AAE552-Session11

AAE552-Session11 - AAE 552 Spring 2009 A. F. Grandt 1 1 AAE...

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Unformatted text preview: 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 11 6 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: Overview LEFM Fracture example Fatigue crack growth Today: LEFM determination of Inspection intervals Damage Tolerant concepts Proof testing 4 Assignment Please read Textbook : Skim Chapter 3 Read 16.5 16.6 Read 4.3 5 Fracture Toughness Criterion Geometry Crack length Remote Stress t tan cons ) a ( a K c = = Material Criterion correlates coupon fracture with structure Note : are limitations and thickness effects associated with crack tip plasticity discuss later 6 Fatigue Crack Growth Criterion Objective : Determine a criterion that specifies cyclic growth of pre-existent cracks Relate cyclic load, crack size, geometry, material Correlate lab tests with structure Evaluate materials Approach : Assume that the cyclic stress intensity factor controls fatigue crack growth rate Verify experimentally AAE 552 Spring 2009 A. F. Grandt 2 7 Correlate Rate da/dN vs K 2a 2a Log K Log da/dN K th K c = K P B a K = a Crack Length (a) Number of Cycles (N) da dN a* da dN Crack Length (a) Number of Cycles (N) 8 da/dN - K is Material Property Log K Log da/dN K th K c K = ( a) 1/2 (a) geometry stress crack length Material da/dN = F( K) 9 Compute Fatigue Life N f a o , a f = initial, final crack sizes F(K) = function of: cyclic stress: , R, . . . crack geometry: (a) crack length: a material N da F K f a a o f = ( ) da dN F K = ( ) time 2a 10 Example 3.2 Life Calculation a Crack = constant time Given : Edge crack in wide plate Initial crack a i Final crack a f Cyclic stress = constant da/dN = C K m Find : cyclic life N f 11 Model da/dN - K Curve Fit data with models such as: da dN C K m = da dN C K R K K m c =-- ( ) 1 C, m, K c are empirical constants R = min/max stress Many other models Paris Forman Log K Log da/dN K th K c da/dN = F ( K) 12 Solution Example 3.2 [ ] = = da C K da C a m m a a a a o f o f 112 ....
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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-Session11 - AAE 552 Spring 2009 A. F. Grandt 1 1 AAE...

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