Functionally graded structure of a nitride-strengthened Mg_(2)Si-based hybrid composite

The ex-situ incorporation of the secondary SiC reinforcement,along with the in-situ incorporation of the tertiary and quaternary Mg_(3)N_(2) and Si_(3)N_(4) phases,in the primary matrix of Mg_(2)Si is employed in order to provide ultimate wear resistance based on the laser-irradiation-induced inclusion of N_(2) gas during laser powder bed fusion.This is substantialized based on both the thermal diffusion-and chemical reactionbased metallurgy of the Mg_(2)Si–SiC/nitride hybrid composite.This study also proposes a functional platform for systematically modulating a functionally graded structure and modeling build-direction-dependent architectonics during additive manufacturing.This strategy enables the development of a compositional gradient from the center to the edge of each melt pool of the Mg_(2)Si–SiC/nitride hybrid composite.Consequently,the coefficient of friction of the hybrid composite exhibits a 309.3%decrease to–1.67 compared to–0.54 for the conventional nonreinforced Mg_(2)Si structure,while the tensile strength exhibits a 171.3%increase to 831.5 MPa compared to 485.3 MPa for the conventional structure.This outstanding mechanical behavior is due to the(1)the complementary and synergistic reinforcement effects of the SiC and nitride compounds,each of which possesses an intrinsically high hardness,and(2)the strong adhesion of these compounds to the Mg_(2)Si matrix despite their small sizes and low concentrations.

Suppression of Co(Ⅱ)ion deposition and hazards:Regulation of SEI film composition and structure

Despite the presence of Li F components in the solid electrolyte interphase(SEI)formed on the graphite anode surface by conventional electrolyte,these Li F components primarily exist in an amorphous state,rendering them incapable of effectively inhibiting the exchange reaction between lithium ions and transition metal ions in the electrolyte.Consequently,nearly all lithium ions within the SEI film are replaced by transition metal ions,resulting in an increase in interphacial impedance and a decrease in stability.Herein,we demonstrate that the SEI film,constructed by fluoroethylene carbonate(FEC)additive rich in crystalline Li F,effectively inhibits the undesired Li^(+)/Co^(2+)ion exchange reaction,thereby suppressing the deposition of cobalt compounds and metallic cobalt.Furthermore,the deposited cobalt compounds exhibit enhanced structural stability and reduced catalytic activity with minimal impact on the interphacial stability of the graphite anode.Our findings reveal the crucial influence of SEI film composition and structure on the deposition and hazards associated with transition metal ions,providing valuable guidance for designing next-generation electrolytes.

Floristic Composition, Population Structure, and Recruitment Status of Plant Species: A Case Study of Farmer-Managed Natural Regeneration Practices in Arid and Semi-Arid Lands in Kenya

The technique of Farmer Managed Natural Regeneration (FMNR) is being promoted as a cost-effective approach for restoring degraded arable dry lands. Its effectiveness has been observed in many countries across the globe, where it is a traditional practice, and is now being encouraged across the African continent. This study aimed to evaluate the impact of FMNR on floristic Composition, Vegetation Structure, and Regeneration Status of woody Plant Species in the severely degraded Central Rift, Kenya. The study systematically assessed how FMNR influenced species composition, vegetation structure and regeneration status from two sample plots involved in FMNR practices. Transect lines and quadrats methods were utilized to collect data, specifically regarding the floristic composition, vegetation structure, and regeneration status of woody plant species. Quadrats and sub-quadrats of varying sizes (10 m by 10 m, 5 m by 5 m, and 1 m by 1 m) were nested along the transect lines for data collection. Furthermore, measurements of tree growth and development, including root collar diameter, diameter at breast height (D130) and heights within the study blocks, were taken. The data was then analyzed using R-software. Results showed a marked progressive increase in numbers of trees, saplings, seedlings, shrubs and herbs in all FMNR sites and reductions in all non-FMNR sites. The study advocates for widespread promotion of the FMNR practice both as an environmental conservation and restoration strategy.

Numerical investigation of the mechanical behavior of the backfill–rock composite structure under triaxial compression

To ensure safe and economical backfill mining,the mechanical response of the backfill–rock interaction system needs to be understood.The numerical investigation of the mechanical behavior of backfill–rock composite structure(BRCS)under triaxial compression,which includes deformation,failure patterns,strength characteristics,and acoustic emission(AE)evolution,was proposed.The models used in the tests have one rough interface,two cement–iron tailings ratios(CTRs),four interface angles(IAs),and three confining pressures(CPs).Results showed that the deformation,strength characteristics,and failure patterns of BRCS under triaxial compression depend on IA,CP,and CTR.The stress–strain curves of BRCS under triaxial compression could be divided into five stages,namely,compaction,elasticity,yield,strain softening,and residual stress.The relevant AE counts have corresponding relationships with different stages.The triaxial compressive strengths of composites increase linearly with the increase of the CP.Furthermore,the CP stress strengthening effect occurs.When the IAs are45°and 60°,the failure areas of composites appear in the interface and backfill.When the IAs are 75°and 90°,the failure areas of composites appear in the backfill,interface,and rock.Moreover,the corresponding failure modes yield the combined shear failure.The research results provide the basis for further understanding of the stability of the BRCS.

Composite wave-absorbing structure combining thin plasma and metasurface

In order to solve the thickness dependence of plasma absorption of electromagnetic waves and further reduce the backward radar scattering cross section(RCS)of the target,we designed a novel composite structure of a metasurface and plasma.A metasurface with three absorption peaks is designed by means of an equivalent circuit based on an electromagnetic resonance type metamaterial absorber.The reflection and absorption of the composite structure are numerically and experimentally verified.The finite integration method was used to simulate a composite structure of finite size to obtain the RCS.The experimental measurements of electromagnetic wave reflection were conducted by a vector network analyzer(Keysight N5234A)and horn antennas,etc.The research showed that the absorption capacity of this composite structure was substantially improved compared to either the plasma or the metasurface,and it is more convenient for application due to its low plasma thickness requirement and easy fabrication.

Tuning energy output of PTFE/Al composite materials through gradient structure

As a typical energetic composite,polytetrafluoroethylene(PTFE)/aluminum(Al)has been widely applied in explosives,pyrotechnics,and propellants due to its ultra-high energy density and intense exothermic reaction.In this work,the radial gradient(RG)structure of PTFE/Al cylinders with three different PTFE morphologies(200 nm and 5μm particles and 5μm fiber)and content changes are prepared by 3D printing technology.The effect of radial gradient structure on the pressure output of PTFE/Al has been studied.Compared with the morphology change of PTFE,the change of component content in the gradient structure has an obvious effect on the pressure output of the PTFE/Al cylinder.Furthermore,the relationships of the morphology,content of PTFE and the combustion reaction of the PTFE/Al cylinder reveal that the cylinder shows a more complex flame propagation process than others.These results could provide a strategy to improve the combustion and pressure output of PTFE/Al.

Failure characteristics and the damage evolution of a composite bearing structure in pillar-side cemented paste backfilling

A backfilling body-coal pillar-backfilling body(BPB)structure formed by pillar-side cemented paste backfilling can bear overburden stress and ensure safe mining.However,the failure response of BPB composite samples must be investigated.This paper examines the deformation characteristics and damage evolution of six types of BPB composite samples using a digital speckle correlation method under uniaxial compression conditions.A new damage evolution equation was established on the basis of the input strain energy and dissipated strain energy at the peak stress.The prevention and control mechanisms of the backfilling body on the coal pillar instability were discussed.The results show that the deformation localization and macroscopic cracks of the BPB composite samples first appeared at the coal-backfilling interface,and then expanded to the backfilling elements,ultimately appearing in the coal elements.The elastic strain energy in the BPB composite samples reached a maximum at the peak stress,whereas the dissipated energy continued to accumulate and increase.The damage evolution curve and equation agree well with the test results,providing further understanding of instability prevention and the control mechanisms of the BPB composite samples.The restraining effect on the coal pillar was gradually reduced with decreasing backfilling body element's volume ratio,and the BPB composite structure became more vulnerable to failure.This research is expected to guide the design,stability monitoring,instability prevention,and control of BPB structures in pillar-side cemented paste backfilling mining.

Constructing BaTiO_(3)/TiO_(2)@polypyrrole composites with hollow multishelled structure for enhanced electromagnetic wave absorbing properties

BaTiO_(3)/TiO_(2)@polypyrrole(PPy)composites with hollow multishelled structure(HoMS)were constructed to enhance the electromagnetic wave absorbing properties of BaTiO_(3)-based absorbing material.BaTiO_(3)/TiO_(2)HoMSs were prepared by hydrothermal crystallization using TiO_(2)Ho MSs as template.Then,FeCl3 was introduced to initiate the oxidative polymerization of pyrrole monomer,forming BaTiO_(3)/TiO_(2)@PPy HoMSs successfully.The electromagnetic wave absorbing properties of BaTiO_(3)/TiO_(2)HoMSs and BaTiO_(3)/TiO_(2)@PPy Ho MSs with different shell number were investigated using a vector network analyzer.The results indicate that BaTiO_(3)/TiO_(2)@PPy HoMSs exhibit improved microwave absorption compared with BaTiO_(3)/TiO_(2)HoMSs.In particular,tripled-shelled BaTiO_(3)/TiO_(2)@PPy HoMS has the most excellent absorbing performance.The best reflection loss can reach up to-21.80 dB at 13.34 GHz with a corresponding absorber thickness of only 1.3 mm,and the qualified absorption bandwidth of tripled-shelled BaTiO_(3)/TiO_(2)@PPy HoMS is up to 4.2 GHz.This work paves a new way for the development of high-performance composite microwave absorbing materials.

An origami shield with supporting frame structures optimized by a feature-driven topology optimization method

In this paper,the design,manufacture and testing of an origami protective shield with a supporting frame structure are presented.It consists of an origami shield surface and a deployable supporting frame structure that needs to be portable and sufficiently stiff.First,for the design of the shield surface,a threestage origami crease pattern is developed to reduce the shield size in the folded state.The shield surface consists of several stiff modular panels and layered with flexible fabric.The modular panels are made of a multi-layer composite where a ceramic layer is made of small pieces to improve durability as those small pieces enable restriction of crack propagation.Then,the supporting frame structure is designed as a chain-of-bars structure in order to fold into a highly compact state as a bundle of bars and deploy in sequence.Thus,a feature-driven topology structural optimization method preserving component sequence is developed where the inter-dependence of sub-structures is taken into account.A bar with semi-circular ends is used as a basic design feature.The positions of the bar’s end points are treated as design variables and the width of the bars is kept constant.Then,a constraint on the total length of the chain of bars is introduced.Finally,the modular panels made of multi-layer composite and the full-scale prototype of the origami shield are fabricated and tested to verify the bullet-proof performance.

Study of the Ballistic Impact Behavior of Protective Multi-Layer Composite Armor

The abalone shell,a composite material whose cross-section is composed of inorganic and organic layers,has high strength and toughness.Inspired by the abalone shell,several multi-layer composite plates with different layer sequences and thicknesses are studied as bullet-proof material in this paper.To investigate the ballistic performance of this multi-layer structure,the complete characterization model and related material parameters of large deformation,failure and fracture ofAl_(2)O_(3)ceramics andCarbon Fiber Reinforced Polymer(CFRP)are studied.Then,3D finite element models of the proposed composite plates with different layer sequences and thicknesses impacted by a 12.7 mm armor-piercing incendiary(API)are built using Abaqus to predict failure.The simulation results show that the CFRP/Al2O3 ceramic/Ultrahigh Molecular Weight Polyethylene(UHMWPE)/CFRP(1 mm/4 mm/4 mm/1 mm)composite is the optimized stack of layers.The simulation results under specified layer sequence and thickness have a reasonable correlation with the experimental results and reflect the failure and fracture of the multi-layer composite protective armor.

A strategy for lightweight designing of a railway vehicle car body including composite material and dynamic structural optimization

Rolling stock manufacturers are finding structural solutions to reduce power required by the vehicles,and the lightweight design of the car body represents a possible solution.Optimization processes and innovative materials can be combined in order to achieve this goal.In this framework,we propose the redesign and optimization process of the car body roof for a light rail vehicle,introducing a sandwich structure.Bonded joint was used as a fastening system.The project was carried out on a single car of a modern tram platform.This preliminary numerical work was developed in two main steps:redesign of the car body structure and optimization of the innovated system.Objective of the process was the mass reduction of the whole metallic structure,while the constraint condition was imposed on the first frequency of vibration of the system.The effect of introducing a sandwich panel within the roof assembly was evaluated,focusing on the mechanical and dynamic performances of the whole car body.A mass saving of 63%on the optimized components was achieved,corresponding to a 7.6%if compared to the complete car body shell.In addition,a positive increasing of 17.7%on the first frequency of vibration was observed.Encouraging results have been achieved in terms of weight reduction and mechanical behaviour of the innovated car body.

Influence of Weave Structures on the Tribological Properties of Hybrid Kevlar/PTFE Fabric Composites

The existing research of the woven fabric self-lubricating liner mainly focus on the tribological performance improvements and the service life raised by changing different fiber type combinations, adding additive modification, and performing fiber surface modification. As fabric composites, the weave structures play an important role in the mechanical and tribological performances of the liners. However, hardly any literature is available on the friction and wear behavior of such composites with different weave structures. In this paper, three weave structures （plain, twill 1/3 and satin 8/5） of hybrid Kevlar/PTFE fabric composites are selected and pin-on-flat linear reciprocating wear studies are done on a CETR tester under different pressures and different frequencies. The relationship between the tensile strength and the wear performance are studied. The morphologies of the worn surfaces under the typical test conditions are analyzed by means of scanning electron microscopy （SEM）. The analysis results show that at 10 MPa, satin 8/5 performs the best in friction-reduction and antiwear performance, and plain is the worst. At 30 MPa, however, the antiwear performance is reversed and satin 8/5 does not even complete the 2 h wear test at 16 Hz. There is no clear evidence proving that the tensile strength has an influence on the wear performance. So the different tribological performance of the three weave structures of fabric composites may be attributed to the different PTFE proportions in the fabric surface and the different wear mechanisms. The fabric composites are divided into three regions： the lubrication region, the reinforced region and the bonding region. The major mechanisms are fatigue wear and the shear effects of the friction force in the lubrication region. In the reinforced region fiber-matrix de-bonding and fiber breakage are involved. The proposed research proposes a regional wear model and further indicates the wear process and the wear mechanism of fabric composites.

Microstructure of Steel Fiber Reinforced Polymer-cement-based Composites

Mercury intrusion porosimetry was used to measure the pore structure of steel fiber reinforced polymer-cement-based composite. The results indicate that the large pore volume decreases by 57. 8% - 51.2% and by 87. 1% - 88% with the addition of steel fibers and polymers respectively. When both steel fibers and polymers are simultaneously added, the large pore volume decreases by 88.3% - 90.1% . As a surface active material , polymer has a favorable water-reduced and forming-film effect, which is contributed to the decrease of the thickness of water film and the improvement of the conglutination between the fibers and the matrix. Polymers could form a microstructure network. This network structure and the bone structure of cement hydration products penetrate each other and thus the interpenetrating network with sticky aggregate and steel fiber inside forms.

Damage Detection of Composite Material Intelligent Structure with a New Photoelectric System

A kind of photoelectric system that is suitable to measuring and to testing the damage of the composite material intelligent structure was presented. It can measure the degree of damage of the composite intelligent structure and it also can tell us the damage position in the structure. This system consists of two parts ： software and hardware. Experiments of the damage detection and the analysis of the composite material structure with the photoelectric system were performed, and a series of damage detection experiments was conducted. The results prove that the performance of the system is well and the effects of the measure and test are evident. Through all the experiments, the damage detection technology and test system are approved to be real-time, effective and reliable in the damage detection of the composite intelligent structure.

Structure and magnetic properties of mechanically alloyed Tb_(0.2)Pr_(0.8)(Fe_(0.4)Co_(0.6))_(1.93) and magnetostriction of its epoxy composite

The C15 Laves phase with composition Tb0.2Pr0.8（Fe0.4Co0.6）1.93 was synthesized by mechanical alloying （MA） and subsequent annealing process. The structure and magnetic properties of Tb0.2Pr0.8（Fe0.4Co0.6）1.93 were investigated by means of X-ray diffraction （XRD）, a vibrating sample magnetometer, and a standard strain technique. The effect of annealing on the structure and magnetic properties was studied. The analysis of XRD shows that the high Pr-content Tb0.2Pr0.8（Fe0.4Co0.6）1.93 alloy with the single phase of MgCu2-type structure can be successfully synthesized by MA method. The sample annealed at 450℃ is found to have a coercivity of 196 kA/m at room temperature. An epoxy/Tb0.2Pr0.8（Fe0.4Co0.6）1.93 composite was produced by a cold isostatic pressing technique. A large magnetostriction of 400 ppm, at an applied magnetic field of 800 kA/m, was found for the composite. The epoxy-bonded Tb0.2Pr0.8（Fe0.4Co0.6）1.93 composite combines a high magnetostriction with a significant coercivitv, which is a oromising magnetostrictive material.

Solidified structure and solute segregation in Al_2O_3/A356-La alloy composites

Al2O3/A356-La alloy composites were fabricated by squeeze casting, and the effects of La on the solidified structure and the solute segregation during alloy solidification were studied. The results indicate that the structure of the matrix alloy becomes fine and small by the addition of La. La has been richened at the interface to help improve the wettability between the fiber and Al alloy, but there are no intermetallic compounds richening La found at the interface yet. There is no special influence of La on the Mg segregation in the matrix alloy. The distribution of Mg and La in the composites has been at the same position--near the interface.

A Study on the Tensile Properties of the MWK Structures for Composite Reinforcement

In this paper, the tensile properties of the MWK structures produced with different basic stitches for composite reinforcement were experimentally studied. The results show that the MWK structures with the double loop pillar stitches have better mechanical properties.

Fabrication and abrasive wear properties of metal matrix composites reinforced with three-dimensional network structure

Reticulated polyurethane was chosen as the preceramic material for preparing the porous preform using the replication process. The immersing and sintering processes were each performed twice for fabricating a high-porosity and super-strong skeleton. The aluminum magnesium matrix composites reinforced with three-dimensional network structure were prepared using the infiltration technique by pressure assisting and vacuum driving. Light interfacial reactions have played a profitable role in most of the ceramic-metal systems. The metal matrix composites interpenetrated with the ceramic phase have a higher wear resistance than the metal matrix phase. The volume fraction of ceramic reinforcement has a significant effect on the abrasive wear, and the wear rate can be decreased with the increase of the volume fraction of reinforcement.

Internal Force Distribution in Steel-Concrete Composite Structure for Pylon of Cable-Stayed Bridge

Adopting a steel-anchor beam and steel corbel composite structure in the anchor zone on pylon is one of the key techniques for the design of Jintang bridge, a cable-stayed bridge in Zhoushan, China. In order to ensure the safety of the steel-concrete composite structure, a stud connector model for the joint section was put forward. Experiments were conducted to obtain the relation between load and slip of specimen, the failure pattern of stud connector, the yield bearing capacity and ultimate bearing capacity of a single stud, etc. The whole process of the structural behavior of the specimen was comprehensively analyzed. The features of the internal force distribution in the steel-concrete composite structure and the strain distribution of stud connector under different loads were emphatically studied. The test results show that the stud connector is applicable for the steel-concrete composite structure for pylon of Jintang bridge. The stud has a good ductility performance and a obvious yield process before its destruction. The stud connector basically works in a state of elasticity under a load less than the yield load.

Magneto-rheological elastomer (MRE) based composite structures for micro-vibration control

Magneto-rheological elastomers （MILEs） are used to construct composite structures for micro-vibration control of equipment under stochastic support-motion excitations. The dynamic behavior of MREs as a smart viscoelastic material is characterized by a complex modulus dependent on vibration frequency and controllable by external magnetic fields. Frequency-domain solution methods for stochastic micro-vibration response analysis of the MRE-based structural systems are developed to derive the system frequency-response function matrices and the expressions of the velocity response spectrum. With these equations, the root-mean-square （RMS） velocity responses in terms of the one-third octave frequency band spectrum can be calculated. Further, the optimization problem of the complex moduli of the MRE cores is defined by minimizing the velocity response spectra and the RMS velocity responses through altering the applied magnetic fields. Simulation results illustrate the influences of MRE parameters on the RMS velocity responses and the high response reduction capacities of the MRE-based structures. In addition, the developed frequency-domain analysis methods are applicable to sandwich beam structures with arbitrary cores characterized by complex shear moduli under stochastic excitations described by power spectral density functions, and are valid for a wide frequency range.