Propulsion system development requires new, more affordable manufacturing techniques and technologies in a constrained budget environment, while future in-space applications will require in-space manufacturing and assembly of parts and systems. Marshall is advancing cuttingedge commercial capabilities in additive and digital manufacturing and applying them to aerospace challenges. The Center is developing the standards by which new manufacturing processes and parts will be tested and qualified. Rapidly evolving digital tools, such as additive manufacturing, are the leading edge of a revolution in the design and manufacture of space systems that enables rapid prototyping and reduces production times. Marshall has unique expertise in leveraging new digital tools, 3D printing, and other advanced manufacturing technologies and applying them to propulsion systems design and other aerospace materials to meet NASA mission and industry needs. Marshall is helping establish the standards and qualifications “from art to part” for the use of these advanced techniques and the parts produced using them in aerospace or elsewhere in the U.S. industrial base.

Additive manufacturing

Fused deposition modelling (FDM) is one of the fastest-growing additive manufacturing methods used in printing fibre-reinforced composites (FRC). The performances of the resulting printed parts are limited compared to those by other manufacturing methods due to their inherent defects. Hence, the effort to develop treatment methods to overcome these drawbacks has accelerated during the past few years. The main focus of this study is to review the impact of those defects on the mechanical performance of FRC and therefore to discuss the available treatment methods to eliminate or minimize them in order to enhance the functional properties of the printed parts. As FRC is a combination of polymer matrix material and continuous or short reinforcing fibres, this review will thoroughly discuss both thermoplastic polymers and FRCs printed via FDM technology, including the effect of printing parameters such as layer thickness, infill pattern, raster angle and fibre orientation. The most common defects on printed parts, in particular, the void formation, surface roughness and poor bonding between fibre and matrix, are explored. An inclusive discussion on the effectiveness of chemical, laser, heat and ultrasound treatments to minimize these drawbacks is provided by this review.

FDM-Based 3D Printing of Polymer and Associated Composite: A Review on Mechanical Properties, Defects and Treatments.

Additive manufacturing of industrially-relevant high-performance parts and products is today a reality, especially for metal additive manufacturing technologies. The design complexity that is now possible makes it particularly useful to improve product performance in a variety of applications. Metal additive manufacturing is especially well matured and is being used for production of end-use mission-critical parts. The next level of this development includes the use of intentionally designed porous metals - architected cellular or lattice structures. Cellular structures can be designed or tailored for specific mechanical or other performance characteristics and have numerous advantages due to their large surface area, low mass, regular repeated structure and open interconnected pore spaces. This is considered particularly useful for medical implants and for lightweight automotive and aerospace components, which are the main industry drivers at present. Architected cellular structures behave similar to open cell foams, which have found many other industrial applications to date, such as sandwich panels for impact absorption, radiators for thermal management, filters or catalyst materials, sound insulation, amongst others. The advantage of additively manufactured cellular structures is the precise control of the micro-architecture which becomes possible. The huge potential of these porous architected cellular materials manufactured by additive manufacturing is currently limited by concerns over their structural integrity. This is a valid concern, when considering the complexity of the manufacturing process, and the only recent maturation of metal additive manufacturing technologies. Many potential manufacturing errors can occur, which have so far resulted in a widely disparate set of results in the literature for these types of structures, with especially poor fatigue properties often found. These have improved over the years, matching the maturation and improvement of the metal additive manufacturing processes. As the causes of errors and effects of these on mechanical properties are now better understood, many of the underlying issues can be removed or mitigated. This makes additively manufactured cellular structures a highly valid option for disruptive new and improved industrial products. This review paper discusses the progress to date in the improvement of the fatigue performance of cellular structures manufactured by additive manufacturing, especially metal-based, providing insights and a glimpse to the future for fatigue-tolerant additively manufactured architected cellular materials.

Architected cellular materials: A review on their mechanical properties towards fatigue-tolerant design and fabrication

Honeycombs are ultra-light materials with outstanding mechanical properties, which mainly originate from their unit cell configurations rather than the properties of matrix materials. Honeycombs are triggering in numerous promising applications in the fields of architecture, automotive, railway vehicle, marine, aerospace, satellite, packaging and medical implants, etc. Here we provide an in-depth overview of some important advances in basic structural design to obtain novel honeycombs with various improved mechanical properties. Firstly, the review introduces the classical honeycomb configurations. Then, a clear classification of advanced designs is established and discussed according to the design scale. The designs on the macro scale are divided into hierarchical, graded and disordered, while the designs on the meso scale are grouped as hybrid, curved ligament and reinforced strut. Moreover, the effects of different designs on the mechanical properties of honeycomb are discussed quantitatively. Finally, we summarize the important potential designs to improve the mechanical properties of honeycombs and the challenges in further research.

Advanced honeycomb designs for improving mechanical properties: A review

Inspired by natural porous architectures, numerous attempts have been made to generate porous structures. Owing to the smooth surfaces, highly interconnected porous architectures, and mathematical controllable geometry features, triply periodic minimal surface (TPMS) is emerging as an outstanding solution to constructing porous structures in recent years. However, many advantages of TPMS are not fully utilized in current research. Critical problems of the process from design, manufacturing to applications need further systematic and integrated discussions. In this work, a comprehensive overview of TPMS porous structures is provided. In order to generate the digital models of TPMS, the geometry design algorithms and performance control strategies are introduced according to diverse requirements. Based on that, precise additive manufacturing methods are summarized for fabricating physical TPMS products. Furthermore, actual multidisciplinary applications are presented to clarify the advantages and further potential of TPMS porous structures. Eventually, the existing problems and further research outlooks are discussed.

Triply periodic minimal surface (TPMS) porous structures: from multi-scale design, precise additive manufacturing to multidisciplinary applications

Gradual and localised changes in mechanical properties can be achieved by functionally graded cellular structures with the aim to improve structural performance. Gyroid belongs to a class of cellular structures that naturally inspired continuous non-self-intersecting surfaces with controllable mechanical properties. In this work, dynamic compression on functionally graded gyroid and sandwich composite panels constructed from functionally graded gyroid core and metallic facets are numerically investigated and compared to evaluate the dynamic behaviours when subjected to extreme loadings. The Finite Element Analysis (FEA) is employed to investigate the deformation behaviours of proposed structures considering the rate-dependent properties, elastoplastic response and nonlinear contact. The Johnson-Cook model is utilised to capture the rate-dependent dynamic responses of the gyroid panels. The numerical model is then validated with experimental results under quasi-static compression. Due to the symmetry, only a quarter of the gyroid panel is modelled using shell elements, which offers significantly reduction in computational cost. Parametric studies are conducted to demonstrate the influences of different functionally graded cores on the blast resistances of gyroid composite panels. Reaction forces and critical stress extracted from underneath protected structure are assessed. Fuctionally graded gyroid sandwich structures clearly demonstrate unique dynamic crushing responses, impact energy mitigation & dissipation mechanisms, which leads to enhancement of the blast resistance.

Bioinspired functionally graded gyroid sandwich panel subjected to impulsive loadings

Multi-material 3D printing has created a wide range of applications because of its high-resolution and multi-functional capabilities. It is important to understand the interaction of the materials both macroscopically and microscopically. This article investigates the mechanical responses of rigid-rubbery polymeric material fabricated using the PolyJet technique as an individual constituent and as an integrated composite unit cell. A series of experiments were conducted to obtain the mechanical responses for individual VeroMagentaV (rigid) and Agilus30 (flexible) polymers with different shore-hardness levels. Tensile results show that the interface of the dual material is strong enough to withstand the stretching during the tensile experiment. The interfacial hardness and local elastic modulus in dual-material parts investigated using nano-indentation and visual inspections showed distinct transition properties. The introduction of different types of rigid reinforcement particles of the 3D-printed composite has been demonstrated and quantified. A numerical model is developed, and the results show good agreement with the compression experiments.

PolyJet 3D Printing of Composite Materials: Experimental and Modelling Approach

Mechanical performance and fatigue life prediction of lattice structures: Parametric computational approach

Triply periodic minimal surface (TPMS) based cellular structures have drawn increasingly attention due to their mathematically controlled topologies and promising mechanical properties. Here, we combine 3D-printing technique, experiments, theoretical formulation and numerical simulation to investigate a novel class of lightweight sandwich structures with TPMS cores. Sandwich structures with Primitive, Neovius and IWP core topologies are designed and fabricated using a 3D-printing technique. The bending properties, failure mechanism as well as energy absorption capacity of these TPMS sandwich structures are evaluated via a three-point bending test. A numerical model is developed to analyse the behaviours of the sandwich structures under bending loading. Theoretical formulation is employed to compare with the experimental data and numerical simulation. A good agreement is achieved between the attendant experimental data, theoretical formulation, and numerical simulation. In addition, a comprehensive parametric study is conducted to understand the effect of core topologies, relative density of the TPMS core, and geometrical parameters on the bending properties and energy absorption capacity of the sandwich structures based on the numerical model proposed. Both the relative density of the core and the geometrical designs of the TPMS sandwich structures exhibit a significant effect on the bending properties and energy absorption capacity. In contrast, the topologies of the TPMS cores have a limited effect on the bending properties at low relative density for designs with a thick face-panel. The sandwich structures with a Neovius core have better performance compared to other core topologies for designs with a thin face-panel. Overall, this study indicates that sandwich structures with TPMS cores could be designed to deliver desirable bending properties and energy absorption capacity, and the findings of this study provide insights into future designs of novel sandwich structures for various engineering applications.

3D printed sandwich beams with bioinspired cores: Mechanical performance and modelling

Triply periodic minimal surfaces are cellular structures that naturally inspired continuous non-self-intersecting surfaces similar to bone microstructure with controllable mechanical properties. In...

Chenxi Peng

Papers

Bioinspired functionally graded gyroid sandwich panel subjected to impulsive loadings

PolyJet 3D Printing of Composite Materials: Experimental and Modelling Approach

Mechanical performance and fatigue life prediction of lattice structures: Parametric computational approach

3D printed sandwich beams with bioinspired cores: Mechanical performance and modelling

Triply periodic minimal surfaces sandwich structures subjected to shock impact