Marks Question 4 (56 Marks Total) A component in an aircraft engine is subjected to cyclic loading during take-off and l

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Marks Question 4 56 Marks Total A Component In An Aircraft Engine Is Subjected To Cyclic Loading During Take Off And L 1 (137.57 KiB) Viewed 37 times

Marks Question 4 (56 Marks Total) A component in an aircraft engine is subjected to cyclic loading during take-off and landing and to continuous loading during flight. A typical flight cycle is illustrated schematically in Fig. 4, for a flight time of 18 hours. Typically, 1,000 cycles are experienced on take-off/landing and the period of continuous loading is 17 hours. A small internal defect of size 2a = 4 mm has been detected while the plane is on the ground. Fatigue crack growth for the material is represented by the Paris law, da dN=C(AK), with C= 1.1 x 10", m= 4, when stress is in MPa and crack length is in m. Under the operating conditions the material has power law creep behaviour, with है - 20 60 = 0.01 h', 0, = 815 MPa and n= 3 when strain rate is in h- and stress is in MPa. Creep crack growth for the material is represented by a power law, à = A(C) with A = 2.5 x 103; 4 = 0.8 when C* is in MPa mh and á is in m/h. (a) Estimate the amount of crack growth during take-off. State any assumptions you make. Give your answer in mm to three significant figures. (6) Estimate the total amount of crack growth during the 18 hour flight cycle of Fig. 24. Ignore any creep crack growth during take-off and landing. State any other assumptions you make. Give your answer in mm to three significant figures. (C) Discuss, briefly, how the result for a single flight from part (b) might be extrapolated over a six month period, assuming four flights per week. 28 8 120 N=1,000 N=1,000 100 80 stress (MPa) 40 20 D 0.5 17.5 18 time (hi Figure Q4 Schematic diagram of the stress experienced by a component during a flight. Page 2 of 2