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Som 6

1. 1. CHAPTER 6 TORSION & SPRINGS SURYAVANSHI PARTH Dept. MECH LJ Polytechnic
2. 2. Torsion & springs Torsion Faculty Name Dept. LJ Polytechnic Rate of twist Shear Strain at the outer surface of the bar For pure torsion the rate of twist is constant and equal to the total angle of twist divided by the length L of the bar d dx    | max bb rd r ab dx      max r r L    
3. 3. Torsion & springs Torsion Faculty Name Dept. LJ Polytechnic  Since the stresses act continuously they have a resultant in the form of moment. The Moment of a small element dA located at radial distance and is given by  The resultant moment ( torque T ) is the summation over the entire cross sectional area of all such elemental moments. 2max dM dA r    2max max p A A T dM dA I r r      
4. 4. Torsion & springs Torsion Faculty Name Dept. LJ Polytechnic Polar moment of inertia of circle with radius r and diameter d 4 4 2 32 p r d I     Maximum Shear Stress max 3 16 p Tr T I d    
5. 5. Torsion & springs Torsion Faculty Name Dept. LJ Polytechnic • The angle of twist of a bar of linearly elastic material can be related to the applied torque T Torsional rigidity …and for a bar in pure torsion… …and circular tubes Copyright 2005 by Nelson, a division of Thomson Canada Limited FIG. 3-10 Circular tube in torsion
6. 6. Torsion & springs Definition of spring Faculty Name Dept. LJ Polytechnic Springs are elastic bodies (generally metal) that can be twisted, pulled, or stretched by some force. They can return to their original shape when the force is released. In other words it is also termed as a resilient member.
7. 7. CLASSIFICATION OF SPRINGS 1) Helical springs: a) Tension helical spring b)Compression helical spring c) Torsion spring d)Spiral spring 2) Leaf springs Torsion & springs Types of spring Faculty Name Dept. LJ Polytechnic
8. 8. TENSION HELICAL SPRING (OR) EXTENSION SPRING 1. It has some means of transferring the load from the support to the body by means of some arrangement. 2. It stretches apart to create load. 3. The gap between the successive coils is small. 4. The wire is coiled in a sequence that the turn is at right angles to the axis of the spring. 5. The spring is loaded along the axis. 6. By applying load the spring elongates in action Torsion & springs Tension helical springs Faculty Name Dept. LJ Polytechnic
9. 9. COMPRESSION HELICAL SPRING Among the four types, the plain end type is less expensive to manufacture. It tends to bow sideways when applying a compressive load. Torsion & springs Compression helical springs Faculty Name Dept. LJ Polytechnic
10. 10. TORSION SPRING 1. It is also a form of helical spring, but it rotates about an axis to create load. 2. It releases the load in an arc around the axis. 3. Mainly used for torque transmission 4. The ends of the spring are attached to other application objects, so that if the object rotates around the center of the spring, it tends to push the spring to retrieve its normal position. Torsion & springs Torsion spring Faculty Name Dept. LJ Polytechnic
11. 11. SPIRAL SPRING 1. It is made of a band of steel wrapped around itself a number of times to create a geometric shape. 2. Its inner end is attached to an arbor and outer end is attached to a retaining drum. 3. It has a few rotations and also contains a thicker band of steel. 4. It releases power when it unwinds. Torsion & springs Spiral spring Faculty Name Dept. LJ Polytechnic
12. 12. Equivalent-when springs are in series Torsion & springs Springs in series Faculty Name Dept. LJ Polytechnic
13. 13. COMBINED SYSTEM(BOTH SERIES AND PARALLEL) Torsion & springs Springs in parallel Faculty Name Dept. LJ Polytechnic
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