Page 74 - Engineering Plastics Handbook

48 Introduction

and by
Tγ
S =
t/J
where S = torsional shear stress
T = torque
γ= factor based on height/thickness ratio
t = thickness
J = polar moment of inertia

The angle of twist for a given applied torque can be estimated by [6]
TL
φ=
JG

where φ= angle of twist, rad (deg)
T = internal torque in the shaft, N⋅m (ft⋅lb)
L = length of shaft being twisted, cm (in)
4
4
J = polar moment of inertia of shaft, cm (in )
G = modulus of rigidity (shear modulus of material), MPa (psi)
When torque is applied, the modulus of elasticity in shear (shear mod-
ulus) can be estimated by using Poisson’s ratio:

G = E
ν
21 + )
(
where G = modulus of elasticity in shear, shear modulus, modulus of
rigidity, MPa (psi)
E = modulus of elasticity of plastics, MPa (psi)
ν= Poisson’s ratio

Shear[8]
ASTM and ISO test methods for shear are as follows

ASTM ISO
D3518 Tensile Shear Stress 14129
Interlaminar Shear Strength 14130
In-Plane Shear Modulus 15310
D3846 Double Notch Shear Test —
D5379 Double V-Notch Shear Test —

Shear modulus can be expressed with rheological variables [14]:
τ
G =
γ