Vacuum‐assisted resin transfer molding model

A model of the vacuum‐assisted resin transfer molding (VARTM) process is developed that includes the most important aspects of the processing physics. The model consists of several submodels, such as preform mechanics, Darcy flow, wicking flow, and void formation. The preform mechanics model treats the preform as a linearly elastic, one‐dimensional (1D) solid. However, the key physical process is the lubrication of the preform due to fluid wetting, and this is modeled as a reduction in preform modulus, an easily measurable parameter. Residual stress, three‐dimensional (3D) structural behavior, and nonlinearity are neglected, but can all be included. The fluid flow model of capillary wicking is not tacked onto the Darcy equation as a modified boundary condition, as was previously done. The wicking is treated simply, but more realistically, by performing a force balance on the fluid in a pore. Balancing the capillary pressure and the viscous drag allows the development of a wicking front that precedes the main Darcy flow front to an extent that depends on several easily measurable factors. It is this wicking front that is responsible for the small void formation that reduces the quality of VARTM parts, relative to resin transfer molding (RTM) parts. POLYM. COMPOS. 26:477–485, 2005. © 2005 Society of Plastics Engineers     

Experimental and numerical analysis of flow behavior in the FASTRAC liquid composite manufacturing process

The success of resin infusion during liquid composite processing depends on several factors; including the complete impregnation of the dry performs, the processing conditions, and the tooling used during processing. New process developments based on the Fast Remotely Actuated Channels (FASTRAC) process aid the infusion with the creation of preferential resin flow paths using a non-contact tooling. Experiments to understand and study the infusion behavior with the presence of the FASTRAC non-contacting tooling have been performed, and compared with vacuum-assisted processes without such tooling. Experimental studies indicate that the infusion time with FASTRAC channel configurations is significantly less despite the additional volume regions to be infused during processing. The use of a non-contacting interchangeable tool, the improved infusion behavior, and the significant reduction in the infusion time provide significant advantages for processing advanced composite systems, including the potential to use high viscosity resin systems, and process automation. The process simulation models of the experimental configurations based on the thin shell model configurations have been compared with experimental observations. Studies indicate that the process simulation models and approaches employed clearly emulate the infusion behavior seen when the channels are present, validating the modeling strategies employed. Similar simulation approaches will thus be effective to study and understand various FASTRAC tooling configurations while processing complex composite structures. Polym. Compos. 25:384–396, 2004. © 2004 Society of Plastics Engineers.     

Rapid Biocatalytic Synthesis of Aromatic Acid CoA Thioesters by Using Microbial Aromatic Acid CoA Ligases

Chemically labile ester linkages can be introduced into lignin by incorporation of monolignol conjugates, which are synthesized in planta by acyltransferases that use a coenzyme A (CoA) thioester donor and a nucleophilic monolignol alcohol acceptor. The presence of these esters facilitates processing and aids in the valorization of renewable biomass feedstocks. However, the effectiveness of this strategy is potentially limited by the low steady-state levels of aromatic acid thioester donors in plants. As part of an effort to overcome this, aromatic acid CoA ligases involved in microbial aromatic degradation were identified and screened against a broad panel of substituted cinnamic and benzoic acids involved in plant lignification. Functional fingerprinting of this ligase library identified four robust, highly active enzymes capable of facile, rapid, and high-yield synthesis of aromatic acid CoA thioesters under mild aqueous reaction conditions mimicking in planta activity.     

Fluid flow reconstruction modeling with application to liquid molding processes

A unique mathematical reconstruction technique is coupled with discrete experimental flow front detection data to provide continuous fluid flow analysis. A fully finite element based methodology for the construction of surfaces from scattered and sparse data is presented and applied to experimental observations derived from a new class of sensors enlisted as monitors of the resin transfer molding (RTM) process. The basic numerical technique is shown to yield interpolant models capable of flow front position and fluid flow velocity reconstruction. The extrapolative/predictive performance is enhanced through the introduction of a new hybrid procedure. Two-dimensional and quasi-three-dimensional examples are used to demonstrate the effectiveness of the techniques.