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

A crash structure is provided for a vehicle. The crash structure includes at least two carriers produced of fiber-reinforced plastic, and at least one planar element produced of fiber-reinforced plastic. The planar element is connected to both carriers to avoid buckling of the carrier in the event of a crash.

Crash structure for a vehicle

Crashworthiness using innovative materials, such as carbon-fiber reinforced composites (CFRP) requires a new understanding of the material response to crash events. Composite fracture differs from existing plastic deformation in metallic structures. Vehicle design using composites requires a detailed understanding of the microstructural material features with respect to a given fracture behavior, as well as updated vehicle concepts and architectures to account for this inherent difference of CFRP to metallic structures. To design composites for energy absorption all factors need to be known and understood. This study was focused on providing an overview of the most relevant material parameters. Current challenges with respect to CFRP vehicle design are discussed and particular attention is devoted to energy absorbing composite structures. The work presented here is a preliminary approach to managing the complexity of composite development including both geometrical and microstructural design. Composite materials offer benefits in energy absorbing structures and are one way of further reducing the weight of a body-in-white while also maintaining safety levels. However, such weight savings can only be achieved with a purposeful composite design. The work presented herein will highlight innovative aspects of crashworthiness with respect to composite materials.

Design Drivers for Enhanced Crash Performance of Automotive CFRP Structures

Es wird ein Strukturelement fur ein Kraftfahrzeug umfassend eine Sandwichstruktur mit einer oberen Decklage aus faserverstarktem Kunststoff und einer unteren Decklage aus faserverstarktem Kunststoff bereitgestellt, wobei die beiden Decklagen zumindest in einem ersten Abschnitt durch eine zwischen der oberen und der unteren Decklage angeordnete Zwischenschicht beabstandet sind, wobei eine Dicke der Sandwichstruktur in dem ersten Abschnitt groser als in einem zweiten Abschnitt des Strukturelements ist, und die obere und die untere Decklage sowie die Zwischenschicht in dem ersten Abschnitt miteinander vernaht sind.

Verstärktes Strukturelement für ein Kraftfahrzeug

In this work, the application of fibre reinforced plastic (FRP) sandwich structures, with a particular focus on aramid fibre tufted sandwiches is being studied for automotive crashworthiness during edgewise impact using impact testing and numerical simulation. This work uses prior coupon data for scaling into a subsystem of a vehicle floor. A novel manufacturing process where Kevlar tufting is inserted through the dry preforms and the core is introduced. Subsystem testing then demonstrates the scalability of the sandwich system into a floor assembly. The specimen exhibits crushing with significant energy absorption. Numerical modelling is then used to validate the test result and demonstrate the simulation capability. Using commercial finite element software (Abaqus) with composite crushing add-in (CZone), the crushing of the sandwich and facesheets can be simulated with good agreement with the test results.

Experimental and numerical investigation of full scale impact test on fibre-reinforced plastic sandwich structure for automotive crashworthiness

The invention relates to a body for a motor vehicle having a beam (1), in particular a longitudinal beam, which is formed from fibre-reinforced plastic, in particular carbon-fibre-reinforced plastic, and which as a supporting structural element having a collision-energy-absorbing effect in the event of a collision, wherein an end face (3; 4) of the beam (1) is oblique in relation to a load plane (11; 12) that runs perpendicularly to a collision load path (7).

Dirk Lukaszewicz

Papers

Crash structure for a vehicle

Design Drivers for Enhanced Crash Performance of Automotive CFRP Structures

Verstärktes Strukturelement für ein Kraftfahrzeug

Experimental and numerical investigation of full scale impact test on fibre-reinforced plastic sandwich structure for automotive crashworthiness

Body for a motor vehicle