The response of an isotropic, nonlinear viscoelastic, thin-walled tube to combinations of axial force
F
, axial couple
G
and pressure difference
p
is considered theoretically and experimentally. Theory is based on the membrane theory of thin shells, applied to a thin-walled circular cylindrical tube. The components of two dimensional stress and strain in the wall of the tube are derived, allowing for arbitrarily large deformations; but restriction to small deformations is shown to be necessary if the history of stress is to be controlled at will through
F
,
G
and
p
. For arbitrary choice of
F
,
G
and
p
as functions of time the strain is shown to depend on three stress tensors
P
,
Q
,
R
independent of time, and three scalar functions of time. An expression for the linear strain tensor in terms of
P
,
Q
,
R
is obtained which involves four scalar functions
ϕ
0
,
ϕ
1
,
ϕ
2
,
ϕ
3
. These functions depend on the invariants of
P
,
Q
,
R
and on the three scalar functions of time. If any one of
P
,
G
,
p
is always zero then
R
=
0
and only
ϕ
0
,
ϕ
1
,
ϕ
2
are required. In the case of proportional loading (
Q
=
R
= 0
) only
ϕ
0
and
ϕ
1
are required and any one of the three strain components can be calculated from the remaining two. Creep and recovery experiments under simultaneous axial force and couple were conducted on a thin-walled tube of polypropylene at 65.5 °C. Theory was used to calculate the circumferential tensile strain from the measured shear strain and longitudinal tensile strain. For this particular tube
ϕ
0
and
ϕ
1
were found to be related in a special manner, implying that nonlinearity can be adcquatcly described by allowing the shear creep compliance to change with stress history. By varying separately combinations of the invariants of
P
,
ϕ
1
was found to depend on both hydrostatic and deviatoric components ofthe applied stress.
Bifurcation Analysis of Thin-walled Tube Subjected to Internal Pressure and Axial Tension
