If someone quickly rubs a very thin layer of ointment, cream, or lotion on the skin, for example, then the shear rate is much higher than if that material is slowly squeezed out of its tube. In more technical terms, it is the rate at which fluid layers move past each other. The shear rate is the rate at which a fluid is sheared or deformed during flow.
However, capillary rheometers cover the other side of the spectrum – processes that happen on a fast time scale. Their functional principle is designed to detect changes on the molecular level up to low or medium deformation. This is also why rotational rheometers are not suitable for these processes. The faster the material’s response, the faster the rate of deformation needs to be. Other processes happen in seconds or milliseconds, e.g., impact behavior or shearing and elongation during processing like extrusion, blow molding and injection molding. The deformation will increase with time.creep. When a constant force is applied to a rubber compound, the initial deformation obtained due to the application of the force is not fixed. Some processes take years such as physical aging and Creep Creep describes a time and temperature dependent plastic deformation under a constant force. The responses of a material to deformation or just the environment itself happen on different time scales. The interest in high shear rates stems from the mode of deformation a material will undergo in processes like extrusion, film blowing, and injection molding.” Traditionally, capillary rheometers have been used to measure the shear viscosity and elasticity of viscous materials at high shear rates. “Rheology studies the deformation and flow of fluids.
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