Nano-scale Reinforcements and Properties of Al-Si-Cu Alloy Processed by High-Pressure Torsion

To improve the comprehensive mechanical properties of Al-Si-Cu alloy,it was treated by a high-pressure torsion process,and the effect of the deformation degree on the microstructure and properties of the Al-Si-Cu alloy was studied.The results show that the reinforcements(β-Si andθ-CuAl_(2)phases)of the Al-Si-Cu alloy are dispersed in theα-Al matrix phase with finer phase size after the treatment.The processed samples exhibit grain sizes in the submicron or even nanometer range,which effectively improves the mechanical properties of the material.The hardness and strength of the deformed alloy are both significantly raised to 268 HV and 390.04 MPa by 10 turns HPT process,and the fracture morphology shows that the material gradually transits from brittle to plastic before and after deformation.The elements interdiffusion at the interface between the phases has also been effectively enhanced.In addition,it is found that the severe plastic deformation at room temperature induces a ternary eutectic reaction,resulting in the formation of ternary Al+Si+CuAl_(2)eutectic.

Lamellar water induced quantized interlayer spacing of nanochannels walls

The nanoscale confinement is of great important for the industrial applications of molecular sieve,desalination,and also essential in bio-logical transport systems.Massive efforts have been devoted to the influence of restricted spaces on the properties of confined fluids.However,the situation of channel-wall is crucial but attracts less attention and remains unknown.To fundamentally understand the mechanism of channel-walls in nanoconfinement,we investigated the interaction between the counter-force of the liquid and interlamellar spacing of nanochannel walls by considering the effect of both spatial confinement and surface wettability.The results reveal that the nanochannel stables at only a few discrete spacing states when its confinement is within 1.4 nm.The quantized interlayer spacing is attributed to water molecules becoming laminated structures,and the stable states are corresponding to the monolayer,bilayer and trilayer water configurations,respectively.The results can potentially help to understand the characterized interlayers spacing of graphene oxide membrane in water.Our findings are hold great promise in design of ion filtration membrane and artificial water/ion channels.

Microstructure and hardness of W-25Re alloy processed by high-pressure torsion

The evolution of microstructure and microhardness was studied in a commercial tungsten-25%rhenium(mass fraction)(W-25Re)alloy processed by the high pressure torsion(HPT)procedure under a pressure of7.7GPa up to10revolutions at different temperatures.The results show that the samples processed by10revolutions at room temperature could have the smallest grain size at around0.209μm.High saturation hardness(HV^1200)could be achieved after the rapid strengthening stage for samples processed by10revolutions both at room temperature and at573K.Microstructural observation and analysis from Hall-Patch relationship could reveal that grain refinement and grain boundaries strengthening are the main factors of hardening mechanism in W-25Re alloy.It is also demonstrated that sintered W-25Re sample may have brittle phase separation phenomenon after HPT processing.

Unusual thermal properties of graphene origami crease:A molecular dynamics study

Graphene is a two-dimensional material that can be folded into diverse and yet interesting nanostructures like macro-scale paper origami.Folding of graphene not only makes different morphological configurations but also modifies their mechanical and thermal properties.Inspired by paper origami,herein we studied systemically the effects of creases,where sp^(2)to sp^(3)bond transformation occurs,on the thermal properties of graphene origami using molecular dynamics(MD)simulations.Our MD simulation results show that tensile strain reduces(not increases)the interfacial thermal resistance owing to the presence of the crease.This unusual phenomenon is explained by the micro-heat flux migration and stress distribution.Our findings on the graphene origami enable the design of the next-generation thermal management devices and flexible electronics with tuneable properties.

Loading direction-dependent shear behavior at different temperatures of single-layer chiral graphene sheets

The loading direction-dependent shear behavior of single-layer chiral graphene sheets at different temperatures is studied by molecular dynamics （MD） simulations. Our results show that the shear properties （such as shear stress-strain curves, buckling strains, and failure strains） of chiral graphene sheets strongly depend on the loading direction due to the structural asymmetry. The maximum values of both the critical buckling shear strain and the failure strain under positive shear deformation can be around 1.4 times higher than those under negative shear deformation. For a given chiral graphene sheet, both its failure strain and failure stress decrease with increasing temperature. In particular, the amplitude to wavelength ratio of wrinkles for different chiral graphene sheets under shear deformation using present MD simulations agrees well with that from the existing theory. These findings provide physical insights into the origins of the loading direction-dependent shear behavior of chiral graphene sheets and their potential applications in nanodevices.

Process Evaluation, Tensile Properties and Fatigue Resistance of Chopped and Continuous Fiber Reinforced Thermoplastic Composites by 3D Printing

The aim of this article was to comprehensively evaluate the manufacturing process,tensile properties and fatigue resistance of the chopped and continuous fiber reinforced thermoplastic composites(CFRTPCs)by 3D printing.The main results included:the common defects of the printed CFRTPCs contained redundant and accumulation defects,scratch and warping defects;the continuous fiber contributed to the dimensional stability and accuracy of width and thickness;associations between mass percentage of fiber reinforcement and the averages of elastic mod-ulus,strain at break and ultimate tensile strength were approximately linear based on tensile test results;the fati-gue resistance improved with the increasing fiber reinforcement based on fatigue test results.As for specimens with four fiber rings,there was a good linear relationship between the stress level and logarithm value of cycles during the whole life while those of pure matrix and specimens with one and two fiber rings were piecewise linear,taking about 10,000 cycles as boundary.The micro morphology showed that the fatigue failure behaved as matrix fracture,large and small fiber bundles and single fibers extracted from matrix.Under the tension-tension fatigue load,the deformations where easily concentrating stress behaved as sunken surfaces along thickness and width directions,and the deformation along width direction was greater than that along thickness direction.

Type Synthesis of fully-Decoupled 2T2R Parallel Mechanisms Based on Driven - Chain Principle

Based on the screw theory and the driven-chain principle,a methodology of structural synthesis for fully-decoupled two-translational(2T) and two-rotational(2R) parallel mechanism is proposed by analyzing the characteristics of the input-output relations for fully-decoupled parallel mechanisms.Firstly,according to the desired kinematic characteristics of fully-decoupled parallel mechanisms,a method is proposed by virtue of screw theory to synthesize the desired forms for both the direct and the inverse Jacobian matrices.Secondly,according to the feature of the direct and the inverse Jacobian matrices,the effective screws,the actuated screws and the mobile un-actuated screws of each leg are established based on the reciprocal screw theory and all possible topology structures fulfilling the requirements are obtained.Finally,the desired fully-decoupled parallel mechanisms can be synthesized by using the structural synthesis rule and structural synthesis of fullydecoupled 2T2R parallel mechanisms can be obtained exploiting the abovementioned methodology.In particular,the direct Jacobian matrix of each synthesized fully-decoupled 2T2R parallel mechanism is a non-zero diagonal matrix throughout the entire workspace.Motors are mounted on each leg and each one of them actuates one degree-of-freedom(Do F) of the fully-decoupled parallel mechanism through a one-to-one velocity relation.

Deformation Behavior and Formability of Gradient Nano-grained AISI 304 Stainless Steel Processed by Ultrasonic Impact Treatment

The deformation behavior and formability of gradient nano-grained（GNG） AISI 304 stainless steel in uniaxial and biaxial states were investigated by means of tensile test and small punch test（SPT）. The GNG top layer was fabricated on coarse grains（CG） AISI 304 by ultrasonic impact treatment. The results showed that the CG substrate could effectively suppress the strain localization of NC in GNG layer, and an approximate linear relationship existed between the thickness of substrate（h） and uniform true strain before necking（ε_（unif））. Grain growth of NC was observed at the stress state with high Stress triaxiality T, which led to better ductility of GNG/CG 304 in SPT, as well as similar true strain after the onset of necking（ε_（neck）） compared with coarse 304 in tensile test. Ei-values of GNG/CG 304 with different structures were nearly the same at different punch speeds, and good formability of GNG/CG 304 was demonstrated. However, punch speed and microstructure needed to be optimized to avoid much lost of membrane strain region in biaxial stress state.

Effect of void size and Mg contents on plastic deformation behaviors of Al-Mg alloy with pre-existing void:Molecular dynamics study

The plastic deformation properties of cylindrical pre-void aluminum-magnesium(Al-Mg)alloy under uniaxial tension are explored using molecular dynamics simulations with embedded atom method(EAM)potential.The factors of Mg content,void size,and temperature are considered.The results show that the void fraction decreases with increasing Mg in the plastic deformation,and it is almost independent of Mg content when Mg is beyond 5%.Both Mg contents and stacking faults around the void affect the void growth.These phenomena are explained by the dislocation density of the sample and stacking faults distribution around the void.The variation trends of yield stress caused by void size are in good agreement with the Lubarda model.Moreover,temperature effects are explored,the yield stress and Young’s modulus obviously decrease with temperature.Our results may enrich and facilitate the understanding of the plastic mechanism of Al-Mg with defects or other alloys.

Structural Synthesis of 3T2R Five-Degree-of-Freedom Hybrid Mechanism

The structural synthesis of mechanisms is a prerequisite of mechanical design,thereby,it is necessary to pay attention to the structural synthesis of mechanisms,especially for the type synthesis of hybrid mechanisms.A very simple yet very effective method was presented for the structural synthesis of hybrid mechanisms based on the set theory.The basic concept and mathematical operation of G_F set were firstly introduced.Based on the G_F set,a type synthesis principle for serial mechanisms,parallel mechanisms and hybrid mechanisms was presented,especially,a detailed algorithm of type synthesis for hybrid mechanisms was proposed as well.It is shown that type synthesis of hybrid mechanisms can be developed by the combination of elements of G_F set and rotation axis transfer theorem.Further investigation shows that structures of 3T2R fivedegree-of-fteedom(DoF) hybrid mechanism only have one category,i.e.,G_F^I.Finally structural synthesis of 3T2R hybrid mechanism for this category is illustrated with example to demonstrate the applicability of the type synthesis principle.

Type Synthesis of Fully-Decoupled 3R2T Parallel Mechanisms Based on Driven-Chain Principle

To avoid the existence of nonlinear and strong coupling in parallel mechanisms,it is necessary to address special care to the type synthesis of mechanisms,especially for the type synthesis of fully-decoupled parallel mechanisms. Based on the screw theory and the driven-chain principle,a methodology of structural synthesis for fully-decoupled three-rotational( 3R) and two-translational( 2T)parallel mechanisms was proposed by analyzing the characteristics of the input-output relations for fully-decoupled parallel mechanisms.Firstly,according to the desired kinematic characteristics of fullydecoupled parallel mechanisms,a method was presented by virtue of screw theory to synthesize the desired forms for both the direct and the inverse Jacobian matrices. Secondly,according to the feature of the direct and the inverse Jacobian matrices,the effective screws,the actuated screws and the mobile un-actuated screws of each leg were established based on the reciprocal screw theory and all possible topology structures fulfilling the requirements were obtained.Finally,the desired fully-decoupled parallel mechanisms could be synthesized by using the structural synthesis rule and structural synthesis of fully-decoupled 3R2 T parallel mechanisms could be obtained exploiting the abovementioned methodology. Furthermore,the Jacobian matrix of a synthesized 3R2 T parallel mechanism was deduced to demonstrate the decoupling feature of the parallel mechanism,which also validated the correctness of the methodology of the type synthesis for fully-decoupled 3R2 T parallel mechanisms.

Structural Synthesis of 2T3R Hybrid Kinematic Mechanism Based on G_F Set

The structural synthesis of mechanisms is a prerequisite of mechanical design. Thereby, it is necessary to address special attention to the structural synthesis of mechanisms,especially for the structural synthesis of hybrid kinematic mechanisms( HKMs). This paper presents a very simple yet very effective method of structural synthesis for HKM based on the set theory. The basic concept and mathematical operation of Generalized Function Set( G_F set) are firstly introduced. Based on G_F set,a type synthesis principle for serial mechanisms,parallel mechanisms and HKMs is presented,respectively. Especially,a detailed algorithm of type synthesis for HKM is proposed as well. It is shown that type synthesis of HKM can be developed by the combination of elements of G_F setand rotation axis transfer theorem. In order to demonstrate the applicability of the type synthesis principle presented in the paper,structure synthesis of 2T3 R HKMs are accomplished,where T and R denote translational and rotational degree-of-freedom( DoF),respectively. And further research shows that the structures of 2T3 R HKMs can be categorized into two types,i. e.,G(_F~Ⅰ) and G(_F~Ⅱ).

UG Programming Development and Digital Design of Globoidal Indexing CAM Mechanism

In the design process of globoidal CAM mechanism,there are some shortcomings such as long structure design cycle,low efficiency,and no modification flexibility of parameters of similar parts.NX Open classic application programming interfaces(APIS)can be connected with Microsoft Visual Studio(VS).Based on NX Open application,users can develop menus,toolbars,dialog boxes and other tools to realize interactive design.Users can also call input parameters through the dialog box callback function,then activate the corresponding control application(callback function)by C++programming language and NX Open API complete code.Based on the secondary development function of UG software and VS,a digital design system suitable for high efficiency modeling of globoidal indexing CAM mechanism was developed to complete the human-machine interface interaction design.The results show that comparing the digital design system with the traditional design,the system after parametric design can not only greatly shorten the design time,but also reduce the tedious repetitive work,which proves the superiority and feasibility of the digital design.

Study on the influence of food emulsion components on its lubrication characteristics and smooth perception

Due to the increasing risk of obesity and cardiovascular diseases caused by high-fat diets,low-fat foods have become a priority demand for consumers’health.However,the smoothness perception and scientific assessment methods of the existing low-fat foods should be improved.In this study,three food emulsions were prepared,and their lubrication characteristics,sensory evaluation of smoothness,and electroencephalogram(EEG)signals were assessed to preliminarily investigate the effects of food emulsion components on their above characteristics.The results showed that fat substitute(FSU)and fat could significantly reduce coefficient of friction(CoF)of the food emulsions,with average CoF reduced by 28%and 63%compared to the original food emulsions.In addition,fat-enriched food emulsions continued to exhibit excellent lubrication characteristics after adding artificial saliva,with an average CoF reduced by 31.1%compared to that of the food emulsions without artificial saliva.Both FSU and fat improved the smoothness of food emulsions,and the lubricating properties of fat were more pronounced,with fat-enriched food emulsion which could provide a substantial improvement in smoothness compared to the fat-free food emulsion.Comparison of subjects’EEG signals revealed that food emulsion with lower CoF and higher smoothness triggered higher P3 amplitudes and longer latencies.These findings provide better insights into the scientific evaluation of food texture and the development of low-fat foods.

Direct-Ink-Writing Printed Strain Rosette Sensor Array with Optimized Circuit Layout

The full-field multiaxial strain measurement is highly desired for application of structural monitoring but still challenging,especially when the manufacturing and assembling for largearea sensing devices is quite difficult.Compared with the traditional procedure of gluing commercial strain gauges on the structure surfaces for strain monitoring,the recently developed Direct-Ink-Writing(DIW)technology provides a feasible way to directly print sensors on the structure.However,there are still crucial issues in the design and printing strategies to be probed and improved.Therefore,in this work,we propose an integrated strategy from layered circuit scheme to rapid manufacturing of strain rosette sensor array based on the DIW technology.Benefit from the innovative design with simplified circuit layout and the advantages of DIW for printing multilayer structures,here we achieve optimization design principle for strain rosette sensor array with scalable circuit layout,which enable a hierarchical printing strategy for multiaxial strain monitoring in large scale or multiple domains.The strategy is highly expected to adapt for the emerging requirement in various applications such as integrated soft electronics,nondestructive testing and small-batch medical devices.

Multiscale Theories and Applications:From Microstructure Design to Macroscopic Assessment for Carbon Nanotubes Networks

Carbon nanotube(CNT)networks enable CNTs to be used as building blocks for synthesizing novel advanced materials,thus taking full advantage of the superior properties of individual CNTs.Multiscale analyses have to be adopted to study the load transfer mechanisms of CNT networks from the atomic scale to the macroscopic scale due to the huge computational cost.Among them,fully resolved structural features include the graphitic honeycomb lattice(atomic),inter-tube stacking(nano)and assembly(meso)of CNTs.On an atomic scale,the elastic properties,ultimate stresses,and failure strains of individual CNTs with distinct chiralities and radii are obtained under various loading conditions by molecular mechanics.The dependence of the cohesive energies on spacing distances,crossing angles,size and edge effects between two CNTs is analyzed through continuum modeling in nanoscale.The mesoscale models,which neglect the atomic structures of individual CNTs but retain geometrical information about the shape of CNTs and their assembly into a network,have been developed to study the multi-level mechanism of material deformation and microstructural evolution in CNT networks under stretching,from elastic elongation,strengthening to damage and failure.This paper summarizes the multiscale theories mentioned above,which should provide insight into the optimal assembling of CNT network materials for elevated mechanical performance.

Mechanical enhancement and weakening in Mo_(6)S_(6)nanowire by twisting

The torsional,bending and tensile mechanical properties of Mo_(6)S_(6)nanowire are examined by molecular dynamics(MD)simulations with a first-principles-based reactive force field(ReaxFF).It is found that Mo_(6)S_(6)nanowire shows unique mechanical properties such as high torsional and bending flexibility,high Young's modulus and strength,and negative Poisson's ratio.The Mo_(6)S_(6)nanowire can be strengthened or weakened via twisting,depending on the twist angle.The Mo_(6)S_(6)nanowire with a slight twist angle shows brittle failure,whereas it with a large twist angle exhibits ductile failure and necking behavior.Twisted Mo_(6)S_(6)nanowires show a crossover in the negative Poisson's ratio at critical strains,that is,Poisson's ratio first decreases but then increases,with a minimum value down to around-0.8 at the strain of 0.01 as the twist angle is 21.0°/nm.The negative Poisson's ratio and the crossover are explained by the bond transform that makes zero angles to the wire cross-section.

Automated X-ray recognition of solder bump defects based on ensemble-ELM

Solder bumps realize the mechanical and electrical interconnection between chips and substrates in surface mount components,such as flip chip, wafer level packaging and three-dimensional integration. With the trend to smaller and lighter electronics,solder bumps decrease in dimension and pitch in order to achieve higher I/O density. Automated and nondestructive defect inspection of solder bumps becomes more difficult. Machine learning is a way to recognize the solder bump defects online and overcome the effect caused by the human eye-fatigue. In this paper, we proposed an automated and nondestructive X-ray recognition method for defect inspection of solder bumps. The X-ray system captured the images of the samples and the solder bump images were segmented from the sample images. Seven features including four geometric features, one texture feature and two frequency-domain features were extracted. The ensemble-ELM was established to recognize the defects intelligently. The results demonstrated the high recognition rate compared to the single-ELM. Therefore, this method has high potentiality for automated X-ray recognition of solder bump defects online and reliable.

Fracture Toughnesses and Crack Growth Angles of Single-Layer Graphyne Sheets

Recently, Shang et al.(Angew Chem Int Ed 57(3):774-778,2018) have developed a method to synthesize ultrathin (around 1.9 nm) graphyne nanosheets. We reported here the mixed-mode I-II fracture toughnesses and crack growth angles of single-layer graphyne sheets using molecular dynamics (MD) simulations and the finite element (FE) method based on the boundary layer model, respectively. The various carbon-carbon bonds of graphyne sheets in the FE method are equated with the nonlinear Timoshenko beams based on the Tersoff-Brenner potential, where all the parameters of the nonlinear beams are completely determined based on the continuum modeling. All the results from the present FE method are reasonable in comparison with those from our MD simulations using the REBO potential. The present results show that both the critical stress intensity factors (SIFs) and the crack growth angle strongly depend on the chirality and loading angle q @= 90° and #= 0° representing pure mode I and pure mode II, respectively). Meanwhile, the fracture properties of single-layer cyclicgraphene and supergraphene sheets are also studied in order to compare with those of the graphyne sheets. The critical equivalent SIFs are derived as 1.55 < Keq.cy (cyclic)< 1.95 nN A-3/2, 1.64 < Keq.gy (graphyne)< 2.64 nN A_3/<2 and 0.61 < Keq-su (super)< 2.04 nN A-3/2 in the corresponding zigzag and armchair sheets using the MD simulations, while the SIFs are 0.32 < Keq-cy (cyclic)< 0.48 nN A-3/,2, 1.96 < Keq.gy (graphyne)< 2.49 nN A-3^2 and 1.42 < Keq-su (super)< 2.95 nN A_3//2 using the FE method. These findings should be of great help for understanding the fracture properties of carbon allotropes and designing the carbon-based nanodevices.

Simultaneous Evaporation and Foaming for Batch Coaxial Extrusion of Liquid Metal/Polydimethylsiloxane Porous Fibrous TENG

The utilization of textile-based triboelectric nanogenerators(t-TENGs)offers great potential for providing sustainable and wearable power.Nevertheless,the current designs of t-TENGs present limitations in terms of low electrical outputs and less developed,straightforward batch processing techniques.Herein,a facile bottom-up foaming-combined coaxial extrusion method is developed for the massive fabrication of liquid metal/polydimethylsiloxane(PDMS)core–shell porous fibrous TENG,which can be directly woven to form t-TENGs.Ink designs are studied for high-fidelity fibrous TENG manufacturing and porosity-controlled micropore formation.Furthermore,porous fibrous TENGs are applied to integrate different woven structures,and the electrical and mechanical performances of the t-TENGs are optimized.Compared with plain surface fibrous TENG,the porous fibrous TENG achieves a~fivefold improvement in the open-circuit voltage(V_(OC))and a~sevenfold improvement in the short-circuit current(I_(SC)).These outcomes indicate that we can prepare a range of polymers for t-TENGs with enhanced output performance even though they do not demonstrate great triboelectrification.This work also demonstrates successful integration for sustainably powering miniature electronics.These results can contribute to human motion energy harvesting for wearable self-powered sensors.