A cylindrical pressure vessel of radius 1.2m and thickness 4 mm is made from Ductile steel.a. If the pressure if varied cyclical
ly between 0 and 0.4p, for the resulting cyclically varying combined biaxial stress state, estimate the equivalent mean stress, stress amplitude and stress ratio. b. Using the Soderberg fatigue failure criteria estimate value of the pressure p that will lead to failure after 108 cycles. The material yield strength is 300Mpa and the fatigue strength is 250 MPa (at 108 cycles).
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Answer:
a) 1.16 m/s
b) 1/216000
c) (√15)/6480000
Explanation:
The parameters given are;
Length of boat prototype, lp = 30 m
Speed of boat prototype = 9 m/s
Length of boat model, lm= 0.5 m
a) lm/lp = 0.5/30 = 1/60 = ∝
(vm/vp) = ∝^(1/2) = √∝ = (1/60)^(1/2)
vm = 9 × (1/60)^(1/2) = 1.16 m/s
b) The ratio of the model to prototype drag, Fm/Fp, is given as follows;
Fm/Fp = (vm/vp)²×(lm/lp)² = ∝³
Fm/Fp = (1/60)³ = 1/216000
c) The ratio of the model to prototype power pm/p = (Fm/Fp) × (vm/vp) = ∝³×√∝
The ratio of the model to prototype power pm/p = √(1/60) × (1/60)³
pm/p = √(1/60) × (1/60)³ = (√15)/6480000