HW9 ENME382 S10 Section0201 solution

# HW9 ENME382 S10 Section0201 solution - Homework 9 Solutions...

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ENME 382 1.) a. Make an S-N Plot (stress amplitude versus logarithm cycles to failure) use these data. b. What is the fatigue limit for this alloy? From the S-N diagram, the fatigue limit, or S fat , is approximately 290MPa. c. Determine the fatigue lifetimes at stress amplitudes of 415MPa (60,000PSI) and 275MPa (40,000PSI). At 415MPa, the diagram S-N chart would predict a lifetime of about 65,000 cycles. At 275MPa, the life is infinite since it falls below the fatigue limit (S < S fat ) d. Estimate the fatigue strengths at 2x10 4 and 6x10 5 cycles. Via S-N Chart, 2x10 4 cycles would be approximately 447MPa. Via S-N Chart, 6x10 5 cycles would be approximately 332MPa. 2.) a.) Determine the maximum length of surface flaw that is possible without fracture. σ c = {(2*E* γ s )/( π *a)} 1/2 40x10 6 Pa = {(2*69x10 9 Pa*0.3J/m 2 )/( π *a)} 1/2 a = 0.000008m or 0.008mm (pretty small) STEEL ALLOY 0 100 200 300 400 500 1000 100000 10000000 1000000000 Number of Cycles, N Stress (MPa), S

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HW9 ENME382 S10 Section0201 solution - Homework 9 Solutions...

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