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JOTwear2004 - Tony L Schmitz Jason E Action David L Burris...

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Tony L. Schmitz Jason E. Action David L. Burris John C. Ziegert W. Gregory Sawyer Department of Mechanical and Aerospace Engineering, University of Florida, Gainesville, FL 32611 Wear-Rate Uncertainty Analysis Wear due to relative motion between component surfaces is one of the primary modes of failure for many engineered systems. Unfortunately, it is difficult to accurately predict component life due to wear as reported wear rates generally exhibit large scatter. This paper analyzes a reciprocating tribometer in an attempt to understand the instrument- related sources of the scatter in measured wear rates. To accomplish this, an uncertainty analysis is completed for wear-rate testing of a commercially available virgin polytet- rafluoroethylene pin on 347 stainless steel counterface. It is found that, for the conditions selected in this study, the variance in the experimental data can be traced primarily to the experimental apparatus and procedure. Namely, the principal uncertainty sources were found to be associated with the sample mass measurement and volume determination. @ DOI: 10.1115/1.1792675 # 1 Introduction Engineered systems are subject to several modes of failure, including plastic deformation, fracture, fatigue, excess deflections, and wear. Of these, wear is generally the least predictable using current design methodologies. This is partially due to imperfect knowledge of the appropriate wear rate for the selected material pair to be used in calculating component life. Wear rate is nor- mally determined experimentally using a tribometer, which at- tempts to mimic the contact conditions of the material pair and system under study. Wear-rate values reported in the literature for many material pairs and contact conditions often show wide varia- tion, even for nominally identical tests. The source of this varia- tion in measured wear rates is currently unknown. It may be due to actual variations in the wear rate of the material pair, or it may be due to intrinsic factors in the experimental apparatus and pro- cedure that lead to variations in the reported wear-rate value. The purpose of this paper is to outline a method for determining the uncertainty of the measured wear rate for a given experimental apparatus as a function of the uncertainty of the measured input quantities and to compare the calculated measurement uncertainty with the experimental variance obtained using the apparatus. It is shown that the uncertainty analysis methodology reported here can also be used to determine the most significant contributors to the overall measurement uncertainty. This information can then be used to aid in redesign of the experimental apparatus and/or pro- cedure to reduce the measurement uncertainty. 2 Wear Rate Measurement Description 2.1 Reciprocating Pin-on-Disk Tribometer. The tribom- eter shown schematically in Fig. 1 creates a reciprocating sliding contact between the two surfaces of interest. This tribometer is located inside a soft-walled clean room with conditioned air that has a relative humidity between 25 percent and 50 percent. A
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