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AAE552-Session10

AAE552-Session10 - 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 10 – 4 February 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 10 4 February 2009 Last Time: Evaluating maturity of technology Overview LEFM Today: LEFM Fracture Fatigue Inspection intervals Proof testing 4 Assignment Please read Textbook : Skim Chapter 3 Read 4.3 5 Time Early Gestation, Primitive Stage Transition Stage Saturation, Mature Stage Performance Potential Technology Maturation “S - Curve” (Fig. 16.20) 6 Criteria for Acceptance of New NDE Methods (Section 16.8) Address real inspection need Capability, economics, etc. Demonstrated for field-level inspections All NDE procedures established & documented Reliability and accuracy demonstrated Confidence in method established Safety concerns addressed
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AAE 552 Spring 2009 – A. F. Grandt 2 7 Predict Crack Growth Goals : Determine crack size that causes fracture (critical crack size) Determine time for sub critical crack to grow to failure size (life, inspection interval) Time (cycles N) Crack size Life 8 Overview of LEFM (see Chapter 3) Goal: Determine critical crack size Discuss fracture criterion Stress intensity factor = constant = K c Determine crack growth life Fatigue crack growth rate related to cyclic stress intensity factor Show how initial crack size influences life Relate to NDE Importance of initial crack size Proof testing 9 Characterize Crack: Objective Find parameter to characterize crack severity Relate lab/application Correlate crack behavior in lab (express material properties) in terms of this parameter Fracture Fatigue crack growth rate da/dN Parameter 10 Stress Intensity Factor K K is a crack parameter Has units of stress (length) 1/2 Relates three variables ) a ( a K β π σ = Geometry Crack length Remote Stress 11 Center-cracked strip Figure 3.2a 2 / 1 W a sec a K = π π σ 8 . 0 W a 2 2a σ σ W K = σ [ π a] 1/2 as a/W 0 12 Edge-cracked strip Figure 3.2b W a σ σ h a W 0 6 . h W 1 0 . a W β K a = σ π a W a W = - + β 112 0 231 10. 55 . . a W a W a W - + 2173 30 39 2 3 4 . . For and K = 1.12 σ [ π a] 1/2 as a/W 0
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AAE 552 Spring 2009 – A. F. Grandt 3 13 c. Figure 3.2c B 2a P P b A ( 29 ( 29 K P B a a b a b = + - π 1 2 At crack tip A P = Concentrated Force B = Thickness Point Loaded Center Crack 2a = crack length b = distance P from crack center 14 Radially Cracked Hole Figure 3.2d 2R a σ σ K a = σ π a R β { When } a R 10 β a R a R
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