Chris Klobedanz
MANE-6960
Homework #1
1. No questions
2. Link 1: Basics of Lubrication – STLE
This link gives a quick, qualitative overview of how lubrication functions on interacting
surfaces and how it aids in the mechanical process to prevent friction and wear. In addition to
outlining the fundamentals of lubrication, the site goes into further detail about the three major
categories of lubrication: hydrodynamic, elasto-hydrodynamic, and boundary. The site explores
the inter-connectivity and distinction of these categories and provides examples of applications
for each category.
The primary function of lubricants is to protect moving parts from friction, wear, heat
generation, and energy loss. These factors play a significant role in impeding productivity and
increasing production expenses. Other benefits include cooling and debris removal.
Most lubricants work by creating a fluid film between two solid surfaces, though solid
film lubrication also exists. The thickness of the fluid film (a factor dependent on material
properties, load, relative speed of the surfaces, temperature, and pressure) determines whether
the lubricant is categorized as hydrodynamic, elasto-hydrodynamic, mixed, or boundary. The
Stribeck curve is a tool used to break down which category a lubricant is function as based on its
viscosity, speed, and load.
Hydrodynamic lubrication is described by the existence of a full fluid film between
surfaces and no surface contact. The load is entirely supported by the fluid film and there is low
friction and no wear on the surfaces.
Elasto-hydrodynamic lubrication is described as the lubrication of a nonconformal
contact (i.e. a ball on a flat surface), where the pressure between solid surfaces is unusually high.
In this situation, the lubricant becomes semi-solid, and a very thin film forms and is able to
support the load.
Mixed lubrication is the region between hydrodynamic and boundary lubrication in
which there is a sharp drop in friction as a result of a growing fluid film and decreasing surface
contact.
Boundary lubrication exists usually at the start-up and shut-down operations of a
machine. The speed between surfaces is low, there is low viscosity, and a high load; these factors
allow lubrication to enter the region between surfaces, but the film does not fully develop.
Boundary lubrication is characterized by a thin layer which only slightly limits friction and wear
from occurring.
Link 2: The Friction Module at NanoWorld
This link discusses the discoveries and laws that led to our current understanding of
friction at a microscopic level. It starts with a look at the laws proposed by Leonardo da Vinci,
Euler, Amontons, and Coulomb. It then explains the impact that those laws had on the present
theories on friction, wear, and boundary layers. The middle section of this page talks about
observations and methods of observing friction phenomena that proved the subject theories.
Then, at the bottom of this site, there are several simulations that aid in visualize what goes on at
the microscopic scale.
The site does not get into any specific equations, but rather looks at friction, lubrication,
and wear from a laboratory perspective. As if starting from a base of zero knowledge, the site
introduces the initial findings, the interpretation of those findings, and then grounds those
interpretations into the established laws of the field.
There is some valuable information about the high school physics explanation of friction,
as well as insight into surface asperities and molecular adhesion. Aside from that, this site
doesn’t go very in-depth when it comes to technical content.
Link 3: Wear Resistance – Gordon England
This link gives a brief introduction to various types of wear that can occur on a surface as
well as describe the appropriate thermal spray coatings that are used to prevent wear. The
definitions and explanations given on this site are not all that in-depth or technical, but provide a
good basis from which to start from. The statements made are mostly generalized and do not get
into exceptions to those rules.
Wear is described as a loss of surface material by a material action. At the microscopic
level, two solid surfaces are said to contact one another only at high-point asperities. These
asperities become focal points for the loads, which become very large in these areas. The surface
material is most susceptible to wear at these points. Many material, and situational properties
(opposing material, speed, lubrication, etc…) are taken into account when determining the most
effective way to resist wear.
Abrasive wear is wear due to hard particles rubbing against a solid surface, as in
grinding, sanding, or scratching; Adhesive wear is due to localized bonding between surfaces in
which material is transferred between surfaces; Erosion is the wear of a surface due to interaction
with a fluid; Cavitation erosion is erosion caused by vapor bubbles in a turbulent liquid; Fatigue
wear is due to material fatigue; and Fretting wear is the result of oscillatory motion between
surfaces in contact.
Thermal spray coatings are used in a number of applications for wear resisting surfaces as
well as for repairing worn surfaces. Determining the most appropriate coating is dependent on a
wide variety of properties. The best applications for certain surfaces are not universally suited for
all, and therefore require material analysis.
3. Website links:
i.
http://hyperphysics.phy-astr.gsu.edu/hbase/mechanics/frictire.html
 Friction and automobile tires
ii.
www.susos.com/uploads/companydirectory/id19/Friction_Measurements_on_Con
tact_Lenses.pdf
 Friction and lubrication in contact lenses
iii.
www.thermallube.com/Publications/Trib%20in%20extreme%20environments%20Beijing%20
STLE.PDF
 Tribology and Lubrication in Extreme Environments
iv.
Tocatchafish.blogspot.com/p/fishing-reel-drags.html?m=1
 Friction factors in fishing reels
v.
www.exploratorium.edu/hockey/ice2.html
 Ice skates and lubrication layer on ice
4. Reviewed Paper: Dental Tribology at the Microscale by Matthias Scherge
This paper describes a microtribological study that was composed to analyze the effects
of friction and wear events on the surface of a tooth sample. This phenomenon, called dental
wear, depends on several factors, including the quality of tooth material, the type of toothbrush,
and the brushing slurry. This experiment provides a unique viewpoint on dental wear by studying
the effect of a single bristle, or microfilament, on the tooth material, rather than analyzing the
effect of all bristles (a macrotribological study) of a toothbrush at once. This approach was taken
because it limits the external influences that could contribute to false conclusions.
In general, various studies have concluded that wear increases with increased load, up to
the point that the bristles spread; Wear also increases with the number of brushing cycles. Dental
wear is limited when a fluid media is introduced (water), but abrasives from toothpaste
contribute to stronger wear. In the subject experiment, three toothpaste samples of various
abrasive identifiers were mixed into a water-toothpaste slurry and their abrasive qualities were
compared to a water (wet) and dry environment.
Cleansing particles in toothpastes are the primary contributor to dental wear. This study
compared RDA (relative dentin abrasion) 30, RDA 75, and RDA 165 toothpastes with the dry
and wet environments. Both dry and water-lubricated systems showed minimal sliding friction
coefficients, whereas all three slurry samples yielded significantly higher values. The highest
sliding friction was found in the RDA 165 slurry sample. Furthermore, the higher the RDA value
of the toothpaste, the greater the depth of wear abrasion (linear correlation). For RDA 30, there
were only subtle changes to the tooth enamel topography, in contrast with RDA 165, which
resulted in clear features of abrasion. Wear was not detectable in the dry or wet samples.
Many of the results attained by this study are sensible and verify the findings of related
studies (i.e. abrasion effects cannot be obtained by dry or (just) wet brushing, Hertzian contact
values, etc…). Analysis of the results further asserts that friction increases due to the trapping of
particles between the tip the filament and the tooth enamel. Energy accumulates between the two
surfaces and is released in stick-slips. The intensity of these stick-slips was found to correlate
with the RDA value. It is likely that as the more abrasive materials created deeper abrasions in
the enamel, it gave more openings for stick-slips to occur.
The study concludes that microtribological studies are just as valuable, if not more robust
than the comparable macrotribological studies. It makes a final recommendation that future
dental wear studies, such as removing stain and/or plaque, may be improved by microtribometry.
5. Possible research project topic: Lubrication design