Multilevel Micro Structures of the Clam Make the Sealing Even Tighter

Excellent fluid sealing performance is crucial to ensuring the safety of important equipment,especially in aerospace field,such as space capsule and fuel chamber.The frequently opening and closing of the sealing devices is particularly important.Driven by this background,clams(Mactra chinensis)which can open and close their double shells with superior sealing performance,are studied in this work.Here,we show that the clam’s sealing ability is the result of its unique multilevel intermeshing microstructures,including hinge teeth and micro-blocks.These microstructures,which resemble gear teeth,engage with each other when the shell closes,forming a tight structure that prevents the infiltration of water from the outside.Furthermore,the presence of micron blocks prevents the penetration of finer liquids.The simulation results of the bionic end seal components show that the multilevel microstructure has a superior sealing effect.This research is expected to be applied to undersea vehicles that require frequent door opening and closing.

Deformation and Locomotion of Untethered Small-Scale Magnetic Soft Robotic Turtle with Programmable Magnetization

Inspired by the way sea turtles rely on the Earth’s magnetic field for navigation and locomotion,a novel magnetic soft robotic turtle with programmable magnetization has been developed and investigated to achieve biomimetic locomotion patterns such as straight-line swimming and turning swimming.The soft robotic turtle(12.50 mm in length and 0.24 g in weight)is integrated with an Ecoflex-based torso and four magnetically programmed acrylic elastomer VHB-based limbs containing samarium-iron–nitrogen particles,and was able to carry a load more than twice its own weight.Similar to the limb locomotion characteristics of sea turtles,the magnetic torque causes the four limbs to mimic sinusoidal bending deformation under the influence of an external magnetic field,so that the turtle swims continuously forward.Significantly,when the bending deformation magnitudes of its left and right limbs differ,the soft robotic turtle switches from straight-line to turning swimming at 6.334 rad/s.Furthermore,the tracking swimming activities of the soft robotic turtle along specific planned paths,such as square-shaped,S-shaped,and double U-shaped maze,is anticipated to be utilized for special detection and targeted drug delivery,among other applications owing to its superior remote directional control ability.

Study of Spectral Response Characteristics of Oilseed Rape (Brassica napus) to Particulate Matters Based on Hyper-Spectral Technique

Haze is mainly caused by the suspended particulate matters in the air,of which the particulate matters pollution harms leaf vegetables.In this paper,oilseed rapes at four different growing periods were investigated in a simulated particulate pollution environment.In combination of hyper-spectral technology and micro examination,the response of hyper-spectral characteristics of the leaf to particulate matters was investigated in-depth.The hyperspectral,chlorophyll content,net photosynthetic rate and stomatal conductance of leaf were obtained.The deposition and adsorption of particulate matters on the leaf were observed by Environmental Scanning Electron Microscope(ESEM).Normalized difference vegetation index(NDVI),modified red edge normalized(mNDVI705)and modified red edge simple ratio index(mSR705)were selected as characteristic parameters and the range of 510 nm~620 nm as the sensitive band.16 methods were used to establish the physiological information inversion model.The main results were as follows:Under the influence of particulate matters,the spectral reflectance decreased as a whole.With the increase of leaf age,the phenomenon of blue shift aggravated.The amplitude of yellow and blue edge decreased with overall decreasing vegetation indices.The furrows and irregular band protrusions in leaves were favorable for keeping particulate matters.With longer affecting time and more deposition of particle matters on the leaf,the stomatal opening became smaller.After comparing,principal component regression(PCR)+multiple scatter correction(MSC)+second derivative(SD)+Savitzky-Golay smooth(SG),and partial least square(PLS)+multiple scatter correction(MSC)+first derivative(FD)+Savitzky-Golay smooth(SG)were determined the best method to establish the inversion model of chlorophyll content and net photosynthetic rate respectively.This study may bring novel ideas for the diagnosis and analysis of the physiological response of leaf vegetables under particulate matters pollution using hyper-spectral technology.

Effects of Particle Matters on Plant: A Review

The particle matter,particularly the suspended particle matter(PM≤2.5)in the air is not only a risk factor for human health,but also affects the survival and physiological features of plants.Plants show advantages in the adsorption of particle matter,while the factors,such as the leaf shape,leaf distribution density and leaf surface microstructure,such as grooves,folds,stomata,flocculent projections,micro-roughness,long fuzz,short pubescence,wax and secretory products,appeared to play an important role determing their absorption capacity.In this paper,the research progress on the capture or adsorption of atmospheric particles was summarized,and the forest vegetation and woody plants were discuessed.In addition,special attentions were paid to the effect of haze-fog weather on greenhouse plant,the different responses of plant leaves to dust particles and suspended particles,as well as the effect of suspended particles on morphological change of plants.In the future,research should focus on the mechanism of the influence of particulate matter on plants.More advanced effective and convenient research methods like spectral detection method also need to be developed.This paper may provide reference for future studies on plants’response to haze and particle matter.

Variations in the Biomechanics of 16 Palmar Hand Regions Related to Tomato Picking

The aim of this study is to systematically reveal the differences in the biomechanics of 16 hand regions related to bionic picking of tomatoes.The biomechanical properties(peak loading force,elastic coefficient,maximum percentage deformation and interaction contact mechanics between human hand and tomato fruit)of each hand region were experimentally measured and covariance analyzed.The results revealed that there were significant variations in the assessed biomechanical properties between the 16 hand regions(p<0.05).The maximum pain force threshold(peak loading force in I2 region)was 5.11 times higher than the minimum pain force threshold(in Th1 region).It was found that each hand region in its normal direction can elastically deform by at least 15.30%.The elastic coefficient of the 16 hand regions ranged from 0.22 to 2.29 N mm−1.The interaction contact force acting on the fruit surface was affected by the selected human factors and fruit features.The obtained covariance models can quantitatively predict all of the above biomechanical properties of 16 hand regions.The findings were closely related to hand grasping performance during tomato picking,such as soft contact,surface interaction,stable and dexterous grasping,provided a foundation for developing a high-performance tomato-picking bionic robotic hand.

Effect of Bionic Unit Shapes on Solid Particle Erosion Resistance of ZrO2-7wt%Y2O3 Thermal Barrier Coatings Processed by Laser

Inspired by the coupling phenomena in biological systems, to improve the solid particle erosion resistance of Thermal Barrier Coatings （TBCs）, different kinds of bionic units were made on the coating surfaces using Bionic Coupled Laser Remelting （BCLR） process. The NiCoCrAlYTa/ZrO2-7wt%Y2O3 double-layer structured TBCs were prepared by air plasma spraying. The microstructure, microhardness and phase composition of the as-sprayed and bionic specimens were examined. The solid particle erosion behaviors of bionic specimens as function of bionic unit shape were investigated. The results indicated that the bionic specimens had better erosion resistance than the as-sprayed specimen. The specimen with striation and grid bionic units had the better erosion resistance, while the dot showed the worse. The bionic units were characterized by the dense columnar crystal structure and the high hardness, which are the main reasons for improving the erosion resistance. Under the synergistic action of the shear stress and normal stress on the protrusive coating surface, the erosion failure of the as-sprayed TBCs was proved to be the fracture and spallation of the splats. By contrast, the spallation of segmented bionic unit occurred in the overlapping area between the adjacent laser irradiation, and the erosive unit surface presented the clear and deep furrows, which revealed that the erosion failure mechanism of bionic TBCs was dominated by brittle and some ductile erosion. These results showed more opportunities for bionic application in improving the solid particle erosion resistance of components in the windy and sandy environment.

Effect of TiAl3 Content on Thermal Shock Resistance of Bionic Self-healing Thermal Barrier Coatings

Inspired by the self-healing function of biological organisms,Bionic Laser Alloying(BLA)process was adopted to fabricate the bionic self-healing Thermal Barrier Coatings(TBCs).The BLA with different fractions of TiAl3 self-healing agent and Ceria and Yttria-Stabilized Zirconia(CYSZ)on the plasma-sprayed 7YSZ TBCs was carried out by a pulsed Nd:YAG laser.The effect of TiAl3 content on the microstructure,phase composition,and thermal shock behaviors of the bionic self-healing TBCs were investigated.Results indicated that the bionic self-healing TBCs had better thermal shock resistance than that of the as-sprayed TBCs.The thermal shock resistance increased first and then decreased with increasing TiAl3 fraction.The thermal shock resistance of the bionic self-healing TBCs with 15%TiAl3 is triple that of the as-sprayed TBCs.On one hand,the columnar crystals and vertical cracks could improve strain compatibility of TBCs during the thermal shock process;on the other hand,the TiAl3 as a self-healing agent reacted with oxygen in air at high temperature to seal the microcracks,thereby delaying the crack connection.

Nanomechanical Behaviour of the Membranous Wings of Dragonfly Pantala flavescens Fabricius

The dragonfly has excellent flying capacity and its wings are typical 2-dimensional composite materials in micro-scale or nano-scale. The nanomechanical behavior of dragonfly membranous wings was investigated with a nanoindenter. It was shown that the maxima of the reduced modulus and nanohardness of the in-vivo and fresh dragonfly wings are about at position of 0.7L, where L is the wing length. It was found that the reduced modulus and nanohardness of radius of the wings of dragonfly are large. The reduced modulus and nanohardness of Costa, Radius and Postal veins of the in-vivo dragonfly wings are larger than those of the fresh ones. The deformation, stress and strain under the uniform load were analyzed with finite element simulation software ANSYS. The deformation is little and the distribution trend of the strain is probably in agreement with that of the stress. It is shown that the main veins have better stabilities and load-bearing capacities. The understanding of dragonfly wings＇ nanomechanical properties would provide some references for improving some properties of 2-dimentional composite materials through the biomimetic designs. The realization of nanomechanical properties of dragonfly wings will provide inspirations for designing some new structures and materials of mechanical parts.

Design and Tests of Biomimetic Blades for Soil-rototilling and Stubble-breaking

Biomimetic blades for soil-rototilling and stubble-breaking were designed learning from the geometrical structure of the tips of toes of mole rat （Scaptochirus moschatus）. The orientation, the number and the central angle of the biomimetic structure were taken as the testing factors. The optimal structure of the biomimetic blade was determined through the tests of soil-rototilling and stubble-breaking operation in an indoor soil bin. The optimal combination of the biomimetic structure pa- rameters is that three arc concave teeth are equally arranged on the front cutting edge with a central angle of 60°. The results of comparative tests between the optimal biomimetic blade and a conventional universal blade show the torque acting on the biomimetic blade is lower during soil-rototilling and stubble-breaking operations. The results of field tests show that the working quality of the biomimetic blades meets the requirements of the national standard of China. Tests of soil-rototilling show that, when the orientation of the biomimetic structure was at low and middle levels, the torque ofbiomimetic blades decreased from 34.17 N·m to 31.03 N·m. The torque also decreased with the increase of the number of biomimetic structure. The average torques were 34.57 N·m, 33.44 N·m and 31.37 N·m, respectively. The maximum different value between two levels of central angle was 0.41 N·m. Tests in field indicate that for soil-rototilling operation, the tillage depth is deeper than 80 mm, the soil-crushing rate （length of soil block less than 40 mm） is over 50 %, and the vegetation coverage rate is over 55 %. For stubble-breaking operation, the stubble-breaking depth is deeper than 70 ram, the stubble-breaking rate （length of stubble less than 40 mm） is over 60%, and the stubble coverage rate is over 80%, which can meet the stubble-breaking requirement of corn.

High flux photocatalytic self-cleaning nanosheet C_(3)N_(4) membrane supported by cellulose nanofibers for dye wastewater purification

Hazardous dye substances discharged from the textile and dyestuff industries not only threaten local the surrounding ecosystems but are also hard to degraded.We report the preparation of process for a photocatalytic membrane device that can degrade dye pollution under visible light.This filtration membrane,with a well-organized multilayer structure,simultaneously achieves continuous and flow-through separation of degradation products.Cellulose nanofibers(CNFs)were used as a template for nanosheet C_(3)N_(4)(NS C_(3)N_(4))preparation;the performance for the photocatalytic degradation of dyes improved as the morphology changed from bulking to nanosheet.NS C3N4 was then attached to the surface of a prepared CNF membrane via vacuum filtration.This device exhibited high efficiency(the degradation rates of both Rhodamine B and Methylene blue both reached 96%),high flux(above 160 L·h^(-1)·m^(-2)·bar^(-1))and excellent stability(maintaining steady flux and high separation were maintained after 4 h).This easy-preparation,easy-scale-up,and low-cost process provides a new method of fabricating photocatalytic membrane devices for dye wastewater treatment.

Compaction Performance of Biomimetic Press Roller to Soil

The compaction characteristics of biomimetic press roller with ridge structures, inspired from the geometrical features of the ventral surface of dung beetle （Copris ochus Motschulsky）, were investigated in this work. Field tests were carried out at three weights （300 N, 500 N and 700 N） and two forward velocities （0.64 m·s^-1 and 1.04 m·s^-1） for biomimetic press roller and conventional press roller. To determine compaction performance, rolling resistance, soil bulk density, soil moisture content, emergence rate and percent change of plant spacing were measured. Roller weight was proved to be the major contributory factor on soil compaction. Biomimetic press roller decreased rolling resistance by 2.98% -17.69% at the velocity of 0.64 m·s^-1, and by 6.59% -18.57% at the velocity of 1.04 m·s^-1 compared with the conventional press roller. Both biomimetic roller and conventional roller can achieve proper bulk density for corn seeds under the experimental conditions. However, compared with the conventional roller, biomimetic roller helped soil conserve more moisture. The highest emergence rate was found when the biomimetic roller worked with a weight of 700 N and velocity of 0.64 m·s^-1. Percent change of plant spacing was lower using the biomimetic press roller compared with that using the conventional roller, because that adjacent ridge structures of the biomi- metic roller can well constrain the flow of soil during compacting process.

Large Curvature Folding Strategies of Butterfly Proboscis

Due to its real-time control,high folding ratio,and structure self-locking,flexible large curvature self-folding devices have broad application prospects,such as foldable human implants,flexible electronics,and flexible robots.Driven by this background,flexible large curvature folding butterfly(Polyura eudamippus)proboscises were studied in this work.The folding ratio of the proboscises was about 15.The curvature of coiled proboscises ranged from about 150 m_1 to 880 m The external and internal structures of the proboscises were studied by different methods.Three main strategies for large-curvature folding of proboscises were identified:a gradual decrease in thickness,a lower elastic modulus,and(most importantly)large numbers of regular corrugated cracks arranged on the surface.These corrugated cracks can effectively accommodate the coiled strain and provide space for the large curvature folding of proboscises.Finally,a 4D printed coiled sample with corrugated cracks was fabricated to mimic the proboscises stretching process.Large-curvature folding strategies,based on these proboscises,provide insights for the biomimetic design of artificial highly folded components.

PEEK modified PLA shape memory blends:towards enhanced mechanical and deformation properties

Polylactic acid(PLA)is one of the most promising shape memory polymers with outstanding biocompatibility,while poly(ether ether ketone)(PEEK)is a special engineering plastic with excellent mechanical performance.In this work,PEEK was selected to modify PLA,and a series of PLA blended with different PEEK contents(PLA/PEEK blends)were obtained.The effects of PEEK on thermodynamic,mechanical and shape memory properties of PLA/PEEK blends were investigated.The results showed that the thermal stabillity of the PL A/PEEK blend was improved with the PEEK content increase.The tensile strength reached the highest value of 20.6 MPa when the PEEK content was 10%.While the best shape memory performance occurred with the PEEK content of 15%,the shape recovery time was less than 2 s,and the shape fixation/recovery ratio was more than 99%.Furthermore,the programmable mimetic flower opening process was achieved by using PLA/PEEK blends with different PEEK content ratios.The above results indicated that the blend of an appropriate proportion of PEEK had positive effects on mechanical and deformation performances of PLA.

Selective laser melted high Ni content TiNi alloy with superior superelasticity and hardwearing

TiNi alloys with high content Ni(52-55 at.%)are perfectly suitable for preparing wear-and corrosionresistant parts that service on the space station,spacecraft,and submarine,because of their superior superelasticity,high strength,and hardwearing.However,the fabrication of complicated Ni-rich TiNi parts by the traditional machining method often faces problems of poor precision,low efficiency,and high cost.In this work,we succeed in preparing an excellent Ti_(47)Ni_(53) alloy by selective laser melting(SLM),and thus,open a new way for the efficient and precise formation of complicated Ni-rich TiNi parts with superelasticity and hardwearing.An optimized processing window for compact parts without defects is reported.The elaborately fabricated Ti_(47)Ni_(53) alloy exhibited a breaking strain of 11%,a breaking stress of 2.0 GPa,a superelastic strain of 9%,and a better hardwearing than that of casting and quenched Ti_(47)Ni_(53) alloy.Besides,the microstructure,phase transformation,and deformation,as well as their influence mechanisms are investigated by in situ transmission electron microscope(TEM)and high-energy X-ray diffraction(HE-XRD).The results obtained are of significance for both fundamental research and technological applications of SLM-fabricated high Ni content TiNi alloys.