YIELD STRESS. Some Observations. A jar of mayonnaise, ketchup, whipped topping or chutney may be tilted without the product flowing A jar of mayonniase can be gently pushed with a spoon, and it may return to its original position Such products may behave as thick liquids or as semi-solids.
Equilibrium flow curve
Dynamic yield stress
Often, data is unavailable at low shear stresses . . . The very part we are most interested in.
Sample is placed in a holding cup of specific dimensions.
Material is inverted and released
The distance “slumped” over a given time is measured
Devices similar to the USDA Consistometer have been used to study canned pumpkin and similar products
time evolution of the stress for imposed shear rate experiments at different imposed rates
A cone is brought into the sample. Several experiments are run at different speeds