Mechanical Failure : Definition of the Problem
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osr nArroABJoa w/iY 1 2 me MFPG ^22ii>+^ Mechanical Failure: Definition of the Problem no I Proceedings of the 20th Meeting of the Mechanical Failures Prevention Group, held at the National Bureau of Standards, Washington, D.C. 20234 May 8-10, 1974, Edited by T. R. Shives and W. A. Willard Metallurgy Division Institute for Materials Research National Bureau of Standards Washington, D.C. 20234 Jointly Sponsored by NBS Institute for Materials Research, Washington, D.C. 20234 Office of Naval Research, Arlington, VA 22217 Consumer Product Safety Commission, Washington, D.C. 20207 Frankford Arsenal, U.S. Army, Philadelphia, PA 19137 Naval Air Development Center, Washington, D.C. 20362 American Society for Mechanical Engineers, New York, NY 10017 Federal Aviation Administration, Washington, D.C. 20591 NASA, Goddard Space Hight Center, Greenbelt, MD 20771 "ates U.S. DEPARTMENT OF COMMERCE, Elliot L. Richardson, Secretary Designate James A. Baker, III, Under Secretary Dr. Betsy Ancker-Johnson, Assistant Secretary for Science and Technology U> NATIONAL BUREAU OF STANDARDS, Ernest Ambler, Acting Director n \ Issued April 1 976 Library of Congress Catalog Card Number: 76-600003 National Bureau of Standards Special Publication 423 Nat. Bur. Stand. (U.S.), Spec. Publ. 423,, 228 pages (Apr. 1976) CODEN: XNBSAV U.S. GOVERNMENT PRINTING OFFICE WASHINGTON: 1976 For sale by the Superintendent of Documents, U.S. Government Printing Office, Washington, D.C. 20402 (Order l)y SD Catalog No. ( ;13.10 :42,S ) Slock Number 00.^003-01451-6 Price $6.10 cents (Add 25 percent addi- tional for other than U.S. mailing). Abstract These proceedings consist of 20 submitted papers and discussions from the 20th Meeting of the Mechanical Failures Prevention Group held at the National Bureau of Standards, May 8—10, 1974. The central theme of the proceedings is the definition of the problem of mechanical failure, with emphasis on modes of failure, consequences of mechanical failure, and implications of me- chanical failure. Key words: Brittle fracture; economics of failure prevention; fatigue failure; mechanical relia- bility; stress corrosion cracking. iii Units and Symbols Customary United States units and symbols appear in many of the papers in these Proceedings. The participants in the 20th Meeting of the Mechanical Failures Prevention Group have used the established units and symbols commonly employed in their professional fields. However, as an aid to the reader in increasing familiarity with and usage of the metric system of units (SI), the following table of conversion factors and references are given: Length 1 inch = 2.54 centimeters (cm) 1 foot = 0.3048 meters (m) 1 mile = 1.609 X 10^ meters (m) 1.609 kilometers (km) Mass 1 pound (Ibm) = 0.4536 kilogram (kg) 1 ton (short, 2000 Ibm) = 907.2 kilograms (kg) Stress 1 psi = 6.895 X 103 pascals (Pa) 1 ksi = 6.895 X 106 pascals (Pa) Velocity 1 mile per hour (mph) = 0.4470 meter per second (m/s) 1.609 kilometers per hour (km/h) Volume 1 gallon = 3.785 X 10"^ cubic meters (m^) Volume/Time 1 cubic foot per minute (cfm) = 4.719 X 10~* cubic meters per second (m^s) References NBS Special Publication, SP330, 1974 Edition, "The International System of Units." ISO International Standard 1000 (1973 Edition), "SI Units and Recommendations for Use of Their Multiples." E380-72 ASTM Metric Practice Guide (American National Standard Z210.1). Disclaimer: Certain trade names and company products are identified in order to adequately specify the ex- perimental procedure. In no case does such identification imply recommendation or endorsement by the National Bureau of Standards, nor does it imply that the products are necessarily the best available for the purpose. iv Contents page Units and Symbols iv Introduction: E. Passaglia vii Intent of the Symposium: D. C. Drucker xi Modes of Failure Session I: 1. What We Can Learn from the Examination of Service Failures: J. A. Bennett 3 2. Failure by Fatigue: A. J. McEvily 13 Session II : 1. Failure by Stress Corrosion Cracking—Current Approaches toward Failure Prediction: J. Kruger 27 2. Elastohydrodynamics in Concentrated Contacts: H. S. Cheng 41 3. Failure in Gears and Related Machine Components: R. A. Wilde 55 4. Bearing Damage Analysis: R. L. Widner and W. E. Littmann* 67 Session III: 1. Anti-friction Bearing Design, Inspection and Recycling: K. M. Glaesner 87 2. Holographic NDI of P-3 Wing Plank Splices: A. J. Koury, M. J. Devine, J. F. Erthal* and P. G. Bhuta 93 Consequences of Mechanical Failures Session III: 3. Economic Considerations in Failure Prevention: H. E. Morgan 107 4. Economic Impact of Tribology: H. P. Jost 117 Session IV: 1. Nuclear Power Plant Safety: P. A. Morris 143 2. Mechanical Failures and Public Expectations of Safe Transportation: H. H. Wakeland 153 3. Public Safety and Construction Surety: J. Feld 165 4. The People Considerations in Automotive Service: F. J. Uhlig 171 Implications of Mechanical Failures Session V: 1. Mechanical Failure: Implication for Science: J. P. Hirth 181 2. Implications for Action for Engineering: H. W. Paxton 193 3. Mechanical Reliability—Implications for Engineering, Manufacturing and Design: W. D. Compton 199 4. Implications for Action—Industry: J. E. Ryan 209 Session VI: 1. The Implications of Mechanical Failures for Consumer Product Safety—Vice Versa: L. M. Kushner 215 2. Mechanical Failure—A Material Matter: R. W. Roberts ; 221 *Indicates speaker when a paper had more than one author. List of Registrants at the 20th MFPG Meeting 227 The following registrants gave presentations at the symposium, but did not submit the manuscript for publication: R. W. Staehle, "Mechanical Failure: An Overview," Session I H. Corten, "Failure by Brittle Fracture," Session 1 V Introduction Elio Passaglia Executive Secretary, MFPG Institute for Materials Research National Bureau of Standards Washington, D.C. 20234 Mechanical failures are a pervasive fact of life in our society. Ranging from the failure of small items that all of us have experienced and that many of us take for granted, to the failure of a large complex structure that often becomes front page news, they have undesirable consequences for our society. The large ones many times cause loss of life or cause serious injury to many people. The minor ones sometimes also cause loss of life or injury, and they always cause frustration and anger on the part of the one to whom they occur. Always they cause loss of valuable material, and have undesirable social and economic consequences. Thus it is not surprising that a large segment of our technological community devotes its efforts to the prevention of mechanical failures, and that numerous agencies of the Government are charged with the responsibility of preventing mechanical failure. These efforts to prevent mechanical failures are wide ranging indeed. They go from the material scientist studying the fundamentals of fracture, to the metallurgist assuring that a steel forging meets specification, to the design engineer designing a new bridge, to the Government administrator considering new specifications to reduce the incidence of me- chanical failures. Yet despite these efforts mechanical failures continue to occur, and continue to present a problem whose solution, if possible, would have highly desirable consequences for our society. The Symposium, the proceedings of which are presented in this volume, was designed to explore with a broad brush the various aspects of mechanical failures. We say "with a broad brush" because no symposium of reasonable length could conceivably grope with all the various aspects of the problem. All that can be done in a reasonable time is to define the problem, not discuss in depth its many detailed aspects and ramifications. As the organizers of the Symposium saw it, the definition of the problem of mechanical failures involved three aspects: (1) The modes of failure (2) The consequences of failure (3) The implications (for action) of the occurrence of failures. Thus the Symposium was divided into sections discussing each of these parts. The section on the modes of failure was constructed on the basis that all failures of machine and structural components are eventually traced to material failure. Following this basis, the investigation of large numbers of mechanical failures shows that the primary modes of failure are fatigue, stress corrosion, and brittle fracture. Thus these topics are treated in individual papers in the Symposium, since they are of central importance to the problem of mechanical failure prevention. The reason this is so, and that these modes of material failure are the most common, is that while adequate design pro- cedures are available for designing against simple overload, procedures to design against fatigue, stress corrosion, or brittle fracture, are either not available or are only now beginning to be used. Thus these modes of failure continue to be prominent because design methods are not yet available to deal ade- quately with them. These topics are dealt with in papers by McEvily, Kruger and Corten.^ When components are assembled into machines, particularly where moving parts are involved, the situation becomes far more complicated. Here we have the situation where one part interacts with another across their surfaces, and this leads to the whole problem of wear in its various forms, and its prevention. Various techniques are used to prevent mechanical failures in these circumstances. These include the use of fluid, solid or semi-solid films to separate the parts that are in relative motion, and the "components" aspects of mechanical failures thus refers to the design, kinds of damage asso- Corten's manuscript was not submined for piili] ir;\iion. vii ciated with various types of components, and inspection. These topics are discussed in papers by Widner and Littmann, and by Wilde, and one of the underlying theories of the lubrication process, elasto- hydrodynamics, is described in some detail by Cheng.