Ryan L. Kobrick and David M. Klaus

University of Colorado at Boulder, Boulder, Colorado

Kenneth W. Street, Jr.

Glenn Research Center, Cleveland, Ohio

Validation of Proposed Metrics for Two-Body

Abrasion Scratch Test Analysis Standards

NASA/TM—2011-216940

February 2011
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Ryan L. Kobrick and David M. Klaus

University of Colorado at Boulder, Boulder, Colorado

Kenneth W. Street, Jr.

Glenn Research Center, Cleveland, Ohio

Validation of Proposed Metrics for Two-Body

Abrasion Scratch Test Analysis Standards

NASA/TM—2011-216940

February 2011

National Aeronautics and

Space Administration

Glenn Research Center

Cleveland, Ohio 44135
Acknowledgments

This research was supported by a NASA Graduate Student Researchers Program (GSRP) grant (NNX07AR55H) provided by 

the Dust Management Project, under the Exploration Technology Development Program. Matlab assistance was provided by 

Kevin Higdon, Ph.D. Candidate (UCB) and Bradley W. Cheetham, Ph.D. Student (UCB). Test equipment and support were 

provided by NASA Glenn Research Center. Additional support was provided by BioServe Space Technologies (UCB) and

the Achievement Rewards for College Scientists (ARCS) Foundation, Inc.

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Trade names and trademarks are used in this report for identifi cation 

only. Their usage does not constitute an offi cial endorsement, 

either expressed or implied, by the National Aeronautics and 

Space Administration.

Level of Review: This material has been technically reviewed by technical management. 
NASA/TM—2011-216940 1 

Validation of Proposed Metrics for Two-Body Abrasion 

Scratch Test Analysis Standards 

Ryan L. Kobrick and David M. Klaus 

University of Colorado at Boulder 

Boulder, Colorado 80309 

Kenneth W. Street, Jr. 

National Aeronautics and Space Administration 

Glenn Research Center 

Cleveland, Ohio 44135 

Abstract 

The objective of this work was to evaluate a set of standardized metrics proposed for characterizing a 

surface that has been scratched from a two-body abrasion test. This is achieved by defining a new 

abrasion region termed “Zone of Interaction” (ZOI). The ZOI describes the full surface profile of all 

peaks and valleys, rather than just measuring a scratch width as currently defined by the ASTM G 171 

Standard. The ZOI has been found to be at least twice the size of a standard width measurement, in some 

cases considerably greater, indicating that at least half of the disturbed surface area would be neglected 

without this insight. The ZOI is used to calculate a more robust data set of volume measurements that can 

be used to computationally reconstruct a resultant profile for detailed analysis. Documenting additional 

changes to various surface roughness parameters also allows key material attributes of importance to 

ultimate design applications to be quantified, such as depth of penetration and final abraded surface 

roughness. Data are presented to show that different combinations of scratch tips and abraded materials 

can actually yield the same scratch width, but result in different volume displacement or removal 

measurements and therefore, the ZOI method is more discriminating than the ASTM method scratch 

width. Furthermore, by investigating the use of custom scratch tips for our specific needs, the usefulness 

of having an abrasion metric that can measure the displaced volume in this standardized manner, and not 

just by scratch width alone, is reinforced. This benefit is made apparent when a tip creates an intricate 

contour having multiple peaks and valleys within a single scratch. This work lays the foundation for 

updating scratch measurement standards to improve modeling and characterization of three-body abrasion 

test results. 

1.0 Introduction 

A key physical property associated with lunar regolith (as well as regolith from other extraterrestrial 

destinations) is its abrasive quality. Abrasion of mechanical components and fabrics by soil on Earth is 

typically minimized by the effects of atmosphere and water eroding sharp and pointed geometrical 

features from potential abrasive particles. In environments where these erosive forces do not exist, such as 

the vacuum of the Moon, particles retain geometries associated with fracturing of their parent particles by 

micrometeorite impacts. The relationship between hardness of the abrasive and that of the material being 

abraded is well understood, such that the abrasive ability of a material can be estimated as a function of 

the ratio of the hardness of the two interacting materials (Ref. 1). Applying this relationship to the lunar 

mineral composition, one would expect the Moon to have modest abrasive ability, considering that many 

of the lunar particles also have sharp edges and points (Ref. 2). 

Similar analogies can be made with regard to the particulate toughness, although direct correlation 

between lunar and terrestrial mineral counterparts has recently come into question (Ref. 3). Recent 

discoveries in lunar geology indicate that the Moon is not as homogeneous as previously thought; 

therefore, a simple generic Mare and Highlands regolith composition may no longer be realistic. Instead, 
NASA/TM—2011-216940 2 

there may be vast regions of interest where the composition is nearly pure spinel, which is considerably 

harder than the bulk constituents of either Mare or Highland material (Ref. 4). Hence, our interest in 

fabricating custom scratch tips for use in fundamental abrasion studies for lunar and other extraterrestrial 

exploration systems are growing. When changing tip materials and geometries, the standard scratch test 

method based on scratch width alone leaves much to be desired, as it ignores a considerable amount of 

information associated with a scratch, such as material removal versus displacement and the magnitude of 

the actual region of interaction in the test material. 

This paper is a continuation of prior work that proposed a set of standardized volumetric displacement 

metrics for analyzing two-body abrasion scratch test results (Ref. 5). Technology limitations were 

identified in the current ASTM G 171 Standard for scratch testing (Ref. 6), which specifies scratch width 

as the key measurement. The development of new imaging capabilities that allow a complete profile to be 

characterized in a three-dimensional array was suggested to enable a more detailed analysis of the 

scratched surface. Table 1 summarizes the proposed new standard attributes. A “Zone of Interaction” 

(ZOI) was defined to characterize the entire abrasive wear area, including volumes outside of the scratch 

width boundaries, as indicated in Figure 1. Two scratches with the same width do not necessarily have the 

same ZOI. This follow on work includes quantitative results obtained using the earlier developed protocol 

(Ref. 5) to demonstrate the benefit of updating the current standard with the enhanced three-dimensional 

volumetric measurements that are now achievable. 

TABLE 1.—SUMMARY OF IMPROVEMENTS TO CURRENT SCRATCH STANDARD 

Current standard 

(ASTM G 171 properties) 

Identified limitations for current 

ASTM G 171 

Proposed new standard 

Manual measurements by 

optical investigation 

Measurement errors/variations 

one-dimensional 

Three-dimensional profile 

generation by optical 

interferometery 

Scratch width is key variable Volume not considered Total volume and 

surrounding area (ZOI) 

Determination of width 

boundary conditions 

Random boundary placement for 

width measurement on fringes 

Knowledge of width 

location not required 

Diamond tip stylus Limited testing scenarios Application specific tip 

materials 

Ex. Lunar mineral tips 

demonstrated 
NASA/TM—2011-216940 3 

The standard roughness parameters, which complement the new proposed metrics and help define the 

material surface before and after abrasion include: surface roughness (Ra); root-mean squared roughness 

(Rq); maximum depth of penetration or deepest point (Rv); maximum displaced height or highest point 

(Rp); peak-to-valley difference (Rt = |Rp| + |Rv|); and average ten greatest peak-to-valley Separations 

(Rz) (Ref. 7). Rq and Rz are included in the calculations in this paper because they are part of an industry 

standard set that may be used in future work. 

The proposed metrics defined in Table 2 use the ZOI to normalize a scratch volume and the length of 

the scratch scanned in each profile (not complete scratch length) yielding units of μm. The surface 

roughness parameters are referred to as Metric Set B, and include initial measurements on the polished 

material and final conditions bounded by the ZOI (units are μm for all six values). 

TABLE 2.—PROPOSED METRICS NORMALIZED BY ZOI AND SCAN LENGTH 

Metric Description Formula, 

μm 

A1 Negative displaced metric 

ZOI Scratch lengthscan 

Negative displaced volume

Average 

A2 Positive displaced metric 

ZOI Scratch lengthscan 

Positive displaced volume

Average 

A3 Net displaced metric A1 + A2 

A4 Absolute displaced metric |A1| + |A2| 

2.0 Materials and Methods 

All two-body abrasion scratches were made using a CSEM (now CSM Instruments, Neuchatel, 

Switzerland) Revetest automatic scratch tester CH-2000 Neuchatel 7 (FR-A 121) per ASTM G 171 

guidelines (Fig. 2). In the scratch tester, a material specimen is horizontally translated at a controlled 

speed while a stationary diamond tip stylus is applied vertically under a specified normal load. For this 

study, a variety of tip sizes with differing mineralogy were examined on typical spacecraft materials to 

investigate the potential abrasive wear from lunar dust for surface exploration design applications. 

Aluminum (Al) 6061-T6 and stainless steel 304 were used as two common spacecraft material 

specimens. Each sample was polished with 1 μm alumina powder and water on a polishing wheel to 

remove minor surface imperfections and even out any material thickness differences. Polycarbonate with 

titanium dioxide (TiO2) coating is typically used for spacesuit helmet visors and represents another 

critical application-driven material to characterize. The two diamond tips used for scratch tests are 

defined by their radius dimension of either 200 or 109 μm, both with a 120 apex tip angle. Custom tips 

were fabricated out of mineral counterparts or analogues that are expected to be similar to lunar 

mineralogy. Discussion of these custom tips is limited to demonstration purposes here, but it was due to 

the need for these tips and their corresponding irregular scar volumes that an alternate method of 

measuring abrasion was sought. 

For each tip and specimen material combination, three independent scratches were conducted. Each 

scratch was then profiled three times using Veeco Instruments Inc.’s NT-1000 optical interferometer and 

WYKO Vision32 software for NT-2000. The Veeco measurement includes 480 cross sections, which is a 

sufficiently larger than the standard three-width measurements in ASTM G 171. A code was developed in 

MATLAB (Mathworks, Inc. software) to measure the key parameters noted above and to calculate the 

indicated metrics based on the three-dimensional data array outputted from the Veeco equipment. During 

coding, several computational challenges were encountered, including correction for minor tilt variations 

in the specimens; proper edge detection of the ZOI that avoided false boundaries from small material 

divots; and tuning the sensitivity of the boundary condition limits using the surface roughness as specified 

in Figure 1. Since the goal of this research was to provide a guideline for standardization measurements 
NASA/TM—2011-216940 4 

and not to deliver a user-ready software package and since these issues were somewhat unique to test 

circumstances and were resolved for our purposes, they are not further described here. They do, however, 

warrant mention to avoid being overlooked in future application of this technique by others. 

3.0 Reconstruction of an Average Surface Profile From Metrics 

Taking the output metrics from actual data and being able to reconstruct the original conditions can 

evaluate the robustness and quality of a set of metrics. To assess the quality of the four proposed “A” 

metrics defined above, a subset of data was tabulated from nine profiles. The nine profiles included three 

consecutive scratches with three Veeco profiles generated from each scratch. The test conditions involved 

a diamond 200 μm radius (120 apex angle) tip on aluminum 6061-T6 with an 80 N normal load during 

each scratch. Measurements were made using two different MATLAB codes to obtain the ZOI, scratch 

width specified by ASTM G 171 (the width boundary end points were located at the Zeroline location on 

the displaced slopes as seen in Fig. 1), and the four “A” metrics. 

The data were averaged for these nine profiles to produce a scratch ZOI of 57547 μm, a width of 

32516 μm, A1 of –44 μm, A2 of 21 μm, A3 of –23 μm, and A4 of 64 μm. These average values for ZOI 

and width were used to recreate a profile as illustrated in Figure 3, demonstrating the ability to restructure 

an X-Y view (top of surface) from test data. One of the nine profiles was placed under the gridlines in 

Figure 3 to show how the averaged values map back to the original data. Likewise, a vertical scale 

reconstruction can be achieved with the set of “A” metrics as displayed in Figure 4. A1 specifies how 

much material is within the scratch valley, while A2 indicates the displaced volume. The difference, A3, 

is the volume balance, which in this case, shows that material was removed in the average of the nine 

profiles. A4 gives us the magnitude within the ZOI from peak to valley. The surface roughness 

parameters can be used similarly within the ZOI, but they do not indicate the volume balance between 

removed and displaced. 
NASA/TM—2011-216940 5 
NASA/TM—2011-216940 6 

4.0 Results and Discussion 

To further evaluate the robustness achieved by characterizing these new metrics compared to using 

width alone, a case study using three different tip-to-material combinations that produced the same 

scratch width was analyzed. The case study examines the volumetric “A” values as well as the surface 

roughness parameters. The ZOI is compared to scratch width versus a range of normal applied loads for 

two different diamond tip dimensions, including the depth of penetration data and a brief discussion of 

custom tip applications. 

4.1 Case Study: Same Width Scratches With Different Volumes 

To contrast these new metrics with results based on the current ASTM G 171 Standard that uses 

width to calculate abrasion properties, three profile cases were found in the research database with 

virtually the same scratch width (207 μm), but with different volumetric profile properties. Figures 5 and 

6 summarize the three different profiles and key test and data parameters including scratch tip, abraded 

material, applied normal load, width (as estimated using ASTM G 171), ZOI, “A” metric, and surface 

roughness parameters (Ra, Rq, Rv, Rp, Rt, and Rz). The cases are pictorially ordered by decreasing ZOI, 

while scratch width remains essentially constant. 
NASA/TM—2011-216940 7 

Figure 6.—Roughness parameter data for three profiles with the same width measurements. 

The three cases contain a diverse sampling pool of variables and tip to material combinations 

including applied load, scratch tip dimensions, and material abraded. The case study results illustrated in 

Figure 5 show that if just the width were measured for all of these cases, they would appear identical. 

However, it is apparent that the ZOI is significantly larger than the width for all cases, but using the 

current standard this extended region of material deformation would be neglected. Furthermore, for the 

stainless steel cases, material has mostly been displaced (A3 is close to zero), but for the aluminum it has 

been removed (A3 is largely negative). Being able to characterize this additional information is important 

because it can be correlated to potential mass changes of a system or severity of abrasion. For example, 

this could be critical if the center of mass changes for a surface vehicle. Finally, while the peak-to-valley 

volume change (A4) in all cases is similar, the normalized volume removed (A1) is almost double for the 

aluminum and the normalized displaced volume (A2) is three times as great for the steel sample. This 

case study shows that the actual differences in the material would not be discernable if width 

measurement alone were used and therefore reinforce the need to analyze the entire ZOI while making 

abrasion measurements. The “A” metrics provide an overview of the abrasion that has occurred to 

produce a comprehensive surface analysis. 

The roughness parameter data in Figure 6 shows the overall change in material shape from abrasion. 

The roughness (Ra) and root-mean-squared (Rq) values are all similar, but the valley depth of penetration 

(Rv) and max ploughed peak (Rp) values are unique. The new proposed metrics combined with the 

surface roughness parameters are designed to remove shape dependency of the abrasion tip, which the old 

standard does not address. Penetration depth is of particular importance for materials that may have a 

critical surface coating. For example, an astronaut’s helmet visor has antiglare and UV protective 

coatings; if these become abraded, protection is reduced and vision becomes obscured, as was reported 

during the Apollo missions (Ref. 8). 
NASA/TM—2011-216940 8 

4.2 Comparing Zone of Interaction to Scratch Width 

In all cases explored in this research, the ZOI was observed to be at least twice as wide as the 

ASTM G 171 Standard specified scratch width. This further indicates that most of the scratch zone is not 

accounted for in previous studies using width as the key metric. To demonstrate the magnitude difference, 

the ZOI and width results from all stainless steel scratch profiles created by both diamond tip dimensions 

(109 and 200 μm radii) are plotted in Figure 7. A polynomial fit of the data shows R-squared correlations 

closer to 1 than linear trends, suggesting that the relationship between load and scratch interaction may 

not be linear as indicated by the scratch hardness number formula specified in the ASTM G 171 Standard 

(Ref. 6). These non-linear trends were also seen in other data acquired for various tips and abraded 

material combinations. The variability that is shown in the ZOI in Figure 7 is attributed to the 

dynamically changing abrasion boundaries of the actual material along the length of the scratch. 

Another observation from Figure 7 is that the different sized diamond tips produced similar results for 

ZOI and scratch width, but penetration depth varied. If only width was used to analyze the abrasion 

caused by these two tips, then a conclusion may be inferred that there is not a significant difference in the 

interaction. If we look more closely at final depth of penetration (Rv), however, we see that sharper 

109 μm radius diamond tip is more than 10 μm deeper for every load combination on stainless steel 

304 (Fig. 8) than the 200 μm radius tip. The initial penetration depth data is included in Figure 8 to show 

that even the polished portions of the stainless steel 304 specimens have divots as deep as –14 μm, which 

means in some materials there will be outlier locations that may skew the comparison of before to after 

data. Other output data for the stainless steel 304 not presented here shows that the volume removed (A1) 

and displaced (A2) for both tips are similar. Because of the similar width, ZOI, and volume 

measurements, measuring roughness parameters such as Rv is necessary to ensure limits for material 

coating penetration are not exceeded. 

Figure 7.—ZOI and width measurements from two different diamond tips abrading stainless steel 304. 
NASA/TM—2011-216940 9 

Figure 8.—Depth of penetration (Rv) from two different diamond tips abrading stainless steel 304. 

4.3 Custom Tip Sample Data 

For our application purposes, custom scratch tips were created using minerals similar to those that are 

expected to be encountered on the Moon. As a consequence of the irregular tip shapes and orientations, 

multiple peaks and valleys were produced along a single, continuous scratch. This observation made it 

apparent that width alone was insufficient to fully characterize the end result on the material and led to the 

definition of the proposed new suite of metrics. In addition, when custom tips were used, it was observed 

that the load applied to the mineral tip was more critical than its shape, as friable minerals would often 

shatter and cause multiple, parallel scratches during the test. An example of a typical scratch that might be 

expected to occur on lunar surface equipment during actual use is shown in Figure 9. The material 

interaction resulted from using a custom enstatite tip (Fig. 10) on Al 6061-T6 with a 10 N applied normal 

load. The irregularity of the tip shape is intended to be more representative of actual lunar dust, thus produce 

operationally relevant abrasion. The finding of large areas of the lunar surface primarily composed of spinel 

indicates that even what are traditionally understood as trace minerals may be more important to test. Spinel 

is extremely hard and expected to be an important abrasive if found in high concentrations. 

Recently available information on the strength of lunar regolith grains as compared to terrestrial 

materials of similar composition further friability concerns. Cole (Ref. 3) has demonstrated that lunar 

plagioclase grains can have two to three times less mechanical strength than terrestrial material when 

compressed. Inspection of Figures 1 and 2 of Cole’s paper clarifies why the terrestrial counterparts are 

considerably more robust. In the figures, the lunar grains appear to be composed of much smaller 

fragments fused or sintered together. This structure is considerably weaker at the fragment boundaries 

than the internal crystal energies holding mineral crystals grains together thus leading to their enhanced 

friability. Should lunar grains be applied to the testing procedure described in section 2.0 of this paper, 

one would expect to see progressive damage to the tip along the entire length of the scratch resulting in a 

profile beginning as shown in Figure 6 (top frame) and ending as shown in Figure 9. Measurement of 

scratch width according to ASTM G 171 would be impossible in such a situation; however, for the 

profilometry method proposed herein, it would be straightforward to identify profile metrics along the 

length of the scratch for diagnostic and reconstruction purposes. 
NASA/TM—2011-216940 10 
NASA/TM—2011-216940 11 

5.0 Conclusions 

A new methodology utilizing advanced profilometry capabilities is proposed to provide a more 

thorough and systematic characterization of surface abrasion using the suite of metrics described in this 

work. Defining the ZOI serves to remove prior ambiguity of measurement boundary conditions, and 

allows a means of normalizing the sample material removal and displacement that can occur during 

scratch testing. It was demonstrated that inclusion of these additional quantifiable variables could be used 

to discern differences in scratch test results that were previously undetectable based on width 

measurement alone. Based on this study, a new standard is put forward for general scratch test analysis 

guidelines. Finally, it is shown how this methodology can be extended toward application-driven needs 

that require customized scratch tips. Overall, this work lays an analytical foundation for characterizing 

more complex material interactions from two-body into three-body abrasion tests that will ultimately be 

needed for system level design applications. 

References 

1. Tylczak, J.H. (1992): “Abrasive Wear,” in ASM Handbook, 18, Friction, Lubrication, and Wear 

Technology. Edited by S.D. Henry, ASM International, Cleveland, OH. pp. 187–189. 

2. Rickman, D., and Street, K.W. (2008): “Expected Mechanical Characteristics of Lunar Dust: A 

Geological View,” Proceedings of the Space Technology and Applications International Forum, 

Albuquerque, NM. 

3. Cole, D.M., Taylor, L.A., Liu, Y., and Hopkins, M.A. (2010): “Grain-scale mechanical properties of 

lunar plagioclase and its simulant: Initial experimental findings and modeling implications,” Earth & 

Space 2010: Engineering, Science, Construction, and Operations in Challenging Environments. 

ASCE. pp. 74–83. 

4. Sunshine, J.M., Besse, S., Petro, N.E., Pieters, C.M., Head, J.W., Taylor, L.A., Klima, R.L., Isaacson, 

P.J., Boardman, J.W., Clark, R.C. and the M3 Team (2010): “Hidden in Plain Sight: Spinel-Rich 

Deposits on the Nearside of the Moon as Revealed by Moon Mineralogy Mapper (M3),” (abstract). 

41st Lunar and Planetary Science Conference. Abstract No. 1508. The Woodlands, Texas. 

5. Kobrick, R.L., Klaus, D.M., and Street, Jr., K.W. (2010, Submitted): “Standardization of a 

Volumetric Displacement Measurement for Two-Body Abrasion Scratch Test Data Analysis,” 

J. WEAR. Manuscript number: IH-6025. Elsevier. 

6. ASTM (2003): “Standard Test Method for Scratch Hardness of Materials Using a Diamond Stylus,” 

G 171-03, Annual Book of ASTM Standards. 

7. WYKO (1999): “WYKO Vision32 Online Help,” WYKO Vision32 software for NT-2000, Version 

2.210, Veeco Instruments, Inc., Metrology Group. Release Date 1/8/1999. Available via software 

package. 

8. Gaier, J.R. (2007): “The Effects of Lunar Dust on EVA Systems During the Apollo Missions,” 

NASA GRC. NASA/TM—2005-213610/REV1. 
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14. ABSTRACT

The objective of this work was to evaluate a set of standardized metrics proposed for characterizing a surface that has been scratched from a 

two-body abrasion test. This is achieved by defining a new abrasion region termed “Zone of Interaction” (ZOI). The ZOI describes the full 

surface profile of all peaks and valleys, rather than just measuring a scratch width as currently defined by the ASTM G 171 Standard. The 

ZOI has been found to be at least twice the size of a standard width measurement, in some cases considerably greater, indicating that at least 

half of the disturbed surface area would be neglected without this insight. The ZOI is used to calculate a more robust data set of volume 

measurements that can be used to computationally reconstruct a resultant profile for detailed analysis. Documenting additional changes to 

various surface roughness parameters also allows key material attributes of importance to ultimate design applications to be quantified, such 

as depth of penetration and final abraded surface roughness. Data are presented to show that different combinations of scratch tips and 

abraded materials can actually yield the same scratch width, but result in different volume displacement or removal measurements and 

therefore, the ZOI method is more discriminating than the ASTM method scratch width. Furthermore, by investigating the use of custom 

scratch tips for our specific needs, the usefulness of having an abrasion metric that can measure the displaced volume in this standardized 

manner, and not just by scratch width alone, is reinforced. This benefit is made apparent when a tip creates an intricate contour having 

multiple peaks and valleys within a single scratch. This work lays the foundation for updating scratch measurement standards to improve 

modeling and characterization of three-body abrasion test results.

15. SUBJECT TERMS

Two-body abrasion; Scratch testing; Lunar dust; Surface topography; Profilometry; Surface analysis 

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