About the
Fracture and Fatigue Division
The mission of the Fracture and Fatigue Division of the Society for Experimental Mechanics is to advance the state of knowledge in the areas of fracture mechanics and fatigue through the timely sharing of research results. The division meets each year at the Annual Spring Conference. Every fourth year the Annual Spring Conference is also the SEM International Congress, as it will be in the year 2000 (June 5-8 at The Radisson Hotel Universal Orlando in Orlando, Florida. Other conferences are also sponsored by SEM). Our work on fracture and fatigue overlaps with the efforts of other divisions resulting in a cooperative effort between researchers from different areas of experimental mechanics.
Background on Fracture and Fatigue
The Fracture and Fatigue Division of the Society for Experimental Mechanics is concerned with the development and dissemination of research in fracture mechanics and fatigue. The modern era of fracture mechanics started during World War II with the failure of U.S. shipping vessels on loan to the United Kingdom. These ships developed fatal cracks in their hulls for a number of reasons that were not well understood at the time. These failures provided the motivation for subsequent research efforts at the U.S. Naval Research Laboratory that later became the basis for linear elastic fracture mechanics. Much of the credit for this early work on fracture can be given to the late George Irwin and his associates at the U.S. Naval Research Laboratory. Subsequently, the principles of linear elastic fracture mechanics were applied to a variety of situations that helped validate the principles and at the same time encouraged more widespread use. Examples from these early years include large steam turbine rotors owned by General Electric and the propagation of fatigue cracks in De Havilland Comet jets.
During the post World War II era, the field of fracture mechanics expanded to include more ductile materials, allowing engineers to use fracture mechanics in a wider range of applications, for example, in materials found in nuclear reactor sites. The related fracture parameter that developed during this time was the J contour integral. Also during this time, researchers learned to predict fatigue crack growth rates in metals using fracture mechanics concepts.
With the development of linear elastic fracture mechanics, elastic-plastic fracture mechanics, and fatigue crack growth laws based on fracture mechanics principles, the field of fracture and fatigue has matured. A new era in fracture and fatigue research is demonstrated by research topics that incorporate increasingly complex phenomena, such as the prediction of crack growth in composites and other nonmetals, research on dynamic fracture mechanics, and research on interfacial cracking phenomena.
Recent Efforts in Fracture and Fatigue
A large part of the Fracture and Fatigue Division's activities take place each year at the SEM Spring Conference. The division meets at these conferences to discuss current business and future trends in fracture and fatigue research. Additionally, we host a number of technical sessions that provide for presentation of fracture and fatigue research, discussions, and interactions. The participants also publish extended abstracts in an abstract proceedings and may also contribute to a related post-conference proceedings.
The Society for Experimental Mechanics held the 1998 Spring Conference in Houston, Texas, and the 1999 conference in Cincinnati, Ohio. The 1999 conference included multiple sessions on general fracture and fatigue as well as more specialized sessions on hybrid experimental/numerical methods, advanced materials, and the mechanics of joints. Two examples of our recent work are described in more detail below. The first relates to dynamic fracture measurements of interfacial cracks and the second relates to minimum size requirements for mode II fracture specimens.
Recent Efforts
Dynamic Interfacial Fracture -- This work was presented by Kavaturu and Shukla in the 1998 Spring Conference.1 The chief innovation was the use of a special specimen to propagate a stress wave across the cracked interface between two materials. The specimen was explosively loaded to induce the desired high loading rates. Also, one half of The specimen was photoelastic so that the researchers could collect fringe patterns that they subsequently analyzed for information on crack growth, velocity, and stress intensity factors.
Here is a schematic of the explosively loaded specimen used in the dynamic
interfacial fracture experiments.
Shown here is one of the photoelastic fringe patterns of the propagating
interfacial crack.
Minimum Size Requirements for Mode II Fracture Specimens-- This research was presented at the 1999 Spring Conference.2 In previous efforts, the American Society for Testing and Materials established certain specimen size requirements for mode I plane strain fracture toughness testing. These requirements ensure validity of the experimental measurements by (1) ensuring that plane strain conditions exist at the center of the specimen and(2) ensuring that the plastic zone size near the crack tip is small compared with other in-plane dimensions. The relationship for these tests is often shown as
B, a, (W-a) > 2.5(KIC/Sys)2
Where B is the specimen thickness, a is the crack length,W is the specimen width, KIC is the plane strain fracture toughness, and Sys is the yield strength of the material. This is illustrated in the figure below.
This is a schematic of the minimum size requirements for mode I loading of a
fracture specimen.
These requirements are well accepted and have been used for some years, however, there is not yet an accepted analogous set of size requirements for when mode II loading is considered. In a recent work2, researchers established similar mode II requirements by considering the size and shape of the mode II plastic zones in plane stress and plane strain. The plastic zone sizes were evaluated using finite element methods and the resulting size requirements were validated using experiments. The figures below show the mode II plastic zone shapes (and relative sizes) for plane stress and plane strain, and also the experimental data that verifies the size restrictions for mode II fracture, which are given as
B > 0.8 (KIIC/Sys)2
H, (W-a) > 10 (KIIC/Sys)2
Here the mode II plane strain fracture toughness is KIIC, and the other variables are as described above.
Here are the plastic zone shapes and sizes for mode II loading (for comparison,
see the other figure above).
These experimental results show the dependence of fracture toughness for mode I
loading (upper diagrams) and mode II loading (lower diagrams) on specimen
thickness (left diagrams) and in-plane specimen dimensions (right diagrams).
1 Kavaturu, M. and Shukla, A., "Subsonic
Fracture of Inclined and Curved Interfaces", Proceedings of the SEM Spring
Conference on Experimental and Applied Mechanics, Houston, Texas, June 1-3,
323-326 (1998).
2 Kalthoff, J. F. and Hiese, W., "Plane
Strain Small Scale Yielding Mode-II Fracture", Proceedings of the SEM
Spring Conference on Experimental and Applied Mechanics, Cincinnati, Ohio, June
7-9, 47-50 (1999).
Future Directions in Fracture and Fatigue
The year 2000 SEM International Congress will convene in Orlando, Florida, from June 5-8. During this conference, the Fracture and Fatigue Division will host two sessions on Micromechanisms in Fracture and Fatigue and two sessions on Validation of Computational Models in Fracture and Fatigue. A session on Fracture and Fatigue Issues in Electronic Packaging will be cosponsored by the Fracture and Fatigue Division and the Electronics Packaging Division.
In addition to these new sessions at the conference, members of the Fracture and Fatigue Division will be exploring new areas of fracture and fatigue research. A number of advanced material issues (MEMS, nanomaterials, functionally graded materials, and biomaterials) are being addressed, as well as composite materials issues (for example, coatings, thin films, and interfaces).
It is hoped that these research efforts will provide useful results for the upcoming millennium. However, a large portion of our membership is from academia, so we are also interested in the teaching of fundamental fracture and fatigue mechanics. Possibilities (still under discussion) include a short course on fracture mechanics, and also a tutorial on case studies in Fracture and Fatigue to be held during one of the conferences.
Links Related to the Fracture and Fatigue Division
The following links may be useful to those researching fracture and fatigue issues, or to experimental mechanics in general:
Links to Other Engineering and Professional Societies
American Society of Testing and Materials
American Society of Mechanical Engineers
American Society of Civil Engineers
American Society of Engineering Education
Sigma Xi (Scientific Research Society)
Links to Fracture and Fatigue
Publications
Elsevier Science Publishing (Publishers of Engineering Fracture Mechanics and Theoretical and Applied Fracture Mechanics)
Kluwer Publishing (Publishers of The International Journal of Fracture)
List of Officers in Fracture and Fatigue Division
|
TITLE |
NAME |
ADDRESS |
EMAIL |
|
Chair |
Arup Maji |
Air Force Research
Laboratory, AFRL/VSDV, 3550 Aberdeen Ave., SE, Albuquerque, New Mexico
87117-5776 |
|
|
Vice-Chair |
Hareesh Tippur |
Auburn University,
Dept. Of Mechanical Engineering, 202 Ross Hall, Auburn, Alabama 36849 |
|
|
Secretary |
Tim Miller |
Air Force Research
Laboratory, AFRL/PRSM, 10 East Saturn Blvd., Edwards AFB, California 93524 |
|
|
Web Page
Development |
Tim Miller |
Air Force Research
Laboratory, AFRL/PRSM, 10 East Saturn Blvd., Edwards AFB, California 93524 |
Fracture and Fatigue Site Development -Tim Miller tim_miller@ple.af.mil
Last updated: August 1999