245 140 458 10 knmm 458 nmm wt total stress on

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Unformatted text preview: ow that length of the crankpin, MC = or lc = ...(ii) FP 314.2 × 103 = = 153.3 say 155 mm Ans. 205 × 10 dc · pb ...(Taking pb = 10 N/mm2) (b) Design of left hand crank web We know that thickness of the crank web, t = 0.65 dc + 6.35 mm = 0.65 × 205 + 6.35 = 139.6 say 140 mm Ans. 1178 n A Textbook of Machine Design and width of the crank web, w = 1.125 dc + 12.7 mm = 1.125 × 205 + 12.7 = 243.3 say 245 mm Ans. We know that maximum bending moment on the crank web, l t M = H1 b2 − c − 2 2 155 140 = 157.1 400 − − = 39 668 kN-mm 2 2 1 1 2 2 3 3 Section modulus, Z = × w .t = × 245 (140) = 800 × 10 mm 6 6 39 668 M = = 49.6 × 10 −3 kN/mm2 = 49.6 N/mm 2 ∴ Bending stress, σb = Z 800 × 103 We know that direct compressive stress on the crank web, 157.1 H1 −3 2 2 σb = . = 245 140 = 4.58 × 10 kN/mm = 4.58 N/mm wt × ∴ Total stress on the crank web = σb + σc = 49.6 + 4.58 = 54.18 N/mm2 or MPa Since the total stress on the crank web is less than the allowable bending stress of 75 MPa, therefore, the design of the left hand crank web is safe. (c) Design of right hand crank web From...
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