Melt flow rate testing

The melt flow rate test moves the molten material at a single flow rate, therefore a single shear rate, and fails to capture the full range of the behavior of a material as a function of changing shear rate. To make matters worse, the shear rate is not even controlled. While the load on the material, or the shear stress, is constant during the course of the test, the shear rate is an output of the test. The MFR itself is a reflection of the shear rate used during the course of the test, but it is a result of the test and not a controlled input.