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WEAR REDUCTION THROUGH PIEZOELECTRICALLY-ASSISTED ULTRASONICLUBRICATION

Sheng DongSmart Materials and Structures Laboratory

NSF I/UCRC on Smart Vehicle ConceptsDept. of Mechanical and Aerospace Engineering

The Ohio State University

Columbus, Ohio 43210Email: [email protected]

Marcelo J. Dapino∗

Smart Materials and Structures Laboratory

NSF I/UCRC on Smart Vehicle ConceptsDept. of Mechanical and Aerospace Engineering

The Ohio State University

Columbus, Ohio 43210Email: [email protected]

ABSTRACT

Ultrasonic vibration has been proven effective in reducing

dynamic friction when superimposed onto the macroscopic rel-

ative velocity between two surfaces. This phenomenon is often

referred to as ultrasonic lubrication. Piezoelectric materials can

be employed to generate ultrasonic vibration. Typically, solid

or fluid lubricants are employed to mitigate wear. However, in

applications such as aerospace systems, which operate in partic-

ularly harsh environments, traditional lubrication methods are

not always applicable. This paper investigates the relationship

between friction force reduction and wear reduction in ultrason-

ically lubricated surfaces. A pin-on-disc tribometer is modified

through the addition of a piezoelectric transducer which vibrates

the contact between pin and disc. A piezo-actuator is installed

to generate 22 kHz vibration in the direction perpendicular to

the disc. Three different linear speeds are employed by changing

rotation speeds of the disc and running time. Friction and wear

metrics such as volume loss, surface roughness, friction forces

and stick-slip effects are compared before and after application

of ultrasonic vibration. Relationships between linear speed and

friction reduction, stick-slip reduction, and wear reduction are

analyzed.

∗Address all correspondence to this author.

INTRODUCTION

Friction exists when two contacting surfaces slide relative

to each other. When this occurs, materials on the surfaces suf-

fer plastic deformation and are broken away from the body of

the material, which is commonly referred to as wear [1]. It has

been shown that by applying ultrasonic vibrations at the inter-

face of two surfaces in sliding contact, the friction force can be

reduced [2–9]. This phenomenon, often referred to as ultrasonic

lubrication, is promising in applications in which traditional lu-

brication methods are unfeasible (e.g., vehicle seats, space mech-

anisms) or where friction modulation is desirable (e.g., steering

components).

Ultrasonic vibration is usually applied only to one of the two

contacting surfaces and may be applied in one of three directions

relative to the macroscopic sliding velocity: perpendicular, lon-

gitudinal or transverse. Several studies have been devoted to each

of the three directions and combinations thereof.

For example, Littman et al. [2, 3] used a piezoelectric actu-

ator generating vibration at 60 kHz, making it slide on a guide

track longitudinally. Bharadwaj and Dapino [4, 5] also applied

longitudinal ultrasonic vibration to investigate the dependence of

friction reduction on macroscopic sliding velocity, normal load,

contact stiffness, and global stiffness. Kumar [6] experimentally

determined that longitudinal vibrations were more effective at

reducing friction force than transverse vibrations and confirmed

that the velocity ratio greatly influences the degree of friction re-

1 Copyright © 2013 by ASME

Proceedings of the ASME 2013 Conference on Smart Materials, Adaptive Structures and Intelligent Systems SMASIS2013

September 16-18, 2013, Snowbird, Utah, USA

SMASIS2013-3216

duction.

Popov et al. [7] studied the influence of ultrasonic vibration

in different material combinations. It was shown that ultrasonic

vibration creates less friction reduction on softer materials than

harder ones. They argued that contact stiffness influences the

amount of force reduction. Dong and Dapino [8,9] used the Pois-

son effect to generate vibrations in combined perpendicular and

longitudinal directions and studied the relationship between fric-

tion reduction and various normal loads, contact materials, and

global stiffness. They proposed an elastic-plastic ”cube” model

to explain ultrasonic friction reduction.

There have been multiple attempts at utilizing ultrasonic lu-

brication in an effort to reduce wear between two contacting

surfaces. For example, Chowdhury and Helali [10] developed

a pin-on-disc test to examine the effects of micro vibration on

wear reduction. The vibration was applied in a direction per-

pendicular to the disc surface, ranging from 0 to 500 Hz. They

studied the correlation between wear reduction and vibration fre-

quency, relative humidity, and sliding velocity. Their results

proved that higher frequency leads to lower wear rate. Bryant

and York [11, 12] did similar work using high amplitude, low

frequency vibration to reduce wear. They created a slider, which

generated vibration from 10 to 100 µm at frequencies ranging

from 10 to 100 Hz. Utilizing this set-up, they achieved wear re-

duction of up to 50%.

Goto and Ashida [13, 14] conducted tests at higher frequen-

cies in the ultrasonic range. They also chose a vibration direction

perpendicular to the disc plane and studied the relationship be-

tween wear rate and normal loads. Their findings proved that ul-

trasonic vibration can drastically reduce wear under various nor-

mal loads. In these tests, the amplitude of the ultrasonic vibration

was 8 µm and the normal load was up to 88 N. They also studied

contact time between two surfaces while ultrasonic vibration is

applied.

It has been shown that linear speed plays an important role in

the performance of ultrasonic lubrication. However, few papers

have addressed the influence of linear speed on wear reduction.

Therefore, this paper focuses on the relationship between friction

and wear reduction at various linear speeds.

EXPERIMENT

Set-up

The experimental set-up used in this study is a modified pin-

on-disc tribometer, as shown in Fig. 1 (a). A tribometer creates

a contact between a still pin and a rotating disc for the purpose

of studying the characteristics of friction and wear on the disc

surface. The pin has been modified with the addition of a piezo-

electric actuator and an acorn nut with a rounded end (Fig. 1

(c)). The actuator imparts ultrasonic vibrations to the rotating

disc along the direction perpendicular to the disc. The tribome-

ter is held by a lever which is part of a gymbal assembly that has

FIGURE 1. EXPERIMENTAL SET-UP: (A) OVERALL (B) GYM-

BAL ASSEMBLY (C) PIEZO-ACTUATOR IN DETAIL

been installed on the frame (Fig. 1 (b)). Weights connected to

the gymbal assembly apply normal loads to the interface. The

normal force is measured by a load sensor pad placed between

the pin and the disc. The resistance of the sensor pad changes as

a function of the applied force, resulting in a change of output

voltage. The gymbal assembly is instrumented to measure fric-

tion forces using a load cell. The load cell is installed on one side

of the assembly frame and pretensioned horizontally by a weight

on the other side.

The piezoelectric actuator generates vibration of 2.5 µm at

a frequency of 22 kHz. The temperature of the actuator can in-

crease rapidly from the heat generated and accumulated during

the test. To maintain even temperatures, air flow and a thermo-

couple are employed to cool down the actuator and monitor the


TABLE 1. TEST PARAMETERS

Parameter Value

Group 1 2 3

Linear speed (mm/s) 20.3 40.6 87

Running time (h) 4 2 0.93

Distance traveled by pin (m) 292.5

Revolutions 1600

Pin material Stainless steel 316

Disc material Aluminum 2024

Nominal normal force (N) 3

Disc run out (mm) ±0.0286

US frequency (kHz) 22

US amplitude (µm) 2.5

Nominal Groove diameter (mm) 50

Nominal temperature (◦C) 21±1

Nominal actuator temperature (◦C) 31±1

Environment Laboratory air

Sampling frequency (Hz) 400

temperature, respectively. The disc is 3 inches in diameter and

held in place by a lathe chuck. The chuck, which is placed on a

platform, is driven by a DC motor under it with adjustable rotat-

ing speeds.

Parameters and Schematics

Three groups of tests were conducted at different linear

speeds, from 20.3 to 87 mm/s. In each group, tests were done

with and without ultrasonic vibrations. Three different angular

velocities were adopted, while the distance traveled by the pin

and the number of revolutions were kept constant by changing

the duration of the test. Other parameters were unchanged as

listed in Table 1.

Friction force was sampled at a frequency of 400 Hz and

each sampling window was 2 seconds. Typical data from a sin-

gle sampling window appears in Fig. 2, in which stick-slip is

observed. The mean value and root mean square value (RMS)

of the variation were calculated for each sampling window. A

profilometer was then employed to measure the volume loss of

the discs and the roughness parameters of the disc surfaces.

FIGURE 2. MEASURED FRICTION FORCE AND STICK-SLIP

EFFECT

Procedures

Each pin-on-disc test was conducted following the proce-

dures suggested by ASTM G99 [15] with modifications:

(a) Clean and dry the acorn nut and disc specimens immediately

prior to testing. Ethanol and acetone were used to remove all

foreign matter.

(b) Insert the sample securely into the chuck so that the disc is

perpendicular to the axis of revolution so that wobbling is

minimized

(c) Install the acorn nut and compress it tightly to the piezo-

actuator

(d) Adjust the position of the pin, making sure that it is perpen-

dicular to the disc surface

(e) Add weight for application of normal loads

(f) Start the motor and adjust the speed to the desired value

while preventing the pin from making contact with the disc.

Then stop the motor.

(g) Record the temperature and ambient environment of the

tests. Prepare the data acquisition system for testing.

(h) Put the pin in contact with the disc. Start the motor and

the piezoelectric actuator (when applicable). Stop the motor

when the desired running time is reached.

(i) Clean the specimens and measure the volume loss and

roughness parameters using a profilometer.

RESULTS AND DISCUSSION

Friction Without Ultrasonic Vibration

Mean friction values for three linear speeds are plotted

against pin travel distance in Fig. 3. In each case, the friction

force increases rapidly in the beginning, reaches a steady state

after a given stabilizing distance, and remains at that level for

the rest of the test. There is fluctuation of friction force after it

reaches steady state. Unlike the fluctuation of friction observed

in Fig. 2, which is due to stick-slip phenomenon, the fluctuation


0 50 100 150 200 2500

0.5

1

1.5

2

Distance (m)

Friction f

orc

e w

ithout

US

(N

)

v=20.3 mm/s

v=40.6 mm/s

v=87 mm/s

FIGURE 3. STEADY STATE FRICTION FORCES WITHOUT UL-

TRASONIC VIBRATIONS

here is caused by the run out of the disc. The disc wobbles a

small amount while rotating during the tests. The inertia from

the up and down pin movement causes fluctuation of the normal

force, and accordingly, a fluctuation of the friction force. The fig-

ure also shows that higher speed results in a higher steady state

value for the force.

Table 2 lists the steady state friction forces, their RMS val-

ues and the stabilizing distances. Results show that natural fric-

tion increases as the speeds increase which is in line with the

conclusions from previous studies [16–18], that is, for metals,

the friction-speed curve has a positive slope when speeds are low

and a negative slope when speeds are high. The speeds adopted

in this study are considered to be low.

Friction Reduction

The mean values of friction force versus sliding distance

during the application of ultrasonic vibration are plotted in Fig. 4

for three linear speeds. Similar to natural friction, friction in each

of these cases reaches steady state after a stabilizing distance. As

in the previous case, the friction force fluctuates because of disc

run out. However, the fluctuation amplitudes are smaller because

of the application of the ultrasonic vibrations. One possible rea-

son is because inertial acceleration, when ultrasonic vibration is

present, is extensively reduced by the superposition of the accel-

eration that occurs from the vibration. Therefore, actual normal

forces and friction forces are reduced.

The friction reduction percentage is defined as

Pf =f0 − f1

f0

× 100, (1)

where f0 is the friction without ultrasonic vibration and f1 is the

friction with the application of ultrasonic vibration. The results

are plotted in Fig. 5. It is shown that all three groups give con-

50 100 150 200 2500

0.5

1

1.5

2

Distance (m)

Friction f

orc

e w

ith U

S (

N)

v=20.3 mm/sv=40.6 mm/sv=87 mm/s

FIGURE 4. MEASURED FRICTION FORCES WITH ULTRA-

SONIC VIBRATIONS

50 100 150 200 2500

20

40

60

80

100

Distance (m)

Friction r

eduction p

erc

enta

ge

v=20.3 mm/s

v=40.6 mm/s

v=87 mm/s

FIGURE 5. MEASURED FRICTION REDUCTION

sistent friction reduction at steady state, and that a lower speed

results in greater reduction.

Table 2 lists the steady-state friction forces, their RMS val-

ues and stabilizing distances. As in the case without ultrason-

ics, the friction forces in the presence of ultrasonic vibrations

increase as the speed increases. The trend is shown in Fig. 6,

where the markers indicate the mean values and the error bars

are the RMS of the steady state values.

It is emphasized that it takes a shorter distance for the force

to stabilize when ultrasonic vibrations are applied, regardless of

the linear speed. We speculate that the ultrasonic vibrations make

it easier for the pin and disc to break into each other, wear out

the oxide-layers, and build up a steady contact at the beginning

of the test while it takes a longer time to accomplish that with-

out the assistance of ultrasonic vibrations. At the intermediate

speed (40.6 mm/s) the force takes longer to stabilize both with

and without ultrasonic vibration.


TABLE 2. STEADY STATE FRICTION FORCES AND DISTANCES TO ACHIEVE STEADY STATE

GroupLinear speed

(mm/s)US

Steady state

friction (N)

Distance to achieve

steady state (m)

RMS of steady

state friction (N)

Distance to achieve

steady state (m)

1 20.3No 1.024±0.063 4.17 0.197±0.039 3.11

Yes 0.379±0.041 2.78 0.081±0.020 35.71

2 40.6No 1.201±0.055 11.61 0.251±0.034 7.97

Yes 0.748±0.035 7.21 0.096±0.033 45.44

3 87No 1.472±0.064 8.94 0.249±0.033 3.22

Yes 1.041±0.056 4.64 0.188±0.021 31.53

FIGURE 6. RELATIONSHIP BETWEEN MEASURED FRICTION

FORCE AND LINEAR SPEED

RMS of Friction Force Variation

As shown in Fig. 2, the instantaneous friction force fluctu-

ates due to the stick-slip phenomenon. As the name suggests,

stick-slip consists of two phases of motion. Stick is the stage

when two objects stay relatively still and friction increases. Slip

happens when the friction increases to such an extent that the

two surfaces release to slide relative to each other again. A typi-

cal measurement of stick-slip is shown in Fig. 2 (inset). A com-

monly accepted explanation for stick-slip is that the static friction

coefficient is usually larger than the dynamic coefficient so that

friction varies within a range during sliding [18]. Another cause

of stick-slip can be the waviness of the surface, which results in

an inconsistency of the friction coefficient [16]. To quantify the

stick-slip phenomenon in this study, an RMS value is derived for

each 2-second window, which represents the average amplitude

of the stick-slip fluctuation. The RMS friction force is plotted

versus travel distance for each of the tests groups without ultra-

sonic vibrations (Fig. 7) and with ultrasonic vibrations (Fig. 8).

In both cases, the RMS values reach steady state after a cer-

0 50 100 150 200 2500

0.1

0.2

0.3

0.4

0.5

Distance (m)

RM

S o

f fr

iction forc

e w

ithout U

S (

N)

v=20.3 mm/sv=40.6 mm/sv=87 mm/s

FIGURE 7. RMS OF FRICTION FORCES WITHOUT ULTRA-

SONIC VIBRATIONS

0 50 100 150 200 2500

0.1

0.2

0.3

0.4

0.5

Distance (m)

RM

S o

f fr

iction forc

e w

ith U

S (

N)

v=20.3 mm/sv=40.6 mm/sv=87 mm/s

FIGURE 8. RMS OF FRICTION WITH ULTRASONIC VIBRA-

TIONS

tain stabilizing distance is reached. Contrary to the mean values,

however, it takes significantly longer for the stick-slip to stabilize

when the ultrasonic vibrations are on than when they are off. The

stick-slip amplitudes are nearly at the same level for three speeds

when the ultrasonic vibrations are absent. When the vibrations


FIGURE 9. RELATIONSHIP BETWEEN THE RMS OF FRICTION

FORCES AND LINEAR SPEEDS

FIGURE 10. WEAR GROOVES: (A) GROUP 1 WITH US; (B)

GROUP 1 WITHOUT US; (C) GROUP 2 WITHOUT US; (D) GROUP

2 WITH US; (E) GROUP 3 WITH US; (F) GROUP 3 WITHOUT US;

are on, all three cases show amplitude reductions with different

levels. The steady state values and the stabilizing distances can

be found in Table 2 and the trends are shown in Fig. 9, where the

markers indicate the mean values and the error bars are the RMS

of the steady state values.

Wear Reduction

The materials in this study, stainless steel and aluminum,

possess a hardness of 700-950 kg/mm2 and 45-50 kg/mm2, re-

spectively. Due to the difference in hardness, the type of wear

between them is abrasive: the harder material digs into the softer

one, removing material and creating grooves [19].

Images of the wear grooves from all test groups are shown

in Fig. 10. Each image shows approximately one quarter of

the whole groove. In these images, it can be observed that the

grooves from tests with ultrasonic vibrations (images A, C, E)

appear more uneven and non-reflective than the ones without it

(images B, D, F). For a closer view of the wear grooves, pro-

filometer scans of the surfaces were conducted. The scanning

provided 2D and 3D profiles, volume of the groove, and rough-

ness parameters of the scanned surface.

Eight spots along the path of each wear ring were selected

for scanning in order to obtain average values of volume loss and

roughness parameters. Each scan was conducted over an area of

1.8 mm by 2.0 mm with a scan stroke of ±100 µm. The 3-D pro-

files of the grooves from all tests groups can be seen in Fig. 11.

The grooves from the tests with ultrasonic vibrations on are nar-

rower and curvier along the edges than those from the tests with-

out ultrasonic vibrations. This explains why they appear more

uneven to the naked eye. Furthermore, the wear groove becomes

even curvier as the speed increases when the ultrasonic vibration

is on. This effect is not observed in any of the cases without

ultrasonic vibrations.

The six pictures share one color code, with different scales

presented in the legends. It shows the grooves on the left are

deeper than the ones on the right. This observation is supported

by the measurement of the roughness parameters, as listed in

Table 4. It can be seen that the maximum height of the pro-

file drops in each group while ultrasonic vibrations are present,

which means that the grooves were created deeper. Not just the

maximum height, but also all the other four indexes are smaller

when ultrasonic vibrations are activated. The roughness parame-

ters indicate evidence of significant wear reduction.

Another quantifiable index is wear rate, which is defined as

w =

V

D, (2)

where V is disc volume loss in mm3 and D is the distance that

the pin travelled in m. The disc volume loss is calculated from

data of groove volume provided by the profilometer. The wear

reduction percentage is defined as

Pw =

w0 −w1

w0

× 100, (3)

where w0 is the wear rate without ultrasonic vibrations applied

and w1 is the wear rate with ultrasonic vibrations applied. The

wear rates of all groups and the wear reduction percentages are

listed in Table 3. The results show a weak dependence of wear

rates on linear speeds, both with and without ultrasonic vibration.

The wear reduction percentage slightly increases as the speed in-

creases. Few previous studies were focused on the relationship

between abrasive wear and sliding speed, but many have been

done on the influence of sliding distance [20, 21]. It was found


TABLE 4. COMPARISON OF SURFACE ROUGHNESS PARAM-

ETERS: Ra ARITHMETIC AVERAGE; Rp MAXIMUM PEAK

HEIGHT; Rq ROOT MEAN SQUARED; Rt MAXIMUM HEIGHT OF

THE PROFILE; Rv MAXIMUM VALLEY DEPTH

Group USRa

(µm)

Rp

(µm)

Rq

(µm)

Rt

(µm)

Rv

(µm)

No wear 0.45 10.071 0.58 18.887 8.816

1N 18.829 48.440 21.421 124.35 75.906

Y 17.238 38.458 18.975 87.011 48.554

2N 21.647 46.646 22.673 109.28 62.638

Y 17.289 42.469 19.922 106.42 63.947

3N 19.825 48.910 21.921 130.52 81.612

Y 17.606 44.245 20.126 111.25 66.877

FIGURE 12. RELATIONSHIP BETWEEN REDUCTION RE-

SULTS AND LINEAR SPEEDS

that, when there is unlimited abrasive material (the harder ma-

terial), the wear rate starts at a low level at the beginning of the

test, increases and remains at a steady state value. However, if

the abrasive material is limited, the wear rate will decrease as the

test continues. In both cases, the wear rate is not dependent on

the sliding velocity.

Discussion

These results indicate that ultrasonic vibration is effective in

reducing friction, stick-slip, and wear at all three linear speeds

(see Fig. 12).

In terms of friction, as speed rises, friction reduction de-

creases from 62.2% for group 1 to 29.3% for group 3. This

conclusion is in line with the studies conducted by Littmann et

al. [2] which focused on the relationship between velocity ratio

and friction ratio. In their study, the velocity ratio was defined

as the macroscopic velocity divided by the velocity of ultrasonic

vibration. The friction ratio was defined as the friction with ultra-

sonic vibrations over the one without ultrasonic vibrations. It was

proposed that a higher velocity ratio results in a higher friction

ratio, up to a limit of 1. In this study, the vibration velocity and

the friction without ultrasonic vibrations remain constant. There-

fore, higher velocities give higher velocity ratio, which results in

a lower amount of friction reduction.

Wear reduction remains confined within a range from 45.8%

to 48.6%, while higher velocity results in slightly higher wear re-

duction. One possible reason could be that, as speed increases,

the actual contact between the pin and the disc is reduced. Stud-

ies showed when the amplitude of ultrasonic vibration is large

enough, contact time between two surfaces will be reduced as

one surface moves away from the other [13, 14]. Assuming that

the pin makes one contact with the disc and then moves away

from it in one cycle of ultrasonic vibration, the number of con-

tact times between the disc and the pin in three tests can therefore

be estimated. These estimated numbers are presented in Table 3.

With the presence of ultrasonic vibration, the contact be-

tween pin and disc is characterized by waviness along the

grooves due to the stick-slip phenomenon. The pin moves up and

down while travelling along the groove, making contacts with the

disc during the stick phase and moving away from it during the

slip phase. This assumption could help explain the curviness of

the wear groove with ultrasonic vibration. As shown in Fig. 11,

as the speed increases, the profile of the groove becomes curvier,

especially seen in profile (F). It appears that the segment of the

groove is formed by two separate pits, which are presumably cre-

ated by the contacts between the pin and the disc during the stick

phase. The distance between the two pits is 0.869 mm based on

the measurement. Theoretically, the distance can be estimated

by

d = ∆t × v, (4)

where d is the distance between the centers, ∆t is the time of one

period of stick-slip, and v is the linear speed. The estimation re-

sults of the distance are respectively 0.213 mm, 0.426 mm, and

0.853 mm for the speeds of 20.3 mm/s, 40.6 mm/s, and 87 mm/s.

It can be seen that the measurement and the estimation match

well for the speed of 87 mm/s. However, the pits separation is

not as evident in the other two cases (profiles (B) and (D)) be-

cause the pits overlap with each other as the speed decreases.

Furthermore, for the cases without ultrasonic vibration, the pin

and disc make contact during both the stick and slip phases, cre-

ating little waviness along the grooves (see profiles (A), (C), and

(E)).

The reduction in stick-slip does not show a clear trend. For

example, with a speed of 40.6 mm/s, group 2 experiences the


(A) (B)

(C) (D)

(E) (F)

FIGURE 11. 3D PROFILES OF WEAR GROOVES: (A) GROUP 1 WITHOUT US; (B) GROUP 1 WITH US; (C) GROUP 2 WITHOUT US; (D)

GROUP 2 WITH US; (E) GROUP 3 WITHOUT US; (F) GROUP 3 WITH US;

most reduction, while group 1, with a speed of 20.6 mm/s, ex-

periences slightly less reduction. However, group 3, at a higher

speed, does not exhibit such reduction. Studies have shown the

amplitude of vibration caused by stick-slip is related to the stiff-

ness and damping of the system and that increasing the stiffness

can greatly reduce the amplitude of vibration [16]. The reason

is that stick-slip can be deemed as an excitation to the system,

and linear speeds in addition to the waviness of the surface can

change the frequency of the excitation. Therefore, at certain

speeds, the system is excited at its resonance frequency, which

results in a magnification of the stick-slip vibration. The sys-

tem resonance frequency can be increased if the system is stiffer.

Therefore, the possibility of magnifying the vibration is reduced

when the surfaces slide at the same range of speeds [22]. One

possible explanation of the significant reduction in stick-slip for

group 2 is because 20.3 mm/s falls in the range of speeds at which

resonance takes place without the presence of ultrasonic vibra-

tion. In short, stick-slip peaks at that speed. However, when ul-

trasonic vibrations are applied, the friction force is reduced and

the waviness is different from the one without vibrations. There-


TABLE 3. COMPARISON OF WEAR AND FRICTION REDUCTION

GroupLinear speed

(mm/s)

Wear without

US (mm3/m)

Wear with US

(mm3/m)

Wear reduction

(mm3/m)

Wear reduc-

tion (%)

Number of

contacts

Friction

reduction (%)

1 20.3 2.237×10−2 1.214×10−2 1.023×10−2 45.76 3.17×108 62.22

2 40.6 2.581×10−2 1.338×10−2 1.243×10−2 48.18 1.58×108 36.11

3 87 2.430×10−2 1.248×10−2 1.182×10−2 48.63 7.39×107 29.32

fore, the system does not vibrate at resonance at the speed of

20.3 mm/s, but at some higher speed (see Fig. 9).

CONCLUDING REMARKS

In this study, a modified pin-on-disc tribometer was built

with the purpose of investigating the influence of ultrasonic vi-

bration on the characteristics of friction and abrasive wear be-

tween stainless steel pins and aluminum discs under a low nor-

mal load of 3 N. Ultrasonic vibration was generated by a piezo-

electric actuator with an amplitude of 2.5 µm and a vibration

frequency of 22 kHz. With the goal to quantify the relationship

between friction, wear, and linear speed, three different speeds,

20.3 mm/s, 40.6 mm/s, and 87 mm/s were adopted while keeping

other parameters unchanged through the tests.

The results of friction forces show that ultrasonic vibration

is effective in reducing dynamic friction, and that higher speeds

result in higher friction both with and without the presence of

ultrasonic vibrations. We also confirm a decrease in friction re-

duction as speeds increase. This result is in line with previous

studies of the relationship between linear speeds and friction re-

duction. Future work will investigate the influence of other pa-

rameters such as initial surface roughness, normal load, and ma-

terial combinations.

The wear tests show a consistent reduction of up to 49%,

which validates the effectiveness of ultrasonic vibration in wear

reduction in addition to the difference between the mechanisms

of friction and wear reduction. There exists a dependence of

wear reduction on linear speeds, which could be explained by a

reduction of contact time between two surfaces when ultrasonic

vibrations are present.

Additionally, stick-slip amplitudes are reduced to 50% under

the application of ultrasonic vibration. However, no clear trend

is found in the relationship between stick-slip reduction and lin-

ear speeds. Future work will focus on the relationship between

system stiffness and stick-slip amplitudes.

ACKNOWLEDGMENT

The authors would like to acknowledge Dr. Tim Krantz

from NASA Glenn and Duane Detwiler from Honda R&D

for their technical support and in-kind contributions. Fi-

nancial support for this research was provided by the mem-

ber organizations of the Smart Vehicle Concepts Center

(www.SmartVehicleCenter.org), a National Science Founda-

tion Industry/University Cooperative Research Center (I/UCRC).

S.D. is supported by a Smart Vehicle Concepts Graduate Fellow-

ship.

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Model for friction and wear reduction through ... · PDF fileslide longitudinally on a guide track. ... low frequency vibrations. ... and E is the combined Young's modulus of the two