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HW9 solutions - HOMEWORK 9 Name ENMA 300 DUE Thursday 1 A...

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HOMEWORK # 9 Name _____________________________________________ ENMA 300 DUE: Thursday, November 11, 2010 1. A through-thickness crack of length 0.5 mm grows from a 10 mm diameter hole in a 25 mm thick plate of hardened Al that has the properties listed below. The crack is subjected to a nominal stress of 200 MPa, perpendicular to the crack. (Y=3.36) Mechanical Properties Value Fracture Toughness (K IC ) 35 MPa-m 1/2 Yield Strength 350 MPa Tensile Strength 425 MPa a) Would this loading cause unstable crack growth at this crack length? m MPa m MPa a Y K 6 . 26 ) 10 5 ( ) 200 )( 36 . 3 ( 4 = × = = - π π σ K < K IC so the loading will NOT cause unstable crack growth at this length. b) If not, at what loading level would unstable crack growth be observed for this crack length? MPa m m MPa a Y K C C C IC 8 . 262 ) 10 5 ( 36 . 3 35 4 = × = = - σ π σ π σ c) At the original loading of 200 MPa, what crack length would be the minimum needed to cause unstable crack growth. mm a a MPa m MPa a Y K C C C IC 86 . 0 ) 200 ( 36 . 3 35 = = = π π σ d) If there was a bolt through the hole with a 15 mm diameter head, would the critical crack at 200 MPa be detectable and why?
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