P Marks) Fatigue crack growth leading to fast fracture is one of the most common mechanisms of failure in steel cranksha

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P Marks Fatigue Crack Growth Leading To Fast Fracture Is One Of The Most Common Mechanisms Of Failure In Steel Cranksha 1 (303.01 KiB) Viewed 19 times

P Marks) Fatigue crack growth leading to fast fracture is one of the most common mechanisms of failure in steel crankshafts. See Figure Q6(b). Figure Q6(b) The crankshaft of an engine is subjected to an alternating completely reversed bending stress of amplitude 60 MNm2 and has an edge crack of 2mm, normal to the applied stress. For the crack geometry, the Stress Intensity Factor may be taken as K =1.120(na) 1/2. For the crankshaft material, yield stress = 280 MNm2, Kic = 20 MNm-3/2, and the rate of fatigue crack growth is given by the expression da/dN = 5 x 10-12 (1K1)4 m per cycle where AK is given in MNm-3/2 5 (0) ( ii Estimate the number of cycles to failure of the crankshaft after the crack was detected. [10 Marks] In addition to the cyclic bending stress, if the crankshaft were to be subjected to a steady tensile axial stress of 40 MNm-2 after the initial crack was detected, what would its life be? [10 Marks]