A New Fretting Test Method

WEAR NEWS Volume 9, Number 4 Fall 2011

A New Fretting Test Method The labs were asked to perform at least three replicate tests and to report ball scar diameter, ball Interlaboratory Tests wear volume, and counterface wear volume. We did not specify the procedure for measuring ball or “ ASTM Standard Test Method for Damage to counterface wear scars or wear volumes. Contacting Surfaces Under Fretting Conditions” was conditionally approved in 2010 pending Results: addition of a statement on reproducibility obtained in interlaboratory tests. It is the purpose of this Ball scar diameters are compared in Figure 1. Two document to report on the status of an labs had ball scare diameters of between 740 and interlaboratory study (ILS) conducted on one test 812 µm and two labs had ball scar diameters in the couple (52100 steel at 60 HRC vs. type A2 tool range of 172 to 405µm. The within laboratory steel at 60 HRC) by four participating laboratories. COV’s are listed below. Test specimens were made from the same lot of material and finished by the same laboratory. The COV Average ball test method covers the testing parameters but Scar diameter allows the use of different test rigs. All four labs that supplied data for this report had rigs of Lab A 0.04 780 µm different design. We did not request design details Lab B 0.008 745 µm on the test rigs used. Lab C 0.03 177 µm Lab D 0.09 367 µm Procedure: The average between-lab scar diameter was 517 The following test conditions were communicated µm. The between-lab COV was 0.56 (s=293). to the five laboratories that agreed to participate as This suggests that the various test machines used in of December 30, 2011. Four laboratories have this study are not producing identical sliding and submitted test data as of June 16, 2011. contact conditions. Some probable causes for these are: Test configuration – 6.3 mm-diameter ball on a 3 x 8 x 30 mm flat 1. There may be ball-on-flat compliance Test surface finish – less than 0.1 µm Ra differences Force on rider – 10 N 2. The required normal force of 10N may not Test amplitude – 50 µm (total indicator movement) have been achieved Test duration – one million cycles (rotations) 3. The relative slip amplitude may be different Test frequency – 13 Hz than the G 204 specifications Test environment – room air, 50% RH, 20 C 4. There may be test frequency differences between the labs

Of course, there could be scar measurement errors Under lubricated conditions, Laboratory A or biases, but the above are more likely. measured an average ball scar diameter of 215 µm Compliance is almost certainly different since each compared with an average of 780 µm in the machine has a different design for holding and unlubricated tests. Each lab could retest the couple moving the rider. Normal force difference could used in this study lubricated and determine if each exist, but this is one of the easiest sources of lab obtained a similar decrease in wear volume specification departure to test for and correct. (ball scar diameter). This would verify that ASTM Relative slip difference between labs are quite G 204 can accurately rank materials even with a possible unless each machine has a dynamic sensor high interlaboratory COV. to continuously record the displacement of counterface and rider throughout a test. For In summary, this study determined that the ASTM example, as wear progresses, the friction force can G 204 test method is very repeatable with-lab, but change and the forces on the rider are different the between-lab reproducibility is less than desired. than they were at setup and rider deflection can be Compliance and slip differences are thought to be different than at setup the sources for the observed high COV.

It is believed that frequency differences are not likely to be the source of the observed reproducibility differences because the first tests with this test method were conducted at 10.7 Hz and the wear volumes were not significantly different than those obtained at the current test frequency of 13 Hz. In addition, with machines using a motor for the source of oscillation, the frequency is simply measured by motor rpm and this is not a measurement usually subject to error.

Slip amplitude can be accurately measured by measuring the ellipse diameter of wear scars early in testing. This study suggested that measuring the difference between major and minor ellipse diameters after 100 to 300 cycles is the most accurate measurement of real slip amplitude. Later in testing, wear debris tends to obscure the Discussion: differences between major and minor diameters. At one million cycles, the wear scars are almost The test metric specified in ASTM G 204 is wear circular under optical examination. volume of both members of the fretting couple. However, the wear measurement that did not The interlaboratory tests did not include other test involve a measuring technique unique to each lab couples, but limited testing suggests that the was ball scar diameter. This can be measured ASTM G 204 test on the 52100/A2 tool steel optically or with profilometry and wear volume couple used in these interlaboratory studies (ILS) can be calculated using the procedures in the will produce a significantly lower wear volume ASTM G 99 pin-on-disk test. For this reason, we when tested in light-weight mineral oil used ball scar diameter as the metric to calculate (pharmaceutical grade). A lubricated 52100/A2 interlaboratory reproducibility. test couple could be a candidate for a second ILS.

ASTM G 204 is a reciprocating test, therefore, the The steel couples produced similar rider wear ball and counterface scars are not really circular; results regardless of alloy type and hardness they are not really diameters, but rather they are differences. The 316 stainless steel/soft-steel elliptical. When the labs reported major and minor (1020) couples and the aluminum alloy/A2 steel ellipse diameters, they averaged to arrive at couple produces counterface divots with negligible average ball scar “diameter”. ball wear (only adhesion). The 52100/A2 couple in air produced ball scars that were only 25% of The test results show that the test couple and the those produced in the same couple in air. ASTM G 204 procedure produce very repeatable results within a lab. The within-lab COV’s are all Thus, a second round of tests could be attempted less than 10 percent which is a rule of thumb limit with the same material couples as the first test, but for reproducibility for abrasion tests. The fretting under a drop of mineral oil. This is what is between-lab COV were much higher than desired recommended for a second ILS. and it would it would be a monumental effort to compare machine designs and mechanics. ASTM G2 Wear and Erosion Activities

Conclusions: Abrasion Subcommittee – Brian Merkle (Nanosteel) was appointed subcommittee chair. 1. ASTM G 204 produces very repeatable He chaired the Fall 2011 meeting in New Orleans. within-lab test results. The standards needing review for reapproval are:

2. ASTM G 204 can have a high between-lab 1. G 81 – Jaw crusher gouging abrasion test COV when different test rigs are used. 2. G105 – Wet sand rubber wheel abrasion test What’s Next 3. G132 – Pin-on-sandpaper drum abrasive test Bud Labs has conducted many additional tests to identify another material couple to test that would The G81 Standard will be reballoted without produce significantly different results than the change. Troy LeValley (Falex) will review the 52100 steel/A2 tool steel couple tested in the G105 test before reballoting as will the G132. “round one” tests. The concept of testing a significantly different couple is that if each lab There was a paper presented in New Orleans on found it, for example, to be one half of the wear work conducted to determine if neoprene rubber volume of the 52100/A2 couple, it would suggest could be used to replace the chlorobutyl rubber that labs can rank couples the same even though currently specified in the G65 dry-sand rubber their test wear volume different by as much as wheel test. After many tests and machine checks, 50%. it was concluded that it can be a suitable substitute to solve the rubber problems that have plagued In an attempt to find a significantly different users for years. It is difficult to make, difficult to couple for a second round of interlaboratory tests, dress, has extremely limited availability and it we tested a hard rider on a soft counterface, two costs more than $1,000 for wheel that could be hard/hard steel couples, a ceramic/hard steel used in one test. An interlaboratory study will be couple, a stainless couple, and a hard/hard couple conducted to determine the suitability of the lubricated with mineral oil. neoprene.

Ken Budinski reported that the ASTM B611 and longer standoff distance (14 vs 10 mm) than standard will be reballoted for the third time after G76 to reduce the severity of the test. resolution of concerns expressed in prior ballots. Miscellany Friction Subcommittee – Scott Hummel (Lafayette College) chaired the meeting. Scott Future Symposium – The next G2 meeting will discussed the laws of friction appendix proposed precede the 3rd International Symposium on for addition to the G115 friction measurement Tribocorrosion to be held April 19-20 at Georgia guide. It was recommended that Ken Budinski Tech University in Atlanta, GA, USA. The (Bud Labs) ballot G115 with the proposed symposium is jointly sponsored by ASTM and appendix to determine its usefulness. other organizations.

Data Acquisition in Tribosystems – Chair, Greg Future Tribology Events Dalton (Tribsys) reported that he will review ASTM G190 for reapproval. This guide is used to The appended tabulation of upcoming tribology select an appropriate wear test for an application. events was prepared by Dr. Peter Blau of Oak Scott Hummel recommended balloting G117 on Ridge National Labs. Thank you, Peter. calculating measures procession tribotest for withdrawal because it used outdated computer Future ASTM G2 Meetings methods. Greg and Bill Ruff (NIST – Retired) will discuss this and G118 for consideration for Spring 2012 reapproval or withdrawal. April 18 – Georgia Tech, Atlanta, GA

Non-abrasive Wear Subcommittee – Chair, Nick Fall 2012 Randall (CSM), requested Ken Budinski to issue a September 20-21, CSM, Boston, MA report on the status of the G204 fretting test round on tests that were conducted over the past two Spring 2013 years. May, ASTM Headquarters, PA

Terminology Subcommittee – Chair Peter Blau Editor’s Note (ORNL), led discussions of some recently balloted terms including: Normally, we report on papers presented at major conferences in the fall. This year, I could not Incubation period attend any because of my wife’s health problems. Wear resistance We reported in our internal research efforts in Abrasion resistance fretting as a substitute. Abrasion

Negatives were received on a previous ballot. NOTE: Wear News is the informal account of After word-smithing by attendees, the terms were selected tribology events and the to be reballoted. activities of the ASTM G2 Committee on Wear and Erosion. Erosion Activities – Swami Swaminathan Contributed tribology articles are presented an update on their high temperature welcome. Send them and other erosion test. They are using a solid particle erosion inquiries to: rig with a larger nozzle (1.5 mm dia vs. 1.0 mm)

Ken Budinski Rochester, NY 14616 (USA) Bud Labs 3145 Dewey Avenue

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