Page 48 - Mechanical Engineer's Data Handbook

STRENGTHS OF MATERIALS 37

I .5.5 Rubber springs Cylindrical torsion spring, torque T

Springs of rubber bonded to metal are made in a wide Maximum shear stress T,,, = 2T/xLDf
variety of configurations. The rubber is usually in T
shear and, because of the high internal damping, such Angle of twist 0 = - (l/@ - l/D:)
springs are used for limiting vibrations. nLG
Two-block shear spring - load P

Shear stress 7 = P/2A
Deflection y = Ph/SAG
where G =shear modulus.

Modulus and strength of rubber

G=0.3 to 1.2MPa
E =0.9 to 3.6 MPa
Allowable shear stress=0.2 to 0.4 MPa
Deflection limited to 10% to 20% of free height.

1.5.6 Form hcton for springt
Cylindrical shear spring, load P
The table gives form factors giving the amount of
Maximum shear stress T, = P/nhDi strain energy stored in different types of spring relative
to a bar with uniform direct stress.
P
Deflection y = - (DJDi)
In
2nhG