DEPARTMENT OF MECHANICAL ENGINEERING S7 ME MACHINE DESIGN - I Assignment No. 2 To be submitted on 04-10-2013

1. The cover of a pressure vessel is held in place by ten M20 bolts. The internal pressure is 1.5 MPa and the effective area of the cover exposed to the pressure is 0.2 m2. The ratio of the stiffness of the bolts to the connected parts is 4. Initially (before the pressure is applied), each bolt is tightened to 30 kN. (a) Will the joint separate as a result of the load due to internal pressure? (b) If the joint does not separate, determine the tensile stress in each bolt due to the axial load.

2. A bolt is used to fasten two members together as shown in figure-1. The members and the bolt are made of different materials so that the effective stiffness of the connected members is 8 times the stiffness of the bolt. The nut is tightened to develop a preload of 14.7 kN on the bolt as well as the members. If an external load W = 1.6 kN is now applied (as shown in the figure), what is the resultant tension in the bolt and the compression in the members.

Figure-1

3. A mild steel bracket is connected to a vertical member by eight bolts of equal diameters, as shown in figure-2. A vertical force of 50 kN acts in the plane of the bolts at a horizontal distance of 300 mm from the centre of the bolt arrangement. Suggest the suitable size of the bolts for a permissible shear stress of 55 MPa.

Figure-2 Figure-3 Figure-4 4. A 10mm25mm (cross-section) bar is welded to a 100mm diameter cylinder and the cylinder itself is welded to a

frame on its vertical face, as shown in figure-3. Both the cylinder and the bar are kept horizontally and a vertical load of 600 N is applied at the end of the bar, as shown. Determine the required sizes of the 45 fillet welds.

5. Find the value of the maximum stress in the welded joint of figure-4. The weld extends across the top and along the vertical edge.

6. The following data apply to the machinists clamp shown in figure-5. Outside diameter of the screw = 12 mm Root diameter = 10.16 mm Pitch (single thread) = 1.5 mm Collar friction radius = 5 mm Collar friction coefficient = 0.15 Screw friction coefficient = 0.15 Assume that the machinist can comfortably exert a maximum force of 120 N on the handle. Determine (a) the clamping force developed between the jaws of the clamp (b) the efficiency of the clamp (c) the torque in the screw body at section A-A. 7. A steel screw driving a bronze nut is to develop an axial load of 300 kN in an extrusion press. The screw has an

outside diameter of 100 mm and a single square thread (depth = pitch) with a lead of 16 mm. The length of nut is to be chosen so that the bearing pressure between screw and nut threads will not exceed 28 MN/m2. Determine a suitable nut length.

W

W

Figure5

8. 8 numbers of close coiled helical springs are arranged in parallel at the bottom of an elevator shaft to absorb the impact in case of an accident. The effective weight of the elevator is 60 kN and the maximum fall of it from rest is 40 m. Evaluate the stress induced on each spring if the diameter of the spring wire is 60mm, spring index is 6, active number of coils is 20 and modulus of rigidity of spring material is 82 GPa. State the assumptions made, if any.

9. The valve spring of a diesel engine is 45mm long when the valve is open and 50 mm long when the valve closed. The load on the spring is 250N with the valve closed and 300N with the valve open. The outer diameter of the coil spring shall be less than 65mm. If the allowable stress in the wire is 420 MPa, determine: (a) the wire diameter; (b) the spring length when it is completely closed and (c) number of active coils.

10. A carbon steel coil spring has a mean diameter of 60 mm and is formed of 12 mm bar. It is subjected to a continuously alternating load between a maximum of 7000 N and a minimum of 4500 N. If the torsional yield point of the material is 700 MN/m2 and the endurance limit due to released loading is 300 MN/m2, determine the factor of safety under which the spring is operating from both the standpoint of endurance and yield.