Evaluate Axonal Adhesion to the Substrate at Piconewton and Millisecond Resolution

In Situ High Pressure Hydrogen Tribological Testing of Common Polymer Materials Used in the Hydrogen Delivery Infrastructure

Ultrasonic Fatigue Testing in the Tension-Compression Mode

Quantifying Elastic Properties of Environmental Biofilms using Optical Coherence Elastography

Fabrication and Characterization of Thickness Mode Piezoelectric Devices for Atomization and Acoustofluidics

Roughness Impact of Piezoelectric Dental Scaler on Two Distinct Flowable Composite Filling Materials