Freedom of design, mass customisation, waste minimisation and the ability to manufacture complex structures, as well as fast prototyping, are the main benefits of additive manufacturing (AM) or 3D printing. A comprehensive review of the main 3D printing methods, materials and their development in trending applications was carried out. In particular, the revolutionary applications of AM in biomedical, aerospace, buildings and protective structures were discussed. The current state of materials development, including metal alloys, polymer composites, ceramics and concrete, was presented. In addition, this paper discussed the main processing challenges with void formation, anisotropic behaviour, the limitation of computer design and layer-by-layer appearance. Overall, this paper gives an overview of 3D printing, including a survey on its benefits and drawbacks as a benchmark for future research and development.

Additive manufacturing (3D printing): A review of materials, methods, applications and challenges

The mechanical properties of ordinary materials degrade substantially with reduced density because their structural elements bend under applied load. We report a class of microarchitected materials that maintain a nearly constant stiffness per unit mass density, even at ultralow density. This performance derives from a network of nearly isotropic microscale unit cells with high structural connectivity and nanoscale features, whose structural members are designed to carry loads in tension or compression. Production of these microlattices, with polymers, metals, or ceramics as constituent materials, is made possible by projection microstereolithography (an additive micromanufacturing technique) combined with nanoscale coating and postprocessing. We found that these materials exhibit ultrastiff properties across more than three orders of magnitude in density, regardless of the constituent material.

/pdf/ultralight-ultrastiff-mechanical-metamaterials-3jtwrdq859.pdf

Ultralight, ultrastiff mechanical metamaterials

Ceramics have some of the highest strength- and stiffness-to-weight ratios of any material but are suboptimal for use as structural materials because of their brittleness and sensitivity to flaws. We demonstrate the creation of structural metamaterials composed of nanoscale ceramics that are simultaneously ultralight, strong, and energy-absorbing and can recover their original shape after compressions in excess of 50% strain. Hollow-tube alumina nanolattices were fabricated using two-photon lithography, atomic layer deposition, and oxygen plasma etching. Structures were made with wall thicknesses of 5 to 60 nanometers and densities of 6.3 to 258 kilograms per cubic meter. Compression experiments revealed that optimizing the wall thickness-to-radius ratio of the tubes can suppress brittle fracture in the constituent solid in favor of elastic shell buckling, resulting in ductile-like deformation and recoverability.

Strong, lightweight, and recoverable three-dimensional ceramic nanolattices

Mechanical metamaterials associated with stiffness, rigidity and compressibility: a brief review

Materials with three-dimensional micro- and nanoarchitectures exhibit many beneficial mechanical, energy conversion and optical properties. However, these three-dimensional microarchitectures are significantly limited by their scalability. Efforts have only been successful only in demonstrating overall structure sizes of hundreds of micrometres, or contain size-scale gaps of several orders of magnitude. This results in degraded mechanical properties at the macroscale. Here we demonstrate hierarchical metamaterials with disparate three-dimensional features spanning seven orders of magnitude, from nanometres to centimetres. At the macroscale they achieve high tensile elasticity (>20%) not found in their brittle-like metallic constituents, and a near-constant specific strength. Creation of these materials is enabled by a high-resolution, large-area additive manufacturing technique with scalability not achievable by two-photon polymerization or traditional stereolithography. With overall part sizes approaching tens of centimetres, these unique nanostructured metamaterials might find use in a broad array of applications.

Multiscale metallic metamaterials

Multifunctional heat exchangers derived from three-dimensional micro-lattice structures

Ordered periodic microlattices with densities from 0.5 mg/cm3 to 500 mg/cm3 are fabricated by depositing various thin film materials (Au, Cu, Ni, SiO2, poly(C8H4F4)) onto sacrificial polymer lattice templates. Young's modulus and strength are measured in compression and the density scaling is determined. At low relative densities, recovery from compressive strains of 50% and higher is observed, independent of lattice material. An analytical model is shown to accurately predict the transition between recoverable “pseudo-superelastic” and irrecoverable plastic deformation for all constituent materials. These materials are of interest for energy storage applications, deployable structures, and for acoustic, shock, and vibration damping.

/pdf/microlattices-as-architected-thin-films-analysis-of-4s2a7m2lnp.pdf

Microlattices as architected thin films: Analysis of mechanical properties and high strain elastic recovery

A scalable method for fabricating architected materials well-suited for heat and mass exchange is presented. These materials exhibit unprecedented combinations of small hydraulic diameters (13.0-0.09 mm) and large hydraulic-diameter-to-thickness ratios (5.0-30,100). This process expands the range of material architectures achievable starting from photopolymer waveguide lattices or additive manufacturing.

Scalable 3D Bicontinuous Fluid Networks: Polymer Heat Exchangers Toward Artificial Organs

An aircraft micro-lattice cross-flow heat exchanger and methods are presented. A first aircraft fluid source inlet provides a first fluid from a first aircraft system, and a second aircraft fluid source inlet provides a second fluid from a second aircraft system. A structural body supports aviation induced structural loads and exchanges heat between the first fluid and the second fluid. The structural body comprises hollow channels forming two interpenetrating fluidically isolated volumes that flow the first fluid within the hollow channels and flow the second fluid external to the hollow channels isolated from the first fluid. The hollow channels comprise a hollow three-dimensional micro-truss comprising hollow truss elements extending along at least three directions, and hollow nodes interpenetrated by the hollow truss elements.

Micro-lattice cross-flow heat exchangers for aircraft

A structure including a hollow porous material with an architected fluid interface to the hollow porous material and methods of forming the same. The architected fluid interface may be in the form of a manifold with tapered openings, each providing a gradually narrowing transition to the hollow channels within which fluid may flow through the hollow porous material. The material may be formed by forming an open-celled sacrificial scaffold, immersing one surface of the open-celled sacrificial scaffold in a bonding agent, attaching a face sheet to the surface to form a sacrificial scaffold assembly, coating the assembly with a coating material, and removing the sacrificial scaffold assembly.

Kevin J. Maloney

Papers

Multifunctional heat exchangers derived from three-dimensional micro-lattice structures

Microlattices as architected thin films: Analysis of mechanical properties and high strain elastic recovery

Scalable 3D Bicontinuous Fluid Networks: Polymer Heat Exchangers Toward Artificial Organs

Micro-lattice cross-flow heat exchangers for aircraft

Hollow porous materials with architected fluid interfaces for reduced overall pressure loss