Stability Of Composite Structures Research Articles

Failure evolution and instability prediction of fiber-reinforced polymer-confined cement mortar specimens under axial compression.

In geotechnical engineering, a large number of pillars are often left in underground space to support the overlying strata and protect the surface environment. To enhance pillar stability and prevent instability, this study proposes an innovative technology for pillar reinforcement. Specifically, local confinement of the pillar is achieved through fiber-reinforced polymer (FRP) strips, resulting in the formation of a more stable composite structure. In order to validate the effectiveness of this structural approach, acoustic emission characteristics and surface strain field characteristics were monitored during failure processes, while mathematical models were employed to predict specimen instability. The test results revealed that increasing FRP strip confinement width led to heightened activity in acoustic emission events during failure processes, accompanied by a decrease in shear cracks but an increase in tensile cracks. Moreover, ductility was improved and deformation resistance capacity was enhanced within specimens. Notably, initial crack generation occurred within unconfined regions of specimens during failures; however, both length and width as well as overall numbers of cracks significantly decreased due to implementation of FRP strips. Consequently, specimen failure speed was slowed down accordingly. Finally, the instability of the partial FRP-confined cement mortar could be more accurately predicted based on the model of FRP-confined concrete. It was verified by the test results.

Photo-cured phase change energy storage material with photo-thermal conversion, self-cleaning and electromagnetic shielding performances via the lamellar structure strengthened by segment rearrangement of dynamic disulfide bond

At present, phase change materials (PCMs) with single function hardly meet the needs of advanced intelligent materials in practical applications, and the multifunction integration is the current trend. However, photo-cured multifunctional PCMs are hampered by insufficient transparency due to adding functional fillers, such as carbon and metal materials. The novel strategy is necessary to overcome this limitation. Here, a photo-cured multifunctional PCM is prepared by using the design of a lamellar structure composing the photo-cured phase change polymer layer and the functional fillers layer. The curing of the phase change polymer is realized by the photo-induced "thiol-ene" click reaction, and reversible dynamic disulfide bonds are introduced into the PCM, which not only gives the phase change crosslinked network reprocessability, but also strengthens the interface layer by the chain rearrangement to form a stable composite structure. The carboxylated multiwalled carbon nanotubes (CCNTs) and silver nanowires (AgNWs), as functional fillers, give the PCM photo-thermal conversion, self-cleaning and electromagnetic shielding (EMI SE) performances. Its phase change latent heat and photo-thermal conversion can reach 105.2 J/g and 78.5%, and the water contact angle is 142° with self-cleaning performance. In addition, due to the dense and well-developed conductive path formed by AgNWs layer on the PCM surface, the EMI SE effect can reach 39 dB with only 6.3% (in mass) filler content and 7.2% phase change latent heat loss. As far as we know, this is the first report about photo-cured PCMs with self-cleaning, photo-thermal conversion and EMI SE performances.

Linking Interfacial Bonding and Thermal Conductivity in Molecularly-Confined Polymer-Glass Nanocomposites with Ultra-High Interfacial Density.

Thermal transport in polymer nanocomposites becomes dependent on the interfacial thermal conductance due to the ultra-high density of the internal interfaces when the polymer and filler domains are intimately mixed at the nanoscale. However, there is a lack of experimental measurements that can link the thermal conductance across the interfaces to the chemistry and bonding between the polymer molecules and the glass surface. Characterizing the thermal properties of amorphous composites are a particular challenge as their low intrinsic thermal conductivity leads to poor measurement sensitivity of the interfacial thermal conductance. To address this issue here, polymers are confined in porous organosilicates with high interfacial densities, stable composite structure, and varying surface chemistries. The thermal conductivities and fracture energies of the composites are measured with frequency dependent time-domain thermoreflectance (TDTR) and thin-film fracture testing, respectively. Effective medium theory (EMT) along with finite element analysis (FEA) is then used to uniquely extract the thermal boundary conductance (TBC) from the measured thermal conductivity of the composites. Changes in TBC are then linked to the hydrogen bonding between the polymer and organosilicate as quantified by Fourier-transform infrared (FTIR)and X-ray photoelectron (XPS)spectroscopy. This platform for analysis is a new paradigm in the experimental investigation of heat flow across constituent domains.

Microwave melting rapid synthesis of CQDs/PpPD heterojunctions with efficient microwave electrodeless lamp photocatalytic performance

A sheet-like carbon quantum dots/poly-p-phenylenediamine (CQDs/PpPD) nanophotocatalyst with stable structure and excellent photocatalytic performance was prepared by a microwave melting method using glucose and p-phenylenediamine as raw materials. The structures of CQDs/PpPD were characterized by X-ray diffraction, Fourier transform infrared spectrometer, X-ray photoelectron spectrometer, scanning electron microscope, and transmission electron microscope. The results showed that the as-prepared nanophotocatalyst was a stable composite structure with sheet-like PpPD as the main body and spherical CQDs of 2.0–5.0 nm evenly distributed on its surface. Combined with the valence band spectrum of X-ray photoelectron spectrometer, Diffuse reflectance spectra, and photoluminescence characterization analysis, the structure of CQDs/PpPD was determined to be a type II heterojunction, which confirmed that CQDs/PpPD is an excellent photocatalyst material with stronger light absorption capacity and greater electron–hole pair separation efficiency. The photocatalytic performance of CQDs/PpPD was investigated in the microwave electrodeless lamp photocatalytic system. The results showed that microwave could greatly improve the photocatalytic performance of CQDs/PpPD, which could degrade 91.8% of 50 ppm rhodamine B within 10 min, and its degradation efficiency was more than twice that of P25. After four cycles of degradation experiments, the degradation rate remained stable above 88.0%. The photocatalytic mechanism of CQDs/PpPD was discussed through active species detection experiments, combined with the structure and performance characteristics of the materials. Taking into consideration the results obtained from this work, CQDs/PpPD prepared by the microwave melting method is a potential high-efficiency photocatalytic material.

The photocatalytic activity and purification performance of g-C3N4/carbon nanotubes composite photocatalyst in underwater environment.

Graphite carbon nitride (g-C3N4) is a promising photocatalyst for its high catalytic activity, low-cost and high-biosafety characteristics. Due to the complexity of underwater photochemical reaction conditions and the disadvantages of g-C3N4 itself such as low specific surface area, easy recombination of photogenerated electron-hole pairs and insufficient light absorption capacity, the application of g-C3N4 in the field of water purification is limited. For improving underwater photocatalytic performance of g-C3N4, a g-C3N4/carbon nanotubes (CNT-CN) composite photocatalyst with high specific surface area and enhanced light absorption capacity were prepared by in situ solvothermal method. Its photodegradation efficiency at different underwater transmission light was further studied. The results show that CNT has good compatibility with g-C3N4. g-C3N4 can grow in situ on the surface of CNT and form a stable composite structure. Moreover, its degradation efficiency under long-wavelength irradiation is improved significantly. The degradation rate of CNT-CN at 550-700nm was about 3 times than that of g-C3N4. Furthermore, CNT-CN can maintain higher photocatalytic activity under water. At 40cm depth where light intensity and ultraviolet spectra were attenuated 63.8% and 80.1%, respectively, the degradation rate of CNT-CN3 can still reach 3.49 times than that of g-C3N4. Based on this study, the introduction of CNT effectively promotes the electron-hole separation efficiency of g-C3N4, widens its spectral response range, and thus improves its underwater degradation efficiency.

Self‐Supported CuO In‐Situ‐Grown on Copper Foil as Binder‐Free Anode for Lithium‐Ion Batteries

AbstractTransition metal oxides as anode materials for lithium‐ion batteries (LIBs) possess the advantages of high specific capacity and abundance. However, most reported transition metal oxides based active anode materials were coated on the copper current collector with the addition of inactive polymer binder and conductive agents, resulting in low utilization of active substances. To solve this problem, nanostructured CuO with different morphologies (CuO bunches, CuO nanosheets, CuO nanotubes) were in‐situ grown on the copper current collectors via a simple wet chemical oxidation method. The as‐obtained CuO@Cu foils were used directly as anode for LIBs. CuO nanotubes exhibited excellent electrochemical performance and sustained a reversible discharge specific capacity of 798 mA h g−1 after 60 cycles at 100 mA g−1. At current density of 1000 mA g−1, a high specific capacity of 758 mA h g−1 can be obtained after 200 cycles. The satisfying electrochemical performances of the CuO nanotubes anode indicated that a stable composite structure of CuO@Cu foils was achieved in the binder free electrode. This work demonstrated the feasibility of this binder free strategy in the development of electrode materials for high performance lithium‐ion batteries design.

Blending of waste biomass for cost-effective chitosan-based biosorbents for removal of reactive dye from aqueous solution

Chitosan (CS) is an attractive natural and biodegradable cationic adsorbent material for treatment of anionic pollutants. For chitosan-based sorbents to be practicable, their price should be low. This study aims at cost reduction of chitosan-based sorbent through making of composite chitosan beads with industrial fermentation waste biomass of Escherichia coli. The maximum biomass content for maintaining stable composite bead structure was approximately 70.4% (w/w). The adsorption properties of the bacterial biomass-chitosan composite beads (BCCB) were evaluated using an anionic dye material, Reactive Yellow 2 (RY 2). At pH 4, the maximum uptake of BCCB was 679.13±23.76 mg/g, whereas those of pristine CS bead (CSB) and raw E. coli biomass were 934.71±50.97 mg/g and 200.77±4.51 mg/g, respectively. However, considering bound amount of RY2 to CS molecules in the CS-based beads, the BCCB showed the 2.1 times higher dye sorption capacity of CS than that of the CS in the CSB. In addition, the cost of RY2 treatment process using BCCB is expected to be shortened by 58% compared to CSB. Therefore, this study suggests that compositing CS with biomass waste can be a practical way to design cost-effective adsorbents.

Stable construction of layered reduced grapheme oxide/copper sulfide composites on cellulose fibers with hyperbranched polyamide-amine for efficient photocatalytic degradation of organic dyes

The use of semiconductor-based photocatalysts to degrade organic dyes in water is receiving more and more attention. However, there are still some problems in practical applications, such as high photogenerated carrier recombination rate, difficulty in recovery, and poor reusability. In this study, reduced graphene oxide (rGO)/copper sulfide (CuS) was loaded onto a dialdehyde cellulose fiber (DACF) with the help of hyperbranched polyamide-amine (HPAMAM) to construct a photocatalytic composite paper (DACF/HPAMAM/rGO/CuS paper). Based on the results, HPAMAM was bonded to DACF and rGO via CN and amide bond, and it could act as a nanoreactor to induce uniform and stable growth of CuS. The photocatalytic activity of the as-prepared DACF/HPAMAM/rGO/CuS paper in the degradation of rhodamine B was about 2.7 times that of the composite paper without HPAMAM and rGO (DACF/CuS paper). Such a high performance could be attributed to the improved charge separation efficiency and the stable composite structure of rGO/CuS in the composite paper. DACF/HPAMAM/rGO/CuS paper was also able to demonstrate excellent stability and reusability, which makes it a promising photocatalyst. This work provides a novel strategy for preparing highly efficient and stable photocatalytic composite paper for degradation of organic dyes.

In-Situ Investigation of Resin Shrinkage in the Composite Manufacturing Environment

Cure shrinkage of the polymer matrix during the composite manufacturing process leads to residual stresses, which can adversely affect the structural integrity and dimensional stability of composite structures. In this paper, a novel approach is developed for measuring the resin shrinkage and strain evolution of an epoxy resin (EPON-862) in the composite manufacturing environment. The resin is cured in a custom designed autoclave with borosilicate viewports, while digital image correlation (DIC) is used to analyze the strain evolution throughout the cure cycle. These processing induced strains are correlated to the cure-state using differential scanning calorimetery (DSC). The different mechanisms involved in the polymer strain evolution during composite processing are discussed.

Multi-Elemental Electronic Coupling for Enhanced Hydrogen Generation.

A robust polyaniline-assisted strategy is developed to construct a self-supported electrode constituting a nitrogen, phosphorus, sulfur tri-doped thin graphitic carbon layer encapsulated sulfur-doped molybdenum phosphide nanosheet array (NPSCL@S-MoP NSs/CC) with accessible nanopores, desirable chemical compositions, and stable composite structure for efficient hydrogen evolution reaction (HER). The multiple electronic coupling effects of S-MoP with N, P, S tri-dopants afford effective regulation on their electrocatalytic performance by endowing abundant accessible active sites, outstanding charge-transfer property, and d-band center downshift with a thermodynamically favorable hydrogen adsorption free energy (ΔGH* ) for efficient hydrogen evolution catalysis. As a result, the NPSCL@S-MoP NSs/CC electrode exhibits overpotentials as low as 65, 114, and 49mV at a geometric current density of 10mAcm-2 and small Tafel slopes of 49.5, 69.3, and 53.8mVdec-1 in 0.5m H2 SO4 , 1.0m PBS, and 1.0m KOH, respectively, which could maintain 50h of stable performance, almost outperforming all MoP-based catalysts reported so far. This study provides a valuable methodology to produce interacted multi-heteroatomic doped graphitic carbon-transition metal phosphide electrocatalysts with superior HER performance in a wide pH range.

ACE-inhibitory peptides from Laminaria japonica and their potential anti-hypertensive mechanism

ABSTRACT Bioactive peptides have been extensively applied for developing health-promoting foods. To improve the value of Laminaria japonica proteins (LJPs), anti-hypertensive peptides were prepared by using controlled enzymatic hydrolysis along with response surface methodology to improve their yields. Eight anti-hypertensive peptides with tyrosine (Tyr) at the C-terminal were determined through an efficient RP-HPLC method and molecular docking was performed to reveal the underlying mechanisms behind their effectiveness of anti-hypertension. According to the results, the strongest activity of hydrolysates was achieved under enzyme ratio (papain: alcalase: trypsin) 1:2:1, pH 8.0, temperature 60°C, substrate concentration 1.7%, enzyme addition 4.4%, and hydrolysis time 5.1 h. Furthermore, molecular docking results displayed that anti-hypertensive peptides could bind with ACE active sites through forming a stable composite structure, thus causing a significant reduction to activities. These results demonstrated the potential applications of LJPs as a source of anti-hypertensive peptides and provided a reference for the industrialized anti-hypertensive productions.

Influences of PVA modification on performance of microencapsulated reversible thermochromic phase change materials for energy storage application

The aim of the paper was to enhance the mechanical properties and anti-permeability performance of microcapsules through shell modification to keep complete and stable structure during the manufacturing process. The effect of PVA adding dosage, modified methods and types of PVA on the performance of microcapsules was discussed in detail. When the PVA/MF ratio (0.04–0.25) was appropriate, the supercooling degree of microcapsules was reduced and thermal stability was improved to some extent. Furthermore, the modified method of adding PVA-1788 into microcapsules after curing probably formed the second protective encapsulation for RTPCMs, which contributed to obtaining MicroRTPCMs-2 with excellent mechanical properties and anti-permeability performance. Compared among the effects of various types of PVA modification on the performance of MicroRTPCMs, PVA with larger polymerization degree and higher alcoholysis degree can form modified resin with larger crosslinking degree, which was beneficial to generating more stable composite shell structure. Therefore, MicroRTPCMs1-2699 presented more outstanding mechanical properties and anti-permeability performance, satisfactory cycle stability and long-term reliability, as well as reversible thermochromic coloration and leakage-prevention performance. In the end, the main characteristic of RTPCMs was to in-situ observe the heat absorption, energy storage and heat release process of PCM cores, which would be great significance for the practical application of MicroRTPCMs in the fields of thermoregulated fibers, thermal energy storage textiles, heat energy transfers and energy-saving building materials.

Hybridization of Bimetallic Molybdenum‐Tungsten Carbide with Nitrogen‐Doped Carbon: A Rational Design of Super Active Porous Composite Nanowires with Tailored Electronic Structure for Boosting Hydrogen Evolution Catalysis

AbstractAn ecofriendly and robust strategy is developed to construct a self‐supported monolithic electrode composed of N‐doped carbon hybridized with bimetallic molybdenum‐tungsten carbide (MoxW2−xC) to form composite nanowires for hydrogen evolution reaction (HER). The hybridization of MoxW2−xC with N‐doped carbon enables effective regulation of the electrocatalytic performance of the composite nanowires, endowing abundant accessible active sites derived from N‐doping and MoxW2−xC incorporation, outstanding conductivity resulting from the N‐doped carbon matrix, and appropriate positioning of the d‐band center with a thermodynamically favorable hydrogen adsorption free energy (ΔGH*) for efficient hydrogen evolution catalysis, which forms a binder‐free 3D self‐supported monolithic electrode with accessible nanopores, desirable chemical compositions and stable composite structure. By modulating the Mo/W ratio, the optimal Mo1.33W0.67C @ NC nanowires on carbon cloth achieve a low overpotential (at a geometric current density of 10 mA cm−2) of 115 and 108 mV and a small Tafel slope of 58.5 and 55.4 mV dec−1 in acidic and alkaline environments, respectively, which can maintain 40 h of stable performance, outperforming most of the reported metal‐carbide‐based HER electrocatalysts.

Facile Fabrication of SrTiO3@MoS2 Composite Nanofibers for Excellent Photodetector Application

Molybdenum disulfide (MoS2), as a kind of transition metal dichalcogenide, has been widely studied for its excellent compatibility with most of inorganic nanomaterials. Nevertheless, its microscale and agglomeration limit the performance severely. Therefore, the special structure of V-MoS2 has drawn a lot of interest, which can not only reduce the size of MoS2 nanosheets but also improve the valence electron structure of the materials. In this work, SrTiO3@MoS2 composite nanofibers were synthesized by the simple electrospinning and hydrothermal method, and it was applied as a novel material for photodetector. SEM, TEM, EDX, XRD, I-T curves, and EIS analysis were used to study the structure and properties of the prepared SrTiO3@MoS2 composite nanofibers. Simulating under sunlight at a potential of 1.23 V, the prepared composite materials exhibited a superior photoelectric performance of photocurrent density of 21.4 μA and a resistance of 2.3 Ω. These results indicate that the composite of SrTiO3 nanofiber adhered with V-MoS2 has a stable composite structure, good electrical conductivity, and photoelectric sensitivity and is a suitable material for photodetectors. This work provides new ideas for the preparation of self-assembled materials and their application in photodetectors.

Mesoporous ZnCo2O4-CNT microflowers as bifunctional material for supercapacitive and lithium energy storage

As one kind of binary transition metal oxide, ZnCo2O4 (ZCO) displays excellent specific capacitance/capacity and high energy density as electrodes of supercapacitors (SCs) and lithium ion battery (LIBs). Introducing carbon materials has become a common method to obtain higher performance. In this work, the electronic property of ZnCo2O4 was firstly studied by Density Functional Theory to provide a theoretical support for the ZnCo2O4-CNT (ZCO-CNT) composite as electrode materials. Then, the composite was synthesized in a facile one-step hydrothermal way. The homogenous combination of the ZnCo2O4 microflower with CNTs provided continuous electron transmission channels and fast electron transfer inside the composite, which also absorbed the stress in electrochemical reactions, and therefore helped maintaining a stable composite structure during cycling. Besides, the microscale dimension of ZCO-CNT flowers can also alleviate self-aggregation and stable structure during electrochemical reactions. As the positive electrode of asymmetric supercapacitor, the ZCO-CNT//activated carbon device demonstrated an energy density of 24.46 Wh·kg−1 at a power density of 750 W·kg−1, as well as a high capacitance retention of 84.6% after 3000 cycles. Furthermore, as for LIBs, ZCO-CNT was regarded as a kind of potential anode electrode material. An excellent reversible capacity of 1200 mAh·g−1 could be obtained after 120 cycles at 200 mA·g−1.

Superior Lithium Storage Capacity of α‐MnS Nanoparticles Embedded in S‐Doped Carbonaceous Mesoporous Frameworks

AbstractHerein, a Mn‐based metal–organic framework is used as a precursor to obtain well‐defined α‐MnS/S‐doped C microrod composites. Ultrasmall α‐MnS nanoparticles (3–5 nm) uniformly embedded in S‐doped carbonaceous mesoporous frameworks (α‐MnS/SCMFs) are obtained in a simple sulfidation reaction. As‐obtained α‐MnS/SCMFs shows outstanding lithium storage performance, with a specific capacity of 1383 mAh g−1 in the 300th cycle or 1500 mAh g−1 in the 120th cycle (at 200 mA g−1) using copper or nickel foil as the current collector, respectively. The significant (pseudo)capacitive contribution and the stable composite structure of the electrodes result in impressive rate capabilities and outstanding long‐term cycling stability. Importantly, in situ X‐ray diffraction measurements studies on electrodes employing various metal foils/disks as current collector reveal the occurrence of the conversion reaction of CuS at (de)lithiation process when using copper foil as the current collector. This constitutes the first report of the reaction mechanism for α‐MnS, eventually forming metallic Mn and Li2S. In situ dilatometry measurements demonstrate that the peculiar structure of α‐MnS/SCMFs effectively restrains the electrode volume variation upon repeated (dis)charge processes. Finally, α‐MnS/SCMFs electrodes present an impressive performance when coupled in a full cell with commercial LiMn1/3Co1/3Ni1/3O2 cathodes.

MgO based composite phase change materials for thermal energy storage: The effects of MgO particle density and size on microstructural characteristics as well as thermophysical and mechanical properties

MgO has been used as a popular ceramic skeleton material (CSM) for shape-stablising inorganic salt based composite phase change materials (CPCMs) for medium to high temperature thermal energy storage applications. This work aims to understand the effects of particle size and density of MgO on the microstructures, and thermophysical and mechanical properties of the CPCMs. A eutectic carbonate salt of NaLiCO3 was used as the phase change material (PCM) with a melting temperature of around 500 °C and graphite flakes as the thermal conductivity enhancement material (TCEM). Two types of MgO were used in the work with one being light MgO and the other heavy MgO. The results demonstrated clear evidence of salt migration within the CPCMs made from both types of MgO during thermal cycling, leading to a more homogenous distribution of the salt as well as the CSM and TCEM. For a given particle size and TCEM loading, the light MgO (with a higher surface energy) gave a more considerable extent of particles migration and rearrangement than the heavy MgO (with a lower surface energy). Due to the higher surface energy, a much denser structure and better PCM containment of the CPCMs were observed with the light MgO formulations. For a given MgO type, smaller MgO particles yielded smaller internal pores and a more rigid structure, leading to a better containment of the PCM and more stable composite structure during thermal cycling. The microstructural characteristics observed were also found to be closely related to the thermophysical and mechanical properties of the CPCMs; a CPCM composite made with ingredients of a similar size gave a more compact structure and hence a better combination of thermal conductivity and mechanical strength.

Research on trajectory planning of non-developable surface for automated tape placement processing of composite

Abstract Tape placement manufacturing process, as one of the automated forming technologies for composite material, not only substantially improves the productivity of composite component and reduces the cost of production significantly but also raises the reliability and stability of composite structure. Automated tape placement technology is mainly applied for manufacturing the fuselage and wing panel of airplane characterized by small curvature and large size. For these kinds of structural components with a non-developable surface, trajectory planning by “natural path” method could reduce the internal stress and improve the quality of composite products to a certain extent but not be optimized by quantitative characterization. On the basis of preliminary work, the theoretical model of “unnatural degree” (UD) is introduced in the first step, which could characterize the tensile and shear strain of the laying tape quantitatively. Secondly, by adjusting the iterative step and laying direction to diminish the UD, local stress could be softened in order to optimize the laying track. Ultimately, the simulation model of the non-developable surface is established under the Matlab software environment, and the “variable step-angle” algorithm is adopted to verify the adjustment effect of the tape-laying track.

Structural Dynamics and Stability of Composite Structures

Structural Dynamics and Stability of Composite Structures

Thermal stability of compound stucture of silicon nanowire encapsulated in carbon nanotubes

To guide the experiment research, the thermal stability of composite silicon nanowire encapsulated in carbon nanotubes is investigated by computer simulation. The cubic-diamond-structured silicon nanowires with the same diameter and [111] orientationt are filled in some armchaired single-walled carbon nanotubes. The heat process of compound structure of silicon nanowire encapsulated in carbon nanotubes is simulated by classical molecular dynamic method. Through the visualization and energy analysis method, the thermal stability of composite structure is studied. The changes in the thermal stability of silicon nanowires and carbon nanotubes are explained by the relationship between carbon nanotube space constraint and van der Waals force. It is found that the diameter of the carbon nanotubes is closely related to the thermal stability of silicon nanowires inside. When the nanotube diameter is small, thermal stability of silicon nanowires increases; when the nanotube diameter increases up to a certain size, the thermal stability of silicon nanowires will suddenly drop significantly: until the distance between silicon nanowires and the wall of carbon nanotube is greater than 1 nm, the thermal stability of silicon nanowires will be restored. On the other hand, silicon nanowires filled into the carbon nanotubes have an effect of reducing the thermal stability of carbon nanotubes.