ASM Metals HandBook Vol. 8 - Mechanical Testing and Evaluation
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12. P.W. Bridgman and I. Simon, Effects of Very High Pressure on Glass, J. Appl. Phys., Vol 24 (No. 4),
1953, p 405–413
13. E.H. Yoffe, Elastic Stress Fields Caused by Indenting Brittle Materials, Philos. Mag. A, Vol 46 (No. 4),
1982, p 617–628
14. K.W. Peter, Densification and Flow Phenomena of Glass in Indentation Experiments, J. Non-Cryst.
Solids, Vol 5, 1970, p 103–115
15. M.V. Swain, Microfracture about Scratches in Brittle Solids, Proc. R. Soc. A, Vol 366, 1979, p 575–597
16. A. Misra and I. Finnie, On the Scribing and Subsequent Fracturing of Silicon Semiconductor Wafers, J.
Mater. Sci., Vol 14, 1979, p 2567–2574
17. S.Y. Chen, T.N. Farris, and S. Chandrasekar, Sliding Microindentation Fracture of Brittle Materials,
STLE Tribol. Trans., Vol 34 (No. 2), 1991, p 161–168
18. Y. Ahn, T.N. Farris, and S. Chandrasekar, Sliding Microindentation Fracture of Brittle Materials: Role
of Elastic Stress Fields, Mech. Mater., Vol 29, 1998, p 1087–1093
19. Y. Ahn, “Deformation about Sliding Indentation in Ceramics and Its Application to Lapping,” Ph.D.
thesis, Purdue University, 1992
20. V.H. Bulsara, “Scratch Formation in Brittle Solids and its Application to Polishing,” Ph.D. thesis,
Purdue University, 1997
21. Lord Rayleigh, Polish, Nature, Vol 64, 1901, p 385
22. L.E. Samuels, Metallographic Polishing by Mechanical Methods, 3rd ed., American Society for Metals,
1982
23. E.C. Rabinowicz, Polishing, Sci. Am., Vol 218 (No. 6), 1968, p 91–99
24. R.L. Aghan and L.E. Samuels, Mechanisms of Abrasive Polishing, Wear, Vol 16, 1970, p 293–301
25. V.H. Bulsara, Y. Ahn, S. Chandrasekar, and T.N. Farris, Polishing and Lapping Temperatures, J.
Tribol., Vol 119 (No. 1), 1997, p 163–170
26. S. Chandrasekar and M.M. Chaudhri, Indentation Cracking in Soda-Lime Glass and Ni-Zn Ferrite under
Knoop and Conical Indenters and Residual Stress Measurements, Philos. Mag. A, Vol 67 (No. 5), 1993,
p 1187–1218
27. B.J. Hockey, Plastic Deformation of Alumina by Indentation and Abrasion, J. Am. Ceram. Soc., Vol 54
(No. 5), 1971, p 223–231
28. V.H. Bulsara S. Chandrasekar, and T.N. Farris, Mechanics of Polishing, J. Appl. Mech. (Trans. ASME),
Vol 65 (No. 2), 1998, p 410–416
Scratch Testing
Vispi Homi Bulsara, Cummins Engine Company;Srinivasan Chandrasekar and Thomas N. Farris, Purdue University
Summary
Scratch testing is useful and simple as a means of comparing the hardness of materials. The ubiquitous presence
of the Mohs scale is testament to the usefulness of scratch testing. The scratch test also provides the basis for
developing models of more complicated processes such as wear or polishing. However, it is not currently used
to obtain more fundamental information, such as stress-strain curves, due to the lack of a robust model of the
process.
Scratch Testing
Vispi Homi Bulsara, Cummins Engine Company;Srinivasan Chandrasekar and Thomas N. Farris, Purdue University
Acknowledgments
The authors acknowledge support from the Materials Processing and Tribology Center at Purdue.
Scratch Testing
Vispi Homi Bulsara, Cummins Engine Company;Srinivasan Chandrasekar and Thomas N. Farris, Purdue University
References
1. D. Tabor, The Hardness of Metals, Oxford University Press, 1951
2. M.M. Chaudhri and Y. Enomoto, Philos. Mag. A., Special Issues on Indentation Hardness, 1996
3. S. Jayaraman, G.T. Hahn, W.C. Oliver, C.A. Rubin, and P.C. Bastias, Determination of Monotonic
Stress-Strain Curve of Hard Materials from Ultra-Low-Load Indentation Tests, Int. J. Solids Struct., Vol
35 (No. 5–6), 1998, p 365–381
4. S. Jacobsson, M. Olsson, P. Hedenqvist, and O. Vingsbo, Scratch Testing, Friction, Lubrication, and
Wear Technology, Vol 18, ASM Handbook, ASM International, 1992, p 430–437
5. S.R. Williams, Hardness and Hardness Measurements, American Society for Metals, 1942
6. J.A. Williams, Analytical Models of Scratch Hardness, Tribol. Int., Vol 29 (No. 8), 1996, p 675–694
7. F.P. Bowden and D. Tabor, The Friction and Lubrication of Solids, Oxford University Press, Vol I,
1951; Vol II, 1964
8. K.L. Johnson, Contact Mechanics, Cambridge, 1985
9. Y. Murakami and K. Matsuda, Analysis of Vickers Hardness by the Finite Element Method, J. Appl.
Mech., Vol 61 (No. 4), 1994, p 822–828
10. S.M. Kulkarni, G.T. Hahn, C.A. Rubin, and V. Bhargava, Elasto-plastic Finite Element Analysis of
Three-Dimensional Pure Rolling Contact above the Shakedown Limit, J. Appl. Mech., Vol 58 (No. 2),
1991, p 347–353
11. C. Sakae and L.M. Keer, Application of Direct Method for a Nonlinear-Kinematic-Hardening Material
under Rolling/Sliding Line Contact: Constant Ratchetting Rate, J. Mech. Phys. Solids, Vol 45 (No. 9),
1997, p 1577–1594
12. P.W. Bridgman and I. Simon, Effects of Very High Pressure on Glass, J. Appl. Phys., Vol 24 (No. 4),
1953, p 405–413
13. E.H. Yoffe, Elastic Stress Fields Caused by Indenting Brittle Materials, Philos. Mag. A, Vol 46 (No. 4),
1982, p 617–628
14. K.W. Peter, Densification and Flow Phenomena of Glass in Indentation Experiments, J. Non-Cryst.
Solids, Vol 5, 1970, p 103–115
15. M.V. Swain, Microfracture about Scratches in Brittle Solids, Proc. R. Soc. A, Vol 366, 1979, p 575–597
16. A. Misra and I. Finnie, On the Scribing and Subsequent Fracturing of Silicon Semiconductor Wafers, J.
Mater. Sci., Vol 14, 1979, p 2567–2574
17. S.Y. Chen, T.N. Farris, and S. Chandrasekar, Sliding Microindentation Fracture of Brittle Materials,
STLE Tribol. Trans., Vol 34 (No. 2), 1991, p 161–168
18. Y. Ahn, T.N. Farris, and S. Chandrasekar, Sliding Microindentation Fracture of Brittle Materials: Role
of Elastic Stress Fields, Mech. Mater., Vol 29, 1998, p 1087–1093
19. Y. Ahn, “Deformation about Sliding Indentation in Ceramics and Its Application to Lapping,” Ph.D.
thesis, Purdue University, 1992
20. V.H. Bulsara, “Scratch Formation in Brittle Solids and its Application to Polishing,” Ph.D. thesis,
Purdue University, 1997
21. Lord Rayleigh, Polish, Nature, Vol 64, 1901, p 385
22. L.E. Samuels, Metallographic Polishing by Mechanical Methods, 3rd ed., American Society for Metals,
1982
23. E.C. Rabinowicz, Polishing, Sci. Am., Vol 218 (No. 6), 1968, p 91–99
24. R.L. Aghan and L.E. Samuels, Mechanisms of Abrasive Polishing, Wear, Vol 16, 1970, p 293–301
25. V.H. Bulsara, Y. Ahn, S. Chandrasekar, and T.N. Farris, Polishing and Lapping Temperatures, J.
Tribol., Vol 119 (No. 1), 1997, p 163–170
26. S. Chandrasekar and M.M. Chaudhri, Indentation Cracking in Soda-Lime Glass and Ni-Zn Ferrite under
Knoop and Conical Indenters and Residual Stress Measurements, Philos. Mag. A, Vol 67 (No. 5), 1993,
p 1187–1218
27. B.J. Hockey, Plastic Deformation of Alumina by Indentation and Abrasion, J. Am. Ceram. Soc., Vol 54
(No. 5), 1971, p 223–231
28. V.H. Bulsara S. Chandrasekar, and T.N. Farris, Mechanics of Polishing, J. Appl. Mech. (Trans. ASME),
Vol 65 (No. 2), 1998, p 410–416
Scratch Testing
Vispi Homi Bulsara, Cummins Engine Company;Srinivasan Chandrasekar and Thomas N. Farris, Purdue University
Selected References
• A. Broese van Groenou, N. Maan, and J.B.D. Veldkamp, Single-Point Scratches as a Basis for
Understanding Grinding and Lapping, The Science of Ceramic Machining and Surface Finishing II, B.J.
Hockey and R.W. Rice, Ed., pages 43–60. NBS SP 562, National Bureau of Standards, 1979, p 43–60
• V. Bulsara, S. Chandrasekar, and T.N. Farris, Direct Observation of Contact Damage Produced by
Vickers Indentation in Diamond-Like Films, Proc. IMECE Symp Dissimilar Material Systems:
Manufacturing Processes, Design, and Mechanics, (Dallas, TX, Nov 1997), Volume MD-80, p 287–292
• M.M. Chaudhri and E.H. Yoffe, The Area of Contact between a Small Sphere and a Flat Surface,
Philos. Mag., Vol 44 (No. 3), 1981, p 667–675
• W. Cheng, E. Ling, and I. Finnie, Median Cracking of Brittle Solids due to Scribing with Sharp
Indenters, J. Am. Ceram. Soc., Vol 73 (No. 3), 1990, p 580–586
• W. Cheng and I. Finnie, A Mechanism for Sub-surface Median Crack Initiation in Glass During
Indenting and Scribing, J. Mater. Sci., Vol 25, 1990, p 575–579
• K. Miyoshi and D.H. Buckley, Ceramic Wear in Indentation and Sliding Contact, ASLE Trans., Vol 28
(No. 3), 1985, p 296–302
• T.O. Mulhearn, The Deformation of Metals by Vickers-Type Pyramidal Indenters, J. Mech. Phys.
Solids, Vol 7, 1959, p 85–96
• J.D.B. Veldkamp, N. Hattu, and V.A.C. Snijders, Crack Formation During Scratching of Brittle
Materials, Fracture Mechanics of Ceramics, R.C. Bradt, A.G. Evans, D.P.H. Hasselman, and F.F.
Lange, Ed., Vol 3, Plenum, 1978, p 273–301
• Sh. Wada, Micro-fracture of Ceramics and Tribology, Jpn. J. Tribol. Vol 35 (No. 8), 1990, p 859–866
Abrasive Wear Testing
Jeffrey A. Hawk, U.S. Department of Energy, Albany Research Center
Introduction
ABRASIVE WEAR is a major problem for the excavation, earth moving, mining, and minerals processing
industries and occurs in a wide variety of equipment, such as bulldozer blades, excavator teeth, rock drill bits,
crushers, slushers, ball mills and rod mills, chutes, slurry pumps, and cyclones. Figure 1 shows the extent of
abrasion that can occur on a bulldozer blade. However, abrasive wear is not limited to these activities. Abrasion
is a problem in most wear environments at one point or another, even though it may not be the primary wear
mechanism initially. In any tribosystem where dust and wear debris are not controlled and excluded, abrasive
wear will be a problem. The wear of parts, the cost of repair and replacement of these parts, and the associated
downtime related to these activities results in significant costs to many industries. As a result, some sort of
preliminary indication of the wear resistance of these parts is desirable. For the most part, however, wear tests
of specific machinery or parts are costly to perform, are very labor intensive, and require a long time to
complete. In addition, the environmental variables change over the course of the test, making correlations
between tests run at different times and in different places difficult. In order to reduce testing costs and speed
up component development laboratory wear tests have been developed (Ref 1, 2, 3, 4). Many of these tests are
company specific and consist of data collected over many years. These data are then used in conjunction with
experience to design and select alloys for use as wear components within that company. However, these data
are not usually available to other competitors or to the general public. Consequently, laboratory abrasive wear
tests that are not specific to any particular tribological environment have also been developed over the years.
Fig. 1 Extent of abrasion on a bulldozer blade. Notice the width and depth of the wear scars.
In general, abrasive wear processes have typically been divided into two broad regimes: high-stress abrasion or
low-stress abrasion. High-stress, or grinding abrasion, occurs when abrasive particles are compressed between
two solid surfaces, as for example, between grinding rods or balls. The high-stress abrasion that occurs, for
example, in grinding mills takes place over a very small contact region, where the ore particles are caught
between the grinding balls or between the grinding balls and the mill liner. The high contact pressure produces
indentations and scratching of the wearing surfaces and fractures and pulverizes the abrasive particles. Hard
minerals such as quartz will indent and scratch martensitic steels having yield strengths of 2100 MPa (300 ksi).
High-stress abrasion is often referred to as three-body abrasion, although two-body, high-stress conditions can
also exist. High-stress abrasion implies that the abrasive particle is fractured and broken apart during the wear
process. Exactly how these small abrasive particles affect the actual removal of the material is not well
understood. It has been speculated that high-stress grinding abrasion facilitates material removal by a
combination of cutting, plastic deformation, and surface fracture on a microscopic scale, as well as by tearing
and fatigue or spalling on a macroscopic scale.
Low-stress, or scratching, abrasion occurs when lightly loaded abrasive particles impinge upon and move
across the wearing surface, cutting and ploughing on a microscopic scale. In aqueous or other liquid
environments, corrosion may also contribute to the overall wear rate, in which case erosion-corrosion is the
operative wear mechanism. In both cases, low-stress abrasion is the primary mode of wear. The wear rates in
terms of metal thickness removed per day are quite low in low-stress abrasion, so a significant portion of the
total wear is probably due to the abrasion of a continually reforming oxide film. This may be especially true in
the handling of particulates in a wet environment, such as agricultural operations and the movement of slurries.
References cited in this section
1. P.A. Swanson, Comparison of Laboratory and Field Abrasion Tests, Wear of Materials, K.C. Ludema,
Ed., ASME, 1985, p 519–525.
2. M.A. Moore, Laboratory Simulation Testing for Service Abrasive Wear Environments, Wear of
Materials: Volume II, KC. Ludema, Ed., ASME, 1987, p 673–687
3. P.A. Swanson, Comparison of Laboratory Abrasion Tests and Field Tests, Tribology: Wear Test
Selection for Design and Application, STP 1199, A.W. Ruff and R.G. Bayer, Ed., ASTM, 1993, p 80–
99
4. J.H. Tylczak, J.A. Hawk, and R.D. Wilson, A Comparison of Laboratory Abrasion and Field Wear
Results, Wear, Vol 225–229, 1999, p 1059–1069
Abrasive Wear Testing
Jeffrey A. Hawk, U.S. Department of Energy, Albany Research Center
Parameters Influencing Wear
A variety of parameters influence all wear mechanisms and thus influence the abrasive wear behavior of
materials. To a certain extent, abrasive wear tests have been designed to emphasize one or more of these
parameters, especially the dominant one in an application. These parameters can be categorized as follows (Ref
5, 6):
• Material parameters: Material parameters of importance include composition, microstructure (e.g.,
grain size), mechanical properties (e.g., yield strength, elastic modulus, ductility), fracture toughness,
thermal conductivity, degree of work hardening, hardness, and so on.
• Design parameters: Design parameters also influence the wear mechanisms, and some of the more
important ones are shape, loading, force/impact level, type of motion (e.g., sliding/rolling), roughness,
vibration, and cycle time.
• Environmental parameters: Of particular importance is the environment of the wear event and
parameters such as temperature, humidity, atmosphere, wet/dry conditions, pH, contamination, and so
on.
• Lubrication parameters: In certain nonabrasive applications, the type of lubricant, lubricant stability,
type of fluid lubrication, and so on are all important.
In abrasive wear, the characteristics of the abrasive particle are also important. Some factors of influence are
particle shape, particle size, hardness, yield strength, fracture properties, and concentration (Ref 7). These
characteristics will influence the severity of the abrasion.
References cited in this section
5. H. Czichos, A Systems Approach to the Science and Technology of Friction, Lubrication and Wear,
Elsevier Science Publishers BV, Amsterdam, Netherlands, 1978
6. R.G. Bayer, Wear Testing, Mechanical Testing, Vol 8, Metals Handbook, 9
th
ed., ASM International,
1985, p 601–608
7. P.J. Mutton, Abrasion Resistant Materials: Volume 1, AMIRA, Melbourne, Australia, 1988, p 5–17
Abrasive Wear Testing
Jeffrey A. Hawk, U.S. Department of Energy, Albany Research Center
Elements of a Wear Test
The general elements of all laboratory wear tests are simulation, acceleration, specimen preparation, test
control, wear measurement, and data reporting (Ref 5, 6). Simulation is the most important element of the wear
test because it ensures that the behavior experienced in the laboratory test is the same as in the application. The
ideal wear test will exactly duplicate the wear situation, but in most cases only an actual field test of the
component will accomplish that. It is important, at the very least, that the laboratory wear test generate the same
wear mechanisms as the application and that the primary wear mechanism in the application is the primary one
in the laboratory test. Other factors of attention include test geometry, load range, surface conformity, break-in,
and so on.
Acceleration of the wear test is important because it reduces the overall time and cost of the testing effort.
Accelerating the wear test, however, can influence or change the material response. For example, if the load or
the speed of the test is increased, one wear mechanism may be emphasized more than another or the wear
regime may pass from mild to severe. Even so, all laboratory wear tests are accelerated to one degree or
another, either through continuous operation, measurement of smaller quantities of wear, or by applying higher
loads, speeds, or temperatures.
Attention to specimen preparation and test control are important in laboratory wear testing because they
determine the degree of scatter in the data (i.e., they either improve or degrade precision and reproducibility). In
any test method, it is important to reduce as much as possible the number of factors that can influence the result
of that test. Ideally, the wear test should reflect differences in the material and not differences in the operation
of the test. Specimen preparation is critical because each test should start with a specimen that is identical to the
last in terms of geometry, surface finish, break-in, and so on. Therefore, it is important that each specimen is
prepared for the test in exactly the same manner (i.e., cleaning, drying, storage, weighing, etc.). In addition,
accurate control of wear test apparatus operating parameters such as load, speed, instrument construction,
ambient environment, location and alignment, and supply of abrasive is critical to controlling the
reproducibility of the test data. Of particular importance in a wear test is the use of a reference material. The use
of a reference material allows the operation of the wear test apparatus to be checked periodically for
conformance to the operating parameters, to test the skill of the operator, and to determine such factors as the
influence of environment (Ref 6).
Determining the most efficient way to measure the extent of wear loss from a test depends primarily on the type
of wear test and the amount of wear generated from the test. Common wear measuring techniques include the
measurement of mass loss, volume loss or displacement, scar width or depth or some other geometrical
measure, or other indirect measures, such as the time required to wear through a coating or the load required to
cause severe wear or a change in surface reflectance (Ref 6). The way in which the degree of wear is measured
is based on convenience, the nature of the wear specimen, and the available measuring techniques. In abrasive
wear, large amounts of material are typically removed, and as a result, mass loss measurements are typically
favored. In the case of microabrasion, where mass loss is minimal, geometrical methods are more effective.
Material wear behavior in terms of the wear rate can be described by either producing a wear curve or by
measuring wear at a single point in the test (Ref 6). Because wear is nonlinear, a wear curve generally provides
more information and allows evaluation of more complex behavior than a single-point measurement (Ref 6).
However, once a wear curve has been established for a material or class of materials, the wear test can be
designed so that a single-point measurement can be used.
Wear is a system response, and when reporting data, a complete description of the system is needed to put the
data in context. Information that should be supplied includes the following where applicable (Ref 5, 6):
• Apparatus
• Geometry of contact
• Type of motion
• Load
• Speed
• Environmental conditions
• Conditions of wearing mediums
• Description of materials
• Description of lubricants and lubrication used
• Description of wear-in period, if appropriate
• Unusual observations (e.g., evidence of material transfer)
• Surface and materials preparations
• Sample surface roughness
The report should describe the material tested, the general nature of the test, conditions of the counterface,
testing environment, and any other significant features.
Wear test data scatter can be significantly reduced by careful testing methods. The number of tests that should
be conducted to provide accurate results depends on the type of wear test being conducted, but it is suggested
that several tests, rather than one, should form the basis for conclusions. In general, a minimum of three tests is
preferred, and the need for replication depends on the testing purpose, degree of control, and scatter (Ref 6).
References cited in this section
5. H. Czichos, A Systems Approach to the Science and Technology of Friction, Lubrication and Wear,
Elsevier Science Publishers BV, Amsterdam, Netherlands, 1978
6. R.G. Bayer, Wear Testing, Mechanical Testing, Vol 8, Metals Handbook, 9
th
ed., ASM International,
1985, p 601–608
Abrasive Wear Testing
Jeffrey A. Hawk, U.S. Department of Energy, Albany Research Center
Standardized Abrasive Wear Tests
Wear testing in general, and abrasion testing in particular, has few standardized tests with well-defined
experimental procedures. In many cases, the standardized tests do not adequately represent the actual wear
environment of interest, and as a result, many ad hoc wear tests have been developed over the years within
specific industries and companies. The American Society for Testing and Materials (ASTM) has tried to
standardize the most popular of these wear tests so that the tests can be performed in a like manner from one
laboratory to the next with a reasonable degree of precision and bias.
The following abrasion and erosion test procedures are listed in the Annual Book of ASTM Standards, Volume
03.02 (Ref 8):
Standard
No.
Description
G 56
Abrasiveness of Ink-Impregnated Fabric Printer Ribbons
G 76
Conducting Erosion Tests by Solid Particle Impingement Using Gas Jets
G 65
Measuring Abrasion Using the Dry Sand/Rubber Wheel Apparatus
G 132
Pin Abrasion Testing
G 75
Slurry Abrasivity (Miller Number) and Slurry Abrasion Response of Materials (SAR
No.)
G 105
Conducting Wet Sand/Rubber Wheel Abrasion Tests
G 81 Jaw Crusher Gouging Abrasion Test
The first six items in the table are all ASTM test methods, while the seventh is an ASTM practice. In the
following sections, some of the test procedures and practices are described in more detail, while others are left
for the reader to explore. Additional nonstandard ASTM abrasive wear tests are also described. For anyone
wishing to do abrasive wear testing, it is useful to read the various ASTM standards and practices in order to
gain an understanding of how to structure a wear test (abrasive or otherwise), calculate mass/volume losses and
wear rates, and report the measures of precision and bias in the data.
Reference cited in this section
8. “Wear and Erosion: Metal Corrosion,” Annual Book of ASTM Standards, ASTM
Abrasive Wear Testing
Jeffrey A. Hawk, U.S. Department of Energy, Albany Research Center
Description of Tests and Equipment
In the following section, abrasive wear testing is broken up into the following general topics: scratch testing,
dry abrasion against fixed particles, dry abrasion against loose particles, wet abrasion against fixed or loose
particles, gouging-abrasion, small particle erosion, impact abrasion, slurry abrasion, and microabrasion. For
these abrasion categories, the general test procedures are outlined, some in more detail than others, selected
results are given, and the advantages and limitations of the tests are discussed.
Scratch Wear Testing
Scratch wear testing is a method of mechanically testing a specimen by moving a stylus or indenter over its
surface (Ref 9). This wear test is important because it provides information on the micromechanics of material
removal for the stylus-material tribosystem. Typically, a single abrasive particle, in the form of a well-defined
and oriented stylus, is moved across the surface of a material in some controlled manner (load and velocity)
generating a groove. By controlling the shape of the stylus and its orientation with the wear surface,
information as to the volume of material removed and the wear mechanism controlling material removal can be
obtained (i.e., cutting or plowing) (Ref 9, 10). The following simple expression has been used as a starting point
for quantifying the volume of material removed from a surface during two-body abrasion by a single conical
abrasive particle (Ref 11):
(Eq 1)
where W
ν
is the volume of material lost to abrasive wear, s is the sliding distance, F
N
is the normal load on the
conical abrasive particle, H is the yield pressure or the hardness of the wearing surface, and α is the angle of
attack of the abrasive particle. Equation 1 is more typically written as:
(Eq 2)
where k
ab
is known as the wear coefficient for abrasion and replaces the first factor (i.e., a geometrical one) in
Eq 1. Many preconditions exist for using Eq 2, the most important of which is that microcutting occurs during
the abrasive process. As a consequence, Eq 2 provides an upper limit for the amount of material removed from
a surface during abrasion. Values of k
ab
fall between 10
-2
and 10
-4
for ductile materials, with the lower values of
k
ab
associated with three-body wear and the greater values with that of two-body wear (Ref 11).
Although diamond indenters are usually used in scratch testing because of their prevalence in hardness testing,
any material can be used as the scratch stylus. Although details of scratch testing are not covered here (see the
article “Scratch Testing” in this Volume), it is important to realize that scratch testing can aid in understanding
the large-scale abrasive wear behavior of materials by fixed particles through understanding what occurs as one
particle moves across the surface (Ref 12). Figure 2 shows the damage mechanisms that occur in a white cast
iron as a result of a single scratch using a diamond stylus.