# HW _9c - 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) a) Would this loading cause unstable crack growth at this crack length? b) If not, at what loading level would unstable crack growth be observed for this crack length? c) At the original loading of 200 MPa, what crack length would be the minimum needed to cause unstable crack growth. 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? e) Is the thickness of the plate sufficient to make the calculation valid? And why? Mechanical Properties Value Fracture Toughness (K IC ) 35 MPa-m 1/2 Yield Strength 350 MPa Tensile Strength 425 MPa

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2. The fatigue data for a steel alloy are given as follows (Callister 9.12): Stress Amplitude [MPa (ksi)] Cycles to failure

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