Personnel in the Quality and Integrity Design Engineering Center (QIDEC) at the University of Utah are working under a two year grant from the FAA to better understand the role of fretting corrosion and fretting fatigue in aircraft rivet hole cracking. The current program follows a one year grant program which was completed in 1993. This paper provides a status report on the results of these grant programs. Recent effort has been focused on developing basic fretting fatigue models which consider variation in the coefficient of friction with time and location within the fretting interface. This is a very important characteristic of the QIDEC model because coefficient of friction varies significantly during the fretting fatigue process. Copies of QIDEC documents discussed in this paper can be obtained by contacting the authors

Elliott, Charles B., III

Hoeppner, David W.

Moesser, Mark

English

NASA Technical Reports Server

THE ROLE OF FRETTING CORROSION AND FRETTING FATIGUE
IN AIRCRAFT RIVET HOLE CRACKING -
A STATUS REPORT ON TWO FAA GRANT PROGRAMS*
Charles B. Elliott HI
Mark Moesser
David W. Hoeppner
Quality and Integrity Design Engineering Center
University of Utah
Salt Lake City, Utah
/ ....._ _
SUMMARY
Personnel in the Quality and Integrity Design Engineering Center (QIDEC) at the University of
Utah are working under a two year grant _om the FAA to better understand the role of fretting corrosion
and fretting fatigue in aircraft rivet hole cracking. The current program follows a one year grant program
which was completed in 1993. This paper provides a status report on the results of these grant programs.
Recent effort has been focused on developing basic fretting fatigue models which consider
variation in the coefficient of friction with time and location within the fretting interface. This is a very
important characteristic of the QIDEC model because coefficient of friction varies significantly during the
fretting fatigue process. Copies of QIDEC documents discussed in this paper can be obtained by
contacting the authors.
INTRODUCTION
Fretting is a process in which two bodies in contact are subjected to relative motion of an amplitude
small enough to allow resulting debris to be trapped between the contacting (faying) surfaces. Because the
faying surfaces and debris are subject to corrosion as well as wear, the process is sometimes called fretting
The FAA has supported this work through Grants No. 92-G-004 and No. 93-G-068. QIDEC is
grateful for this support and the efforts of the FAA Grant Monitor, Dr. Thomas Flournoy.
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corrosion. When one or both of the bodies also undergo cyclic tensile (fatigue) loading, the process is
called fretting fatigue. The simultaneous action of wear, corrosion and fatigue mechanisms often results in
a synergistic degradation of the components with a reduction in life which can be an order of magnitude
more than would be expected based upon the operation of only one of the three mechanisms.
Fretting fatigue is increasingly being recognized in the aircraft industry as a major cause of failure.
It is a failure mechanism which frequently leads to high maintenance and inspection costs and could
potentially lead to catastrophic failure of aircraft components. Thus, it represents both a durability and a
safety problem. Costs associated with fretting fatigue are significant. The 1988 Aloha Airlines disaster
focused new attention on fretting in the aircraft industry as it was thought fretting could have played an
important role in that failure. 1 Fretting can be present in any area of an aircraft structure (e.g. engines,
aircraft primary and secondary structure, and landing gear components) in which small amplitude cyclic
slip between adjacent contacting materials is possible. Rivets and mechanically fastened joints in general
are particularly susceptible to fretting and fretting fatigue multiple-site damage. This damage can link up in
aircraft structures and create catastrophic results. Thus, it is imperative to understand the role of fretting
and fretting fatigue in producing multiple-site damage in riveted aircraft joints.
RESULTS FROM THE PREVIOUS GRANT PROGRAM
Based on a search of government and private literature from 1960 to 1992 a report was prepared.
This report, "Literature Review and Preliminary Studies of Fretting and Fretting Fatigue Including Special
Applications to Aircraft Joints" has been submitted to the FAA and is being considered for publication as
an National Technical Information Service document.
The aircraft industry needs the ability to predict the role and influence of fretting on the fatigue life
of riveted joints. For this reason, an extensive effort was started during the previous grant program and is
continuing during the current program to improve quantitative prediction of fretting fatigue in aircraft
joints. Due to the complex geometry of such joints, an accurate quantitative analysis could best be
performed with the use of finite element methods.
QIDEC personnel presented four papers at the International Conference on Fretting Fatigue held in
Sheffield, England in April 1993. These papers which will be published by the European Structural
Integrity Society are as follows:
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• Mechanisms of Fretting Fatigue (invited keynote paper) by Dr. Hoeppner.
• The Role of Normal Pressure in Modeling Fretting Fatigue by Dr. Adibnazari and Dr. Hoeppner.
• Finite Element Model of Fretting Fatigue With Variable Coefficient of Friction Over Time and Space
by Mr. Moesser, Dr. Adibnazari and Dr. Hoeppner.
• A Fretting Fatigue System Useable in a Scanning Electron Microscope by Dr. Elliott and Dr.
Hoeppner.
Additionally, Dr. Hoeppner and Dr. Adibnazari co-authored a paper titled "Fretting Fatigue in
Aircraft Joints" which Dr. Hoeppner presented to the June 1993 International Committee of Aeronautical
Fatigue in Sweden.
OVERVIEW OF THE CURRENT GRANT PROGRAM
QIDEC is currently working under FAA Grant 93-G-068 which was received in late September
1993 and will last two years. The objectives of the program are as follows:
• Construct, calibrate and verify a computer simulation model of a riveted joint.
• Perform a sensitivity study on some parameters which could influence fretting fatigue in riveted aircraft
joints.
• Model the nucleation of fretting damage at riveted aircraft joints.
• Establish a design method that will allow an assessment of the likelihood that the fretting fatigue
damage threshold will be exceeded.
• Conduct an assessment of the design approaches used by industry to alleviate fretting corrosion and
fretting fatigue.
• Develop experimental techniques that allow assessment of fretting fatigue in riveted joints.
• Make all methods and fmdings applicable to a global aircraft reliability model.
• Maintain liaison with FAA technical personnel, other FAA programs, aircraft industry activities and
ASTM activities with respect to fretting.
To accomplish these objectives, the program has been organized into the following major tasks:
Develop and verify basic fretting fatigue models which consider variation in the coefficient of friction
with time and location within the fretting interface. This is a very important (and to our knowledge a
unique) characteristic of the QIDEC model because coefficient of friction varies significantly during the
fretting fatigue process.
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• Determinethecoefficient of friction and faying surface sealant materials data necessary as input to the
models.
• Plan and conduct a sensitivity study on some of the parameters which affect fretting fatigue in riveted
aircraft joints.
• Plan and conduct an examination of riveted joints used in service.
• With knowledge gained from the basic fretting fatigue models, develop and verify a fretting fatigue
model of a riveted joint.
• Use the results of this program to develop fretting fatigue design methods useful to the aviation
community.
• Report results of this program to the aviation community through the FAA and the open literature.
This is one of several research programs being conducted by QIDEC that are leading to improved
understanding throughout the aviation community of the adverse synergistic effects of wear, corrosion and
fatigue mechanisms on aircraft structural integrity. Related research is being conducted for the Boeing
Commercial Airplane Company and the Boeing Defense and Space Group in coordination with the U. S.
Air Force. Non-aviation programs funding fretting-related research within QIDEC, which will indirectly
benefit the aviation industry, include an orthopedic implant designer and a manufacturer of truck and trailer
hubs.
STATUS OF THE PROGRAM
Major advances are being made in development of the basic fretting fatigue model. Recent activity
included the transition from the ANSYS finite element program, used in preliminary work under FAA
Grant No. 92-G-004, to the ADINA program. This switch was necessary to take advantage of the
increased capability of the ADINA code available at the University of Utah. Two and three dimensional
models were constructed using the ADINA code. These models were used to verify that the commercially
available ADINA program can be used with the methods being developed by QIDEC. As part of this
work, Fortran and C-shell codes were developed which proved the applicability of planned analytical
methods for predicting changes in coefficient of friction as a function of time and location between the
fretted surfaces. Basic fretting fatigue model development activities will continue with emphasis on
incorporation of materials data when it is determined.
Development of the experimental methods and hardware to determine the coefficient of friction and
faying surface sealant materials data necessary as input to the models is progressing on schedule. A rough
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analysisof arivetedjoint wasconductedto determinethe expectedvariability of normal surface tractions
and relative displacements within a riveted joint. From this analysis it was determined that coefficient of
friction data are desirable for relative slip an order of magnitude less than that reported in the literature.
Collecting such data will present a challenge, but one which we are working to meet. Significant effort
was expended developing and analyzing possible methods for determining coefficient of friction data at
relative displacements as low as two microns. A preliminary test apparatus design was developed and is
being refined. Methods and equipment for conducting faying surface sealant tests also will be developed.
QIDEC is in the process of developing a partnership with an industrial representative to help with
planning the "sensitivity study on parameters important to fretting fatigue in riveted aircraft joints", and the
"examination of riveted joints used in service" portions of the program. We are optimistic that such a
partnership will be beneficial to both parties.
As part of the requirement to maintain liaison with the FAA and other aircraft industry activities,
QIDEC personnel attended and made presentations at the FAA/NASA conferences in November 1993 at
Lehigh University and March 1994, when QIDEC was the host organization. Additionally, QIDEC
representatives attended the December 1993 USAF Structural Integrity Program Conference, where the
Director of QIDEC made a presentation.
CONCLUDING REMARKS
The Quality and Integrity Design Engineering Center is pleased to have the opportunity to conduct
this important research for the FAA and the aviation community in general. We will make every effort to
disseminate our findings as they are developed.
REFERENCE
1. Brewer, John C.: Fretting Issues for the Aging Aircraft Program, U.S. DOT/FAATC, Oct. 1991.
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BIBLIOGRAPHY OF QIDEC REPORTS AND PAPERS
Copies of the following reports and papers can be obtained by providing your name and address to
Dr. Charles B. Elliott, III, University of Utah, Department of Mechanical Engineering, Merrill
Engineering Building Room 3209, Salt Lake City, Utah 84112; phone: (801) 585-6429;
FAX: (801) 581-8692; email: elliott@me.mech.utah.edu.
• Hoeppner, D. W., Adibnazari, S. and Moesser, M. W.: Literature Review and Preliminary Studies of
Fretting and Fretting Fatigue Including Special Applications to Aircraft Joints. Submitted to the FAA
in November 1993.
• Hoeppner, D. W.: Mechanisms of Fretting Fatigue. Invited keynote paper presented at the
International Conference on Fretting Fatigue, Sheffield, England, April 1993.
• Adibnazari, S. and Hoeppner, D. W.: The Role of Normal Pressure in Modeling Fretting Fatigue.
Presented at the International Conference on Fretting Fatigue, Sheffield, England, April 1993.
• Moesser, M. W., Adibnazari, S. and Hoeppner, D. W.: Finite Element Model of Fretting Fatigue
With Variable Coefficient of Friction Over Time and Space. Presented at the International Conference
on Fretting Fatigue, Sheffield, England, April 1993.
• Elliott, C. B. III and Hoeppner, D. W.: A Fretting Fatigue System Useable in a Scanning Electron
Microscope. Presented at the International Conference on Fretting Fatigue, Sheffield, England, April
1993.
• Hoeppner, D. W. and Adibnazari, S.: Fretting Fatigue in Aircraft Joints. Presented to the
International Committee of Aeronautical Fatigue in Stockholm, Sweden, June 1993.
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The role of fretting corrosion and fretting fatigue in aircraft rivet hole cracking

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