_STP_495-1971.pdf

METAL FATIGUE DAMAGE MECHANISM,DETECTION,AVOIDANCE,AND REPAIR With Special Reference to Gas Turbine Components S.S.Manson,editor ASTM SPECIAL TECHNICAL PUBLICATION 495 List price$21.00 04-495000-30 l AMERICAN SOCIETY FOR TESTING AND MATERIALS 1916 Race Street,Philadelphia,Pa.19103?9 by American Society for Testing and Materials 1971 Library of Congress Catalog Card Number:70-158437 NOTE The Society is not responsible,as a body,for the statements and opinions advanced in this publication.Printed in Baltimore,Md.September 1971 Foreword The work presented in the publication Metal Fatigue Damage-Mechanism,Detection,Avoidance,and Repair was sponsored by the ASTM-ASME Joint Committee on the Effect of Temperature on the Properties of Metals and financed by The Metal Properties Council.The Applied Research Panel under the Chairmanship of M.Semchyshen and the Gas Turbine Panel Chaired by G.J.Wile,cooperated in this project.Mr.S.S.Manson,who headed th e Task Group under the Applied Research Panel,was responsible for the coordination of the papers presented in this publication.Related ASTM Publications Fatigue at High Temperature,STP459(1969),$11.25 Effects of Environment and Complex Load History on Fatigue Life,STP 462(1970),$22.00 Manual on Low Cycle Fatigue Testing,STP 465(1969),$12.50 Achievement of High Fatigue Resistance in Metals and Alloys,STP 467(1970),$28.75 Contents Introduction 1 Fatigue Mechanisms in the Sub-Creep Range-J.C Grosskreutz 5 Mechanisms of Fatigue in the Creep Range-C.H.Wells,C.P.Sullivan,and M.Gell 61 Fatigue Damage Detection-J.R.Barton and F.N.Kusenberger 123 Field Practices in the Repair of Fatigue Damaged Jet Engine Components-H.G.Popp,L.G.Wilbers,and K J.Erdeman 228 Avoidance,Control,and Repair of Fatigue Damage-S.S.Manson 254 Copyright by ASTM Intl(all rights reserved);Mon Dec 7 13:17:27 EST 2015Downloaded/printed byUniversity of Washington(University of Washington)pursuant to License Agreement.No further reproductions authorized.STP495-EB/Sep.1971 Introduction Fatigue is one of the most common of the failure mechanisms of gas turbine engine components.Both the cool parts and hot parts are susceptible to this mode of failure,and the origin may be either mechanical or thermal.The importance of fatigue as a limiting factor in jet engine reliability was brought out clearly in a study conducted some time ago by the NACA(the forerunner of the NASA).This study was made in the middle 1950s(Ref 1)on military jet engines,using statistics obtained from Air Force overhaul bases as a framework for the analysis.All the major components studied-bearings,com-pressor blades,combustors,turbine nozzle vanes and buckets,and turbine disks were,to a serious extent,life limited,because of fatigue problems.Some of the problems encountered were due to the high performance demanded of the engines by the military requirements;others were due to the fact that the jet engine was then in its early formative years and experience was limited.How-ever,the major reason for the prevalence of the fatigue problem relates to the very nature of the service to which jet engine components are subjected.High fluctu-ating loads,high temperatures and temperature gradients,frequent starts and stops,stress concentrations resulting from complex geometrical shapes and from surface discontinuities produced by service conditions-all contribute to making the components fatigue-prone.Add to this the fact that light weight and high performance provide the strongest of motivations in gas turbine design and service,and it becomes clear that fatigue will continue to be an important limitation in the life of gas turbine engines.The NACA study(Ref 1),it is true,related to gas turbine engines of early design in which information now available could not be incorporated.Also,in military engines,performance comes first;cost of overhaul and frequent part replacement is accepted as an appropriate price to pay for the high performance sought.It might be properly asked whether the picture has not changed in the intervening years,and whether trade-offs between performance and life cannot be suitably made in commercial gas turbines for both stationary and aircraft use.To a limited extent the answer to both of these questions is affirmative.Much research has been conducted in the intervening years since the NACA study was made,and this information can be well used to increase fatigue life of corn-1 National Aeronautics and Space Administration Lewis Center Staff,Factors that Affect Operational Reliability of Turbojet Engines,NASA TR R-54,1960.Copyright*1971 by ASTM International www.astm.org Copyright by ASTM Intl(all rights reserved);Mon Dec 7 13:17:27 EST 2015Downloaded/printed byUniversity of Washington(University of Washington)pursuant to License Agreement.No further reproductions authorized.2 METAL FATIGUE DAMAGE ponent parts.Furthermore,the trade-off constants are reasonably well known;increase in life for a reduction in temperature can be reasonab