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Unformatted text preview: 1 Chapter 12 Springs 121 Introduction Springs are elastic members that exert forces, or torques, and absorb energy. Functions: 1. To apply force and to control motion. 2. To alter the vibratory characteristics of a member 3. To reduce the magnitude of the transmitted force due to impact or shock loading 4. To store energy 5. To measure force Springs are often used to provide several functions at same time. Most springs are made by metals. 122 Torsion Bar Spring Copy Fig. 12.1 and explain it. Basic equations: Figure 12.1 (p. 470) Torsion bar springs. 2 Torsional Stress J Tr = τ , where J: polar moment of inertia, T: torque, and r; distance to the polar center. Angular Deflection JG TL = θ , where L: spring length, G: torsional or shear modulus of elasticity. Spring Rate L JG K = For a solid round rod of diameter d , these become: 3 16 d T π τ = G d TL 4 32 π θ = L G d K 32 4 π = Shear modulus can be calculated as ) 1 ( 2 ν + = E G 12.3 Coil Spring Stress and Deflection Equations See Fig. 12.2, Helical coil compression and tension springs with relatively small helix angle λ . Two requirements: 1) Load should not exceed a save value of the stress. 2) The forcedeflection or spring rate F/ δ , must be satisfactory for the given application. See Fig.12.2(b), free body diagram for compression spring. D: Mean coil diameter d: Wire diameter 3 F: Force T: Torque J: Polar moment of inertial of crosssection area. Figure 12.2 (p. 471) Helical (coil) compression and tension springs. 4 If effect of the curvature of the wire is neglected, the shear stress is, see Philan’s book in Fig. 92, Stress distribution across wire neglecting effect of curvature....
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This note was uploaded on 12/01/2010 for the course MEM MEM 431 taught by Professor Jackzhou during the Fall '10 term at Drexel.
 Fall '10
 JackZhou

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