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AAE552-Session8

AAE552-Session8 - AAE 552 Spring 2009 A F Grandt AAE 552...

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AAE 552 Spring 2009 – A. F. Grandt 1 1 AAE 552: Nondestructive Evaluation of Structures and Materials A. F. Grandt, Jr. Professor of Aeronautics and Astronautics Purdue University W. Lafayette, IN 47907 Session 8 – 30 January 2009 2 Contact Information Alten F. (Skip) Grandt, Jr. Email: [email protected] Telephone: Office: 765-494-5141 Home: 765-463-4276 FAX: 765-494-0307 Course webpage accessed at: http://www.itap.purdue.edu/tlt/blackboard 3 AAE 552 Session 7 28 January 2009 Last Time: POD test requirements Today: NDE design requirements Evaluating maturity of technology 4 Assignment Please read : Textbook Chapter 16.1 – 16.3, 16.5, 16.7-16.9 Web page NASA NDE Guidelines and Requirements 1978 USAF POD Study Please Submit : Session 9 (2 February) – Abstract for Paper #1 – see webpage for more details 5 Possible Inspection Results (Fig. 4.7) A1 -- Cracks are detected (correct rejection) Type II error (Safety problem) A2 -- cracks are undetected (incorrect acceptance) N1 specimens contain cracks Type I error (Economic problem ) A3 -- cracks are detected (false rejection ) A4 -- no cracks are detected (correct acceptance) N2 specimens are uncracked N total specimens N = N1 + N2 POD = A1/N1 6 Probability of Detection Note: will be “scatter” in experimentally determined POD vs a curve – determine “confidence” bounds Probability of Detection (POD) 1.0 0.9 0.0 Crack Size (a) a nde 90/95 Crack Size 95% Confidence Mean 90% POD 95% confidence Figure 4.10
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AAE 552 Spring 2009 – A. F. Grandt 2 7 Sun Tzu: The Art of War (circa 500 B.C.) Eliminate Errors “He wins his battles by making no mistakes. Making no mistakes is what establishes the certainty of victory, for it means conquering an enemy that is already defeated ” “1978 Have Cracks Will Travel” 8 9 Conclusions: 1970’s USAF NDE Round Robin NDE reliability less than previously assumed could not satisfy USAF damage tolerant design requirements MIL-A-83444 assumes ~ 0.25 inch crack 90/95 reliability could not be attained for any flaw size by “average” technician difficult to achieve 50/95 for 0.5 inch crack 10 Conclusions: 1970’s USAF NDE Round Robin (cont) “Average” capability in field and depot was uniform little difference between installations, commands, equipment, … Significant difference among individuals >> human factors important Exception : Superior performance at one installation due to individual proficiency organization exclusively dedicated to NDI skilled staff acquired by selective process certification procedure in place 11 USCG Search and Rescue Probability of Detection Goal : describe POD issues associated with U.S. Coast Guard visual search and rescue (Thanks to LCDR Erik Langenbacher) Reference : U. S. Coast Guard Addendum to the United States National SAR Supplement Appendix H – Search Planning Handbook 12 Search Coverage Factor ) ( ) ( ) ( S Spacing Track W Width Sweep C Factor Coverage = S W C = 1.0 (S = W) C = 0.5 (S = 2W) COVERAGE FACTOR, C = W / S W W W S C = 1 C = 0.5
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AAE 552 Spring 2009 – A. F. Grandt 3 13 POD vs Coverage Factor 0% 10% 20% 30% 40% 50% 60% 70% 80% 90% 100% 0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1 1.1 1.2 1.3 1.4 1.5 1.6 1.7 1.8 1.9 2 Coverage Factor
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