Minimal Surface Structures Research Articles

Method for preparing biomimetic ceramic structures with high strength and high toughness

Ceramic materials are highly regarded for their exceptional chemical and mechanical stability; however, their inherent brittleness limits their resistance to impact fractures. Researchers have investigated the design of biomimetic ceramic structures to overcome this problem, demonstrating the ability to toughen ceramics and expand their applications. However, the complexity of these structures makes the implementation of traditional processing methods challenging. To address this problem, a new preparation method for high-strength and high-toughness biomimetic ceramic structures is proposed. First, the primitive structure with the best mechanical performance was selected as the experimental object. Second, the vat photopolymerization printing process was optimized; further, primitive structures were designed with different wall thicknesses to investigate the effects of graded and variable-graded structures on the performance of triply periodic minimal surface structures. Finally, a polymer was used to impregnate the ceramic parts to prepare biomimetic structures. In the experiments, the biomimetic structures outperformed their pure ceramic counterparts in terms of toughness and avoided catastrophic failure. In particular, when the ceramic had graded structures, the energy absorption capability of the part increased by 202%. Finite-element modeling was used to analyze the stress concentration and distribution. Peridynamic simulations provided insights into the strengthening and toughening mechanisms at the micro level and guidance for developing damage-resistant, high-energy-absorbing materials.

Enhancing the performance of composite phase change materials using novel triply periodic minimal surface structures

Organic phase change materials (PCMs) are widely used in thermal management applications owing to their high latent heats of fusion and low cost. Unfortunately, their poor thermal conductivities severely hamper the thermal transport process. Hence, PCMs are often hybridized with high thermal conductivity materials that promote phase change for time-sensitive applications and potentially increase the power density of thermal energy storage (TES) devices. Optimized thermally conductive networks with high-latent-heat PCM matrices are critical in the thermal management of high heat flux applications. With advancements in additive manufacturing, it has become easier to create complex topologies, such as triply periodic minimal surfaces (TPMS), that can further augment the performance of composite PCMs. TPMS surfaces have shown great promise in improving thermal transport performance but investigations into their thermal properties remain limited. In this study, the thermal performances of PCM infused TPMS structures of wall thicknesses varying from 0.4 mm to 0.8 mm were systematically investigated. The TPMS structures were designed using level-set equations, and each system of structures was fabricated by selective laser melting, a metal additive manufacturing technique. Numerical investigations were performed to understand the phase change dynamics of PCM in TPMS cells and experiments were performed to determine their thermal properties and phase change performance for thermal energy storage applications. Our simulations revealed that for structures with uniform wall thickness of 0.4 mm, the novel Neovius structure resulted in the highest effective thermal conductivity enhancement. For a given thickness, it is thus hypothesized that more complex TPMS topologies have higher surface areas and volumes which enhance their thermal conductivities. However, the complex shape of the Neovius structure could not be further uniformly thickened without self-intersecting geometries. Ultimately, a balance of both the surface area and thickness of the TPMS cell determines the thermal conductivity enhancement. Overall, the 0.6 mm thick IWP cells had the highest thermal conductivity of 13.84 W/m K, which was consistently verified in experiments. This is likely due to the fact that it has a larger surface area than the P structure but is also thicker than the 0.4 mm Neovius structure. To further demonstrate the potential application of our PCM-based TPMS design, low temperature thermal cycling tests were performed. Our results showed the IWP cell structure promoted a more uniform temperature distribution as compared to the P cell. Phase change in the 0.6 mm thick IWP cell structure was completed 1.4 times faster than the 0.8 mm thick P cell and 1.8 times faster than the 0.6 mm thick P cell. The purpose of this study is to provide useful guidelines for the selection of TPMS structures for various applications such as battery packs and spacecraft and to open doors for the co-optimization of materials and device geometry for enhanced energy and power density.

Compression and resilient behavior of graded triply periodic minimal surface structures with soft materials fabricated by fused filament fabrication

Additive manufacturing is an effective method to realize complex biomimetic topology and tunable mechanical property. In the current work, to meet the requirements of damping buffers and energy absorbers, triply periodic minimal surface (TPMS) structure using two soft polymeric blends as feedstock materials were gradient design and manufactured via fused filament fabrication. The internal topography of Schwarz P, Gyroid and Diamond TPMS structures were observed by scanning electron microscope and micro-computed topography. The compressive test results demonstrated that Diamond possessed superior load-carrying and energy absorption capacity to Gyroid and Schwarz P structure. The energy absorption for graded Diamond and Gyroid structures were better than the uniform controls, whereas Schwarz P displayed an opposite trend. Meanwhile, less internal damage and good resilient behavior were observed for polymeric blends with better resistance to plastic deformation. Lastly, cycle loadings were conducted, and the elastic energy, consumed energy as well as the specific damping capacity for graded and uniform TPMS soft structures were explored. With the increase of loading cycles, the Diamond TPMS structure exhibited a better damping behavior whereas Schwarz P displayed an elastic behavior. The elastic deformation was gradually replaced by the inelastic deformation of energy consumption and dissipation.

Strontium-doped calcium silicate scaffolds with enhanced mechanical properties and tunable biodegradability fabricated by vat photopolymerization

 Strontium-doped calcium silicate (SrCS) bioceramics have demonstrated outstanding vasculogenic ability to repair large segmental bone defects, while their poor mechanical properties and rapid degradation rate remain the major obstacles in clinical treatment. Here, we proposed a novel approach to significantly enhance the mechanical properties of SrCS bioceramics with tunable biodegradability using micron barium titanate-based (BTA) powders as a dopant. Biomimetic SrCS-BTA scaffolds with triply periodic minimal surface structures were fabricated by vat photopolymerization. The effects of BTA content on microtopography, mechanical properties, degradability, and bioactivity of composite scaffolds were studied. On the one hand, the BTA greatly increased the maximum densification rate of SrCS ceramics by 84.37%, while the corresponding densification temperature decreased by 95°C. On the other hand, CaTiO3 generated by the reaction of SrCS and BTA intercepted cracks at the grain boundaries, and thus, the mechanical properties were enhanced due to the pinning effect. The SrCS-40BTA scaffold exhibited much higher compressive strength and elastic modulus by 296% compared with the pure SrCS scaffold. The energy absorption of SrCS-40BTA scaffolds was 5.6 times higher than that of the pure SrCS scaffold. In addition, biocompatible SrCS-BTA scaffolds with lower degradation rates can play a supporting role in the process of repair for a longer duration. This work provides a promising strategy to fabricate biomimetic scaffolds with highly enhanced mechanical properties and tunable biodegradability for repairing damaged large segmental bone tissues.

Freeform thermal-mechanical Bi-functional Cu-plated diamond/Cu metamaterials manufactured by selective laser melting

The leverage of selective laser melting (SLM) successfully fabricate metal matrix composites (MMCs) metamaterials with freeform intricate triply periodic minimal surface (TPMS) structures that are not possibly fabricated by conventional methods and exhibit exceptional mechanical properties. SLM fabricated high precision MMCs metamaterial TPMS structures are of great potential in energy conversion, heat management and lightweight applications. Due to the self-supporting geometric characteristics of TPMS, the metamaterial structures could effectively overcome the manufacturing constraints of SLM. Besides, their freeform capability offers great opportunities to be bi-functional or multi-functional through the selection of materials as well as the design optimization of structure. Diamond can offer unique advantages in the field of heat management due to its outstanding thermal and mechanical properties. The addition of micro-sized diamond particles into copper can tailor its coefficient of thermal expansion (CTE) while enhancing its thermal conductivity (TC). SLM fabricated diamond reinforced copper MMCs metamaterials with TPMS structure could bring outstanding thermal-mechanical bi-functional properties for prospective lightweight thermal management applications. In our previous work, the interfacial bonding issue between diamond particles and Cu matrix was resolved by a coating of copper on micro-sized diamond particle reinforcement. In this present work, 1 vol% Cu-plated diamond/Cu metamaterials with three various TPMS (Gyroid-G, Schwarz Primitive-P, Diamond-D) structures were successfully fabricated via SLM for the first time. Their bi-functional heat transfer and compression behaviors were evaluated by measurement and numerical simulation for three TPMS (G, P, D) structures and TPMS (D) structures with various lattice thicknesses. From the lightweight perspective of three TPMS structures with 0.2 mm wall thickness, the order of these structure is TPMS P structure, TPMS G structure, TPMS D structure (0.2 mm wall thickness, 0.2 P > 0.2 G > 0.2D). If heat transfer performance is an important consideration, The 0.2D structure can be selected from the three TPMS structures. This research also investigated the continuous design of TPMS D structure with various wall thickness and creatively proposed a flexible TPMS design paradigm toward advanced thermal-mechanical bi-functional Cu-plated Diamond/Cu metamaterials via SLM for prospective lightweight thermal management applications.

Mechanical properties and failure analysis of 3D-printing micron-scale ceramic-based triply periodic minimal surface scaffolds under quasi-static-compression and low-speed impact loads

Numerous developments in additive manufacturing have endowed triply periodic minimal surface (TPMS) structures with excellent mechanical properties, providing possibilities for the wide application prospects of such scaffolds in repairing bone defects. However, current studies mainly focus on the basic mechanical and biomedical properties of TMPS with relatively large scale and low precision made from conventional materials such as stainless powder. Therefore, challenges exist in manufacturing ceramic-based TPMS bone scaffolds that stratify the precision requirements for human bones at the micron scale and further investigating their dynamic mechanical properties. Herein, we successfully design and fabricate two TPMS scaffolds named TPMS-B and TPMS-C with microstructures similar to that of human bone utilizing advanced 3D-printing technology. The experiments reveal that TPMS-C outperforms conventional porous scaffold (Normal-A) and TPMS-B for certain parameters such as specific strength and specific energy absorption. Moreover, the numerical simulation analysis illustrates that structural asymmetry and discontinuous boundaries are the main causes of completely destructive disparities in TPMS-C when exposed to given loads. Meanwhile, the cytocompatibility and osteogenic differentiation of the three scaffolds are verified. The objective of this work is to reveal the mechanical properties and failure analysis of novel 3D-printing materials that can be used to fabricate advanced TPMS bone scaffolds for bone defects treatment.

Finite element analysis of the mechanical properties of sheet- and skeleton-gyroid Ti6Al4V structures produced by laser powder bed fusion

Additive manufacturing, and laser powder bed fusion (L-PBF) in particular, can produce complex geometric components with high resolution, and is very suitable for manufacturing lightweight triple periodic minimal surface (TPMS) structures to achieve lightweight. With regard to the two forms of the same structure, most of the previous studies focused on sheet-TPMS, but lacked the understanding of the difference between skeleton-TPMS and sheet-TPMS structures. In order to explore the characteristics of these two structures and provide theoretical support for the development of lightweight structure design, this paper compares the manufacturing performance and defect distribution of skeleton-gyroid (GSK) and sheet-gyroid structures (GSH). It employs high-precision finite element analysis (FEA) prediction and experimental verification to compare comprehensively the mechanical properties, failure behavior and energy absorption characteristics of the two structures. The results show that, compared to GSK, the larger specific surface area of GSH leads to more unmelted powder and draping adhesion, without affecting its higher stiffness and strength. Moreover, the more stable failure mode of GSH leads to more gentle stress platform stage and superior energy absorption performance. The results predicted by simulation are highly consistent with the experimental results. This improved understanding allows better prediction of the mechanical properties of the specimens using the Gibson–Ashby theory, which can reduce the experimental cost and time, and improve the resource consumption of TPMS structural performance research. This study can open new possibilities for the design and application of TPMS structures.

INFLUENCE OF STRAIN RATE ON THE ASHBY-GIBSON PARAMETERS OF SHEET DIAMOND LATTICE STRUCTURES

Triply periodic minimal surface structures (TPMSs) can be used as a substitute for polymeric foams in applications where is necessary to absorb a large amount of energy with high structural deformation. Diamond TPMS offers higher energy absorption per unit weight. This structure is based on the Ashby-Gibson material model that establishes the main mechanical material properties as functions of the relative density and material properties. However, since TPMSs are used in dynamic applications, it is essential to analyse them under dynamic loads. In this study, we investigate the influence of the strain rate on the Ashby-Gibson parameters of sheet diamond Keywords: Triple periodic minimal surface; strain rate; additive manufacturing; diamond; Ashby-Gibson

Effect of heat treatment on mechanical properties, failure modes and energy absorption characteristics of lattice skeleton and sheet structures fabricated by SLM

Triply periodical minimal surface (TPMS) structures have attracted much attention in the biomaterials, aerospace, and automotive industries because they are lightweight, have high strength, and can absorb energy and shocks. In this study, uniform skeletal (USK), uniform sheet (USH), grade skeletal (GSK), and grade sheet (GSH) diamond lattice structures with the same 20% volume fraction were fabricated by selective laser melting (SLM) using AlSi10Mg metal powder. Their mechanical properties, deformation behavior, and energy absorption performance were systematically investigated by compression tests and finite element analysis (FEA). The skeleton structures had a higher elastic modulus, yield strength, and more severe stress fluctuation than the sheet structures. In addition, comparing the 45° shear deformation for as-built uniform structures accompanied by a mixture of ductile and brittle fracture modes, both gradient structures fractured by a sub-layer pattern from the layer with a lower volume fraction. Furthermore, the numerical simulation results illustrated that the stress of the skeleton structures was mainly concentrated at the skeleton joint, while the sheet structures were distributed evenly on the thin wall, without being concentrated in the interconnection region. For skeleton structures, heat treatment controlled the failure degree by improving the microstructure of the material, while for GSH structures at 300 °C, the fracture mode changed from the previous layer-by-layer fracture to a 45° shear failure. The accumulated energy absorption of gradient structures was more than that of the uniform structure, especially the GSH structures and the energy absorption efficiency of the skeleton structures was higher.

Biomimetic design and fabrication of PEEK and PEEK/CF cage with minimal surface structures by fused filament fabrication

The interbody fusion cages are critical implants in spinal fusion surgeries, which stabilize the spine and treat pains resulting from degenerative disc disease. The commercial used poly (ether-ether-ketone) (PEEK) cages are non-porous and manufactured by machining, which cause material waste and insufficient bioactivity. Fused filament fabrication (FFF) technology provides opportunities to fabricate fusion cages with specific shape and intricate porous architectures for bone ingrowth and nutrient exchange. Herein, PEEK-based lattice structures are designed and firstly fabricated by FFF based on three minimal surfaces including Schwarz P (P), Diamond (D) and Gyroid (G). The effects of cellular architecture and unit cell on the compressive properties are investigated. The results demonstrate that D and G surfaces possess superior load-carrying and energy absorption capacity. The prototyping defects in PEEK lattices were lesser than those in PEEK/CF samples. Also, it is notable that the compression performance of FFF-printed samples exhibited a strong anisotropy depending on the printing direction. After printing, annealing is an effective post treatment to further improve the crystallinity and compressive strength of PEEK lattice surfaces. Therefore, the novel PEEK porous structures with optimized mechanical performance show great potentials in the applications as fusion cage implants.

Experimental investigations into nonlinear dynamic behaviours of triply periodical minimal surface structures

Natural frequency, damping ratio and dynamic stiffness are fundamental to the performance of structures subjected to dynamic loads. Triply Periodic Minimal Surface (TPMS) composite structures, celebrated for their superior energy absorption capacity and specific strength, represent some of the most promising meta-structures. However, their dynamic properties are yet to be fully understood, thereby hindering their practical applications within civil engineering domains. Damping properties, crucial to vibration reduction, remain particularly elusive; previous studies have not successfully established a connection between these properties and the force excitation amplitude in TPMS structures. This study aims to compare the damping properties of different TPMS structures and to investigate their potential for adoption within civil engineering fields. Three types of TPMSs, including Schoen I-graph-wrapped package surface (IWP), Schwarz primitive (Primitive) and Schoen Gyroid (Gyroid), have been adopted to design solid and sheetal TPMS composite structures with identical relative density (50%) to compare their damping properties under varying excitation amplitudes. These TPMS structures are manufactured from photosensitive resin (UV resin) using stereolithography 3D printing technology. Owing to the lack of previous research into the damping properties and dynamic stiffness of TPMS structures as support structures, we have conducted single-freedom modal tests to determine the modal parameters, including natural frequency and damping ratios. Our novel results indicate that the natural frequency and damping ratio of the TPMS structures vary with the excitation amplitude. Additionally, the dynamic stiffness of TPMS structures reveals a similar decreasing trend to frequency when load amplitude escalates. As the excitation amplitude increases, the TPMS structures demonstrate softening and are capable of offering a higher vibration damping coefficient. Notably, the SS-Gyroid structure exhibits higher stiffness and damping ratio compared to other TPMS structures. These fresh insights pave the way for the integration of 3D printed smart TPMS structures within civil engineering, particularly for vibration reduction and efficient material usage. A judicious TPMS structure design can provide relatively high stiffness and damping ratio without excessive material use.

Performance optimization of Si/SiC ceramic triply periodic minimal surface structures via laser powder bed fusion

AbstractSiC ceramic lattice structures (CLSs) via additive manufacturing (AM) have been recognized as potential candidates in engineering fields owing to their various merits. Compared with traditional SiC CLSs, SiC triply periodic minimal surface (TPMS) CLSs could possess more outstanding properties, making them more promising for wider applications. Since SiC CLSs are hard to be fabricated through stereolithography techniques because of inferior light performance, the laser powder bed fusion (LPBF) process via selective sintering is an effective method to prepare near‐net‐shaped SiC TPMS lattices. As the mechanical performances of lattice structures are the foundation for future practical applications, it is of great significance to optimize the preparation process, thus improving the mechanical properties of SiC TPMS structures. In this work, the optimal printing parameters of the LPBF and liquid silicon infiltration process for SiC ceramic TPMS CLSs with three different volume fractions were systematically illustrated and analyzed. The effects of the printing parameters and carbon densities on the fabrication accuracy, microstructure, and mechanical performance of SiC TPMS CLSs were defined. The mechanism of the reactive sintering process for the SiC TPMS lattice structure was revealed. The results reveal that Si/SiC TPMS CLSs with optimum preparation have superior manufacturing accuracy (most less than 6%), relatively high bulk densities (about 2.75 g/cm3), low residual Si content (6.01%), and excellent mechanical properties (5.67, 15.4, and 44.0 MPa for Si/SiC TPMS CLSs with 25%, 40%, and 55% volume fractions, respectively).

Field-driven design and performance evaluation of dual functionally graded triply periodic minimal surface structures for additive manufacturing

Triply periodic minimal surface (TPMS) structures prepared by additive manufacturing (AM) have been widely used in aerospace and thermal management systems due to their functional advantages such as high specific strength and excellent heat transfer coefficient. However, lattices with uniform or simple gradients cannot match the regional diversity needs of functional advantages in service. This study proposed a field-driven AM data processing framework for dual functionally graded TPMS lattices. For unified data processing, mathematical functions, simulated outcomes, and geometric models were transformed into fields. I-WP and Diamond units were selected as the primitive and filling structures of Ti-6Al-4V lattices, respectively. According to the functional requirements, the gradient distribution design guided by the simulated stress field is completed through the proposed framework. The results illustrate that the field-driven dual graded lattices present superior compressive mechanical response. At almost equal volume fractions, their compressive strength is approximately 100% more than that of primitive lattices and 69% greater than that of dual uniform lattices. Furthermore, the dual lattices have larger specific surface areas than the primitive lattices, making them better at heat insulation and heat dissipation. This field-driven digital framework will show enormous potential in the matching design of functionally graded lattices.

Assessment of flow and heat transfer of triply periodic minimal surface based heat exchangers

An efficient intermediate heat exchanger is crucial for ensuring the safe operation, lifespan and energy efficiency of the advanced nuclear systems. Benefiting from the development of additive manufacturing technology, it is possible to design and optimize heat exchangers by introducing triply periodic minimal surface (TPMS) structures. With the excellent mechanical and thermal performance of TPMS, further improvements in the energy efficiency of advanced nuclear systems are achievable. In this study, I-WP surface, Primitive surface based heat exchangers and a printed circuit heat exchanger for accelerator driven subcritical systems are constructed in three dimensions. In order to obtain the potential enhancement of thermal performance of TPMS-based heat exchangers, the fluid flow and conjugate heat transfer characteristics in TPMS heat exchangers, especially for the specific working medium of lead-bismuth eutectic (LBE) are investigated. A parametric analysis is conducted on the key design variables including the solid volume fraction and hydraulic diameter. The results indicate that TPMS-based heat exchangers could achieve about 2–3 times the total heat transfer rate with half the volume of a printed circuit heat exchanger. The TPMS topologies contribute greater heat transfer enhancement on the Helium side than the LBE side, which helps to optimize the thermal resistance allocation in Helium-LBE heat exchangers. An increase of solid volume fraction enhances the convective heat transfer of Helium in I-WP heat exchanger, while homogenizing the local thermal performance. This study provides a database for the design and optimization of TPMS-based heat exchangers, which contributes to the sustainable future target.

Novel modified triply periodic minimal surfaces (MTPMS) developed using genetic algorithm

The desirable properties of natural porous materials have inspired humans to design cellular materials with remarkable properties such as high energy absorption, acoustic and thermal insulation, and high specific strength structures. Triply Periodic Minimal Surface (TPMS) structures are particularly important among the architected materials. In this research, we have developed a novel approach based on a genetic algorithm for geometry modification of TPMS structures. The approach is exploited to enhance the effective thermal and mechanical properties of TPMS structures, namely Primitive, IWP, Gyroid, and GPrime. New modified TMPS structures (MTPMS) have much higher Young's modulus and thermal conductivity than their base structures, and some of them have properties very close to the upper Hashin-Shtrikman bounds. Unlike previous studies conducted to improve the properties of TPMS structures, MTPMS can be expressed by simple equations. Although MTPMS are not generally considered minimal surfaces, they nonetheless possess the desirable geometric qualities of TPMS structures, such as being smooth and splitting space into two non-intersecting and continuous domains, etc.

3D-Printed PEEK/Silicon Nitride Scaffolds with a Triply Periodic Minimal Surface Structure for Spinal Fusion Implants.

The issue of spine-related disorders is a global healthcare concern that requires effective solutions to restore normal spine functioning. Spinal fusion implants have become a standard approach for this purpose, making it crucial to develop biomaterials and structures that possess high osteogenic capacities and exhibit mechanical properties and dynamic responses similar to those of the host bone. This study focused on the fabrication of 3D-printed polyether ether ketone/silicon nitride (PEEK/SiN) scaffolds with a triply periodic minimal surface (TPMS) structure, which offers several advantages, such as a large surface area and uniform stress distribution under load. The mechanical properties and dynamic response of PEEK/SiN scaffolds with varying porosities were evaluated through mechanical testing and finite element analysis. The scaffold with 30% porosity exhibited a compressive strength (34.56 ± 1.91 MPa) and elastic modulus (734 ± 64 MPa) similar to those of trabecular bone. In addition, the scaffold demonstrated favorable damping properties. The biological data revealed that incorporating silicon nitride into the PEEK scaffold stimulated osteogenic differentiation. In light of these findings, it can be inferred that PEEK/SiN TPMS scaffolds exhibit significant potential for use in bone tissue engineering and represent a promising option as candidates for spinal fusion implants.

3D-Printed Graphene Nanoplatelets/Polymer Foams for Low/Medium-Pressure Sensors.

The increasing interest in wearable devices for health monitoring, illness prevention, and human motion detection has driven research towards developing novel and cost-effective solutions for highly sensitive flexible sensors. The objective of this work is to develop innovative piezoresistive pressure sensors utilizing two types of 3D porous flexible open-cell foams: Grid and triply periodic minimal surface structures. These foams will be produced through a procedure involving the 3D printing of sacrificial templates, followed by infiltration with various low-viscosity polymers, leaching, and ultimately coating the pores with graphene nanoplatelets (GNPs). Additive manufacturing enables precise control over the shape and dimensions of the structure by manipulating geometric parameters during the design phase. This control extends to the piezoresistive response of the sensors, which is achieved by infiltrating the foams with varying concentrations of a colloidal suspension of GNPs. To examine the morphology of the produced materials, field emission scanning electron microscopy (FE-SEM) is employed, while mechanical and piezoresistive behavior are investigated through quasi-static uniaxial compression tests. The results obtained indicate that the optimized grid-based structure sensors, manufactured using the commercial polymer Solaris, exhibit the highest sensitivity compared to other tested samples. These sensors demonstrate a maximum sensitivity of 0.088 kPa-1 for pressures below 10 kPa, increasing to 0.24 kPa-1 for pressures of 80 kPa. Furthermore, the developed sensors are successfully applied to measure heartbeats both before and after aerobic activity, showcasing their excellent sensitivity within the typical pressure range exerted by the heartbeat, which typically falls between 10 and 20 kPa.

Effective Thermal Conductivity and Heat Transfer Characteristics of a Series of Ceramic Triply Periodic Minimal Surface Lattice Structure

Triply periodic minimal surface (TPMS) structures with high surface area, high porosity, complex pore channels, and pore size distribution have great potential for application in thermal metamaterials and thermal engineering applications. To demonstrate the possibility of the use of TPMS structures as thermal metamaterials, the thermal insulation properties and heat transfer mechanisms of TPMS structures are investigated in detail. The results show that modulation of the volume fraction to within 15% by a rational geometric design indicates the possibility to obtain excellent lightweight properties. The effective thermal conductivity is within 0.25 W m−1 K−1, which is much lower than this component, indicating that the TPMS structure is designed to reduce the effective thermal conductivity and provide a lightweight design. However, in a high‐temperature environment, reasonable structural parameters can shield the cavity radiation in the TPMS structure and play an effective role to provide high‐temperature thermal insulation. Finally, based on the relationship between structural parameters and thermal insulation performance, a dynamic density TPMS‐graded structure is proposed, which exhibits a better thermal insulation performance than the conventional TPMS structure both at room temperature and at high temperature.

3D Nanoarchitectured Hexagonal Boron Nitride with Integrated Single Photon Emitters

AbstractTwo‐dimensional (2D) hexagonal boron nitride (hBN) is one of the most promising candidates to host solid‐state single photon emitters (SPEs) for various quantum technologies. However, the 2D nature with an atomic‐scale thickness leads to inevitable challenges in spectral variability caused by substrate disturbance, lattice strain heterogeneity, and defect variation. Here, three‐dimensional (3D) nanoarchitectured hBN is reported with integrated SPEs from native defects generated during high‐temperature chemical vapor deposition (CVD). The 3D hBN has a quasi‐periodic gyroid minimal surface structure and is composed of a continuous 2D hBN sheet with built‐in convex and concave curvatures that promote the formation of optically active and thermally robust native defects. The free‐standing feature of the gyroid hBN with a nearly zero mean curvature can effectively eliminate the substrate disturbance and minimize lattice strain heterogeneity. As a result, naturally occurring defects with a narrow SPE spectral distribution can be created and activated as color centers in the 3D hBN, and the density of the SPEs can be tailored by CVD temperature.

Experimental study on flow and heat transfer performance of triply periodic minimal surface structures and their hybrid form as disturbance structure

The triply periodic minimal surface (TPMS) structure is widely used in forced convection heat transfer. Additionally, developing of parametric modeling and additive manufacturing technology makes TPMS manufacturing possible. In this work, the forced convective heat transfer performance of three standard TPMS, the Gyroid (G-type), the Diamond (D-type), and the Primitive (P-type) structures and their hybrids, the Gyroid/Diamond (GD-type), the Gyroid/Diamond (GP-type), and the Diamond/Primitive (DP-type) was studied. The pressure drop, heat transfer coefficient, and overall heat transfer performance are comprehensively investigated. The results show that for the air Reynolds number (Re) range of 412.48 to 1257.96 the average pressure drop of G-type is 43.2% and 38.86% lower than that of P-type and D-type, respectively. The important influencing factor related to pressure drop is structural characteristics. The D-type has the highest heat transfer coefficient (1398 W/m2·K) with an average value exceeding 30.83% of the G-type and 28.39% of the P-type, respectively. Hybrid GD-type and DP-type both show good heat transfer performance. The heat transfer coefficient of the GD-type is 8.41% higher than that of the G-type, and the DP-type was 4.41% higher than of the P-type.