Highly consistent quality and cost-effective manufacture of advanced composites can be achieved through automation. It may therefore open up new markets and applications for composite products in aerospace, automotive, renewable energy, and consumer goods. Automated Tape Laying (ATL) and Automated Fibre Placement (AFP) are the two main technologies used to automate the layup of prepreg. The historical development and past research of both technologies is reviewed; with an emphasis on past issues in application and capability as well as their solution, including both thermoset and thermoplastic material layup. It is shown that past developments have moved away from simply emulating manual layup into the now unique layup procedures for ATL, and into the current AFP technology base. The state of the art for both technologies is discussed and current gaps in the understanding of both processes highlighted. From this, future research needs and developments are derived and discussed.

The engineering aspects of automated prepreg layup: History, present and future

Fused filament fabrication (FFF) is a 3D printing technique which allows layer-by-layer build-up of a part by the deposition of thermoplastic material through a nozzle. The technique allows for complex shapes to be made with a degree of design freedom unachievable with traditional manufacturing methods. However, the mechanical properties of the thermoplastic materials used are low compared to common engineering materials. In this work, composite 3D printing feedstocks for FFF are investigated, wherein carbon fibres are embedded into a thermoplastic matrix to increase strength and stiffness. First, the key processing parameters for FFF are reviewed, showing how fibres alter the printing dynamics by changing the viscosity and the thermal profile of the printed material. The state-of-the-art in composite 3D printing is presented, showing a distinction between short fibre feedstocks versus continuous fibre feedstocks. An experimental study was performed to benchmark these two methods. It is found that printing of continuous carbon fibres using the MarkOne printer gives significant increases in performance over unreinforced thermoplastics, with mechanical properties in the same order of magnitude of typical unidirectional epoxy matrix composites. The method, however, is limited in design freedom as the brittle continuous carbon fibres cannot be deposited freely through small steering radii and sharp angles. Filaments with embedded short carbon microfibres (∼100 μm) show better print capabilities and are suitable for use with standard printing methods, but only offer a slight increase in mechanical properties over the pure thermoplastic properties. It is hypothesized that increasing the fibre length in short fibre filament is expected to lead to increased mechanical properties, potentially approaching those of continuous fibre composites, whilst keeping the high degree of design freedom of the FFF process.

https://research-information.bris.ac.uk/files/159707908/1_s2.0_S2214860417305687_main.pdf

An investigation into 3D printing of fibre reinforced thermoplastic composites

The review outlines modern trends in theoretical developments, novel designs and modern applications of sandwich structures. The most recent work published at the time of writing of this review is considered, older sources are listed only on as-needed basis. The review begins with the discussion on the analytical models and methods of analysis of sandwich structures as well as representative problems utilizing or comparing these models. Novel designs of sandwich structures is further elucidated concentrating on miscellaneous cores, introduction of nanotubes and smart materials in the elements of a sandwich structure as well as using functionally graded designs. Examples of problems experienced by developers and designers of sandwich structures, including typical damage, response under miscellaneous loads, environmental effects and fire are considered. Sample applications of sandwich structures included in the review concentrate on aerospace, civil and marine engineering, electronics and biomedical areas. Finally, the authors suggest a list of areas where they envision a pressing need in further research.

Review of current trends in research and applications of sandwich structures

Voids, the most studied type of manufacturing defects, form very often in processing of fiber-reinforced composites. Due to their considerable influence on physical and thermomechanical properties ...

https://journals.sagepub.com/doi/pdf/10.1177/0021998318772152

Voids in fiber-reinforced polymer composites: A review on their formation, characteristics, and effects on mechanical performance:

Bonded repair of composite aircraft structures: A review of scientific challenges and opportunities

Two major targets of current composites manufacturing research are the automation of lay-up and the development of vacuum bag only (VBO) cure. Currently regular debulk cycles are often required to obtain good as-laid quality, and autoclave cure is needed to obtain an adequate cured laminate quality. This paper will present data from a purpose-built automated lay-up simulator that has been developed to offer very well controlled lay-up. It is shown that high quality laminates may be manufactured without debulk cycles and cured under a vacuum bag without additional pressure by sufficiently compacting each ply during layup. This is achieved using layup temperatures and pressures falling outside the range attainable by the current generation of ATL/AFP machines and a development strategy is proposed to achieve the development of more capable equipment.

A concept for the in situ consolidation of thermoset matrix prepreg during automated lay-up

Experimental investigation and evaluation of numerical modeling approaches for hybrid-FRP-steel sections under impact loading for the application in automotive crash-structures

Automated processing of composite tape relies on high quality material. High quality can be defined as tight dimensional tolerances and low variability of the material properties. Here, we study the variability of voidage, resin content and surface roughness of uncured prepreg tapes and discuss the implications for automated processing. A characteristic voidage distribution in the uncured tapes is observed that can be linked to initial manufacture. Resin content significantly varies spatially and may affect automated layup detrimentally. Finally, it is shown that both prepregs have a characteristic surface roughness, which may be linked to tack and the amount of entrapped air during layup.

Dirk Lukaszewicz

Papers

The engineering aspects of automated prepreg layup: History, present and future

A concept for the in situ consolidation of thermoset matrix prepreg during automated lay-up

Experimental investigation and evaluation of numerical modeling approaches for hybrid-FRP-steel sections under impact loading for the application in automotive crash-structures

The internal structure and conformation of prepreg with respect to reliable automated processing

Automotive Composite Structures for Crashworthiness