Meaning
Laboratory testing techniques that measure the flow behavior and viscoelastic response of fluid or molten polymers between two flat plates provide essential data for process modeling. When utilizing parallel plate rheometry, a sample is placed between a stationary and a rotating disk to measure the torque required to deform the material. This measurement yields the viscosity as a function of temperature and shear rate.
Understanding these flow characteristics is essential for optimizing resin infusion and molding processes.
Rheological Testing
Viscous and elastic responses of polymer melts are isolated by applying either steady shear or oscillatory deformation to the test specimen. In parallel plate rheometry, the distance between the plates is adjusted to accommodate different material thicknesses and to ensure uniform contact. The test provides a direct measure of how the material flows under the stresses encountered during factory processing.
Viscosity Profiling
Temperature sweeps are conducted to simulate the thermal histories experienced during the manufacturing cycle. As the sample is heated, the viscosity initially drops, reaching a minimum before the curing reaction causes it to climb rapidly. This minimum viscosity determines the processing window, as it defines the period of easiest flow for fiber bed wetting.
If the minimum viscosity is too high, the resin will not properly infiltrate the dry reinforcement, leading to defective regions in the finished part, while a minimum that is too low can lead to excessive bleeding and dry fibers.
Sample Setup
Preparation of the test specimen requires careful attention to avoid trapping air bubbles between the plates, as these bubbles can distort the measurements. The sample must be trimmed flush with the edges of the plates to maintain a consistent shear field. This procedural detail is necessary to produce reliable data for cure simulation software.
