We present a highly-resolved 2D numerical simulation of a wedge-induced Oblique Detonation Wave (ODW) using a 9-species 21-reaction chemical kinetic mechanism for a stoichiometric H2-air mixture. ...Adaptive Mesh Refinement (AMR) is leveraged to obtain a resolution close to the continuum limit at the finest level (Δxfinest=0.78μm=20λ, where λ is the mean-free path of the fuel–air mixture), which spans the ODW front and its transverse waves. The simulation is performed for a sufficiently large domain, enabling us to unveil the multi-zonal structure of the ODW. We capture, for the first time, the onset of microscopic hypersonic jets (micro-jets) far downstream of the wedge tip associated with cellular structures resembling those of a multi-headed Normal Detonation Wave (NDW). In contrast, the upstream “cell-like” structure (christened as “pseudo-cellular” hence) are found to be devoid of these micro-jets with a morphology similar to that of single-headed NDWs, such as spinning/zig-zag detonations in tubes/2D channels, respectively. A detailed investigation into the transverse-shock structure downstream reveals that a colliding pair of transverse waves lead to the micro-jetting phenomenon. The absence of one of the pair of transverse waves in the upstream region results in the observed pseudo-cellular structures. The origin of these transverse waves in an ODW, unclear in previous literature, is shown to arise from coalescing and strengthening of Compression Waves (CWs) that are produced from two distinct mechanisms. During the “early” phase of the ODW stabilization, CWs are formed as a result of local blast events. In the subsequent “middle” phase, these are formed as a result of the shear-layer instabilities coupling with the local shock structure, leading to the so-called left-running transverse waves (LRTWs) upstream and the right-running transverse waves (RRTWs) downstream. The identified mechanisms offer a plausible explanation on why ODWs exhibit a multi-zonal morphology.
Novelty and Significance Statement
The present study is one of the very few studies in the Oblique Detonation Wave (ODW) literature that includes multi-step chemistry while solving for the compressible reacting Navier-Stokes equations on a large simulation domain revealing the multi-zonal structure of the ODW. Furthermore, the resolution employed for the study approaches the continuum limit, making it on-par with the current state-of-the-art for ODW simulation. For the first time, this study has demonstrated the existence of microscopic hypersonic jets (micro-jets) far downstream of the wedge tip in a wedge-induced ODW and a method to isolate them in numerical simulations, leading to insights on the broader micro-jetting phenomenon in detonations. The existence of a cell-like (which we term as “pseudo-cellular”) region bearing similarity with that of single-headed spinning detonations is also noted due to the absence of a transverse wave family upstream. The exact physical mechanisms leading to the formation of transverse waves in ODW are also investigated, which were previously ambiguous in the literature.
This paper provides an overview on the main additive manufacturing/3D printing technologies suitable for many satellite applications and, in particular, radio-frequency components. In fact, nowadays ...they have become capable of producing complex net-shaped or nearly net-shaped parts in materials that can be directly used as functional parts, including polymers, metals, ceramics, and composites. These technologies represent the solution for low-volume, high-value, and highly complex parts and products.
Melt electrowriting (MEW) is an additive manufacturing technology that fabricates high‐resolution objects. Printing curved and complex patterns, however, requires additional attention and planning to ...achieve accurate fiber placement. In this context, the jet speed, as measured by the critical translation speed (CTS), is found to be an essential factor for accurately direct‐writing complex nonlinear patterns. When the jet and the translation speed match, the vertical jet better approximates the tool path when the printing is nonlinear. As demonstrated here, the entire printed structure gradually deforms when the jet lag increases. For the first time with MEW, circular arc toolpaths are focused on to expand the design complexity, and there is evidence that the resolution is further improved by printing slightly under the CTS. When using such circular arc toolpaths, inwards tilting of the fiber walls can be observed and can be corrected with microscale layer shifting, shown with scaffolds based on knitting‐type designs. The combination of printing at the CTS with circular arcs increases the manufacturing complexity of curved patterns and has implications for the design and utility of MEW.
A variety of complex nonlinear scaffolds fabricated by melt electrowriting are reported for the first time. Arcs used as a repeating building block is a simple‐to‐implement but versatile avenue enabling to expand the design freedom of melt electrowriting and 3D print new, complex microstructures tailored for tissue engineering applications.
At the intersection between chemical and materials engineering, binder jetting is an additive manufacturing technique that foregoes many of the limitations of the conventional metal 3D printing ...technique. Binder composition and thermal post‐processing influence final part quality. Herein, three different atmospheres, ranging from reactive (air) to non‐reactive (vacuum, argon), are studied to determine their effect on the quality of binder jetting printed parts after thermal treatments, namely debinding and sintering. These parts were printed using SS316L powder. Samples debound in air were negatively affected as they presented high porosities and low densities, averaging 6.80 (±0.4) g/cm3, whereas samples debound and sintered under vacuum demonstrated the best outcome with low porosities and high densities, averaging 7.65 (±0.1) g/cm3. This study highlights how oxide formation during debinding causes ferrite phase formation during sintering and how it affects atomic diffusion in the samples during both thermal treatments. This research also demonstrates the respective effects of these on the densification and porosity of parts.
Additive manufacturing has revolutionized manufacturing across a spectrum of industries by enabling the production of complex geometries with unparalleled customization and reduced waste. Beginning ...as a rapid prototyping tool, additive manufacturing has matured into a comprehensive manufacturing solution, embracing a wide range of materials, such as polymers, metals, ceramics, and composites. This paper delves into the workflow of additive manufacturing, encompassing design, modeling, slicing, printing, and post-processing. Various additive manufacturing technologies are explored, including material extrusion, VAT polymerization, material jetting, binder jetting, selective laser sintering, selective laser melting, direct metal laser sintering, electron beam melting, multi-jet fusion, direct energy deposition, carbon fiber reinforced, laminated object manufacturing, and more, discussing their principles, advantages, disadvantages, material compatibilities, applications, and developing trends. Additionally, the future of additive manufacturing is projected, highlighting potential advancements in 3D bioprinting, 3D food printing, large-scale 3D printing, 4D printing, and AI-based additive manufacturing. This comprehensive survey aims to underscore the transformative impact of additive manufacturing on global manufacturing, emphasizing ongoing challenges and the promising horizon of innovations that could further elevate its role in the manufacturing revolution.
A limitation of binder jetting additive manufacturing is the low density of fabricated parts. Mixing powders with different sizes is a promising approach to increase powder bed packing density and, ...hence, printed part density. However, in previous studies mixed powder feedstock was prepared by trial and error method. In this research, both modeling and experimental methods were used to prepare the bimodal powder feedstocks. Analytical packing model was introduced for irregular powders. A bimodal powder was prepared by mixing two different-sized silicon carbide powders (i.e. coarse and fine) using ball mill, and their tap densities were measured. Silicon carbide plates were printed using the coarse and bimodal powders by a commercial binder jetting system. Results showed that the modeling method could predict the tap density of bimodal powders with high accuracy. The printed parts from bimodal powder achieved higher green densities than those from the unimodal powder.
This article provides an overview of different particle-bed 3D printing techniques for the production of concrete elements. A classification is proposed which considers the direct production of ...concrete components, the production of formwork as well as composite components by means of a permanent formwork. Three techniques are considered as relevant for concrete construction, i.e. selective binder activation, selective paste intrusion and binder jetting. Design as well as material aspects are addressed. The underlying physics of fluid infiltration into the particle-bed and its effect on the properties of the hardened material are discussed on the basis of recent research results. Finally, the first applications of particle-bed 3D printing are presented which demonstrate the potential of this technique in concrete construction.
Binder jetting is a promising additive manufacturing process to fabricate a wide range of materials, including ceramics. The objective of this research is to investigate the effects of particle size ...on flowability and sinterability of the feedstock powder and resultant properties of fabricated parts. A commercial ceramic composite powder was sieved into three different particle size ranges: designated as fine, medium, and coarse powders, respectively. Flowability and sinterability measurements were performed on the sieved powders. After printing and sintering, the density of samples was measured with the Archimedes’ method. Compressive tests were performed to investigate the mechanical properties of the fabricated parts. The experimental results showed that flowability increased but sinterability decreased as particle size increased. The printed and sintered density was dependent on both flowability and sinterability: the highest density was achieved by the medium powder due to the balance between flowability and sinterability. The compressive strength was dominated by sinterability: the highest strength was achieved by the fine powder because of the highest sinterability.
Binder-jetted parts require a subsequent sintering process to achieve the desired density and mechanical properties, resulting in anisotropic shrinkage and creep distortion. To compensate for this, ...accurate prediction of densification behavior is required. Although there has been research on optimizing the printing and sintering process to increase the reproducibility of Ti–6Al–4V parts, there is no accessible literature on modeling the densification behavior. In this study, the densification of binder-jetted Ti–6Al–4V samples is investigated experimentally through experiments with interrupted sintering cycles and dilatometry. Through these experiments, it is possible to determine the density changes throughout the entire sintering cycle as well as the anisotropic shrinkage of the printed samples. The results are used to calibrate phenomenological diffusion models for intermediate stage and final stage sintering capable of mapping the densification behavior throughout the entire sintering process. Due to experimental limitations, material parameters for grain growth are determined from experimental densification data.
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•Phenomenological diffusion based densification model calibrated via experimental data for binder jetted Ti–6Al–4V parts.•Measurement of thermal expansion and anisotropy with dilatometry experiments.•Good agreement between sintering experiments in furnace and dilatometry experiments.•Determine material parameters for grain growth only through experimental data of densification.
Spray drying, binder jetting and chemical vapor infiltration (CVI) were used in combination for the first time to fabricate SiC whisker-reinforced SiC ceramic matrix composites (SiCW/SiC). Granulated ...needle-shaped SiCW was spray dried into SiCW spherical particles to increase flowability and thereby increase printability. Then, binder jetting was employed to print a novel SiCW preform with two-stage pores using the SiCW spherical particles. The subsequent CVI technology produced pure, dense, and continuous SiC matrix with high modulus and strength. Consequently, SiCW/SiC with appropriate mechanical properties was obtained. Finally, the challenges of the novel method and the ways to improve the mechanical properties of SiCW/SiC are discussed.
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