Brookfield R/S Coaxial Cylinder Rheometer - Manual (Page 69)

Brookfi eld Engineering Labs., Inc. Page 69 Manual No. M08-219-B1211
Typical results plots:
Figure D-4
Mayonnaise shows a distinct gel breakdown after the peak yield point. Other samples, such as some
pastes and slurries, may not peak but instead equilibrate at an equilibrium stress plateau:
Equilibrium stress
Figure D-5
D.2.2 The Creep Test
For products like: gels, custard, gravies, sauces, jams and marmalades.
Properties measured: Instantaneous compliance/strain, low shear viscosity/creep rate, elasticity
index.
Description: A single stress/torque is applied at time (t = 0) and maintained on the sample over a period
of time, usually between one and fi ve minutes. The degree of subsequent movement in the sample, is
recorded against time in the form of angular displacement (in radians), strain (unit-less) or compliance
(strain divided by applied stress – in m2/N).
Example method: A constant stress of 1250 Pa is applied over a period of 120 seconds. 60 data points
are collected over this period.
CR Test on mayonnaise with stress (Tau,
in Pascals) plotted against strain (Gamma,
unit-less).
The peak value is yield stress. The gradient
of the stress/strain up curve indicates gel
rigidity, a steeper curve: a stiffer gel and
vice-versa.
CR Test on toothpaste. Equilibrium stress
is an indication of low shear viscosity or
“consistency”.