Overhanging and floating layers which are introduced during the build in selective laser melting (SLM) process are usually associated with high temperature gradients and thermal stresses. As there is ...no underlying solid material, less heat is dissipated to the powder bed and the melted layer is free to deform resulting undesired effects such as shrinkage and crack. This study uses three-dimensional finite element simulation to investigate the temperature and stress fields in single 316L stainless steel layers built on the powder bed without support in SLM. A non-linear transient model based on sequentially coupled thermo-mechanical field analysis code was developed in ANSYS parametric design language (APDL). It is found that the predicted length of the melt pool increases at higher scan speed while both width and depth of the melt pool decreases. The cyclic melting and cooling rates in the scanned tracks result high VonMises stresses in the consolidated tracks of the layer.
Metallic additive manufacturing techniques, in particular the selective laser melting (SLM) process, are capable of fabricating strong, lightweight and complex metallic lattice structures. However, ...they still face certain process limitations such as geometrical constraints and in some cases the need for support structures. This study evaluates the manufacturability and performance of SLM produced periodic cellular lattice structures, which are designed by repeating a unit cell type called gyroid consisting of circular struts and a spherical core. The effect of unit cell size on the manufacturability, density and compression properties of the manufactured cellular lattice structures were investigated. Micro-computer tomography (CT) scan results reveal that the gyroid cellular lattice structures with various unit cell sizes ranging from 2 to 8mm can be manufactured free of defects by the SLM process without the need of additional support structures. The Scanning Electron Microscope (SEM) micrographs show that the lattice structures made by SLM have a good geometric agreement with the original computer-aided design (CAD) models, but many partially melted metal particles are bonded to strut surfaces. The struts within the gyroid cellular lattice structures with smaller unit cell sizes have higher densities due to their shorter scan vector lengths in the SLM process. The yield strength and Young's modulus of the Gyroid cellular lattice structures increase with the decrease in the unit cell size due to the denser struts of the lattice structures with smaller unit cell sizes.
► Cellular lattice structures are generated by a novel unit cell type called “Schoen Gyroid”. ► The lattice structures with a wide unit cell size range were manufactured by SLM. ► Struts within the lattice structures with smaller unit cell sizes have higher densities. ► The yield strengths and Young's moduli both decrease with the increase in unit cell size.
Anisotropy is the characteristic of a material to exhibit variations in its mechanical, electrical, thermal, optical properties, etc. along different directions. Anisotropic materials have attracted ...great research interest because of their wide applications in aerospace, sensing, soft robotics, and tissue engineering. 3D printing provides exceptional advantages in achieving controlled compositions and complex architecture, thereby enabling the manufacture of 3D objects with anisotropic functionalities. Here, a comprehensive review of the recent progress on 3D printing of anisotropic polymer materials based on different techniques including material extrusion, vat photopolymerization, powder bed fusion, and sheet lamination is presented. The state‐of‐the‐art strategies implemented in manipulating anisotropic structures are highlighted with the discussion of material categories, functionalities, and potential applications. This review is concluded with analyzing the current challenges and providing perspectives for further development in this field.
3D printing offers an unparalleled freedom in the design and fabrication of anisotropic polymer materials with controlled compositions and complex architecture. This article provides a comprehensive review on recent developments in the 3D printing techniques and relevant implementing strategies for fabricating anisotropic polymer materials. The potential applications, existing challenges, and future perspectives are discussed.
Functional graded cellular materials (FGCMs) have attracted increasing attentions for their improved properties when compared to uniform cellular structures. In this work, graded Gyroid cellular ...structures (GCSs) with varying gradient directions were designed and manufactured via selective laser melting (SLM). As a reference, uniform structures were also manufactured. The surface morphology and mechanical response of these structures under compressive loads were investigated. Results indicate high manufacturability and repeatability of GCSs manufactured by SLM. Optimized density distribution gives these structures novel deformation and mechanical properties. GCSs with density gradient perpendicular to the loading direction exhibit deformation behaviours similar to uniform ones, while GCSs with the gradient parallel to the loading direction exhibit layer-by-layer deformation and collapse behaviour. A novel phenomenon of sub-layer collapses is found in GCSs with gradient parallel to the loading direction. Furthermore, mathematical models were developed to predict and customize the mechanical properties of graded cellular structures by optimizing the relative density of each layer. These significant findings illustrate that graded cellular structures have high application prospect in various industries, particularly given the fact that additive manufacturing has been an enabler of cellular structure fabrication.
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•Continuous graded Gyroid cellular structures (GCSs) were fabricated by SLM.•Novel deformation and mechanical properties were gained compared to uniform cellular.•The effect of gradient direction was investigated for GCSs.•Novel sub-layer collapses are founded in GCSs with gradient along building direction.•Mathematical models were developed to calculate Young's modulus and strength of GCSs.
The present paper systematically investigated the influence of solution and artificial aging heat treatments on the microstructures and mechanical properties of SLM-produced AlSi10Mg alloy parts. Due ...to the high cooling rate of SLM, an ultrafine eutectic microstructure in the as-built samples is characterized by spherical nano-sized network eutectic Si embedded in the Al matrix, which gives rise to significantly better tensile properties and Vickers micro-hardness. The solubility of Si atom in the Al matrix of as-built SLM samples is calculated to be 8.89at%. With the increase in the solution temperature, the solubility decreases rapidly. The artificial aging causes the further decrease of the solubility of Si atoms in the Al matrix. Upon solution heat treatment, Si atoms are rejected from the supersaturated Al matrix to form small Si particles. With increasing the solution temperature, the size of the Si particles increases, whereas their number decreases. After artificial aging, the Si particles are further coarsened. The variation in size of Si particles has a significant influence on the mechanical properties of the AlSi10Mg samples. The tensile strength decreases from 434.25±10.7MPa for the as-built samples to 168.11±2.4MPa, while the fracture strain remarkably increases from 5.3±0.22% to 23.7±0.84% when the as-built sample is solution-treated at 550°C for 2h. This study indicates that the microstructure and mechanical properties of SLM-processed AlSi10Mg alloy can be tailored by suitable solution and artificial aging heat treatments.
•A unique cell type called gyroid is designed to construct lattice structures.•Curved cell surface as a self-supported feature avoids support structures.•Lattice structures with a wide volume ...fraction range were made.•Lattice structures were made at different orientations.•Strength and modulus increase with the increase in the volume fraction.
This paper investigates the manufacturability and performance of advanced and lightweight stainless steel cellular lattice structures fabricated via selective laser melting (SLM). A unique cell type called gyroid is designed to construct periodic lattice structures and utilise its curved cell surface as a self-supported feature which avoids the building of support structures and reduces material waste and production time. The gyroid cellular lattice structures with a wide range of volume fraction were made at different orientations, showing it can reduce the constraints in design for the SLM and provide flexibility in selecting optimal manufacturing parameters. The lattice structures with different volume fraction were well manufactured by the SLM process to exhibit a good geometric agreement with the original CAD models. The strut of the SLM-manufactured lattice structures represents a rough surface and its size is slightly higher than the designed value. When the lattice structure was positioned with half of its struts at an angle of 0° with respect to the building plane, which is considered as the worst building orientation for SLM, it was manufactured with well-defined struts and no defects or broken cells. The compression strength and modulus of the lattice structures increase with the increase in the volume fraction, and two equations based on Gibson–Ashby model have been established to predict their compression properties.
Shape memory polymers (SMPs), a type of promising smart materials, are gradually applied into digital light processing (DLP) technology to realize four-dimensional (4D) printing. However, there is ...still a great lack of shape memory photosensitive resins suitable for DLP. In this work, novel acrylate-based photosensitive resins designed for DLP are prepared to fabricate SMP parts with tert-Butyl acrylate/1, 6-hexanediol diacrylate (tBA/HDDA) networks. The influence of crosslinker concentration on the shape memory and mechanical properties is systematically investigated. The results show that the developed SMP with 10 wt% crosslinker can withstand 16 consecutive cycles and retain extremely high shape recovery ratio of 100% even after 14 cycles, the one with 20 wt% crosslinker possesses the best shape fixity ratio of over 96%, and the storage modulus can reach up to 1.48 × 103 MPa with 50 wt% crosslinker. Furthermore, these 4D printed SMPs only spends 7–13 s in the 180° shape recovery, indicating a good shape recovery rate. This work confirms that the designed SMPs have potential applications in many areas due to their excellent shape memory performance, and provides valuable guidance for the shape memory properties optimization of other SMPs.
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•A new type of shape memory polymer is developed by digital light processing technology to achieve 4D printing.•The correlation of crosslinker concentration and shape memory properties is established.•The printed shape memory polymer parts show desirable shape recovery ratio and durable cycle life.•The shape memory mechanism is comprehensively revealed.
► A novel lattice support structures for metal additive manufacturing is proposed. ► Low volume lattice supports are faster to build and efficient for material saving ► Residual stresses which ...remained in the part was released in the form of deflection ► Supports having bigger gap involve greater deformation and manufacturing failure ► Very thin lattice structures are too fragile to be consistently manufactured in SLM.
Metal additive manufacturing (MAM) of complex parts with overhangs typically requires the use of sacrificial support structures to hold the part during the process. This structures which are built simultaneously with the part, anchors the overhang geometry to the base plate and prevent distortion/curling resulting from thermal stresses. They are necessary, but add constraints to the geometries that the processes can make. The design and selection of support structure can influence the manufacturability of complex metal parts, material and energy utilization, manufacturing time and cost. This study takes a new step on the design and manufacturing a more efficient support through the novel application of lattice structures with very low volume fraction. Experiments were conducted in direct metal laser sintering (DMLS) machine using titanium alloy Ti6Al4V powder. Experimental results revealed that the type of structure, volume fraction and cell size are the main factors influencing the manufacturability, amount of support, and built time of lattice support structures. Lattice supports with very low volume fraction up to 8% were built, saving significant amount of materials used in the support while reducing built time of making MAM parts.
Solar cells are conventionally used to harvest energy in outer space, but they are ineffective in dark locations. Here, it is shown that superconducting materials—which work best in cold ...environments, such as those found in outer space—provide a mechanism to harvest energy that does not require light. A superconducting magnetic levitation (maglev) magnetoelectric generator (SMMG) can convert mechanical impacts to electricity at its working temperature <90 K. The SMMG device consists of a permanent magnet, a conductive coil, and a superconducting layer (SL). Owing to the existence of the SL, the permanent magnet levitates over the SL and rapidly returns to an equilibrium height after being displaced by a mechanical impact. The impact changes the gap between the levitated magnet and the coil, resulting in a variation in magnetic flux that induces electrical current in the coil. Thus, the SMMG converts low‐frequency (<3.7 Hz) mechanical energy to electricity. The output maximum peak voltage, peak power, and peak power density of the SMMG are 4.3 V, 35 mW, and 17.8 W m−2, respectively, with a load resistance of 300 Ω. The SMMG can charge a capacitor of 10 000 µF to 3.8 V with a continuous impact, which is sufficient to power critical wireless communication. The superconductor works best in cold environments and therefore is well‐suited for providing electricity to sensors and communication devices in outer space, particularly in places where the sun may not reach.
Superconducting materials—which work best in cold environments, such as those found in outer space—are shown to provide a mechanism to harvest energy that does not require light. A superconducting magnetic levitation (maglev) magnetoelectric generator can convert mechanical impact to electricity.
Inspired by shape‐morphing organisms in nature, researchers have developed various hydrogels with stimuli‐responsive swelling, shrinking, bending, folding, origami, rolling, twisting, or locomotion. ...These smart hydrogels are usually created by patterning or 4D printing. The shape morphing of hydrogels allows the fabrication of helixing, twisting, and rolling microstructures, all of which are hard to reproduce directly by ordinary techniques. More importantly, under external stimuli (e.g., solvent, humidity, temperature, light, pH, and electric/magnetic fields), many hydrogels exhibit recoverable shape morphing and thus find promising applications in grippers, sensors, valves, soft robotics, etc. Since shape morphing determines the functions of hydrogels in a great number of cases, herein, recent advances of stimuli‐responsive hydrogels are summarized, with their types, shape‐morphing mechanisms, fabrication methods, shape‐morphing modes, and extensive applications covered. The conclusion and perspectives are also presented to guide the design and fabrication of functional hydrogels.
The stimuli‐responsive shape morphing of hydrogels allows for the fabrication of helixing, twisting, and rolling structures, which can find promising applications in grippers, sensors, valves, soft robotics, etc. In this review, recent advances of stimuli‐responsive hydrogels are summarized, with their types, shape‐morphing mechanisms, fabrication methods, shape‐morphing modes, and extensive applications covered.
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