Vol. 17, 2016
It will be two years on July 1, 2016 since I was appointed Managing Director of GRI. I’d like to thank Suren Rao and Linda Jones (GRI’s administrative assistant for the last 20 years) for their continued support. Their experience and guidance have made the transition much easier than expected.
Plus ça change, plus c'est la même chose (Jean-Baptiste Alphonse Karr, 1849) or as more commonly quoted, the more things change, the more they stay the same. Searching for a topic for this Foreword, I reviewed the last several newsletters and the word change has been used more often than in a presidential campaign. GRI has recently endured the retirement of many long time fixtures on our staff. We’ve formally said farewell to Sam Haines as GRI president, Doug McPherson as lead engineer and Suren Rao as managing director. Interestingly enough, two of them have been in my office today and I spoke to the third on the phone less than a week ago. Sam is currently serving as treasurer of the GRI Board, and both Doug and Suren are utilized as consultants on a very regular basis. There have indeed been many changes at GRI over the past two years, but the depth of experience and knowledge is still front and center in our repertoire. Things have changed but at GRI we are doing the things we have always done. Our mission of supporting the gear industry through performance testing and characterization while educating future engineers has held strong for 34 years and I certainly plan to do everything in my power to ensure that this does not change.
Continuing with this theme, the GRI Board of Trustees has a new member. Mr. Geary Smith from Caterpillar has replaced the recently retired Bryan Lammers (also from CAT). Geary is the Engineering Manager of Mechanical Components at CAT. I would like to personally welcome Geary to the Board and look forward to working with him. Geary will have the challenging task of replacing Bryan on the Board. Bryan’s unique combination of worldliness, wit and wisdom will certainly be missed.
Now on to a new topic. Something that hasn’t changed over the past three years is the happy singing of the spur gears in the Aerospace Bloc’s VLC test rig (which happens to be buzzing constantly right outside my office door). The average test lasts about three months, which is a long time for an accelerated fatigue test!
Gear boxes in military and commercial aircraft operate well over a billion cycles in their lifetime. Consequently significant interest exists in the aerospace gearing community for bending and surface durability characteristics of gear materials at a very high number of load cycles. Based on this interest the Gear Research Institute has been conducting an experimental program to evaluate the bending fatigue and surface durability behavior of AMS 6308 subject to Very Long Cycles (VLC). “Runout” for this project was set at one billion (109) cycles. This project has been ongoing since 2013, for reasons that are explained below and is anticipated to be complete in 2017.
These tests are being conducted on a modified, 4-square, recirculating gear test rig, shown in figure 1, where the gear sets mounted in the two gear boxes are identical. The modifications to the test rig consisted of retrofitting this machine to run at speeds of 6,400 rpm, so that data could be obtained in a reasonable amount of time. Even at these speeds it takes over a100 days to complete 109 cycles. Hence the long duration of this effort, as many tests need to be conducted to establish the material properties of interest in this project. This machine was also instrumented with a failure detection system consisting of accelerometers and algorithms developed at PSU/ARL (described in earlier newsletters) so that it could run 24/7/365 on an unattended basis.
Figure 1: Four-Square gear test rig
The underlying assumption in this project is that there is no “second knee” in the stress-cycles strength relationship for AMS 6308 at some point over 100 million cycles. While several test plans were evaluated the test plan adopted for this project consisted of a modified staircase sequence at a predetermined series of loads. If a given test results in a bending failure before 109 cycles the next test was run at the next lower load in the series. If a given test ran 109 cycles without failure the next test was run at the next higher load. Since tests were run at different loads it was impossible to accurately account for the cycles accrued by the pair of gears that didn’t fail at one load when they are run at the next. Thus all four gears were changed after each failure. This increased the testing time and required twice the number of gear pairs for testing. The advantage gained by this additional effort and cost is that the G50 bending load at 109 cycles can be determined with some statistical reliability.
It has been a very successful project as bending and surface durability failures have been obtained near the “runout” limit. Detailed analysis of the failures to establish causes of failure are also being conducted. The outcome of this project will be a detailed report to the sponsors at the end of the project.
Education and Training
In order to assist the gear industry augment its aging work force, the Gear Research Institute has developed two initiatives to train more gear knowledgeable engineers at the undergraduate and graduate levels. This involves incorporating engineering undergraduate students, at the junior/senior level and graduate students in the Institute’s research laboratory while being paid by a grant from the sponsoring industrial entity. Summer internships have also been arranged at the sponsor’s facility are also a part of the deal, so that the student and the sponsor have an opportunity to assess each other with future employment in mind.
We had our first graduate of this program in the spring of 2013, who then joined John Deere at their Coffeyville, KS facility. We had a second student selected by John Deere, Byron Stuart, who graduated last spring and joined John Deere at their Waterloo, Iowa facility in August 2014. Our third student supported by John Deere, William Jaundalderis, a senior in Mechanical Engineering, graduated in 2015 but joined the United States Air Force upon graduation. We now have a fourth student, David Reed supported by John Deere working with us and prospectively joining John Deere upon graduation in 2016. John Deere has indicated that it plans to continue this sponsorship and candidates are currently being selected.
Typically, students get hands on experience by setting up and monitoring gear test equipment with additional training topics such as gear metrology, failure analysis, metallurgical characterization, vibration monitoring for failure detection, statistical analysis of test data and more.
The Gear Research Institute is a non profit corporation. It has contracted with the Applied Research Laboratory of The Pennsylvania State University to conduct its activities, as a sponsor within the Drivetrain Technology Center. The Gear Research Institute is equipped with extensive research capabilities. These include rolling contact fatigue (RCF) testers for low- and high-temperature roller testing, power circulating (PC) gear testers for parallel axis gears with a 4-inch center distance (testers can be modified to accommodate other center distances), single tooth fatigue (STF) testers for spur, helical and spiral bevel gears, and gear tooth impact tester. Extensive metallurgical characterization facilities are also available at Penn State in support of the Gear Research Institute. For further details on our testing capabilities please go to www.gearresearch.org or call Aaron Isaacson, Managing Director, at (814) 865-5832..