Rheologists are encouraged to join in the development of a proposed new practice that will help standardize the calibration of rotational rheometers to ensure that end users are able to obtain accurate normal force measurements.
Kenneth Aniunoh, E37.08 chairman and senior product specialist, Shimadzu Scientific Instruments, explains there is a current trend in industry toward the use of normal force measurements for characterizing the viscoelastic properties of materials. Normal force measurements, in rotational rheometers, provide an indication of the normal stresses generated in a material undergoing deformation.
“Normal force measurements can be used to characterize material viscoelasticity and also for quality control,” says Aniunoh. “A layman example of normal force/normal stress effects is the rod climbing phenomena or Weissenberg effect in which, for instance, we notice that bread dough climbs a stirring rod whereas water and glycerol flow outward from a stirrer. The behavior of the bread dough is due to normal stresses generated in the dough.”
Technical Information: Kenneth Aniunoh, Shimadzu Scientific Instruments, Laurel, Md.
ASTM Staff: Thomas O’Toole