Standardization of a Volumetric Displacement Measurement for Two-Body Abrasion Scratch Test Data Analysis
- Monday, 24 October 2011
A more robust method is proposed that takes into account the full three-dimensional profile of the displaced material.
A limitation has been identified in the
existing test standards used for making
controlled, two-body abrasion scratch
measurements based solely on the width
of the resultant score on the surface of the
material. A new, more robust method is
proposed for analyzing a surface scratch
that takes into account the full three-dimensional
profile of the displaced
material. To accomplish this, a set of four
volume-displacement metrics was systematically
defined by normalizing the overall
surface profile to denote statistically the
area of relevance, termed the Zone of
Interaction. From this baseline, depth of
the trough and height of the plowed
material are factored into the overall
deformation assessment. Proof-of-concept
data were collected and analyzed to
demonstrate the performance of this proposed
methodology. This technique takes
advantage of advanced imaging capabilities
that allow resolution of the scratched
surface to be quantified in greater detail
than was previously achievable.
When reviewing existing data analysis
techniques for conducting two-body
abrasive scratch tests, it was found that
the ASTM International Standard G 171
specified a generic metric based only on
visually determined scratch width as a
way to compare abraded materials. A
limitation to this method was identified
in that the scratch width is based on
optical surface measurements, manually
defined by approximating the boundaries,
but does not consider the three-dimensional
volume of material that
was displaced. With large, potentially
irregular deformations occurring on
softer materials, it becomes unclear
where to systematically determine the
scratch width. Specifically, surface
scratches on different samples may look
the same from a top view, resulting in an
identical scratch width measurement,
but may vary in actual penetration
depth and/or plowing deformation.
Therefore, two different scratch profiles
would be measured as having identical
abrasion properties, although they differ
With these refined measurements, a wider variety of testing needs can be addressed with greater resolution while using the most appropriate abrasive tip and test material combination for the intended application. The core of this innovation in two-body abrasion research involved scratch testing with ASTM G 171 used as a guideline for determining the number of tests to be conducted. The resultant profiles of each scratch were digitized using an optical interferometer and accompanying software. To accomplish this objective, software code was developed to produce a suite of metrics based on a zero line (ZL) through the scratch, which allowed quantitative definition of the scratch and associated wear metrics.
The computer code determines a ZL through individual cross-sections, then produces the following metrics: Negative Volume Displaced, Positive Volume Displaced, Net Volume Displaced, and Absolute Volume Displaced, along with a secondary set of metrics composed of six roughness parameters that allow definition of the ZL. From these metrics, a Zone of Interaction (ZOI) can be established.
This work was done by K. W. Street, Jr. of
Glenn Research Center and R. L. Kobrick and
D. M. Klaus of the University of Colorado –
Inquiries concerning rights for the commercial use of this invention should be addressed to NASA Glenn Research Center, Innovative Partnerships Office, Attn: Steven Fedor, Mail Stop 4–8, 21000 Brookpark Road, Cleveland, Ohio 44135. LEW-18675-1
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