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  IEI AGARDograph No. 257 * Pnictwical Applications of Fracture Mechanics SI DTIC SP 12 T9OJ DISTRIBUTION AND AVAILABILITY -~ ON SACK COVkR  ('qFAG ~-AG-2 57/ NORTH ATLANTIC TREATY ORGANIZATIONADVISORY GROUP FOR AEROSPACE RESEARCH AND DEVELOPMENT(ORGANISATION DU TRAITE DE L'ATLANTIQUE NORD) AGARDograph No.257 SPRACTICAL APPLICA-TIO)NS OF FRACTURE MECHANICS S Edited by YI-'jI Harold LiebowitzJ Dean and Profei-r orrnimneering and Applied ScienceSchool of Engineering and Applied Science George Washington UniversityWashington DC 20052 USA This AGARDograph was sponsored by the Structures and Materials Panel of AGARD. 0 .0 1-)  THE MISSION OF AGARD The mission of AGARD is to bring together the leading personalities of the NATO nations in the fields of science and technology relating to aerospace for the following purposes: - Exchanging of scientific and technical information; - Continuously stimulating advances in the aerospace sciences relevant to strengthening the common defence posture; - Improving the co-operation among member nations in aerospace research and development; - Providing scientific and technical advice and assistance to the North Atlantic Military Committee in the field of aerospace research and development; - Rendering scientific and technical assistance, as requested, to other NATO bodies and to member nations in connection with research and development problems in the aerospace field; - Providing assistance to member nations for the purpose of increasing their scientific and technical potential; - Recommending effective ways for the member nations to use their research and development capabilities for the common benefit of the NATO community.The highest authority within AGA RD is the National Delegates Board consisting of officially appointed seniorrepresentatives from each member nation. The mission of AGARD is carried out through the Panels which arecomposed of experts appointed by the National Delegates, the Consultant and Exchange Programme and the AerospaceApplications Studies Programme. The results of AGARD work are reported to the member nations and the NATO Authoiities through the AGARD series of publications of which this is one. Participation in AGARD activities is by invitation only and is normally limited to citizens of the NATO nations. T. ,,unrent of this publication has been reproduceddirectly from material supplied by AGARD or the authors. ,Accession ForNTIS GF.A&I MCx TAB jtkm2oancled Justifioat n...... Published May 1980 Dit to -... Copyright O AGARD 1980 sil. .Cn, S - All Rights Reserved Avail aid/Or ISBN 92-835-1359-2 Dist. special Printed by Technical Editing and Repmduction LtdHarford House, 7-9 Charlotte St. London, WIP IHD a  PREFACEThe Structures and Materials Panel of the NATO Advisory Group for Aerospace Research and Development(AGARD) consists of engineers, scientist- and technical administrators from industry, government and universities throughout the NATO nations, and is concerned with the advancement of aerospace research and development and the application of the results to the design and construction of, and the solution of problems arising during the operation of NATO military vehicles, systems and equipment. The biannual Panel Meetings provide forums for specialist multi-national discussions of problems and research information and for initiating and monitoring cooperative studies and experimental programmes. The Panel also provides a mechanism for the planning, preparation and distribution ofsurveys and reports on the present state of knowledge in technical areas within the fields of Structures and Materials selected because of their importance and their relevance to current or future problems facing the NATO aerospace community. In recent years, fracture mechanics became an important factor in aircraft design and development. Even though considerable progress has been made with the application of advanced calculation methods and computer programmesimproving the accuracy of flight-load prediction and calculated stresses, it has to be envisaged that cracks in aircraftstructures may occur, initiated during manufacture or in service. These initial cracks will propagate under service loading and finally could lead to a complete failure of the part, i.e. the structure. Therefore, adequate measures have to be taken by the designer to avoid catastrophic service failures.With the aim of ensuring the required safety in aircraft operation, different design philosophies have been developed in the last twenty years. However, it was learned by service experience that the fail-safe and safe-life philosophies applied in the fifties and sixties were not satisfactory. The progressing development of fracture mechanics theory opened new possibilities to investigate the fracture behaviour of aircraft components and predicting crack propagation and residual strength characteristics. New testing techniques were developed to determine the required material data necessary for fracture mechanical calculation. The application of fracture mechanics concepts in aircraft design, the theoretical and experimental investigation of the fracture behaviour of complete aircraft structures are also reflected in MIL-STD-83444.Realizing the different problems in the field of aerospace-structures experienced with new high-strength materials, e.g. flaw susceptibility, stress corrosion, crack detection, crack propagation and residual strength aspects, the Panel was of the opinion that the existing knowledge and the experience gained by the application of fracture mechanics concepts in aircraft design should be collected and made available to engineers and designers in a handbook on Practical Applica- tions of Fracture Mechanics. The Panel set up a Fracture Mechanics Working Group to commission and monitor the preparation of a comprehensive survey of the pertinent information presently available on the application of fracture mechanics to the fracture of metals and actual structures. In addition, this work had to cover engine components,built-up structures, integral structures, joints, lugs and fasteners, forgings, effects of stress corrosion and problems of scatter including fundamentals of determining stress concentration factors, fatigue crack propagation and residual strengthcalculations. It was recognized that fracture mechanics was an inter-disciplinary growth area of research of ever increasing importance to those people concerned with the design and operational management of aircraft, especially in the light of the modern airframe fail-safe design philosophy and aircraft safety. It was therefore decided that the resultingcritical survey report should be given a wide circulation within the NATO nations. The Panel was very fortunate from the outset in securing the services as Coordinator and Editor of Dean Harold Liebowitz, School of Engineering and Applied Science, The George Washington University, Washington, D.C., a world renowned expert on the fracture of material.. An essential feature of AGARD activities is the pooling of relevant knowledge within the NATO nations and the bringing together of specialists for informed discussions and debate on the subject concerned. This occurred in fullmeasure within the Fracture Mechanics Working Group and the Panel is indebted not only to Dean H.Liebowitz, thL Coo-dinator and Editor for his outstanding efforts but especially to the many contributors to the monograph Practical Applications of Fracture Mechanics itself from the nations: Canada, Belgium, France, Germany, Italy,Netherlands, UK and USA. H.J.ZOCHER Chairman, Fracture Mechanics Working Group AGARD Structures and Materials PanelMunich. Germany January 25. 1980 6 ,I
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