An Overview of Measurement Techniques for Determination of Yield Stress

Many complex fluids like food and pharmaceuticals do not flow until the applied stress exceeds a critical value, the Yield Stress. This is evident in everyday life in tasks such as squeezing toothpaste from a tube, getting ketchup out of the bottle or stirring the yoghurt in the yoghurt beaker and this is important in many industries and applications. The determination of a yield stress as a true material constant can be difficult as the measured value can be very much dependent on the measurement technique employed and the conditions of the test, of which there are many. Consequently, there is no universal method for determining yield stress and there exist a number of approaches, which find favour across different industries and establishments. This presentation explains and discusses the various approaches available to measure yield stress, and aspects of the practical measurement set-up and test parameters that need to be considered to obtain relevant, robust and reliable yield stress data using a rotational rheometer.

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