Page 77 - Analysis and Design of Machine Elements

Strength of Machine Elements
and = 700 MPa. If the combined influence factor is K = 1.5 and the allowable 55
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safety factor is selected as [S] = 1.25, please do the following:
(1) Draw a simplified − diagram of the shaft material;
m a
(2) Find out the safety factor from the diagram;
(3) Calculate the safety factor of the shaft;
(4) Decide the possible failure mode of the shaft;
(5) Propose at least three methods to improve the fatigue strength of the shaft.
5 An element is to be subjected to a spectrum of completely reverse stress. It will
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be cycled at 500 MPa for 10 cycles. Then the stress will be changed to 400 MPa
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for 10 cycles. Finally, the stress will be changed to 350 MPa for 10 cycles. The
material has endurance limit of = 300 MPa, material constant of m = 9and
−1
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critical number of cycles of N = 10 . Calculate the safety factor.
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