Richard~undefined~undefined~undefined~undefined~undefined Parnas

Optical coherence tomography of glass reinforced polymer composites

Abstract Optical coherence tomography (OCT) is a nondestructive and noncontact technique to image microstructure within scattering media. The application of OCT to highly scattering materials such as polymer composites is especially challenging. In this work, OCT is evaluated as a technique to image fiber tows and voids in two materials: an epoxy E-glass-reinforced composite and a vinyl-ester E-glass-reinforced composite. Features detected using OCT are compared with optical microscopy. Fiber architecture and voids of glass-reinforced polymer composites can be successfully imaged using OCT. The quality of the OCT image is strongly affected by the refractive index mismatch between the fibers and reinforcement. The largest sources of noise in the images arise from fiber lens effects, interference from within the sample, and a very large reflection at the surface.

The Application of Optical Coherence Tomography to Problems in Polymer Matrix Composites

Abstract The Composites Group at the National Institute of Standards and Technology has found optical coherence tomography (OCT) to be a powerful tool for non-destructive characterization of polymer matrix composites. Composites often exhibit superior properties to traditional materials such as wood and metal. However, the barrier to their widespread infiltration into consumer markets is cost. Composites can be made more cost competitive by improved composite design, process optimization, and quality control. OCT provides a means of evaluating the three aforementioned areas. OCT is a very versatile technique that can be applied to a variety of problems in polymer composites such as: microstructure determination for permeability and mechanical property prediction, void, dry spot, and defect detection, and damage evaluation. Briefly, OCT uses a low coherence source such as a superluminescent diode laser with a fiber optic based Michelson interferometer. In this configuration, the composite is the fixed arm of the interferometer. Reflections from heterogeneities within the sample are mapped as a function of thickness for any one position. Volume information is generated by translating the sample on a motorized stage. Information about the location and size of a feature within the composite is obtained. In this work, the power of OCT for imaging composite microstructure and damage is presented. An example of permeability prediction using the composite microstructure imaged from OCT is demonstrated. The effect of image processing on the value of permeability is discussed. Using the same sample, OCT imaging of composite impact damage is compared to more traditional techniques, X-ray computed tomography and confocal microscopy.

Model-assisted feedback control for liquid composite molding

A model-assisted feedback control algorithm, a type of generic model control, is implemented to control cure in resin transfer molding. This control algorithm calculates an apparent temperature of reaction based on the cure data input form a sensor, and this temperature is used to compare the actual rate of reaction to the desired rate and to calculate the mold set-point temperature. The model input into the control algorithm is an empirical cure model of a pre-ceramic polymer with an Arrhenius temperature dependence from 55 to 95 °C. In this work, the effect of varying control parameters is evaluated through cure simulations and experiments. Also, the effect of noise on the controller robustness is evaluated through simulation and experiment. Control parameters are evaluated for 55 and 95 °C.