Microstructure characteristics and mechanical properties of Al/Mg joints manufactured by magnetic pulse welding

The effective connection of 1050 Al and AZ31 Mg was realized by magnetic pulse welding.The maximum tensile-shear force of the dissimilar Al/Mg metal lap joint reached 97%of that of the 1050 Al alloy base material by optimizing the process parameters.The microstructure of dissimilar Al/Mg welded joints was analysed by Scanning Electron Microscope(SEM),Energy Dispersive Spectrometer(EDS)and Electron Backscattered Diffraction(EBSD).The results show that the key to obtaining high shear strength of Al/Mg dissimilar metal joints is mainly due to the following two reasons.On the one hand,grain refinement and element interdiffusion occur at the interface.On the other hand,no intermetallic compounds are formed at the interface.

Effects of Irradiation on the Structure-activity Relationship of Konjac Glucomannan Molecular Chain Membrane

To know the effects of irradiation on the konjac glucomannan （KGM） molecular chain membrane, KGM membrane solution was treated with the irradiation dose of 0-20 kGy in this study, and the structure and properties of KGM membrane were analyzed with Infrared spectrum, Raman spectrum, X-ray, SEM scanning and so on. The results revealed that the effects of different irradiation doses on the KGM molecular chain structure were different. Higher irradiation dose （20 kGy） resulted in partial damage against KGM membrane crystal structure, and there was no obvious change for the amorphous structure; with membrane property test, the tensile strength of KGM membrane gradually increased with the increase of irradiation dose and its elongation at break reduced, but these changes were not significant, WVP value reduced; with SEM, the membrane surface treated with irradiation was smoother even than the membrane without treatment. In addition, when increasing the irradiation dose, membrane surface became more even, and arrangement was more orderly and compact. KGM membrane nrooerties, and it is an ideal Irradiation modification could effectively improve the modification method.

EFFECTS OF RARE EARTH MIXTURE ON MECHANICAL PROPERTIES OF CuZnAl SHAPE MEMORY ALLOYS

With thehelpofquantitative metallograph ,tensiletest,electron probeandscan electron mi croscope,theinfluencesof mixture rareearth ( RE) on the grain size, dynamics of grain growth and mechanicalpropertiesof CuZnAlshape memoryalloys wereinvestigated . Theex perimentalresultsshowsthat REcanrefinegrainsgreatly,improvethe mechanicalpropertiesremarkably andchangethetensilefracturefrom brittletypebordered grainstoplastictypeinthecondition of maintainingshape memory properties. Moreover microstructuresrevealthatREwhich accumulates on the grain boundariescan restrain grains’growing. In addition, the mechanismsofrefininggrainsizeandimproving mechanicalpropertiesarealsodiscussed.

NOVEL OXIDATION RESISTANT CARBON SILICON ALLOY FIBRES

Anovel silicon containing carbon precursor was synthesised by reacting a petroleum pitchfraction and polydimethylsilane. The precursor containing about 26wt% Si was meltspunintofibresand then oxidativelystabilised in airto renderthefibresinfusiblebefore pyrolysisat1200℃underinertatmospheretoproduceC Sialloy( CSA) fibres. Theextentofstabili sation wasfoundto becriticalto the development of mechanicalstrength of thefibres which varied with heattreatmenttemperature, showing a maximum at 1200 ℃when thestrength was 1 4 1 6 GPa. Thesestrengthsareremarkably goodconsideringthelow modulus whichis duetothe quite high failurestrains. Thefibrescanshow excellentresistanceto oxidation if given an initialshortexposureto oxygen athigh temperature duetotheformation of an im perceptiblelayer of silica. CSAfibreshavethe advantagesof both carbon fibresand SiCfi bres,thusextended application areascan beenvisaged .

Preparation and Mechanical Properties of a Novel Textile Pad for Wound Debridement

Various types of wound debridement approaches are currently available in clinical practice such as autolytie, enzymatic. biodebridement, mechanical, and surgical debridemenl techniques. A critical look at these various options can explain their potential but also their limitations. In this study, a novel textile pad, which is composed of polyester filaments on the fleecy side and a bioeompatible coating on the opposite side, was made to provide a safe, inexpensive, easier and especially more efficient debridement process that can be used in all healthcare settings by all healthcare practitioners. Eighteen kinds of samples were prepared with different pile density, ground yarn count and coating amount. Dimensional morphology, stitch density, mass per unit area and mechanical properties were investigated to study the intrinsic relationship of structure and properties of textile pad for wound debridement. Results showed that tensile strength and suturing strength at piped site increased obviously with the increment of ground yarn count, while the amount of coating could also have a slight impact on these two properties. However, compressive load was mainly affected by pile density, with no obvious relation to ground yarn count and coating amount.

Comparative study of β-Si_3N_4 powders prepared by SHS sintered by spark plasma sintering and hot pressing

β-Si3N4 powders prepared by self-propagating high-temperature synthesis （SHS） with additions of Y2O3 and Al2O3 were sintered by spark plasma sintering （SPS）. The densification, microstructure, and mechanical properties of Si3N4 ceramics prepared using this method were compared with those obtained by hot pressing process. Well densified Si3N4 ceramics with finer and homogeneous microstructure and better mechanical properties were obtained in the case of the SPS technique at 200°C lower than that of hot pressing. The microhardness is 15.72 GPa, the bending strength is 716.46 MPa, and the fracture toughness is 7.03 MPa·m1/2.

Effects of salinity on the nail-holding power of dimension lumber used in light-frame wood building

We studied the effect of salinity on nail-hold- ing power in wood construction. In saline solution, the holding power of nails was less than in purified water. With the increase of salt concentration, the surface and side nail- holding power of the wood specimens both declined, but the differences between salinity treatments were not sig- nificant. However, compared to the surface and side nail- holding power, the power on the edge was generally less and the difference was not obvious in different salt con- centrations. In the same salt concentration, with the extension of the processing cycle, the performance of holding power of nails showed a downward trend, expect the temporary rise in the middle.

Microstructural characterization and mechanical properties of self-reinforced Si_3N_4 ceramics containing high oxynitride glass

Self-reinforced Si_3N_4 ceramics containing high oxynitride glass have beenfabricated by the control of microstructure evolution and p-Si_3N_4 grain growth. The effects of thesize distribution of the elongated p-Si_3N_44 grains, and the p-Si_3N_4 grain growth as well as theoxynitride glass chemical characteristic on the microstructure and mechanical properties wereinvestigated. The experimental results show that the p-Si_3N_4 grains in high oxynitride glass growto elongated rod-like crystals and form the stereo-network structure. Under the sintering conditionsof 1800 deg C and 60 min, a quite uniform microstructure with an average aspect ratio of 6.5 and anaverage of 1 mu m can be obtained. A large amount of oxynitride glass phase with high nitrogencontent enhances the elevated temperature fracture toughness because of its high softeningtemperature and high viscosity. In the present material, the crack deflection and pullout of theelongated rod-like P-Si_3N_44 grains are the primary toughening mechanisms.

High-frequency induction heated sintering of ball milled Fe-WC nanocomposites

Fe-WC nanocomposites were successfully fabricated by high-frequency induction heated sintering of ball milled nanostructure powders. The ball milled powders were characterized by X-ray diffraction. Density measurements by the Archimedes method show that all sintered samples have the relative density higher than 95%. Studies on the effects of WC content, milling speed, and milling time indicate that a higher milling speed and a more WC content lead to the improvement of mechanical properties. There is a very good distribution of WC particles in the Fe matrix at the milling speed of 650 r/rain. For the sintered sample 20-5-650 （20wt% WC, milling time of 5 h, and milled speed of 650 r/min）, the maximum Brinell hardness and yield stress are obtained to be 3.25 GPa and 858 MPa, respectively. All sintered samples have brittle fracture during compression test except the sample 20-5-650.

EFFECT OF Fe_2O_3 ON WELDING TECHNOLOGY AND MECHANICAL PROPERTIES OF WELD METAL DEPOSITED BY SELF-SHIELDED FLUX CORED WIRE

Five experimental self-shielded flux cored wires are fabricated withdifferent amount of Fe_2O_3 in the flux. The effect of Fe_2O_3 on welding technology and mechanicalproperties of weld metals deposited by these wires are studied. The results show that with theincrease of Fe_2O_3 in the mix, the melting point of the pretreated mix is increased. LiBaF_3 andBaFe_(12)O_(19), which are very low in inherent moisture, are formed after the pretreatment. Themechanical properties are evaluated to the weld metals. The low temperature notch toughness of theweld metals is increased linearly with the Fe_2O_3 content in the flux due to the balance betweenFe_2O_3 and residual Al in the weld metal. The optimum Fe_2O_3 content in flux is 2.5 percent approx3.5 percent.

Experimental Study on the Influence Mechanism of Carbon Fiber/Epoxy Composite Reinforcement and Matrix on Its Fire Performance

The effects of the number of layers,the arrangement of carbon fiber(CF)tow and the epoxy resin(ER)matrix on the fire performance of carbon fiber/epoxy composites(CFEC)were studied by a variety of experimental methods.The results show that the number of layers of CF tow has influence on the combustion characteristics and fire propagation of the composites.The arrangement of CF tow has influence on flame propagation rate and high temperature mechanicalproperties.The mechanism of the influence of the number of layers of CF tow on the composite is mainly due to the different thermal capacity of ER matrix.The effect of the arrangement of CF tow on the fire performance of the composite is mainly due to the inhibition and obstruction of the tow on the combustion of ER matrix.The influence on the high temperature mechanicalproperties is mainly due to the different arrangement direction of CF tow.The fitting equation of the mechanicalproperties of the samples was obtained.This equation could be used to predict the samples’tensile strength from 25°C to 150℃by comparing with the experimental results.Taking the carbon fiber woven cloth(C)applied in the fuselage material as an example,combining the influencing factors of various parameters in the fire field,some suggestions are put forward combined with the research conclusion.

Effect of PLA Knitted Structure on the Mechanical Properties of Composite Vascular Scaffold

A new entire biodegradable scaffold has been developed which does not require precelluiarization before transplantation. This new kind of vascular scaffold prototype made from porous poly- e-caprolactone （PCL） membrane to provide three-dimensional environment for cell growth, and embedded with weft-knitted polylactic acid （PLA） fabric to support mechanics. The aim of this paper is to study the variation tendency of mechanical properties with the fabric spacing changing. The basic geometrical parameters were measured to characterize properties of the samples. The tensile and compressive elastic recovery of the samples were tested by the universal mechanical tester and radial compression apparatus, respectively. Both tensile and compressive properties enhanced when reducing the fabric spacing of the composite vascular scaffold.

Thermo-Mechanical Processing of Iron-Phosphorous-Carbon Alloys

Phosphorous is widely considered as an impurity in steels. Consequently, its role as an important alloying element in iron could never be established. The present paper deals with the exploitation of phosphorous as a useful alloying element in iron in conjunction with carbon by way of improved thermo-mechanical processing leading to a tough steel equivalent to high strength low alloy steels. It was observed that phosphorous is pushed towards ferrite grains by carbon which in turn forms pearlite along ferrite grains. Suitable adjustment in the amounts of carbon and phosphorous yields an attractive set of mechanical properties after appropriate processing. Typical chemistry and processing combinations yields UTS: 700 MPa and % El: 25% Area under the stress-strain curve: 60 Joules.

Investigation of Mechanical Behavior of Defective Carbon Nanotubes Using Molecular Dynamics Simulation

Carbon nanotubes （CNTs） having pristine structure （i.e., structure without any defect） hold very high mechanical properties. However, CNTs suffer from defects ＇which can appear at production stage, purification stage or be deliberately introduced by irradiation with energetic particles or by chemical treatment. In this article, mechanical properties of single-walled nanotubes with defects are studied under both compressive and tensile loads using molecular dynamics （MD） simulations. Two types of defectStone-Wales and vacancy defects with different defect densities are considered for present investigation. Molecular simulations are carried out using the classical MD method. The Brenner potential is used for carbon-carbon interaction in the CNT. Temperature of the system is controlled by velocity scaling. Simulation results show that the defects have negligible effect on the modulus of elasticity of nanotubes. However, they have significant effect on the failure stress and strain of the nanotubes.

Research and development of nanocrystalline W/W-based materials: novel preparation approaches, formation mechanisms, and unprecedented excellent properties

Tungsten(W)has become the most promising plasma-facing material(PFM)in fusion reactor,and W still faces performance degradation caused by low-temperature brittleness,low recrystallization temperature,neutron irradiation effects,and plasma irradiation effects.The modification of wW-based materials in terms of microstructure manipulation is needed,and such techniques to improve the performance of materials are the topics of hot research.Researchers have found that refining the grain can significantly improve the strength and the irradiation resistance of Ww-based materials.In this paper,novel approaches and technique routes,including the"bottom-up"powder metallurgy method and"top-down"severe plastic deformation method,are introduced to the fabrication of nanocrystalline WW-based materials.The formation mechanisms of nanocrystalline WW-based materials were revealed,and the nanostructure stabilization mechanisms were introduced.The mechanical properties of nanocrystalline WW-based materials were tested,and the irradiation behaviors and performances were studied.The mechanisms of their high mechanical properties and excellent irradiation-damage resistance were illustrated.This article may provide an experimental and theoretical basis for the design and development of high-performance novel nanocrystallineW/W-based materials.

Deep drawing of aluminum alloy 7075 using hot stamping

In this paper, simulations of deep drawing tests at elevated temperatures were carried out with experimental validation. The aim of this work was to study the effect of process parameters on formability and mechanical properties of aluminum alloy 7075 in hot stamping process.Process parameters, including blank temperature, stamping speed, blank holder force and friction coefficient, were studied. Stamping tests were conducted at temperatures between 350 and 500 ℃, blank holder force between 0 and 10 kN, stamping speed between 50 and 150 mm·s^-1, and friction coefficient between 0.1 and 0.3. Based on the analysis, it is shown that thickness homogeneity could be improved when the blank is formed at lower temperature,lower blank holder force and lower friction coefficient.Formability could be improved when the blank was well lubricated at about 400 ℃. Formability at stamping speed 50 mm·s^-1 is far better than those at other speeds. The mechanical property analysis shows that the hot stamping process could make the formed part to obtain high quality.

Strength and fatigue properties of three-step sintered dense nanocrystal hydroxyapatite bioceramics

Dense hydroxyapatite （HA） ceramic is a promising material for hard tissue repair due to its unique physical properties and biologic properties. However, the brittleness and low compressive strength of traditional HA ceramics limited their applications, because previous sintering methods produced HA ceramics with crystal sizes greater than nanometer range. In this study, nano-sized HA powder was employed to fabricate dense nanocrystal HA ceramic by high pressure molding, and followed by a three-step sintering process. The phase composition, microstructure, crystal dimension and crystal shape of the sintered ceramic were examined by X-ray diffraction （XRD） and scanning electron microscopy （SEM）. Mechanical properties of the HA ceramic were tested, and cytocompatibility was evaluated. The phase of the sintered ceramic was pure HA, and the crystal size was about 200 nm. The compressive strength and elastic modulus of the HA ceramic were comparable to human cortical bone, especially the good fatigue strength overcame brittleness of traditional sintered HA ceramics. Cell attachment experiment also demonstrated that the ceramics had a good cytocompatibility.

Microstructure and Mechanical Properties of Mg–7.4% Al Alloy Matrix Composites Reinforced by Nanocrystalline Al–Ca Intermetallic Particles

Mg-7.6% Al （in mass fraction） alloy matrix composites reinforced with different volume fractions of nano- crystalline Al3Cas particles were synthesized by powder metallurgy, and the effect of the volume fraction of reinforcement on the mechanical properties was studied. Room temperature compression test reveals considerable improvement on mechanical properties as compared to unreinforced matrix. The compressive strength increases from 683 MPa for unre- inforced alloy matrix to about 767 and 823 MPa for the samples having 20 and 40 vol% of reinforcement, respectively, while retaining appreciable plastic deformation ranging between 12 and 24%. The specific strength of the composites increased significantly, demonstrating the effectiveness of the low-density AlaCas reinforcement.

EFFECT OF NANO-FILLER DISPERSION ON THE THERMAL,MECHANICAL AND WATER SORPTION PROPERTIES OF GREEN ENVIRONMENTAL POLYMER

Partially exfoliated nanocomposite （2） has been synthesized by intercalation of poly（propylene carbonate） （PPC） into commercial clay, Cloisite 20B （PPC/C-20B）. Nanocomposite 2 was characterized phiso-chemically and exhibited high thermal, mechanical and anti-water sorption properties as compared to PPC and intercalated nanocomposite （1） of PPC/C- 20B having same amount of clay. TGA results revealed that the thermal decomposition temperature （Td, 50%） of 2 increased significantly, being 40 K and 17 K higher than that of pure PPC and 1, respectively, while DSC measurements indicated that the nano-filler dispersion of 2 increased the glass transition temperature from 21℃ to 31℃. Accordingly, 2 showed high elastic modulus, hardness and anti-water absorption capacity. These thermal, mechanical alad anti-water absorption improvements are of great importance for the application of PPC as packaging and biomaterials.

Modified poly(methyl methacrylate) bone cement in the treatment of Kümmell disease

Kuümmell disease(KD)causes serious vertebral body collapse in patients.However,only a few case reports have been conducted and the number of patients with KD investigated was limited.Additionally,the frequently used poly(methyl methacrylate)(PMMA)bone cement for KD is limited by excessive modulus and poor biocompatibility.Herein,we aimed to modify PMMA bone cement with mineralized collagen(MC),and compare the clinical effects,image performance and finite ele-ment analysis between the modified bone cement and PMMA bone cement for the treatment of phase I and II KD.Thirty-nine KD patients treated with PMMA bone cement and 40 KD patients treated with MC-modified PMMA bone cement from June 2015 to March 2017 were retrospectively analyzed.The surgical procedure,intraoperative blood loss,hospital stay and complications were compared between different groups.Visual analog scale,Oswestry disability index,anterior verte-bral height,posterior vertebral height,computed tomography value,adjacent vertebral re-fracture,Cobb angle and wedge-shaped correction angle were evaluated.Additionally,the representative sample was selected for finite element analysis.We found that the MC-modified PMMA bone ce-ment could achieve the same effect as that of PMMA bone cement and was associated with better vertebral height restoration in the long term.