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ME 3180 - Mechanical Engineering Design

ME 3180 - Mechanical Engineering Design. Example #1. Example #1. Given:

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ME 3180 - Mechanical Engineering Design

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  1. ME 3180 - Mechanical Engineering Design Example #1

  2. Example #1 • Given: • The pressure vessel lids of nuclear power plants are bolted down to seal the high pressure exerted by the water vapor ( in a boiler reactor) or the pressurized water ( in a pressurized water reactor). The bolts are so heavily stressed that they are replaced after the reactors are opened 25 times. A 20% decrease in stress would give 104 cycles of life. The ultimate strength is 1080MPa. How low does the stress needs to be to give a life of 104 cycles?

  3. Example #1 • Solution: • Type of material was not given; therefore we can’t calculate Marian factors (fatigue modifying factors). • For axial load: S’e = 0.45Sut and Sf at 103 cycles = 0.75Sut • Sf = aNb (eq 7-5) : log(Sf) =log(a) + b.log(N) • Sf = (1350)(104)-0.07395 (eq 7-5) • Sf = 683.2 MPa • The stress need to be decreased to 683.2 MPa to give 104 cycles. eq 7-6

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