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pa4_oct7_09

# pa4_oct7_09 - steady-state creep rate for these test...

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AERO3700 PA 4 Questions Only Tuesday Oct 7 Purpose: Familiarization and review of fatigue and creep using the notes and textbook. Attendance will be taken – be sure to show the TA your AERO3700 work. Callister: 8.24. 8.28 (fig 8.31, 6.1 mm), 8:30 (fig 8.30, 10,000 hrs) A. The crack growth rate of an Al alloy in the linear region of the da/dN vs Δ K curve is given by da/dN = 8.5 x 10 -12 Δ K 4 where Δ K has units of MPa m ½ and da/dN has units of m/cycle. A large component of this allow is observed to have an existing flow of 2a = 5 mm (Y = 1). The fracture toughness is 27 MPa m 1/2 . Estimate the fatigue life for this component if the applied stress varies from 0 to 200 MPa, (Ans: N = 1696 cycles) B . The following creep data were obtained for a Ti alloy at 350 MPa and 400 o C. Plot the creep strain vs time (hours). Show the initial elastic strain and determine the
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Unformatted text preview: steady-state creep rate for these test conditions. (Ans: about 4.4 x 10-7 hr-1 ) (Note how strain is elastic + creep strain, recall ε tot = ε el +... + ε cr ) Strain m/m Time hr 0.010 x 10-2 2 0.030 x 10-2 18 0.050 x 10-2 40 0.075 x 10-2 80 0.090 x 10-2 120 0.110 x 10-2 160 C . A creep test of a Ni-based alloy is carried out at 815 o C. The following data were obtained: 1% strain at 10 hrs; 2% strain at 200 hrs; 4% strain at 2000 hrs; 6% strain at 4000 hrs; localization of failure region at 5000 hrs (this is also called neck-down); rupture at 5500 hrs. a) Plot the appropriate creep-rupture cure of strain vs. time. b) Estimate the steady-state creep rate. (Ans: 0.001% strain) D . Give two reasons why shot peening improves fatigue life. M. McDill October 2009 AERO3700 - PA4...
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