Enhanced energy-absorbing and sound-absorbing capability of functionally graded and helicoidal lattice structures with triply periodic minimal surfaces

Lattice structures have drawn much attention in engineering applications due to their lightweight and multi-functional properties.In this work,a mathematical design approach for functionally graded(FG)and helicoidal lattice structures with triply periodic minimal surfaces is proposed.Four types of lattice structures including uniform,helicoidal,FG,and combined FG and helicoidal are fabricated by the additive manufacturing technology.The deformation behaviors,mechanical properties,energy absorption,and acoustic properties of lattice samples are thoroughly investigated.The load-bearing capability of helicoidal lattice samples is gradually improved in the plateau stage,leading to the plateau stress and total energy absorption improved by over 26.9%and 21.2%compared to the uniform sample,respectively.This phenomenon was attributed to the helicoidal design reduces the gap in unit cells and enhances fracture resistance.For acoustic properties,the design of helicoidal reduces the resonance frequency and improves the peak of absorption coefficient,while the FG design mainly influences the peak of absorption coefficient.Across broad range of frequency from 1000 to 6300 Hz,the maximum value of absorption coefficient is improved by18.6%-30%,and the number of points higher than 0.6 increased by 55.2%-61.7%by combining the FG and helicoidal designs.This study provides a novel strategy to simultaneously improve energy absorption and sound absorption properties by controlling the internal architecture of lattice structures.

Adaptive enhancement design of triply periodic minimal surface lattice structure based on non-uniform stress distribution

The Schwarz primitive triply periodic minimal surface(P-type TPMS)lattice structures are widely used.However,these lattice structures have weak load-bearing capacity compared with other cellular structures.In this paper,an adaptive enhancement design method based on the non-uniform stress distribution in structures with uniform thickness is proposed to design the P-type TPMS lattice structures with higher mechanical properties.Two types of structures are designed by adjusting the adaptive thickness distribution in the TPMS.One keeps the same relative density,and the other keeps the same of non-enhanced region thickness.Compared with the uniform lattice structure,the elastic modulus for the structure with the same relative density increases by more than 17%,and the yield strength increases by more than 10.2%.Three kinds of TPMS lattice structures are fabricated by laser powder bed fusion(L-PBF)with 316L stainless steel to verify the proposed enhanced design.The manufacture-induced geometric deviation between the as-design and as-printed models is measured by micro X-ray computed tomography(μ-CT)scans.The quasi-static compression experimental results of P-type TPMS lattice structures show that the reinforced structures have stronger elastic moduli,ultimate strengths,and energy absorption capabilities than the homogeneous P-TPMS lattice structure.

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

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.

Innovative Design and Additive Manufacturing of Regenerative Cooling Thermal Protection System Based on the Triply Periodic Minimal Surface Porous Structure

The new regenerative cooling thermal protection system exhibits the multifunctional characteristics of load-carrying and heat exchange cooling,which are fundamental for the lightweight design and thermal protection of hypersonic vehicles.Triply periodic minimal surface(TPMS)is especially suitable for the structural design of the internal cavity of regenerative cooling structures owing to its excellent structural characteristics.In this study,test pieces were manufactured using Ti6Al4V lightweight material.We designed three types of porous test pieces,and the interior was filled with a TPMS lattice(Gyroid,Primitive,I-WP)with a porosity of 30%.All porous test pieces were manufactured via selective laser melting technology.A combination of experiments and finite element simulations were performed to study the selection of the internal cavity structure of the regenerative cooling thermal protection system.Hence,the relationship between the geometry and mechanical properties of a unit cell is established,and the deformation mechanism of the porous unit cell is clarified.Among the three types of porous test pieces,the weight of the test piece filled with the Gyroid unit cell was reduced by 8.21%,the average tensile strength was reduced by 17.7%compared to the solid test piece,while the average tensile strength of the Primitive and I-WP porous test pieces were decreased by 30.5%and 33.3%,respectively.Compared with the other two types of unit cells,Gyroid exhibited better mechanical conductivity characteristics.Its deformation process was characterised by stretching,shearing,and twisting,while the Primitive and I-WP unit cells underwent tensile deformation and tensile and shear deformation,respectively.The finite element predictions in the study agree well with the experimental results.The results can provide a basis for the design of regenerative cooling thermal protection system.

The effect of porosity on the mechanical properties of 3D-printed triplyperiodic minimal surface (TPMS) bioscaffold

Prevailing tissue degeneration caused by musculoskeletal maladies poses a great demand on bioscaffolds,which are artificial,biocompatible structures implanted into human bodies with appropriate mechanical properties.Recent advances in additive manufacturing,i.e.,3D printing,facilitated the fabrication of bioscaffolds with unprecedented geometrical complexity and size flexibility and allowed for the fabrication of topologies that would not have been achieved otherwise.In our work,we explored the effect of porosity on themechanical properties of a periodic cellular structure.The structure was derived from the mathematically created triply periodic minimal surface(TPMS),namely the Sheet-Diamond topology.First,we employed a series of software including MathMod,Meshmixer,Netfabb and Cura to design the model.Then,we utilized additive manufacturing technology to fabricate the cellular structures with designated scale.Finally,we performed compressive testing to deduce the mechanical properties of each cellular structure.Results showed that,in comparison with the highporosity group,the yield strength of the low-porosity group was 3 times higher,and the modulus was 2.5 times larger.Our experiments revealed a specific relationship between porosity and Young’s modulus of PLA-made Sheet-Diamond TPMS structure.Moreover,it was observed that the high-and low-porosity structures failed through distinctive mechanisms,with the former breaking down via buckling and the latter via micro-fracturing.

Gyroid Triply Periodic Minimal Surface Lattice Structure Enables Improved Superelasticity of CuAlMn Shape Memory Alloy

Improving the shape memory effect and superelasticity of Cu-based shape memory alloys(SMAs)has always been a research hotspot in many countries.This work systematically investigates the effects of Gyroid triply periodic minimal surface(TPMS)lattice structures with different unit sizes and volume fractions on the manufacturing viability,compressive mechanical response,superelasticity and heating recovery properties of CuAlMn SMAs.The results show that the increased specific surface area of the lattice structure leads to increased powder adhesion,making the manufacturability proportional to the unit size and volume fraction.The compressive response of the CuAlMn SMAs Gyroid TPMS lattice structure is negatively correlated with the unit size and positively correlated with the volume fraction.The superelastic recovery of all CuAlMn SMAs with Gyroid TPMS lattice structures is within 5%when the cyclic cumulative strain is set to be 10%.The lattice structure shows the maximum superelasticity when the unit size is 3.00 mm and the volume fraction is 12%,and after heating recovery,the total recovery strain increases as the volume fraction increases.This study introduces a new strategy to enhance the superelastic properties and expand the applications of CuAlMn SMAs in soft robotics,medical equipment,aerospace and other fields.

3D-printed strontium-incorporatedβ-TCP bioceramic triply periodic minimal surface scaffolds with simultaneous high porosity,enhanced strength,and excellent bioactivity

In bone tissue engineering,scaffolds with excellent mechanical and bioactive properties play prominent roles in space maintaining and bone regeneration,attracting increasingly interests in clinical practice.In this study,strontium-incorporatedβ-tricalcium phosphate(β-TCP),named Sr-TCP,bioceramic triply periodic minimal surface(TPMS)structured scaffolds were successfully fabricated by digital light processing(DLP)-based 3D printing technique,achieving high porosity,enhanced strength,and excellent bioactivity.The Sr-TCP scaffolds were first characterized by element distribution,macrostructure and microstructure,and mechanical properties.Notably,the compressive strength of the scaffolds reached 1.44 MPa with porosity of 80%,bringing a great mechanical breakthrough to porous scaffolds.Furthermore,the Sr-TCP scaffolds also facilitated osteogenic differentiation of mouse osteoblastic cell line(MC3T3-E1)cells in both gene and protein aspects,verified by alkaline phosphatase(ALP)activity and polymerase chain reaction(PCR)assays.Overall,the 3D-printed Sr-TCP bioceramic TPMS structured scaffolds obtained high porosity,boosted strength,and superior bioactivity at the same time,serving as a promising approach for bone regeneration.

Bioceramic scaffolds with triply periodic minimal surface architectures guide early-stage bone regeneration

The pore architecture of porous scaffolds is a critical factor in osteogenesis,but it is a challenge to precisely configure strut-based scaffolds because of the inevitable filament corner and pore geometry deformation.This study provides a pore architecture tailoring strategy in which a series of Mg-doped wollastonite scaffolds with fully interconnected pore networks and curved pore architectures called triply periodic minimal surfaces(TPMS),which are similar to cancellous bone,are fabricated by a digital light processing technique.The sheet-TPMS pore geometries(s-Diamond,s-Gyroid)contribute to a 3‒4-fold higher initial compressive strength and 20%-40%faster Mg-ion-release rate compared to the other-TPMS scaffolds,including Diamond,Gyroid,and the Schoen’s I-graph-Wrapped Package(IWP)in vitro.However,we found that Gyroid and Diamond pore scaffolds can significantly induce osteogenic differentiation of bone marrow mesenchymal stem cells(BMSCs).Analyses of rabbit experiments in vivo show that the regeneration of bone tissue in the sheet-TPMS pore geometry is delayed;on the other hand,Diamond and Gyroid pore scaffolds show notable neo-bone tissue in the center pore regions during the early stages(3-5 weeks)and the bone tissue uniformly fills the whole porous network after 7 weeks.Collectively,the design methods in this study provide an important perspective for optimizing the pore architecture design of bioceramic scaffolds to accelerate the rate of osteogenesis and promote the clinical translation of bioceramic scaffolds in the repair of bone defects.

Fabrication of Ceramic-Polymer Piezo-Composites with Triply Periodic Minimal Interfaces via Digital Light Processing

The geometry of the phase interface in co-continuous piezoelectric composites is critical in improving their piezo-electric properties.However,conventional co-continuous piezoelectric composites are mostly simple structures such as wood stacks or honeycombs,which are prone to stress concentrations at the joints,thus reducing the fatigue service performance and force-electric conversion efficiency of piezoelectric composites.Such simple structures limit further improvements in the overall performance of co-continuous piezoelectric composites.In this study,based on the digital light processing 3D printing method,we investigated the influence of three dif-ferent structures-the gyroid,diamond,and woodpile interfaces-on the piezoelectric and mechanical properties of co-continuous ceramic/polymer piezoelectric composites.These findings demonstrate that the gyroid and di-amond interfaces outperformed the ceramic skeleton of the woodpile interface in terms of both mechanical and electrical properties.When the ceramic volume percentage was 50%,the piezo-composite of the gyroid surface exhibited the greatest hydrostatic figure of merit(HFOM),reaching 4.23×10^(−12) Pa^(−1),and its piezoelectric coeffi-cient(d_(33))and relative dielectric constant(εr)reached 115 pC/N and 748,respectively.The research results lay the foundation for the application of co-continuous piezoelectric composites in underwater communication and detection.

Mechanical Response of Triply Periodic Minimal Surface Structures Manufactured by Selective Laser Melting with Composite Materials

It is of significance but remains a pivotal challenge to simultaneously enhance the strength and lightweight levels of porous structures.We provide an innovative strategy to improve the strength of porous structures with unchanged lightweight levels by applied composite materials.Selective laser melting(SLM)is convenient for integral forming of materials and structures.Hence,in this study,the research about the mechanical response of triply periodic minimal surfaces(TPMS)porous structures with 316 L and composites fabricated by SLM was conducted.The compression test and finite element method(FEM)were used to characterize mechanical properties.The composite structures exhibit enhanced elastic modulus,yield strength,unvaried lightweight level and refined grain microstructure,which are difficult to realize for porous structures made by pure 316 L materials.The elastic modulus,yield strength,plateau stress and energy absorption of composites were 3187.50,67.73,15.24 and 17.09 MJ/m^(3),respectively.

Design and Mechanical Characterization of an S-Based TPMS Hollow Isotropic Cellular Structure

Cellular structures are regarded as excellent candidates for lightweight-design,load-bearing,and energy-absorbing applications.In this paper,a novel S-based TPMS hollow isotropic cellular structure is proposed with both superior load-bearing and energy-absorbing performances.The hollow cellular structure is designed with Boolean operation based on the Fischer-Koch(S)implicit triply periodic minimal surfaces(TPMS)with different level parameters.The anisotropy and effective elasticity properties of cellular structures are evaluated with the numerical homogenization method.The finite element method is further conducted to analyze the static mechanical performance of hollow cellular structure considering the size effect.The compression experiments are finally carried out to reveal the compression properties and energy-absorption characteristics.Numerical results of the Zener ratio proved that the S-based hollow cellular structure tends to be isotropic,even better than the sheet-based Gyroid TPMS.Compared with the solid counterpart,the S-based hollow cellular structure has a higher elastic modulus,better load-bearing and energy absorption characteristics.

Bioadaptable bioactive glass-β-tricalcium phosphate scaffolds with TPMS-gyroid structure by stereolithography for bone regeneration

Bone defect repair remains a troubling problem in clinical orthopedics,which involves complex biological processes.Calcium phosphates(CaPs)have been widely used owing to their advantage of biocompatibility.However,single component and traditional fabrication methods cannot meet the requirements of bioadaptability during the tissue repair process.In this work,0%,5%,15%,25%wt%of BG-TCP(bioactive glass-β-tricalcium phosphate)bioresorbable scaffolds with triply-periodic minimal surfaces(TPMS)-gyroid structure were prepared by the stereolithography(SLA)technology.TPMS-gyroid structure provided an accurate mimicry of natural bone tissue,and the incorporation of BG improved the compressive strength ofβ-TCP matrix,matched with the defective bone(2–12 MPa).Rapid but tunable degradation kinetics(compared with pure TCP)of BG enabled the BG-TCP system to sh8ow adaptable biodegradability to new bone generation.In vitro studies have shown that composite scaffolds have better mechanical properties(7.82 MPa),and can released appropriate contents of calcium,phosphorous,and magnesium ions,which promoted the osteogenic differentiation of bone marrow mesenchymal stem cells(BMSCs)and angiogenic ability of endothelial progenitor cells(EPCs).Moreover,the in vivo assessment of rat femoral defect revealed that TPMS-structure-based TCP scaffolds accelerated bone ingrowth to the pores.Moreover,BG-TCP scaffolds,especially 15BG-TCP group,exhibited superior bone regeneration capacity at both 4 and 8 weeks,which achieved an optimal match between the rate of material degradation and tissue regeneration.In summary,this study provides insight into influences of bioactive components(BG)and bionic structures(TPMS)on the physical-chemical properties of materials,cell behavior and tissue regeneration,which offers a promising strategy to design bioadaptive ceramic scaffolds in the clinical treatment of bone defects.

Isogeometric Analysis-Based Topological Optimization for Heterogeneous Parametric Porous Structures

Porous structures widely exist in nature and artifacts,which can be exploited to reduce structural weight and material usage or improve damage tolerance and energy absorption.In this study,the authors develop an approach to design optimized porous structures with Triply Periodic Minimal Surfaces(TPMSs)in the framework of isogeometric analysis(IGA)-based topological optimization.In the developed method,by controlling the density distribution,the designed porous structures can achieve the optimal mechanical performance without increasing the usage of materials.First,the implicit functions of the TPMSs are adopted to design several types of porous elements parametrically.Second,to reduce the cost of computation,the authors propose an equivalent method to forecast the elastic modulus of these porous elements with different densities.Subsequently,the relationships of different porous elements between the elastic modulus and the relative density are constructed.Third,the IGA-based porous topological optimization is developed to obtain an optimal density distribution,which solves a volume constrained compliance minimization problem based on IGA.Finally,an optimum heterogeneous porous structure is generated based on the optimized density distribution.Experimental results demonstrate the effectiveness and efficiency of the proposed method.

Stereolithography printing of bone scaffolds using biofunctional calcium phosphate nanoparticles

Calcium phosphate(CaP)has been widely used for bone defect repair due to good biocompatibility and osteoconductivity.Additive manufacture of calcium phosphate bioceramics with tailored architectures and improved mechanical properties has recently attracted great attention.Herein,calcium phosphate nanoparticles with the size of~89-164 nm were synthesized by the hydrothermal treatment of amorphous calcium phosphate(ACP)precursors at 180°C for 24 h.Biofunctional elements including Mg,Sr and Zn have been doped into these calcium phosphate nanoparticles.Our results revealed that Mg^(2+)ions played critical roles in formation of whitlockite-type calcium phosphate(not hydroxyapatite)from ACP precursors.Moreover,gyroid scaffolds with bionic triply periodic minimal surface structures were fabricated using stereolithography printing of these calcium phosphate nanoparticles,which are likely used as biofunctional scaffolds for bone repair.

Heat transfer effectiveness characteristics maps for additively manufactured TPMS compact heat exchangers

Increased power density in modern miniaturized electronics caused difficulty in keeping electronic performance effective.This challenge leads to the search for high-performance compact heat exchanger as one of the thermal management solutions.Conventionally manufactured heat exchangers had limitations that thwart the develop-ment of geometrically complex heat exchangers which are capable of exploiting topological aspects to enhance thermal performance.Subsequently,additive manufacturing(AM)is proposed as a powerful fabrication tech-nique for compact heat exchanger based on the mathematically known triply periodic minimal surfaces(TPMS).In this work,we present 3D compact crossflow heat exchanger computational fluid dynamics(CFD)modelling of geometrically complex structures based on TPMS using STARCCM+CFD platform.Moreover,CFD modelling is used to obtain new characteristics maps that relate heat transfer effectiveness(Ɛ)and number of transfer units for the proposed heat exchanger.The convection heat transfer coefficient,pressure drop,and inlet and outlet fluid temperature are all examined.

Laser Powder Bed Fusion-built Ti6Al4V Bone Scaffolds Composed of Sheet and Strut-based Porous Structures: Morphology, Mechanical Properties, and Biocompatibility

Laser powder bed fusion(L-PBF)-built triply periodic minimal surface(TPMS)structures are designed by implicit functions and are endowed with superior characteristics,such as adjustable mechanical properties and light-weight features for bone repairing;thus,they are considered as potential candidates for bone scaffolds.Unfortunately,previous studies have mainly focused on different TPMS structures.The fundamental understanding of the differences between strut and sheet-based structures remains exclusive,where both were designed by one formula.This consequently hinders their practical applications.Herein,we compared the morphology,mechanical properties,and biocompatibility of sheet and strut-based structures.In particular,the different properties and in vivo bone repair effects of the two structures are uncovered.First,the morphology characteristics demonstrate that the manufacturing errors of sheet-based structures with diverse porosities are comparable,and semi-melting powders as well as the ball phenomenon are observed;in comparison,strut-based samples exhibit cracks and thickness shrinking.Second,the mechanical properties indicate that the sheet-based structures have a greater elastic modulus,energy absorption,and better repeatability compared to strut-based structures.Furthermore,layer-by-layer fracturing and diagonal shear failure modes are observed in strut-based and sheet-based structures,respectively.The in vivo experiment demonstrates enhanced bone tissues in the strut-based scaffold.This study significantly enriches our understanding of TPMS structures and provides significant insights in the design of bone scaffolds under various bone damaging conditions.