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 significantly.
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 – Boulder.
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