Search

Flexible piezoelectric pressure sensors have been paid great attention in wearable electronic devices, obtaining mechanical energy and driving portable devices. Presently, membranes based on piezoelectric ceramic/polymer composite materials encounter problems such as filler agglomeration and surface defects, which affects the energy conversion performance of piezoelectric devices. Herein, the surface of lead zirconate titanate (Pb(Zr0.52Ti0.48)O3, PZT),was modified by coupling agent-polydopamine (Pdop), and combined with the polyimide (PI) matrix by in-situ polymerization to form a uniform Pdop@PZT/PI composite. This polydopamine modification method increases the compatibility between the two components, and promotes the dispersion of PZT in the polyimide matrix more uniform. Under the external force of 10 N, the maximum open circuit voltage of Pdop@PZT/PI-based piezoelectric pressure sensor (PPS) can reach 12.8 V. In addition, the sensitivity of the sensor is 1.4 V/N (0.24 V/kPa), which can maintain a stable output voltage under different frequencies of external force. After 10,000 cycles of periodic impacting/releasing, the open circuit voltage of PPS remained stable, indicating that the device has excellent stability and durability. It has the potential to be used as self-powered wearable sensors and detect human motion in daily life.

As an emerging material, MXene has attracted wide interest in the field of microwave absorption due to its unique two-dimensional stratified structure and high electrical conductivity. However, the non-magnetic nature of MXene and the inherent agglomeration phenomenon are a huge obstacle to meeting the performance requirements of novel microwave absorbers. The introduction of magnetic components is an effective strategy to improve the microwave dissipation capacity of MXene. Herein, MXene/MgFe 2 O 4 composites with dielectric and magnetic components were prepared by the solvothermal synthesis and subsequent hydrothermal reaction. The results of microscopic morphology analysis demonstrated that a special entangled structure was formed between MgFe 2 O 4 and wrinkled MXene. Furthermore, by adjusting the weight concentration of MXene, the impedance matching of the absorbers could be regulated to optimize its microwave dissipation capacity. Remarkably, the as-fabricated MXene/MgFe 2 O 4 composite with a weight concentration of 2 mg/mL exhibited excellent microwave dissipation capacity. Specifically, the minimum reflection loss was as low as −53.1 dB and the maximum effective absorption bandwidth reached 7.44 GHz, which covered a part of X-band and the whole Ku-band. The significant improvement in microwave dissipation performance could be attributed to the optimization of magnetodielectric synergistic effect, resulting in improved impedance matching. It was expected that the research results of this paper would provide reference for the preparation of MXene-based composites as efficient and broadband microwave absorbers. [Display omitted] • MXene/MgFe 2 O 4 composites were prepared by a facile two-step method. • The composites had a unique entangled structure and rich heterogeneous interfaces. • Microwave absorption capacity was modulated by the weight concentration of MXene. • Maximum effective absorption bandwidth was 7.44 GHz, covering the whole Ku-band. • The RCS value of −49.4 dB m2 in the far-field is simulated by CST. [ABSTRACT FROM AUTHOR]

The development of high-performing solid fuels with desired mechanical and combustion properties is critical to future air-breathing propulsion systems for space exploration and hypersonic navigation. Boron (B)/hydroxyl-terminated polybutadiene (HTPB) composite has been studied for this purpose due to the high energy density (heat of combustion) of B and the appropriate processability and mechanical properties of HTPB. However, the weak interface between B and HTPB results in weakened mechanical properties, agglomerated B particles, and slow and inefficient combustion, especially for composites with high B loading (30 wt% and above). In this study, the effect of interface between B and HTPB on the combustion and mechanical performance of high-loading B/HTPB composites was investigated by surface functionalization of B particles. Three interfacial characteristics were compared: polar (pristine B)/nonpolar (HTPB), nonpolar (hydrocarbon-functionalized B)/nonpolar (HTPB), and covalently bonded (amine-functionalized B/HTPB) interfaces. It was found that both covalently bonded and nonpolar/nonpolar interfaces effectively reduced the aggregation of B particles in the HTPB matrix, even with up to 45 wt% B loading, thus promoting the combustion efficiency and burning rate. Moreover, covalently bonded interfaces in B/HTPB composites led to strain-hardening behaviors, resulting in enhanced strength, ductility, and toughness. This work highlights the significance of interface engineering in B/HTPB composites for the efficacy and safety of future air-breathing solid-fueled propulsion devices. [Display omitted] • Three interfacial characteristics were formed in B/HTPB composite solid fuel via facile B particle functionalization. • Three interfacial characteristics include: polar/nonpolar, nonpolar/nonpolar, and covalently bonded interfaces. • B/HTPB composite solid fuel with a B loading up to 45 wt% has been manufactured. • Both covalently bonded and nonpolar/nonpolar interfaces in B/HTPB promote its combustion efficiency and burn rate. • Covalently bonded interface in B/HTPB composite leads to strain-hardening behaviors and enhanced mechanical properties. [ABSTRACT FROM AUTHOR]

In this study, in-situ aluminum oxide-poly(dopamine)-silver (Al 2 O 3 -PDA-Ag) hybrid nanoparticles were synthesized using simple and eco-friendly approach. Al 2 O 3 nanoparticles were first modified by PDA through mussel-inspired method, and Ag nanoparticles were then anchored on Al 2 O 3 -PDA nanoparticles surfaces through reduction of Ag+ by glucose. The as-obtained Al 2 O 3 -PDA-Ag nanoparticles were subsequently incorporated into natural rubber (NR) matrix to yield elastomer composites. The synergistic effect of Ag and Al 2 O 3 nanoparticles resulted in high thermal conductivity of 10 vol% Al 2 O 3 -PDA-Ag/NR composite reaching up to 0.20 W/mK. This value was two-fold superior to that of pure NR (0.10 W/mK). In addition, Al 2 O 3 -PDA-Ag/NR composites showed excellent electromechanical and mechanical properties. Overall, the proposed method looks promising for future preparation of high-thermal-conductive dielectric materials. [ABSTRACT FROM AUTHOR]

Owing to the development of modern micro-electronic devices, polymer composites with high thermal conductivity and low dielectric constant have become increasingly important. Herein, a combination of covalent and non-covalent modification was used to functionalize boron nitride (BN) platelets via first deposition with poly(dopamine) (PDA) followed by grafting with γ-methacryloxypropyl trimethoxy silane (KH570) (denoted as BN-PDA-KH570). The as-prepared BN-PDA-KH570 platelets were incorporated into the natural rubber (NR) matrix to prepare thermal conductive composites. After modification with PDA-KH570, the BN platelets were uniformly dispersed into the NR matrix, which is beneficial for improving the thermal conductivity of NR. The interfacial thermal resistance of the composites was also reduced due to the stronger interfacial interaction via vulcanization of NR with double bonds in KH570. Thus, the NR composites filled with 30 vol% BN-PDA-KH570 platelets exhibited a relatively high thermal conductivity of 0.39 W/mK, which is about 1.5 times and 4 times of 30 vol% BN/NR composite (0.26 W/mK) and pure NR (0.10 W/mK), respectively. In addition, the BN-PDA-KH570/NR composites exhibited a low dielectric constant (3.51 at 100 Hz) and a low dielectric loss tangent (0.25 at 100 Hz), which holds promising applications as thermal management materials for electronic devices. [ABSTRACT FROM AUTHOR]

Conductive polydimethylsiloxane (PDMS) composites have attracted extensive attention worldwide due to its potential application on wearable electronics and strain sensors. In this work, silicon dioxide micro-particles (μ-SiO 2) were added into the flexible PDMS/multi-walled carbon nanotubes (MWCNT) composites to improve their electrical conductivity and piezoresistive sensitivity. First, the μ-SiO 2 particles can exhibit volume exclusion effect to dense MWCNT fillers in PDMS matrix, which leads to the high electrical conductivity and low percolation threshold. Furthermore, the larger μ-SiO 2 particles could give higher electrical conductivity and lower percolation threshold. For examples, the electrical conductivity and percolation threshold of the PDMS/MWCNT composites with 0.3 vol% MWCNT increased from 3.5 × 10−9 to 2.2 × 10−4 S/m and decreased from 0.44 to 0.08 vol%, respectively, by the incorporation of 30 vol% 85 μm-SiO 2 particles. Second, the piezoresistive sensitivity of PDMS/MWCNT composites was abruptly enhanced by the addition of μ-SiO 2 particles because of the high modulus of μ-SiO 2 particles, which resulted in the asymmetric deformation in the composites. The deformation of PDMS/MWCNT phase was higher in the PDMS/MWCNT/μ-SiO 2 composites than that of the PDMS/MWCNT composites, which leaded to high piezoresistive sensitivity. For example, the gauge factor (GF) of the PDMS/MWCNT composites increased from 1.3 to 62.9 at 30% compression strain by the addition of 30 vol% 1 μm-SiO 2 particles. The highest piezoresistive sensitivity was found in the PDMS/MWCNT/μ-SiO 2 composites with lowest size of μ-SiO 2 particles due to the highest deformation of PDMS/MWCNT phase. [ABSTRACT FROM AUTHOR]

Structural carbon-fiber composites with high electrical conductivity and high interlaminar toughness are important for the next generation of aircraft. Highly electrically conductive and simultaneously high toughness carbon fiber reinforced epoxy composites were hence developed by interleaving silver-plated veils. Two electrically conductive veils of nylon and Kevlar fibers were prepared by electroless silver plating, respectively. The effect of the veil structure and silver-plating on the conductivity and interlaminar fracture toughness was studied. It was found that the in-plane electrical conductivity perpendicular to the fiber direction (R Y) and the through-thickness conductivity (R Z) increases from about 0.21 S/cm to 333 S/cm and 0.122 S/m to over 3.45 S/cm for the both samples interleaved with the nylon and Kevlar veils, respectively. The improvement is attributed to the electrical contact of the highly conductive veils in the interlayer's, forming an electrical network throughout the media. At the same time, the Mode I and Mode II interlaminar fracture toughness were also increased for the both composites, and it was more effective for the nylon-interleaved samples than for the Kevlar interleaved ones. Mechanism study showed that the interlaminar fracture mechanism can be controlled by the structural design of the veils. The failure mechanism of the nylon-interleaved composites was dominantly affected by the restraint of the fusion-bonded dots and pre-cracking which may compensate the negative effect of Ag-plating on the toughening, whereas the weak interfaces were responsible for the relatively lower toughness performance of the system interleaved with the Kevlar veils. [ABSTRACT FROM AUTHOR]

Abstract In this study, the stress distribution of fiber axial stress and interfacial shear stress in fiber reinforced polymer (FRP) composites at different temperatures was derived as a function of fiber axial position. The maximum shear stress criterion was extended to be temperature dependent. Based on the extended criterion, the temperature dependent fiber debonding length of FRP composites was predicted, which is indirectly verified by other scholar's experimental study. Then, by introducing the maximum fiber axial stress transferred from the matrix to fiber by their interface including the effect of partial interfacial debonding, we modified the law of mixtures, and finally established the temperature dependent tensile strength model for FRP composites. The model considers the combined effects of temperature, constituents' properties, interfacial properties and residual thermal stress. Reasonable agreement is obtained between the model predictions and available temperature dependent tensile strength of FRP composites. Additionally, the influencing factors analysis for FRP composites is performed in detail. This work provides some important insights on the strength control mechanisms of FRP composites at different temperatures, which are beneficial to the material evaluation, strengthening, and optimization. [ABSTRACT FROM AUTHOR]

Abstract According to surface chemistry and topography of different high-modulus carbon fiber (HMCF), interfacial properties of various HMCF composite were evaluated, and nanoscale wetting analysis of HMCF were studied using experimental methods and molecular dynamics simulation. Hierarchical amount of active functional groups and nanoscale grooves were detected on the surface of pristine HMCF (p-HMCF), anodic oxidized HMCF (a-HMCF) and sized HMCF (s-HMCF). Remarkable enhancements in interfacial properties of a-HMCF and s-HMCF composites were obtained, which was ascribed to free-void interface from improved surface energy and wettability. Poor interfacial bonding of p-HMCF composites was due to generation of many nanobubbles with pinned contact lines during the wetting of the surface microgrooves with high aspect ratio and chemical inertness. Schematic of interfacial compatibility mechanisms was proposed to illustrate the correlation between surface features of carbon surface and interfacial properties of their composites. [ABSTRACT FROM AUTHOR]

Abstract Percolation behavior of electrical conduction that is related to the formation of conductive networks has been well demonstrated in conductive polymer composites (CPC). However, the electromagnetic interference (EMI) shielding of CPC is normally very low at the percolation threshold due to the different mechanism. Here, we first predicted the percolation behavior of EMI shielding existing in CPC because the EMI shielding effectiveness (SE) was mainly dependent on the conductivity of CPC if assuming the constantly magnetic permeability. In practice, we also found the percolation behavior of EMI shielding in the multi-walled carbon nanotube (MWCNT) filled poly(l -lactide) (PLLA) with good dispersion and isotactic polypropylene (iPP) with poor dispersion. Furthermore, the percolation threshold of EMI shielding was higher than the percolation threshold of electrical conduction. The percolation thresholds of EMI shielding and electrical conduction were ∼2.00 and ∼0.40 vol% for PLLA/MWCNT nanocomposites, and ∼5.40 and ∼1.40 vol% for iPP/MWCNT nanocomposites, respectively. The SEM and TEM image shows the sparse and dense MWCNT network near the percolation threshold of electrical conduction and EMI shielding, respectively, indicating that the sparse network of MWCNT can create high electrical conductivity as long as the formation of conductive paths. However, the high performance EMI shielding requires dense network of MWCNT. Graphical abstract Image 1 [ABSTRACT FROM AUTHOR]

Abstract Surface modification of fillers has a profound influence on the dispersion of filler and interfacial adhesion, and thus the final performance of polymer-based composites. In this contribution, the modification of silica by polymethylhydrosiloxane (PMHS) is conducted via an efficient and fast tris(pentafluorophenyl)borane-catalyzed functionalization, which can be completed within a few minutes at room temperature. A highly hydrophobic surface and an uncompromised reactivity are concurrently observed in the modified silica. By comparison between the composites filled with pristine and modified silica, it is revealed that such PMHS modification can not only improve the dispersibility of silica by lowering the surface energy, but also enhance the interfacial interaction in virtue of the reactivity of the residual Si H bonds. With a PMHS grafting content as low as 1.5 wt%, the modified composite exhibits tremendous improvements in mechanical properties (116% increase in modulus) and dynamic performances (116% increase in wet traction and 26% reduction in rolling resistance). Considering the superior overall performance of the modified composites, together with the simplicity and rapidity of the modification process, we envision that the hydrosilane-modified silica has great potential in the fabrication of high-performance polymer composites such as energy-saving tire treads. [ABSTRACT FROM AUTHOR]

Thermochromic phase change composites (TPC) exhibit versatile functions under electrothermal stimuli, which are extensively applied as packaging, insulation and circuit components in considerable advanced smart electronics. However, space charge accumulation under DC voltages is still a critical and universal issue for the serious deterioration of functionalities and life-span of TPC and electronics. This study presents a novel strategy of suppressing space charge in thermochromic phase change epoxy composites (TPCE) by constructing interfacial barrier from tribo-positive shell thermochromic phase change microcapsules. The strong tribo-positive melamine-formaldehyde (MF) shell of microcapsules can establish negative charge barriers in the interfaces between microcapsules and epoxy matrix through triboelectrification, which is directly verified by Kelvin probe force microscopy. Pulsed electroacoustic measurement results exhibit the space charge accumulation in TPCE under an extreme electric field strength of 50 kV/mm and an elevated temperature of 70 °C can be significantly diminished by 39.3% compared to that of neat epoxy resin after incorporating merely 1 phr MF shell microcapsules, affirming the effect of interfacial barrier on space charge inhibition. The interfacial barrier could improve the charge carrier dissipation and mitigating the space charge accumulation as confirmed by hopping conduction analysis. Moreover, DC breakdown strength of TPCE can also be enhanced by 12.3% and 6.1% with 1phr microcapsules at 30 °C and 70 °C compared to that of neat epoxy resin owing to the suppressed space charge. The results provide a potential approach of designing high-performance thermochromic phase change composites for smart electrical and electronic devices. [Display omitted] [ABSTRACT FROM AUTHOR]

Abstract TiC-Fe interpenetrating phase composites were fabricated by infiltrating molten iron into porous TiC preforms prepared by the organic template dipping method. The TiC-Fe interpenetrating phase composites exhibited a three-dimensional network structure, in which Fe and TiC phases interconnected with each other. The microstructures of porous TiC preforms and TiC-Fe interpenetrating phase composites were respectively characterized by SEM, and the phase compositions of preforms and composites were analyzed by XRD. No other amorphous phases were detected on the interface between TiC and Fe matrix, indicating that no reaction occurred between them. The Vickers hardness of a 4 vol% TiC (with Fe addition)-Fe interpenetrating phase composite increased gradually from 1.13 GPa for the pure Fe zone to 3.42 GPa for the TiC ceramic zone. The tensile strength of a 4 vol% TiC (with Mo addition)-Fe composite reached 343 MPa. The tensile fracture surfaces showed a strong interfacial bond between TiC and iron matrix. The TiC-Fe interpenetrating phase composites are more suitable for wear resistance applications as compared with Fe-matrix composites reinforced with discontinuous TiC particles. [ABSTRACT FROM AUTHOR]

Abstract A combination of malleability, supramechanical properties and multi-stimuli response into catalyst-free and commercially available polymer-based networks is particularly attractive to extend the realm of thermally malleable polymers. Toward this goal, herein we demonstrated a paradigm by introducing dynamic imine bonds into styrene-butadiene rubber (SBR)/graphene composites. SBR was firstly grafted with aldehyde groups and then cross-linked with p -phenylene diamine and it-modified graphene through imine condensation between aldehyde and amino groups. The crosslinked networks were able to alter their topologies via imine exchange reactions in both the bulk network and SBR-graphene interphase in the absence of catalyst, enabling them to be recycled and reshaped under heating or IR irradiation. The incorporation of graphene led to spectacular improvements on the mechanical properties of vitrimer composites, and the mechanical properties could be tuned through solid-state drawing. The relationships between morphological structure and dynamic properties as well as mechanical properties of the vitrimer composites were addressed. [ABSTRACT FROM AUTHOR]

Abstract Covalently cross-linked elastomers with high elasticity are widely found in daily life and high-tech areas. However, the irreversibility of the crosslinked networks hinders the rubber products from reprocessing or recycling, causing a major environmental problem. Recently developed vitrimer chemistry provides fantastic avenues for cross-linked elastomers to achieve full reprocessability and recyclability. Herein, we disclose a novel C N transalkylation of pyridinium by model studies and implant this chemistry into the interfaces of an elastomeric composite. As a proof of concept, (3-bromopropyl)trimethoxysilane modified silica was used to crosslink butadiene-styrene-vinylpyridine rubber, forming pyridiniums in the interfaces. The composites were prepared by straightforward mechanical compounding and subsequent hot-pressing. Because of the covalent interfacial bridges and excellent dispersion of silica, the composites possess robust mechanical properties. Furthermore, the C N transalkylation reactions of pyridiniums at elevated temperature endows the composites with vitrimer properties, such as malleability and reprocessability. As the pyridine moieties can be easily introduced into a great variety of commercial polymers, we envision this newly demonstrated C N transalkylation of pyridinium possesses significant potential in broadening the gallery of vitrimer materials. [ABSTRACT FROM AUTHOR]

Abstract It is a challenge to achieve considerable shape-memory (SM) effect for typical sea-island structured polymer blends. In this paper, we successfully realized the SM behavior for classical ethylene-propylene-diene rubber/polypropylene (EPDM/PP) thermoplastic vulcanizates (TPVs) through a strong rubber/plastic interface compatibilized by in-situ formed zinc dimethacrylate (ZDMA) which came from methacrylic acid (MAA) and excess zinc oxide (ZnO) nanoparticles. With MAA/ZnO, the average size of EPDM particles reduced to 400–500 nm, which significantly enlarged EPDM/PP interfacial contact surfaces. The enhanced interface improved the efficiency of stress delivery between PP and EPDM phases, which was critical to fulfill the SM behavior. At the same time, residual ZnO nanoparticles stressed a reinforcement on EPDM phase and PP phase, which further improved the shape recovery (SR) and shape fixing (SF) of TPVs. Enhanced tensile strength (∼9.1 MPa) and Young' modulus (∼380 MPa), improved SF (∼99%) and SR (∼98%) of TPVs were achieved by tailoring the content of residual ZnO nanoparticles (MAA/ZnO = 2:1.3) and the shape deformation temperature (120 °C). Graphical abstract Image 1 [ABSTRACT FROM AUTHOR]

Abstract Conventional crosslinking endows rubbers with excellent mechanical properties, at the same time, turn them to be thermosets with the impossibility of recycling and self-healing. From the perspective of sustainable development of material, it is crucial and meaningful to integrate these charming properties into crosslinked commercial rubbers. In this paper, we prepared a recyclable and healable epoxidized natural rubber (ENR)/citric acid-modified bentonite (CABt) composite. CABt with numerous carboxyls on surface served as cross-linker to covalently crosslink ENR through exchangeable β -hydroxyl ester linkages, as well as efficient reinforcer for ENR. Because of the transesterification reactions of β-hydroxyl ester linkages between CABt and ENR, ENR/CABt composites could alter the network topology at elevated temperature. Meanwhile, the low crosslink degree of network and inherent stickiness of ENR matrix facilitated chain diffusion and transesterification reactions of β-hydroxyl ester linkages, which made ENR/CABt composites recycled and healed. Thus, we envision that our work would open up new avenues to design more crosslinked rubber composites showing recyclable, healable and adaptable abilities. Graphical abstract Image 1 [ABSTRACT FROM AUTHOR]

Abstract Self-sensing capability of carbon nanotube buckypapers (BPs), played as in situ sensor on delamination damage in multi-directional laminates, was investigated in this paper. BPs were interleaved into these interfaces of the laminates, where delamination tends to happen firstly under tensile loading. The inserted BPs are porous and conductive, which can benefit infiltration of epoxy resin and give contribution to damage monitoring. Systematic analysis of resistance variation (Δ R/R 0 %) against strain has demonstrated that BPs are sensitive to the initiation and growth of delamination. When delamination initiates, a sudden rise of the Δ R / R 0 % or the slope of the Δ R / R 0 %-strain curves is observed and corresponding delamination initiation stresses are simultaneously obtained. Moreover, effect of thicker laminates on the sensitivity is also examined and the self-sensing ability of BPs has been further proved. Finally, tensile properties of the BPs interleaved laminates slightly change compared with these of base laminates. [ABSTRACT FROM AUTHOR]

Dually self-reinforced Poly(ε-caprolactone) (PCL) composites were prepared to broaden its load-bearing applications as tissue engineering scaffolds. The composites were prepared from bi-component PCL yarns composed of self-nucleated PCL drawn fibers and PCL matrix by a combined process of yarns winding and hot pressing. Differential Scanning Calorimetry (DSC) results showed that incorporating of self-nucleating agents can improve the melting points of the fibers, creating a process temperature window for hot pressing. The orientation parameters of the fibers were accurately measured by Confocal Raman microscopy (CRM) and the results showed that the orientation parameter of the fibers could be up to 0.9 after drawn. Tensile tests showed that the self-nucleated drawn fibers had stronger mechanical properties than the control fibers with the same draw ratios. The hot pressing parameters (temperature and pressure) were also optimized during hot-pressing. The Young's modulus and break strength of the dually self-reinforced composites in longitudinal direction could be up to 118% and 400% higher than that of pristine PCL although their elongation at break decreased. Decline of mechanical properties of the composites in transverse direction was not observed, indicating good adhesion between the fibers and the matrix, which was confirmed by scanning electron microscope analysis. [ABSTRACT FROM AUTHOR]

A reactor granule technology (RGT) is a new method for the in-situ fabrication of polyolefin-based nanocomposites. It involves the impregnation and confinement of inorganic molecular precursors in the porosity of polyolefin reactor granule, and subsequent conversion of the precursors into highly dispersed inorganic nanoparticles during melt processing. In this contribution, the RGT was applied to develop thermally conductive polypropylene (PP)/aluminum oxide (Al 2 O 3 ) nanocomposites with the aid of two strategies. By melt-blending highly filled reactor granule with unfilled reactor granule, filler-rich and polymer-rich domains were created at around 10 μm scale, in which the filler-rich domains offered a thermally conductive pathway. The other strategy was based on tailoring the interfacial interaction between PP and Al 2 O 3 : An aluminum alkoxide precursor and a silane coupling agent were co-impregnated and converted into organically modified Al 2 O 3 nanoparticles. Both of the strategies successfully improved the thermal conductivity of the nanocomposites at a fixed Al 2 O 3 loading. The highest enhancement was achieved based on the interfacial modification using (2-phenylethyl)trimethoxysilane, where the thermal conductivity reached 0.74 W/m K at 20 wt% compared to 0.21 W/m K for pristine PP. [ABSTRACT FROM AUTHOR]

Abstract A micromechanics-based 2D numerical model is proposed to comprehensively trace the longitudinal compressive failure of unidirectional carbon fiber reinforced polymers (UD-CFRP), in which microscopic damage mechanisms (namely the fiber fracture, matrix plastic yield and fiber-matrix interface crack) are considered. With this model, the predicted compressive modulus, strength and failure pattern are in good agreements with the experimental results, which validate the effectiveness of the proposed model. It concludes that the longitudinal compressive failure is governed by the matrix damage rather than the fiber fracture and the interface crack triggers the matrix damage. In addition, the influence of some microscopic parameters, including the fiber volume fraction, initial fiber misalignment, initial fiber-matrix interface stiffness, interface strength and fracture energies, on the longitudinal compressive failure is disclosed. The compressive modulus increases with the fiber volume fraction while it is almost unaffected by the rest four parameters. The compressive strength increases with the increment of the initial interface stiffness or the decrement of the initial fiber misalignment while it is immune to the interface fracture energies. Moreover, a limited increment of the fiber volume fraction or the interface strength is beneficial for enhancing the compressive strength. [ABSTRACT FROM AUTHOR]

To further understand effects of titanium dioxide (TiO 2 ) nanoparticles on thermal, optical, microstructural, interfacial and mechanical properties of shape memory polyurethane (SMPU), TiO 2 /SMPU nanocomposites with different TiO 2 contents were synthesized. Then various properties of TiO 2 /SMPU nanocomposites were characterized. Results indicate that the melting temperature of soft segments in SMPU can be used as the shape memory transition temperature of TiO 2 /SMPU nanocomposites. TiO 2 nanoparticles are almost filled in SMPU pores to form compact skeleton structures in TiO 2 /SMPU when the TiO 2 content is 3% by weight. Further, the used TiO 2 is rutile phase, and lowers the SMPU crystallinity. The suitable TiO 2 content can increase the absorptivity to UV light and enhance the reflectivity to visible light of TiO 2 /SMPU nanocomposites, lowering its photo-aging properties and prolonging its service life. Also, TiO 2 /SMPU shows a higher scattering intensity and a faster decreasing trend than SMPU due to the larger electron density difference between TiO 2 and SMPU. The microphase separation and ordered structures in SMPU are decreased due to added TiO 2 nanoparticles. There are electron density fluctuations at the interfaces between hard and soft phases in SMPU, and between SMPU and TiO 2 nanoparticles. Finally, the prepared TiO 2 /SMPU nanocomposites have better shape memory effects and tensile properties when TiO 2 content of 3% is proposed to synthesize TiO 2 /SMPU nanocomposites for practical engineering applications. [ABSTRACT FROM AUTHOR]

In this paper, two poly(styrene- b -ethylene-ran-butylene- b -styrene) (SEBS) with different styrene segment content were adopted to explore the relationship between varying π-π stacking interaction and the mechanical performance of polymer composites. The results showed that the high styrene content on SEBS (SEBS-30, 30 wt% styrene segment) endows SEBS a stronger π-π stacking interaction with GO and a better dispersion of GO in the matrix than that in SEBS with low styrene content (SEBS-12, 12 wt% styrene segment), resulting in a high efficiency on enhancing the performance of SEBS. By adding 0.5 wt% GO, the tensile strength and modulus of SEBS-30 was increased by 44% and 64%, respectively, while that of SEBS-12 was increased by 24% and 39%. Furthermore, the GO also exhibited the ability to toughen SEBS via forming microcrack and GO-induced fibrillation of SEBS during the fracture process. The elongation at break and fracture toughness of SEBS-30 was increased by 10% and 64%, respectively. This study gives us a deep insight into the influence of varying π-π stacking interaction between graphene oxide (GO) and polymer on achieving high-performance polymer nanocomposites. [ABSTRACT FROM AUTHOR]

Over recent years, researchers have noticed that recovery rates of shape memory composites (SMCs) would vary due to the addition of fillers. So far, although several superficial reasons are discussed, a thorough analysis has not been presented yet probably due to the absence of a microscopic mechanism of SMCs. Here, a molecular mechanism of SMCs is clarified by identifying the differences lying in molecular motions of shape memory polymers and SMCs. On the basis of the molecular mechanism of SMCs, both a positive effect and a negative effect of fillers on recovery rates are revealed. Because interfaces between fillers and matrices play a decisive role in the two effects of fillers, several experiments are designed to verify the role of interfaces. The experimental results prove that the interfaces are benefit and harmful for recovery rates at the same time. Moreover, the results are able to qualitatively predict that the recovery rates of SMCs would increase or decrease with more addition of fillers. [ABSTRACT FROM AUTHOR]

The dielectric response of a nano-ATH (Aluminium Tri-hydrate) filled silicone rubber is investigated over the frequency range 10 −4 to 10 3  Hz and compared with that of the micro-ATH composite. An equivalent circuit has been used to decompose the dielectric response into: a loss peak process, a quasi-dc (Q-DC) process, a dc-conductance and constant high frequency capacitance. It was found that the Q-DC and loss peak were a result of the ATH filler with the loss peak more clearly resolved in the nano-ATH filled material than in the micro-ATH material where it is weaker and partly obscured by the Q-DC process. In contrast to the micro-ATH material the characteristic frequencies of all the dielectric responses in the nano-ATH filled samples have the same activation energy. The physical mechanisms of the Q-DC process and loss peak are discussed in terms of long range transport between nano-ATH clusters and the dipolar behaviour of isolated clusters respectively. [ABSTRACT FROM AUTHOR]

Tailored-modulus epoxy matrix was designed on basis of surface analysis of high-modulus carbon fibers (HMCF), and the effects of modulus intermediate layer on interfacial and mechanical properties of HMCF composites were investigated. Narrow grooves and active functional groups were detected on HMCF surface. The modulus of epoxy was tuned by stiff organic molecular structure of cycloaliphatic epoxy (CE) and amide acid (AA). Modulus intermediate layer was established along with modulus gap shrinkage and interphase extension between HMCF and high-modulus epoxy, causing remarkable improvements in interfacial properties of composites. Schematic model of interphase reinforcing mechanism was proposed, and modulus intermediate layer with a platform in the composites with high modulus epoxy matrix could facilitate the shift in stress concentration and suppress initiation and propagation of cracks, which resulted in improved mechanical properties of HMCF composites by enhancement of interfacial bonding and stress transfer capability between fiber and matrix. [ABSTRACT FROM AUTHOR]

Kissing defects remain difficult to detect due to insufficient contrast. Herein we proposed a microwave equiphase frequency truncation method (EFTM) to detect and evaluate the thickness of kissing defects in GFRP laminates. It is found that the frequency difference varies linearly with the kissing defect thickness under the assumption of single reflection, and the linear slope is approximately in inverse proportion to the product of the thickness and permittivity term of the specimen. Theoretical calculation, simulation and experimental detection results of GFRP laminates and Teflon specimens all showed a fine linearity relationship between the frequency difference and the thickness of kissing defect. Besides, the experimental linear slopes were in good agreement with theoretical predictions for both GFRP and Teflon specimens, which indicates the applicability of this method for different dielectric materials. The experimental results clearly showed that kissing defects of 2.92 μm was successfully detected and quantified. In summary, this method is feasible and effective in detecting and evaluating kissing defects in dielectric laminates. [ABSTRACT FROM AUTHOR]

A hybrid nanostructure consisting of montmorillonite−multi-walled carbon nanotube (Mt−MWCNT) was designed and assembled, and further used as reinforcing nanofillers for preparing epoxy-based composites. It was found that Mt could efficiently resist microcrack extension and hinder thermal transfer while MWCNTs anchored on the Mt nanosheets could facilitate the stress and heat transfers and provide mechanical interlocking with the epoxy matrix. Making use of the synergistic effect of Mt and MWCNT, considerable enhancement in thermal and mechanical properties was achieved in the composites. With addition of just 0.5 wt% Mt−MWCNT (Mt:MWCNTs = 10:1, w/w), the tensile strength and modulus of epoxy-based composites were improved by 42.0% and 20.3%, respectively, compared with pure epoxy. Furthermore, the storage modulus in the glassy region increased by 21.2%. Moreover, the glass-transition and onset decomposition temperatures were also significantly enhanced, implying the superior thermal stability of these composites. [ABSTRACT FROM AUTHOR]

It remains a huge challenge to realize the homogeneous graphene dispersion in elastomer matrix by a simple and general compounding method. Herein, we develop a straightforward slurry compounding method for preparation of rubber/graphene composites with well-dispersed graphene. Specifically, TPG (tea polyphenol reduced graphene)/ethanol slurry was first collected by solvent exchange after the reduction of graphene oxide by tea polyphenol and then directly melt compounded with chlorosulfonated polyethylene (CSM) in a two-roll mill to produce the composites. As revealed by the XRD and morphological studies, TPG homogeneously dispersed in CSM matrix, which together with the strong interfacial interaction between TPG and CSM contribute to the remarkable improvement in mechanical properties of the resulted composites. We envision that the present work offers a straightforward yet effective methodology for preparing high-performance elastomer/graphene composites via conventional melt compounding. [ABSTRACT FROM AUTHOR]

This paper aims to study the evolution of the 3D strain fields in a single yarn composite during fragmentation test. The internal full-field strains were obtained by coupling micro-CT scans with digital image correlation (DIC) and digital volume correlation (DVC). An ex-situ step-by-step fragmentation test was carried out on a sample made of a hemp yarn and a polymer matrix filled with metal oxide powder, playing the role of a three dimensional speckle. Macroscopic markers were also added to enable a precise geometric alignment during the 3D reconstruction. The analysis of the tomographic images showed a stepwise progression of the damage occurrence: yarn breaks appeared first, followed by internal matrix cracks and then edge cracks occurred for high strain levels. DIC method allowed to easily and quickly determine 2D strain maps in selected planes. The use of DVC was more complex and needed powerful computing systems but it gave the volumetric strains in the whole sample. DVC calculations were compared and validated by DIC results in central planes. Experimental results were also compared with finite element simulations. This study demonstrates the viability and benefits of combining DVC and micro-CT for a deeper understanding of complex 3D strains in single yarn composites. [ABSTRACT FROM AUTHOR]

Improving the adhesion between metal sheet and resin is an important issue for the development of high-performance fiber metal laminates (FMLs). In this study, a novel rare-earth surface modification is applied for the first time to enhance the interfacial bonding strength of titanium sheets and polyetheretherketone (PEEK). Density functional theory (DFT) calculations show that cerium element could form coordination bonds at the interfaces between metallic titanium and resin. The surface wettability of titanium sheet is boosted, which is beneficial to PEEK infiltration and physical adhesion improvement. Meanwhile, with the existence of coordination bonds at the interface, the interfacial shear strength between titanium and PEEK, and the flexural strength and interlaminar shear strength of CF/PEEK-Ti laminates are enhanced significantly. Therefore, the cerium surface modification method proposed in this study has great potentials for FMLs, which provides a new strategy for generating chemical bond at interfaces between metal and resin. [Display omitted] • Proposed a novel and facile rare-earth surface modification method. • The interface between titanium and PEEK was bonded by rare-earth coordination. • The single lap shear strength of rare-earth modified interface between titanium and PEEK had an increment of 178.0%. • The flexural strength (180.0%), and ILSS (40.0%) of rare-earth modified CF/PEEK-Ti composites were significantly enhanced. [ABSTRACT FROM AUTHOR]

The contribution of the interfacial layer thickness to composite properties was investigated using 2,2,6,6-tetramethylpiperidine-1-oxyl (TEMPO)-oxidized cellulose nanofiber (TOCN) and cellulose triacetate (CTA). To control the interfacial layer thickness, the surface of the TOCNs was modified by grafting amine-terminated poly(ethylene glycol) (PEG-NH 2 ) with different molecular weights. Neat TOCNs or PEG-grafted TOCNs were compounded with CTA to prepare nanocomposite films with different interfacial layer thicknesses. We demonstrated that thinner interfacial layers enhanced the stiffness of the nanocomposite films, whereas thicker interfacial layers enhanced their ductility. The high transparency and low birefringence of the CTA films were preserved even with the addition of TOCNs or PEG-grafted TOCNs. Although the thermal expansion of the nanocomposite films was suppressed by TOCN addition, the presence of PEG layers on the TOCN surfaces had a negative impact on their restraint of the thermal expansion. These results suggest that the interfacial layer thickness plays an important role in the mechanical and thermal properties of nanocellulose-reinforced composites. [ABSTRACT FROM AUTHOR]

The water-driven expansion of folded BNNSs on the surface of the tobermorite is studied by molecular dynamics simulation. It shows that the expansion of folded BNNSs is significantly dependent on the deterioration of water molecules on the interfacial interactions between the folded BNNSs and tobermorite and between interlayers of the folded BNNSs. The interface deteriorations allow the relative sliding between folded BNNSs and tobermorite and between interlayers of folded nanosheets. Afterward, the vibration of the monolayered BNNS induces expansion due to its flexibility. To quantify the deterioration of the adhesion between folded BNNSs and tobermorite and between interlayers of folded BNNSs, steered molecular dynamics simulations are performed to calculate the energy barrier between them. It indicates that the presence of water molecules significantly reduces the energy barrier, resulting in the release of strain energy in folded BNNSs and the expansion behavior of BNNSs. Due to the presence of water, the hydration of unhydrated cement particles occurs and releases heat. Hence, the effect of temperature on the expansion degree of BNNS is studied, which shows an acceleration in the expansion degree of BNNS and envisions the self-healing of cracks in the tobermorite composite when the temperature is increased. [Display omitted] • Water molecules drive the expansion of BNNSs on the surface of tobermorite. • Interfacial sliding in the BNNS-tobermorite system initiates expansion of BNNS. • Water molecules decrease energy barriers per unit area at interfaces. • Expanded BNNS provides nucleation sites for self-healing tobermorite composite. [ABSTRACT FROM AUTHOR]

Ceramic/polyetheretherketone (PEEK) composites show a wide range of applications and have attracted extensive interest in the scientific community due to their outstanding dielectric and mechanical characteristics. However, the interface connection between the ceramic and PEEK is a vital issue that must be addressed to improve their physical and electrical properties. In this work, the polyethersulfone resin (PES) was selected as interface modifier between barium strontium titanate (Ba 0.6 Sr 0.4 TiO 3 , BST) and PEEK. Cold-pressing sintering was used to create BST/PEEK materials with superior dielectric frequency stability and dielectric tunability. The effects of PES content on the morphology and dielectric characteristics of PES modified BST/PEEK materials were investigated. The results showed PES could improve the dispersion of BST particles in polymer. The dielectric constant, dielectric tunability, and breakdown strength increased first, then reduced as PES content increased. The composite had the most homogeneous microstructure and the best dielectric properties when the PES content was 7.5 vol%. The frequency dispersion factor F (x) was much smaller than that of other ceramic/polymer composites reported. In addition, the dielectric tunability of the composites could reach a relatively high level (34.18%) while the dielectric constant was as low as 14. The dielectric tunable efficiency (T uE) was proposed to evaluate the property of low dielectric constant and high dielectric tunability under DC bias. The T uE of PES modified BST/PEEK composites show the highest value comparing with reported dielectric tunable composites. This research laid the path for the development of a novel ceramic/polymer composite with good interface bonding and high dielectric tunability. The structure of a material plays a decisive role in its properties. We obtained PES-BST/PEEK composites with higher dielectric properties by improving the interfacial bonding of ceramic and polymer phases in the composites. The high dielectric tunability with low dielectric constant of the PES-BST/PEEK composites is beneficial to the engineering applications of composite materials in integrated circuits and microwave dielectric devices. [Display omitted] [ABSTRACT FROM AUTHOR]

• The interfacial tensile and shear strength of PMH structures is characterized experimentally. • A series of CZMs for PMH interface with various mechanical interlocks are established. • The mapping relationship between micro parameters and macro performance is developed. • The failure propagation mechanisms of PMH interface at micro/macro-scale are revealed. This paper studies the polymer-metal hybrid (PMH) structures, formed by direct injection over-molding the glass fiber-reinforced polymer (GFRP) composite on the surface of high-strength steel (HSS), which integrate the advantage of HSS and GFRP, and have been applied in the lightweight design of vehicles. However, the existence of an interface between GFRP and HSS weakens the ultimate carrying capacity of the overall PMH structures, and hence, the interface needs further improvement. First, five kinds of PMH specimens with different micro-interlock features were designed and fabricated, and the corresponding interfacial tensile and shear strength (σ I c and σ II c) and fracture toughness (G I C and G II c) were characterized experimentally. An interface constitutive model suitable for describing different mechanical interlocks was established, and the general program for parameter identification was developed in a finite element code. Using this model, the crack evolution mechanisms of PMH structures under tensile and bending loading were revealed. Finally, the micro–macro mapping rule between the interlock features and the ultimate loading of overall PMH structures is proposed. These results are conducive to the lightweight design and performance prediction of PMH structures. [ABSTRACT FROM AUTHOR]

Cellulose nanocrystals (CNC) are natural, renewable, and biocompatible materials that have been widely used as new sustainable reinforcing nanofillers in polymer composites. We present polyvinyl alcohol (PVA)/CNC composites with improved mechanical and antibacterial properties using CNC-based nanofillers. The surface esterified CNC (ECNC) was prepared by 6-bromohexanoyl chloride via surface esterification. Subsequently, the alkyl bromide group of the ECNC was transferred to quaternary ammonium groups for preparing quaternized CNC (ECNC-Q n) by introducing tertiary amino groups with different carbon chain lengths (C8–C16). Then, ECNC-Q n were blended with a PVA matrix to prepare PVA/ECNC-Q n nanocomposite films via a solvent casting procedure. Diverse features, including light transmission, mechanical properties, and antibacterial activity against Gram-positive (Staphylococcus aureus) and Gram-negative (Escherichia coli) bacteria were investigated. Compared with pure PVA films, the PVA/ECNC-Q n nanocomposite films had higher tensile strength and higher antibacterial activity. Specifically, the maximum tensile strength and elongation at break of PVA/ECNC-Q n nanocomposite films were 45.4 MPa and 318.4%, respectively, which were 37.2% and 94.3% higher than those of pure PVA film, respectively. Moreover, the ECNC-Q 8 exhibited the highest antibacterial efficiency, leading to the best antibacterial activity for PVA/ECNC-Q 8 nanocomposite films among all films. This study demonstrates an efficient method for preparing a functional, environment-friendly PVA composite film. The prepared PVA/ECNC-Q n nanocomposite films exhibited considerable application potential in the packaging field, owing to their good mechanical and antibacterial barrier properties. [Display omitted] • The quaternized CNC (ECNC-Q n) were prepared via two-step surface modification. • ECNC-Q n were used as nanofillers to introduce multi-functions for PVA composites. • Both antibacterial and mechanical properties of PVA/ECNC-Q n films were enhanced. • The films showed almost 100% bactericidal efficiency against E. coli and S. aureus. [ABSTRACT FROM AUTHOR]

In graphene-based systems, the interface between graphene and other materials creates a mechanically weak region. Therefore, understanding the mechanical behaviour of graphene interfaces is critically important in designing reliable graphene-based systems. On the other hand, defects such as surface impurities are unavoidable during the fabrication of nanoscale systems. We developed a nonlinear spring model to characterize the influence of surface defects on the adhesion properties of graphene interfaces. The model was extensively validated using molecular dynamics simulations for graphene–silicon dioxide interface, and the computed cohesive energy is also in agreement with the recently measured energies. Our results indicate that low concentrations of hydrogen adatoms highly degrade the interfacial strength, whereas vacancies have a negligible effect on the interfacial strength. We also compared the influence of hydrogen adatoms on the properties of several commonly encountered graphene interfaces. In addition, we developed a novel analytical framework to compute the required graphene-substrate interfacial area to withstand an applied force during the indentation test. These findings are useful in designing graphene-based nanoelectromechanical systems and composite materials. More importantly, the developed spring model can be parameterized to investigate the mechanical behaviour of any material interface, which is vitally important in designing reliable nanodevices and nanocomposites. [ABSTRACT FROM AUTHOR]

The effects of surface treatment and carbonized pitch (CP) coating on the silicon carbide (SiC) in a SiC epoxy composite were investigated in this study, with a focus on the thermal stability and oxidation resistance of the composites. The thermal stability and oxidation resistance properties of the composites were affected by this CP coating. The SiC pitch coating improved the thermal stability and oxidation resistance of the epoxy composite, and the CP coated-SiC filler improved the thermal stability of the epoxy composites over that of the pure SiC filler. In addition, the surface treatment increased the thermal stability and oxidation resistance due to the interaction at the surface between the SiC and the CP. CP-coated acidic surface treated-SiC (CP/aSiC) composites featured improved oxidation resistance and thermal stability compared to the CP coated-SiC (CP/SiC) composites. [ABSTRACT FROM AUTHOR]

To improve the interfacial adhesion of carbon fiber reinforced polymer composites (CFRP), carbon fiber usually has to be carried out surface treatment under harsh conditions. However, enhancing the interfacial property is usually accompanied by deteriorating tensile strength of carbon fiber, due to some defects on fiber surfaces after surface modification. In this paper, a layer of amine-capped poly (cyclotriphosphazene- co -4,4′-oxydianiline) coating was introduced onto the carbon fiber surfaces by a facile in-situ polymerization under mild condition. The amines on polyphosphazene coating surface help to improve the surface wettability and activity of carbon fibers, significantly improving the interfacial shear strength of carbon fiber/epoxy composites by 70.5%. Besides the enhanced surface wettability, the chemical bonds also play a key role in such an interfacial enhancement. Moreover, the polyphosphazene sheath can heal the surface defects of fiber effectively, thus increasing the fiber tensile strength by more than 10.0%. [ABSTRACT FROM AUTHOR]

Recent trends in the application of advanced processing techniques, such as vacuum assisted resin infusion (VARI) or heated vacuum bag only (HVBO), compel generalization of the bond–slip laws for prediction of the interface behaviour in adhesively bonded joints. In this research, a new analytical approach is presented to determine the interface behaviour. Since the model is developed solely based on boundary conditions, it can be applied to any types of the FRP processing technique. With this method, the interface characteristics can be obtained from the applied load at each stage and the properties of the materials. Comparisons between experimental and analytical results of strain, shear stress and slip profiles indicate that the proposed analytical model is capable of predicting the interfacial behaviour between FRP-to-concrete bonded joints manufactured with different the FRP processing techniques (FPTs). [ABSTRACT FROM AUTHOR]

Polymer nanocomposites can enable innovative designs of multifunctional materials. Metallic fillers in polymer matrices exhibit improved electrical properties at low volume fractions, often maintaining the low density, transparency and easy processing of polymers. Surprisingly, enhanced mechanical properties have also been observed at uncharacteristically low volume fractions in these nanocomposites. The majority of mathematical models used to describe this novel mechanical behavior are based on percolation models of microstructural connectivity. Changes in mechanical properties, however, are likely to be affected by complex microstructures, beyond simply connected, as well as by the micromechanical mechanisms associated with a composite material. Both microstructural and micromechanical mechanisms are thought to be significantly influenced by the presence and properties of an interface region, between particles and matrix, which functions as a third composite phase. In this work, the relative influence of the competing and compounding effects of the spatial position/distribution of the particles (microstructure) and of the composite constitution (micromechanics) are examined. The results show that models based solely on the inclusion of a third composite phase do not predict the experimentally observed mechanical response. This work continues with a study of the micromechanical effects of microstructure using a probabilistic and statistical characterization of the local strain fields associated with random microstructures. These continuous fields are not only more amenable to statistical characterization than the spatial ternary (matrix, particle and interface) fields that describe the microstructure, but offer a more direct, and potentially more visual, link between microstructure and mechanics. An apparent percolation threshold for a 2D material model is identified based on statistical characterization of the elastic moduli, distributions of local strains and spatial autocorrelation of local strain fields. The statistics of strain fields associated with microstructures producing minimum and maximum moduli are also compared. [ABSTRACT FROM AUTHOR]

The attention of the present work is focused on the behaviour of interlaminar graded interface strength (IGIS) laminated structures under impact. IGIS structures are made of layers of a woven glass fabric alternated with compatibilized and not compatibilized polypropylene film layers, symmetrically and asymmetrically arranged with respect to the middle plane. For each configuration some specimens are subjected to impact tests at energies of 6 and 25 J while one specimen is left unloaded. Impacted and not impacted specimens are non-destructively evaluated with lock-in thermography (LT). Results highlight the role played by the stacking sequence in the IGIS laminate and confirm data previously obtained through mechanical characterization. [ABSTRACT FROM AUTHOR]

C/C composites and Ti 6 Al 4 V sheets were joined using a novel Cu/TiCuZrNi composite braze and the effect of Cu foil thickness on the microstructure and mechanical properties of the joints were investigated. A composite joining material, consisting of a TiC particle reinforced brazing alloy formed in situ during the brazing process was obtained. Before the joining process, the C/C composite surface was modified by solid state reaction with chromium to form a chromium carbide coating. This carbide reaction layer can react with the Ti-based brazing alloy and form evenly distributed TiC particles. The maximum apparent shear strength of as-received joint was 39±8.5 MPa obtained by using a 40 μm thick Cu foil together with the TiCuZrNi alloy; this value was 70% higher than the mechanical strength obtained for joints brazed with the TiCuZrNi alloy only. [ABSTRACT FROM AUTHOR]

This study proposes producing polymer composites with a sandwich structure. The surface layers are identical with two alternative interlayers. The surface layers are composites that are composed of polypropylene and multi-walled carbon nanotubes. Interlayers are polyvinyl alcohol (PVA)/MWCNTs composites and PVA/graphene nano-sheets composites. Maleic anhydride grafted polypropylene (PP-g-MA) serves as the coupling agent for the surface layers and the interlayer, in order to create sandwich-structured composites. The polymer composites that are constructed with different combinations are then evaluated for electromagnetic interference shielding effectiveness (EMI SE). The test results show that the incorporation of PP-g-MA reinforces the interfacial adhesion between the sandwich-structured composites, and thereby fortifies their tensile strength. When consisting of a PVA/MWCNTs interlayer, the polymer composites have an optimal electrical conductivity of 5.8 S/cm, and EMI SE of −28.60 dB for 0.0003GHz–1 GHz, −32.89 dB for 1 GHz–2 GHz, and −33.52 dB for 2 GHz–3 GHz. The sandwich-structured polymer composites that have good mechanical properties, good flexibility and high EMI SE can be achieved by using a simple and effective manufacturing method. [ABSTRACT FROM AUTHOR]

The effect of WC content on microstructure and mechanical properties of the TiC–Ni 3 Al system cermets was investigated. Ni 3 Al-bonded cermets showed a core–rim structure with carbide particle coupled with rim embedded in Ni 3 Al binder. With WC content increasing, TiC grains were refined and the white rim became complete and got thicker gradually. Interface between core and rim showed a completely coherent relationship. The rim enriched in W constituted an ideal coherence between hard phase and Ni 3 Al binder phase. With WC content increasing, the densification of cermets was enhanced, and hardness and TRS were increased firstly and then reduced, reaching peak values 90.9 HRA (HV 30 15 GPa) and 1629 MPa, respectively in cermet N5 (25 wt% WC). Similarly, fracture toughness got a peak value (11.6 MPa m 1/2 ), at the composition with 20 wt% WC. [ABSTRACT FROM AUTHOR]

In the present study, the macroscopic and microscopic structure, chemical composition and mechanical properties of rice stalk were explored and the corresponding interfacial bonding strength with high-density polyethylene (HDPE)/polylactic acid (PLA) were evaluated. The stalk is composed of core and sheath. The epidermal tissue under the outer surface of core is thicker than that of the sheath, which is an important factor contributing to its mechanical properties. FT-IR, SEM and mapping reveals a hydrophobic outer surface of the stalk covered with a waxy and silicon layer. The inner surface of stalk is smoother compared with the outer surface and the core inner surface had the best wettability. The mechanical properties indicate that it is necessary to maintain a longer core of rice straw in composites because of its higher tensile strength than the sheath. The inner area of the rice stalk is exposed because of its stronger shear strength when pulling out of matrix than outer surface. PLA is chosen as the matrix because of its better compatibility with the rice straw than HDPE. In addition, the protruded bumps enhance the mechanical locking with matrix. This study provides strong support for design and manufacture of straw-reinforced green composites. [Display omitted] [ABSTRACT FROM AUTHOR]

The mechanical integrity of a structural composite is strongly affected by the strength and toughness of the fiber–matrix interface/interphase (Norwood, 1994), with interfacial shear strength (IFSS) being generally accepted as the best quantifying metric. The value of the IFSS is not directly measurable, but it can be approximated by several micromechanics based test methods with the value obtained being dependent on the choice of the model. The most popular of these test methods is the embedded single fiber fragmentation test (SFFT) which provides the experimental data needed to estimate the IFSS: (a) mean fragment length at saturation and (b) fiber strength at the critical fragment length. Because the IFSS is used in unidirectional composite models to predict strength and failure behavior, where the interaction between fibers can be important, the validity of extrapolating from test results based upon the repeated failure of a single isolated fiber has often been questioned. In this paper, the spatial distribution of fiber breaks in a 2-D array of glass fibers is compared with break locations observed from SFFT specimens. In both cases, the break locations in each fiber were found to evolve to a uniform distribution, thereby confirming that the ordered fragment lengths from the repeated fracture process conforms for both SFFT and multi-fiber fragmentation test (MFFT) specimens to a cumulative distribution function (CDF) derived by Whitworth (1887) and cited by others (Read, 1988; Pyke, 1988; Holst, 1980). The array break density was also observed to be less than the break density in isolated fibers, and break locations across array fibers were observed to be highly coordinated and mostly aligned. [ABSTRACT FROM AUTHOR]

Stress waves scatter upon entering a new medium. This occurs due to the reflection and transmission of the waves, which depends on the impedance mismatch between the two materials and the angle of incidence. For a bi-layered structure with finite dimensions and constant impedance ratio, the scattering and intensity of the stress waves may be varied by changing the interface profile between the two layers. In this paper, a methodology is proposed for optimizing the interface profile between the layers of a finite bi-layered plate for the objective of planar stress wave attenuation. The bi-layered plates are subjected at one end to highly impulsive loadings with various durations, and the geometry of the internal interface is optimized for the purpose of minimizing the amplitude of the maximum reaction force at the opposite fixed end. The optimization methodology is based on a genetic algorithm, which is coupled with a finite element method for analyzing the wave propagation behavior of the plates. It is observed that the interface profile and the amount of stress wave attenuation depend on the duration of the applied impulsive loading, with higher amounts of attenuation obtained when the wavelength associated with the impulsive load is small compared to the dimensions of the bi-layered plates. [ABSTRACT FROM AUTHOR]

Both silane and multiwall carbon nanotubes (CNTs) were grafted successfully onto carbon fibers (CFs) to enhance the interfacial strength of CFs reinforced methylphenylsilicone resin (MPSR) composites. The microstructure, interfacial properties, impact toughness and heat resistance of CFs before and after modification were investigated. Experimental results revealed that CNTs were grafted uniformly onto CFs using 3-aminopropyltriethoxysilane (APS) as the bridging agent. The wettability and surface energy of the obtained hybrid fiber (CF-APS-CNT) were increased obviously in comparison with those of the untreated-CF. The CF-APS-CNT composites showed simultaneously remarkable enhancement in interlaminar shear strength (ILSS) and impact toughness. Moreover, the interfacial reinforcing and toughening mechanisms were also discussed. In addition, Thermogravimetric analysis and thermal oxygen aging experiments indicated a remarkable improvement in the thermal stability and heat oxidation resistance of composites by the introduction of APS and CNTs. We believe the facile and effective method may provide a novel interface design strategy for developing multifunctional fibers. [ABSTRACT FROM AUTHOR]

Pb 0.8 La 0.1 Ca 0.1 Ti 0.975 O 3 (PLCT)/(Na 0.85 K 0.15 ) 0.5 Bi 0.5 TiO 3 (NKBT) hierarchical composite thin films were fabricated by a sol–gel process. The interface diffusion and electrical properties of the films were investigated in detail. X-ray diffraction patterns indicated that the PLCT/NKBT hierarchical composite thin film annealed at 500 °C possessed perovskite structure; X-ray reflectivity measurements suggested that no interface diffusion occurred in the PLCT/NKBT hierarchical composite thin film annealed at 500 °C, which effectively decreased its dielectric constant. The leakage current behavior and ferroelectric and pyroelectric properties of the films were then studied. The PLCT/NKBT hierarchical composite thin films annealed at 500 °C possessed the lowest dielectric constant (142), low loss (0.029), and highest pyroelectric coefficient (321 μC/m 2 K) of the films, which resulted in the highest figure of merit of 158 μC/m 2 K. [ABSTRACT FROM AUTHOR]