AAE552-Session12

AAE552-Session12 - AAE 552 Spring 2009 A. F. Grandt AAE...

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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 12 – 9 February 2009 2 Contact Information Alten F. (Skip) Grandt, Jr. Email: aae552@ecn.purdue.edu 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 11 6 February 2009 Last Time: Damage Tolerant concepts Today: Proof testing Visual inspection 4 Assignment Please read Textbook : Read 4.3 Chapter 10 Webpage powerpoint references “Visual inspection” – collaboration for NDT education “Endoscopes: The Borescope for Humans,” Christine Poulin AAE 552 term paper 5 secondary skin crack easily detectable from outside skin broken stringer – primary failure not detectable from outside Multi load path Scenario 1: Primary failure not detectable Fig. 16.14 6 Crack size Time safe inspection period stringer fracture detectable skin crack skin fracture Multi load path Scenario 1: Primary failure not detectable Fig. 16.14
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AAE 552 Spring 2009 – A. F. Grandt 2 7 Damage Tolerant Design Considerations Keys to damage tolerant design Structural configurations (Section 16.5) Impede or arrest crack growth Redundant structure via multiple load paths Materials selection (Section 16.6) High toughness to resist fracture Superior fatigue crack growth and corrosion resistance to delay growth to critical damage size 8 Tougher coupling material individual segments of pipeline longitudinal crack Schematic Pipeline Showing “Tough Material” Crack Stopper (Fig. 16.11) 9 Schematic Crack Arrestment by “Flapping” (Fig. 16.10) “Flap” develops when longitudinal crack turns direction at frames – allows pressure to escape escaping pressure unloads structure internally pressurized cylinder longitudinal crack internal frames 10 Proof Testing as NDE Goal : interpret results in terms of initial crack size Approach : Assume structure cracked and “almost” fractures K proof = K c = σ proof ( π a p ) 1/2 β (a p ) Solve for a p = largest possible crack that could be present after proof test σ o σ proof = α σ o σ time σ a p 11 Crack Size Calculation Assume fracture “almost” occurs during proof test K proof = K c = σ proof ( π a p ) 1/2 β (a p ) Know Fracture toughness K c Proof load σ proof Assumed crack geometry: β (a) Solve for crack length a p K proof = K c = σ proof ( π a p ) 1/2 β (a p ) Doesn’t prove crack of this size is present But, guarantees can’t be bigger crack 12 Proof Testing a Critical Crack Size (a) Elapsed Cycles Stress ( σ ) a f Guaranteed Life Proof Operating stress σ o σ p σ β( β( a 29 29 29 (a) 1/2 = constant = K c a i a f a i
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AAE 552 Spring 2009 – A. F. Grandt 3 13 F-111 “Cold” Proof Test Initiated in
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This note was uploaded on 11/04/2010 for the course AAE 552 taught by Professor Longuski during the Spring '10 term at IUPUI.

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AAE552-Session12 - AAE 552 Spring 2009 A. F. Grandt AAE...

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