Microtopography for ductile fracture process characterization Part 2: application for CTOA analysis |
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| Affiliation: | 1. Idaho National Engineering and Environmental Laboratory, P.O. Box 1625, Idaho Falls, ID 83415-2218, USA;2. Massachusetts Institute of Technology, 77 Massachusetts Avenue, Rm 1-304, Cambridge, MA 02139, USA;1. Institute of Plasma Physics Chinese Academy of Sciences, Hefei, China;2. University of Science and Technology of China, Hefei, China;1. Department of Materials & Metallurgical Engineering, PEC University of Technology, Chandigarh PIN-160012, India;2. Department of Materials Science and Engineering, Indian Institute of Technology, Kanpur PIN-208016, India;1. School of Aerospace Engineering, Tsinghua University, Beijing, China;2. Department of Mechanical Engineering, University of Bristol, Bristol BS8 1TR, United Kingdom;1. Nuclear Energy and Safety, Laboratory for Nuclear Materials, Paul Scherrer Institut, Villigen-PSI 5232, Switzerland;2. Department of Metallurgical Engineering, Indian Institute of Technology (Banaras Hindu University), Varanasi 221005, India;3. School of Material Science and Technology, Indian Institute of Technology (Banaras Hindu University), Varanasi 221005, India;4. Institute of Nuclear and Physical Engineering, Slovak University of Technology, Ilkovicova 3, Bratislava 81219, Slovakia |
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| Abstract: | The crack tip opening angle (CTOA) is seeing increased use to characterize fracture in so-called “low constraint” geometries, such as thin sheet aerospace structures and thin-walled pipes. With this increase in application comes a need to more fully understand and measure actual CTOA behavior. CTOA is a measure of the material response during ductile fracture, a “crack tip response function”. In some range of crack extension following growth initiation, a constant value of CTOA is often assumed. However, many questions concerning the use of CTOA as a material response-characterizing parameter remain. For example, when is CTOA truly constant? What three-dimensional effects may be involved (even in thin sheet material)? What are the effects of crack tunneling on general CTOA behavior? How do laboratory specimen measurements of CTOA compare to actual structural behavior?Measurements of CTOA on the outer surface of test specimens reveal little about three-dimensional effects in the specimen interior, and the actual measurements themselves are frequently difficult. The Idaho National Engineering and Environmental Laboratory (INEEL) use their microtopography system to collect data from the actual fracture surfaces following a test. Analyses of these data provide full three-dimensional CTOA distributions, at any amount of crack extension. The analysis is accomplished using only a single specimen and is performed entirely after the completion of a test. The resultant CTOA distributions allow development of full and effective understanding of CTOA behaviors. This paper presents underlying principles, various sources of measurement error and their corrections, and experimental and analytical verification of CTOA analysis with the microtopography method. |
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