Stella-Marissa Hughes

Out-of-autoclave (OoA) processing offers a sustainable, cost-efficient alternative to conventional autoclave manufacturing of composite aerospace parts. Flat or low curvature parts made with OoA prepregs have demonstrated comparable mechanical properties to their autoclave counterparts; however, challenges still remain with the fabrication of parts with more complex features. The dry fibre evacuation channels within out-of-autoclave prepregs leads to significant material bulk. As the material… Show more

Out-of-autoclave (OoA) processing offers a sustainable, cost-efficient alternative to conventional autoclave manufacturing of composite aerospace parts. Flat or low curvature parts made with OoA prepregs have demonstrated comparable mechanical properties to their autoclave counterparts; however, challenges still remain with the fabrication of parts with more complex features. The dry fibre evacuation channels within out-of-autoclave prepregs leads to significant material bulk. As the material compacts, inter-ply friction combined with reduced consolidation pressure prevents the prepreg from conforming to the corner region. This leads to defects such as corner thickening, elevated void content, and resin rich areas.

Performing debulks at an elevated temperature reduces the viscosity of the resin during compaction, allowing plies to more readily slip with respect to one another. Additionally, the resin infiltrates the tows earlier into the layup process, decreasing the pre-cure laminate thickness. The combination of these phenomena means that subsequent plies are laid up closer to the idealized final part geometry, minimizing corner thickening and associated defects.

The potential drawback of applying heat early on in the layup process is a premature advancement in the degree of cure. This could lead to a decrease in interlaminar properties as crosslinking between plies would be reduced. Thus, the use of heated debulks for OoA prepregs must be optimized to reduce both process induced defects and interlaminar strength degradation. A process window for elevated temperature debulks was found. Show less

This paper summarizes a industry-academic collaborative project to evaluate Out-of-Autoclave (OOA) prepreg material and its behavior during processing of complex parts. This was done by manufacturing two crew door demonstrator parts; one made from traditional epoxy autoclave cure prepreg while the other was with OOA prepreg. The goal was to evaluate the main differences between manufacturing with OOA prepreg versus standard prepreg material. The results from this study showed the impact of… Show more

This paper summarizes a industry-academic collaborative project to evaluate Out-of-Autoclave (OOA) prepreg material and its behavior during processing of complex parts. This was done by manufacturing two crew door demonstrator parts; one made from traditional epoxy autoclave cure prepreg while the other was with OOA prepreg. The goal was to evaluate the main differences between manufacturing with OOA prepreg versus standard prepreg material. The results from this study showed the impact of using sharp radii and difficult corners for both processing methods. Ultimately, this project established the capability to manufacture a part with OOA material that was of similar quality to the part manufactured with the traditional epoxy prepreg material.
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Out-of-autoclave (OOA) processing offers the potential for significant cost reduction for the manufacturing of composite aerospace structures. At a lab-scale, it has been shown that OOA prepregs meet design requirements. However, aerospace applications require large-scale parts with complex geometries in order to meet the structural demands. Such parts require deviations from the idealized OOA manufacturing configuration. In this paper, we present how OOA prepregs were applied to replace an… Show more

Out-of-autoclave (OOA) processing offers the potential for significant cost reduction for the manufacturing of composite aerospace structures. At a lab-scale, it has been shown that OOA prepregs meet design requirements. However, aerospace applications require large-scale parts with complex geometries in order to meet the structural demands. Such parts require deviations from the idealized OOA manufacturing configuration. In this paper, we present how OOA prepregs were applied to replace an autoclave curable structure. The complex features of the chosen part led to significant corner thickness variation due to the high bulk modulus of OOA material. Numerous splices were required in order to form the material to the tool’s geometry, thereby reducing considerably in-plane porous zone connectivity. Another scale-up challenges came from the inability to properly edge breathe the part. This reduced the connection of the dry in-plane porous regions of the prepreg to the vacuum source. Void content and thickness variation of the final part were analyzed and compared to lab-scale parts of similar geometries. The study serves to evaluate the ability of lab-scale tests and models at predicting part quality in full-scale parts. Furthermore, it discusses the manufacturing challenges when moving from experimental work to complex composite structures. Show less

The traditional manufacturing method for flight-critical aerospace structures made of composite materials is the autoclave. Autoclave processing is robust and well-understood, but involves high acquisition and operation costs. Out-of-autoclave materials and techniques are increasingly considered as cost-effective replacements to autoclaves; however, their capacity to accommodate scale-up issues commonly encountered when manufacturing larger parts has not yet been thoroughly investigated. The… Show more

The traditional manufacturing method for flight-critical aerospace structures made of composite materials is the autoclave. Autoclave processing is robust and well-understood, but involves high acquisition and operation costs. Out-of-autoclave materials and techniques are increasingly considered as cost-effective replacements to autoclaves; however, their capacity to accommodate scale-up issues commonly encountered when manufacturing larger parts has not yet been thoroughly investigated. The present study considers two such issues for a representative out-of-autocalve prepreg: the effects of resin out-time at room temperature and the material’s ability to evacuate entrapped air. Room-temperature out-time is shown to affect the resin flow phenomena that occur during processing and lead to dramatic increases in porosity; however, different temperature cure cycles are shown to mitigate this issue. The material’s permeability is shown to be adequate in-plane but practically non-existent through-thickness in the as-received condition; however, modifications are shown to increase this permeability to acceptable levels. Show less

This paper presents work on a project that seeks to combine elements of composite material mechanical design with industrial design. The main goal was to produce a set of everyday items using advanced composite material manufacturing techniques that incorporate themes and elements of Japanese folk art known as Mingei. The items produced from the final designs were finished to form a complimentary set. The project makes use of a variety of manufacturing techniques such as inner bladder molding… Show more

This paper presents work on a project that seeks to combine elements of composite material mechanical design with industrial design. The main goal was to produce a set of everyday items using advanced composite material manufacturing techniques that incorporate themes and elements of Japanese folk art known as Mingei. The items produced from the final designs were finished to form a complimentary set. The project makes use of a variety of manufacturing techniques such as inner bladder molding, compression molding and tape-winding. In summary, the created product is a created set of composite parts that match traditional Japanese design in terms of surface finish, shape and quality while incorporating modern composite manufacturing methods. Show less