查看更多>>摘要：Thermal expander metadevices can yield a large uniform temperature field powered by a linear heat source.Previous design of thermal expander metadevices can be regarded as a combination of achieved thermal cloaks and their background materials.However,these thermal-cloak-inspired expander metadevices have an inherent flaw,i.e.,their thermal functionality will be lost when the background material is changed,thus limiting their practical applications.To solve this problem,the multiscale topology optimization(MTO)method is employed to design thermal expander metadevices that can maintain their expander functionality under different background materials.In MTO,transformation thermotic technology is used to determine the anisotropic thermal conductiv-ities inside a thermal expander metadevice and topology optimization is performed to generate the topological configuration of each microstructure with the target effective thermal conductivity.Subsequently,the thermal functionalities of thermal double and triple expander metadevices with different background materials are nu-merically verified via simulations.Finally,the thermal double expander metadevice is fabricated via additive manufacturing and experimentally tested for its thermal functionality.The findings of this study address the challenge of designing thermal expander metadevices with background material-independent functionality.
查看更多>>摘要：In bone tissue engineering,good structural and forming qualities are prerequisites for the long-term implantation of scaffolds.To mitigate the stress-shielding effect between porous bone scaffolds and the human skeleton,this study proposes a method for designing non-linear gradient gyroid porous structures with radial-axial hybrid gra-dients that are precisely controlled by multivariate polynomial functions to simulate human bone characteristics.The influence of the volumetric energy density on the forming quality of the porous structures was evaluated by characterizing the internal strut morphology and measuring the strut width and porosity.Finite element analysis combined with experimental observations revealed that during compression,the thin struts at the top and bottom of the hybrid-gradient porous structure deformed first,and the compressive stress and shear stress were gradually transferred from the thin struts at the upper and lower ends of the structure to the thicker struts in the middle.Compared with the axial gradient,the edge struts of the hybrid-gradient porous structures can withstand higher shear and compressive stresses.Furthermore,owing to the variation in the radial gradient,compared to struc-tures with 20％axial porosity variation,the hybrid-gradient porous structure with 40％radial porosity variation and 20％axial porosity variation exhibited an 18.10％increase in elastic modulus and a 4.29％increase in yield strength.Additionally,its effective energy absorption was 20.39％higher than that of the homogeneous structures.Compared to radial-gradient porous structures,the hybrid-gradient porous structure showed a lower sensitivity of the elastic modulus and yield strength to the volumetric energy density.
查看更多>>摘要：Arbitrary and high-precision thermal patterning has long been desired in the field of thermal functional materials.However,existing thermal patterning strategies have not been widely applied,either hampered by the difficulty in fabricating anisotropic metamaterials or limited by complex thermal manipulation.We propose an on-demand thermal patterning scheme that sandwiches geometrically engineered heating arrays between a substrate and an encapsulation layer to form composite structures and control the omnidirectional transfer of the heat flux gen-erated by the heating arrays.These heating arrays are digitally assembled from multiple heater cells of varying widths and continuously printed using electric-field-driven 3D printing.A design strategy for thermal patterning with good uniformity within individual regions and high contrast between regions is proposed.The performance of the on-demand thermal patterning is verified via high-precision thermal printing.The proposed scheme pro-vides a general and reproducible method for designing thermal functional materials,with potential applications in thermochromics,messaging,thermal camouflage,and illusions.
查看更多>>摘要：Nickel-based superalloys(Haynes 230)fabricated by laser powder bed fusion suffer from high cracking suscepti-bility,leading to a decrease in mechanical performance.In this study,the cracking mechanism of Haynes 230 was investigated based on microstructural and thermodynamic calculations.It was found that C and carbide-forming elements(such as Mo and Cr)were segregated at the grain boundaries,which increased the solidification range and impeded liquid film backfalling by forming nano-carbides.Additionally,the coalescence of high-angle grain boundaries(>15°)requires a higher undercooling ATbthan that of low-angle grain boundaries(2-15°),which increases the susceptibility to hot cracking.Through gradually reducing laser energy input,the grain size is sig-nificantly decreased from 27.86 pm(47.40 J/mm3)to 14.66 pm(31.81 J/mm3).Moreover,the calculated cooling rate|dT/dt|and temperature gradient|dT/ds|gradually increase with decreasing energy input,which reduces the duration of dendrite merging and shortens the length of the liquid film.Compared with cracked samples,the optimized sample showed superior mechanical properties,including high yield strength(678 MPa),ultimate tensile strength(943 MPa),and elongation to failure(19.2％),which increased by 16.1％,9.7％,and 77.7％,respectively.
查看更多>>摘要：3D printing technology is considered the perfect modern manufacturing technology for military/industrial en-terprises worldwide.Applying 3D printing in explosives and propellants fabrication enables precise performance control and accurate structure formation,revolutionizing traditional manufacturing concepts and improving con-tinuous,automated,integrated,and flexible explosives and propellants manufacturing.As key components in the 3D printing of explosives and propellants,adhesives/binders play a crucial role in determining the formation rate,stability,and structural integrity of explosive formulations.This paper provides an overview of the four major 3D printing technologies suitable for explosives and propellants manufacturing:vat photopolymerization,binder jetting,fused deposition modeling,and direct ink writing,with their typical production processes,technical characteristics,principles,and limitations discussed.Specific solutions to the limitations of vat photopolymeriza-tion(printing speed),binder jetting(low accuracy and limited applicable materials),fused deposition modeling(poor mechanical properties and dimensional stability),and direct ink writing(product performance defects)are presented.Additionally,future development directions and prospects for the 3D printing of explosives and propellants are discussed,thus providing valuable insights into the application of 3D printing technology in the fields of explosives and propellants.
查看更多>>摘要：Sand mold 3D printing technology has been recognized as a digital,high-quality,and promising sand mold forming method.However,sand mold 3D printing technology has drawbacks,such as single molding material and long curing time,which limit its further industrial application.Therefore,this study proposes a method for forming composite sand molds based on a layer-stacking structure and a strengthening method based on interlayer heating.The influence of the process parameters on the properties of traditional and composite sand molds was systematically studied.Experimental results demonstrated that when the heating temperature was 150 ℃,the enhancement of the sand mold was obvious,with an increase of approximately 20％compared to untreated sand mold.When the composite sand mold with a laminated thickness of 1.5 mm was heated at this temperature,its tensile strength reached 1.53 MPa,and compressive strength reached 5.80 MPa,which met the casting requirements.The composite sand mold printed by interlayer heating has excellent casting performance and economic advantages,which provide theoretical guidance for the high-performance printing of sand molds.
查看更多>>摘要：Although laser powder bed fusion(LPBF)technology is considered one of the most promising additive man-ufacturing techniques,the fabricated parts still suffer from porosity defects,which can severely impact their mechanical performance.Monitoring the printing process using a variety of sensors to collect process signals can realize a comprehensive capture of the processing status;thus,the monitoring accuracy can be improved.However,existing multi-sensing signals are mainly optical and acoustic,and camera-based signals are mostly layer-wise images captured after printing,preventing real-time monitoring.This paper proposes a real-time melt-pool-based in-situ quality monitoring method for LPBF using multiple sensors.High-speed cameras,photodiodes,and microphones were used to collect signals during the experimental process.All three types of signals were transformed from one-dimensional time-domain signals into corresponding two-dimensional grayscale images,which enabled the capture of more localized features.Based on an improved LeNet-5 model and the weighted Dempster-Shafer evidence theory,single-sensor,dual-sensor and triple-sensor fusion monitoring models were in-vestigated with the three types of signals,and their performances were compared.The results showed that the triple-sensor fusion monitoring model achieved the highest recognition accuracy,with accuracy rates of 97.98％,92.63％,and 100％for high-,medium-,and low-quality samples,respectively.Hence,a multi-sensor fusion based melt pool monitoring system can improve the accuracy of quality monitoring in the LPBF process,which has the potential to reduce porosity defects.Finally,the experimental analysis demonstrates that the convolutional neural network proposed in this study has better classification accuracy compared to other machine learning models.
查看更多>>摘要：For effective anterior cruciate ligament(ACL)reconstruction,an interference screw(IFS)is employed to force transplantation of the ligament into the bone tunnel.In this study,IFSs were successfully designed and pre-pared,and the top tooth width,thread depth,and drive structure were parameterized with a forming accuracy of 80.0±21.1 pm using SLA-3D printing technology.To improve the initial stability of ACL reconstruction,a biomechanical model was established,and the results were optimized through insertion torque and tensile test-ing.Consequently,the IFS with the top tooth width of 0.4 mm,thread depth of 0.8 mm,and hexagon drive,matching with the Φ8 mm bone tunnel,exhibits the best mechanical properties(maximum insertion torque of 1.064±0.117 N m,ultimate load of 446.126±37.632 N,stiffness of 66.33±27.48 N/mm).Additionally,the ZrO2/PDA/RGD/Zn2+bioactive coating was found to significantly improve the surface bioactivity of zirconia IFS.In conclusion,this study has significant implications for ACL reconstruction.
查看更多>>摘要：Additively manufactured bimetallic structures combine the advantages of dissimilar materials and can achieve localized properties through a customized composition distribution.However,additively manufactured parts may still lack the dimensional accuracy and surface integrity essential for precision mechanical assemblies that the post-machining process can address.Therefore,this study aims to systematically investigate the microstructure and machinability of 316L/CuSn10 bimetallic structures fabricated using laser powder bed fusion.The results show that the fusion zone of the bimetallic structure had refined grains of microscale size owing to the mixture of the primary elements of the bimetals,which resulted in the highest microhardness of 3.4 GPa.The difference in microstructure and microhardness between the single-material and fusion zones also causes significant differences in the cutting response during the ultraprecision process.The 316L stainless steel side exhibited the highest cutting force and more severe material accumulation in the chips.The cutting force drops when cutting through the fusion zone,with an observable fracture in the chips and separation of dissimilar materials on the machined grooves,indicating that the heterogeneous properties of additively manufactured 316L/CuSn10 bimetallic structures pose challenges to the improvement of surface quality.The simulation results also showed that stress accumulation occurred in the tool path through the fusion zone owing to the higher yield strength and hardness of stainless steel,indicating that lower cutting speeds and depths of cut are favorable for reducing cutting force and improving surface quality.This study provides deep insight into the microstructure evolution mechanism and a theoretical basis for improving the surface quality of additively manufactured bimetallic structures using an ultraprecision machining process.
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