IMC SEMINAR:Process Analysis of VBO Manufacturing Composites Structures

                                                                          SEMINAR ANNOUNCEMENT :

Title                : Process Analysis of Manufacturing Composites Structures with Vacuum-Bag-Only Prepregs and the Co-curing Process                                for Honeycomb Core Sandwich Structure.

Speaker         : Dr.Tom CENDER

Time               : August 07, 2018, 13:30-14:30

Place              : Teknopark- KTMM

Abstract: 

Vacuum bag-only processes, used in the manufacture of composite structures (fiber reinforced polymer), are inexpensive alternatives to similar high pressure processes which can reliably produce highly consolidated - high fiber volume fraction, low void content - composite laminates. Prepregs (fiber plies, pre-impregnated with thermoset resin or thermoplastic) are normally processed in an Autoclave with elevated temperature and pressure, which consolidates and cures the prepregs to form the composite structure. Research within the last decade has proven that low void content composite laminates can be produced using prepregs with a vacuum bag only process (in ambient atmosphere) if the prepregs are only partially impregnated with resin. This breakthrough launched a research initiative to understand, optimize, and improve reliability of this process class.

A cornerstone of this process is the ”open porosity” (dry, non-impregnated cross-sections) of the prepreg architecture. Dry cross-sections of the laminated prepreg structure must contain a percolating network of connected pores, which will serve as ”air pathways” for gas evacuation. Gases entrapped in the laminate are evacuated at room temperature when vacuum pressure is applied to the boundaries of the part (known as edge-breathing). With the success of this process hinging on sufficient volatile removal, the need for a ”complete” process model has called for deeper investigation.

In this work, a method for in-situ monitoring of resin impregnation in partially impregnated prepregs is developed, which can produce a ’qualitative’ but reproducible result. By imaging the pattern of resin through a tool surface, and capturing the area of resin saturation, a particular state of resin saturation can be defined. With a defined state of resin impregnation, properties pertaining to the evacuation of gases - namely the gas permeability and the Klinkenberg effect - are evaluated in a controlled way. It is shown that the progression of resin saturation into the fiber bed occurs in an non-uniform fashion, in which larger pores saturating before smaller ones, causing the gas permeability to decrease exponentially and in turn making the Klinkenberg effect more pronounced.

In a separate but similar line of inquiry, the production of sandwich structures by co-curing prepreg facesheets onto a honeycomb core requires the application of vacuum pressure in the initial stage of the process to remove gas entrained in the factsheets. However, this in turn, induces gas from the honeycomb core to transport through the prepreg factsheets because the resin embedded in the prepreg has a very low viscosity at the cure temperature. This process calls for a multiphase flow model which introduces additional material parameters, such as pore size distribution and a threshold capillary pressure (known as the “bubbling pressure”). These additional parameters can bae leveraged during material selection in order to control the gas transport during the curing process.

Biograph:

Tom completed his PhD in Mechanical Engineering at the University of Delaware while conducting his thesis work at the Center for Composite Materials. His research focused on flow processes in forming fiber reinforced polymeric composite structures, where understanding the transport of gases, liquid resin, and bubbles is important for producing fully consolidated (low void content) composite materials. Interim to his PhD he spent some months as a visiting researcher at the University of Bristol's Advance Composites Collaboration for Innovation and Science, as well as with Pratt and Whitney's MPE Composites Group. Currently he is a postdoctoral fellow with the Laboratory for Energy and Thermal Sciences (LTeN) at the Univeristy of Nantes and the IRT Jules Verne in Nantes, France, where he is studying continuous thermoplastic welding of composite structures.