Assuming s 10 nmm 25 10 250 n total load on the

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Unformatted text preview: B. We know that maximum bending moment at A – A and B – B. l3 = l 2 + 2 × Fig. 32.28 60 M = 2460 180 − = 369 × 103 N-mm 2 The rocker arm is of I-section. Let us assume the proportions as shown in Fig. 32.28. We know that section modulus, 1 2.5 t (6 t )3 − 1.5 t (4 t )3 37 t 4 12 = = 12.33 t 3 Z= 6t / 2 3t ∴ Bending stress (σb), M 369 × 103 29.93 × 103 = = 70 = Z 12.33 t 3 t3 t3 = 29.93 × 103 / 70 = 427.6 or t = 7.5 say 8 mm ∴ Width of flange = 2.5 t = 2.5 × 8 = 20 mm Ans. Depth of web = 4 t = 4 × 8 = 32 mm Ans. and depth of the section = 6 t = 6 × 8 = 48 mm Ans. Normally thickness of the flange and web is constant throughout, whereas the width and depth is tapered. 4. Design for tappet screw The adjustable tappet screw carries a compressive load of Fe = 2460 N. Assuming the screw is made of mild steel for which the compressive stress (σc) may be taken as 50 MPa. 1200 n A Textbook of Machine Design Let dc = Core diameter of the tappet screw. We know that the load on the tappet screw (Fe), π π 2 2 2 2460 = (dc ) σc = (dc ) 50 = 39.3 (dc ) 4 4 ∴ (dc)2 = 2460 / 39.3 = 62.6 or dc = 7.9 say 8 mm and outer or nominal...
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