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The synergistic combination of carbon nanotubes (CNTs) and ductile thermoplastic resin has shown the large potential in the improvement of fracture resistance of the epoxy matrix composites using the interleaving toughening method in recent years. The hybrid structure of CNTs and thermoplastic resin in interlayers affects directly the interlaminar structure and the resultant crack propagation path of the interleaved composites. In this work, the CNTs and thermoplastic polyetherketone-cardo (PEK-C) were used to prepare the interlayer with different hybrid structures to interleave the carbon fiber reinforced epoxy composites and the influence of hybrid structure on the interlaminar structure and the fracture toughness was investigated. The results showed that PEK-C/CNT/PEK-C sandwich interlayer produced the best toughening effect in mode I interlaminar fracture toughness ( G) and the G was 446.76 J/m , increased by 138.11% compared to blank composites, which benefited from the multilayered structure in the interlaminar region formed during curing process and the resultant tortuous crack propagation.

Retaining elongated grain microstructure during thermo-mechanical processes would be attractive for obtaining high-strength aluminium alloys with good toughness. A small Zr addition promotes the fo...

We investigated the effect of cyclic chain topology on the molecular ordering and thermal stability of comb-shaped polypeptoid thin films on silicon (Si) substrates. Cyclic and linear poly(N-decylglycine) (PNDG) bearing long n-decyl side chains were synthesized by ring-opening polymerization of N-decylglycine-derived N-carboxyanhydrides. When the spin-coated thin films were subjected to thermal annealing at temperatures above the melting temperature (T > Tm), the cyclic PNDG films exhibited significantly enhanced stability against melt-induced dewetting than the linear counterparts (l-PNDG). When recrystallized at temperatures below the crystallization temperature (T < Tc), the homogeneous c-PNDG films exhibit enhanced crystalline ordering relative to the macroscopically dewetted l-PNDG films. Both cyclic and linear PNDG molecules adopt cis-amide conformations in the crystalline film, which transition into trans-amide conformations upon melting. A top-down solvent leaching treatment of both l/c-PNDG films revealed the formation of an irreversibly physisorbed monolayer with similar thickness (ca. 3 nm) on the Si substrate. The physisorbed monolayers are more disordered relative to the respective thicker crystalline films for both cyclic and linear PNDGs. Upon heating above Tm, the adsorbed c-PNDG chains adopt trans-amide backbone conformation identical with the free c-PNDG molecules in the molten film. By contrast, the backbone conformations of l-PNDG chains in the adsorbed layers are notably different from those of the free chains in the molten film. We postulate that the conformational disparity between the chains in the physically adsorbed layers versus the free chains in the molten film is an important factor to account for the difference in the thermal stability of PNDG thin films. These findings highlight the use of cyclic chain topology to suppress the melt-induced dewetting in polymer thin films.

It is important to develop flexible and conductive materials for various wearable applications, whereas metal foams are seldom used because of their thick cell walls, rigidity, and lack of elastici...

Phenyl-silicone rubber composite components have been used in the sealing field under various working conditions. However, research on friction behavior during service is somewhat lacking. Thermal-oxidative aging’s effects on the tribological properties of phenyl-silicone rubber composites are investigated in this work. With the addition of nano-CeO2 and graphene, the coefficient of friction (COF) gradually decreases between the GCr15 steel ball and phenyl-silicone rubber composites, which can be attributed to nano-CeO2’s and graphene’s protection of surface matrices during aging and friction-heat generating processes. The results of this study indicate that the COF gradually decreases as the load increases because frictional heat generation increases with loads, resulting in softening the matrix and decreasing friction resistance. When the graphene content increases (0.8–1.5 phr), the wear rate (Ws) of phenyl-silicone rubber composites increases due to the destruction of graphene transfer films and severe fatigue wear. This study provides new ideas for improving the friction and wear properties of phenyl-silicone rubber composites before and after thermal-oxidative aging.

Inspired from natural materials, functionally graded materials (FGMs) with gradual variations in their compositions and microstructures have drawn considerable attention in structural materials design to achieve superior stiffness, strength, and toughness. Taking Cu-Ni alloy as a representative model system, herein, we systematically explore the mechanical properties of Cu-Ni FGMs with varying Ni distributions and Ni contents, respectively, where the lattice constant of Cu-Ni FGMs is found to decrease with increasing Ni content. By carrying out uniaxial tension and compression, it is observed that Young’s modulus of Cu-Ni FGMs is nearly independent of the atomic distribution profile but sensitive to the Ni content. Yield stress also shows the strong dependency of Ni content; under the same Ni content, however, due to the sharpness of the interface and different deformation mechanisms, the yield stress becomes sensitive to the Ni distribution. Remarkably, there exists a tension-compression (T-C) asymmetry in Cu-Ni FGMs – the T-C asymmetry of yield stress is more heavily influenced by Ni distribution and content compared to Young’s modulus. Our study provides fundamental insights into the mechanical response of Cu-Ni FGMs with varying Ni distribution profiles and contents from an atomic perspective, aiding in the computational design of FGMs.

Thermal stability mechanism of CeO2/graphene/phenyl silicone rubber composites (PMVQ) are investigated by means of SEM, TGA, swelling and mechanical testing. First, the degradation mean activation energy E of rubber composites with Td (the temperature of 50% weight loss, TGA) are used to analyze the action mechanism of CeO2 and graphene in thermal oxidative aging process. The results rev eal that CeO2 and graphene have joint effects on improving thermal stability of phenyl silicone rubber composites. Second, swelling test indicates that aging of rubber composites is dominated by oxidation crosslinking at 300°Cfor 48 h. Finally, mechanical analysis shows tensile strength of PMVQ-3 (PMVQ containing graphene: 0.8phr and CeO2: 2phr) can reach 4.67 MPa increasing by 82.4% compared with PMVQ-1 (PMVQ without graphene and CeO2) after aging, and elongation at break of PMVQ-3 can remain at 180%, and even at 213% in PMVQ-4 (PMVQ containing graphene: 1.5phr and CeO2: 2phr).

The abundance of sodium and potassium elements in the earth has trigged great research interests in Na-ion and K-ion batteries. Compared to Li-ion batteries, slashed fabrication cost has been predicated for Na-ion and K-ion batteries, making them promising candidates for stationary energy storage. Potassium ion has a much larger radius than that of lithium ion, which would lead to a more severe volume change during K ions insertion. An intriguing question is whether the electrode optimization strategies developed in Li-ion batteries could be extended to K-ion batteries. In this study, Sb is used as a model alloy anode to explore the effect of nanocarbon incorporation on the cyclic stability. Through the preparation of Sb/reduced graphene oxide composite electrode, a reversible capacity of over 300 mAh/g is obtained with decent capacity retention. In contrast, neat Sb shows a fast capacity fading due to the volume expansion during alloying with K ions. This study suggests that the preparation of alloy/nanocarbon composite remains an effective approach in developing advanced anodes for K-ion batteries. Schematic of the materials synthesis process: (a) GO precursor; (b) Adsorption of Sb3+ on the surface of GO and (c) thermal annealing to reduce GO (into -rGO) and SbCl3 (into Sb) nanoparticles.

The wear resistance and tear strength of silicone rubber can be greatly improved by warp knitted polyester fabric, but the application of fabric rubber composites is limited by the poor bonding interface between the fabric and the rubber. In this study, the fabric is immersed in an alkaline solution first and a coupling agent in sequence with ultrasonic treatment. Then, fabric rubber composites with high bonding strength between fabric and rubber are prepared through a co-vulcanization process. The adhesion mechanism between the fabric and the rubber is analyzed through Fourier transform infrared spectra (FT-IR), Raman spectrum, contact angle test and peel test. The adhesion strengths of samples treated by KH570 along warp and weft direction of fabric reach 8.0 N·mm-1 and 4.82 N·mm-1, respectively, which are 10.35 times and 5.91 times higher than those of original fabric samples. This greatly improves the delamination resistance of fabric rubber composites under large strain and expands its application range.

Multiscale modeling strategy development of graphene and its composites is of critical importance in engineering and technological applications. In this work, we systematically developed a chirality preserved coarse-grained graphene model and the corresponding potential, TersoffCG(16–1). The robustness of this potential is verified through structural and mechanical characterization analysis comparison between coarse-grained and all-atomistic models. The Lennard-Jones potential is emphasized to adjust the interlayer properties of the interlayer distance and binding energy. Furthermore, in-plane properties of multilayer graphene assembly tensile and monolayer graphene crack, and out-of-plane properties of nanoindentation are fully analyzed. The copper/graphene nanocomposite tensile test indicated that the coarse-grained graphene model is compatible with the copper matrix. Our efficient and portable coarse-grained graphene model successfully reproduced the architectural parameters, elastic, fracture, and interlayer adhesion properties of graphene sheets compare with the reported experiment and theoretical results, which can serve as an effective strategy to research more hybrid composite systems.

Stretchable conductors with excellent flexibility, stretchability and electrical conductivity are among critical components for the next-generation electronics. A novel wavy graphene foam (wGF)/thermoplastic polyurethane (TPU) composite for large-strain stretchable conductors is fabricated by drop coating of matrix solutions on freestanding wGFs. Hierarchical morphologies with a microscopic dense cellular structure and a macroscopic wave shape are observed on wGFs. Decent electrical conductivities of 4.3 S/cm and outstanding mechanical properties are obtained. The wGF/TPU composites exhibit great potentials as large-strain stretchable conductors, with resistance increments of 9.4, 14, and 22 % at tensile strains of 50, 100 and 150 %, respectively, which are among the bests of carbon reinforced polymer conductive nanocomposites. Synergic effects of the extension of wavy structure and the reshaping of highly compacted graphene frameworks during stretching, which results in little true strain on conductive graphene skeletons, are mainly responsible for the stable conductive performances. Demonstrations of wGF/TPU composites as stretchable conductors exhibit superb resistance stabilities under different deformation conditions, suggesting great potentials for real-world applications.

Attempts to improve the strength of Gen3 Al–Li alloys without obviously deteriorating the ductility have been directed towards enhancing the matrix precipitation of T1 phase and reducing its enrichment at sub-grain boundaries. In this study, a novel artificial aging treatment during which uniaxial tensile stress was applied has been carried out on the AA2055 Al–Li alloy while a certain temperature was maintained. The microstructure, fractography, dislocation density, and the mechanical properties were analyzed by HAADF-STEM, HRTEM, DSC, SEM, FWHM of XRD patterns, and tensile tests. It was found that matrix T1 precipitation could be enhanced at the expense of θ’ phase by the stress applied. The enrichment of T1 phase at sub-grain boundaries could be observed in all specimens. However, the degree decreased as the pre-stretch and the applied external stress imposed. A good combination between strength and ductility was obtained for the specimen aged in T8SA100 temper (2% pre-stretch, 155 °C, 24 h, 100 MPa) and the average YS, UTS, and EI were 623 MPa, 649 MPa and 10.5%, respectively. The dislocation density in the stress aged specimens was higher than that in the stress-free aged specimens, indicating that the dislocation mechanism plays an important role in the enhanced T1 matrix precipitation during stress aging. The present study suggests that the novel stress aging treatment has great potential in improving the overall performance of advanced Al–Li alloys.

In this paper, a new exact analytical solution of buckling of sandwich panels/beams is presented. The transverse shear deformation of the face-sheet (caused by the interlayer shear effect), which has been usually neglected in previous works, is considered for the first time in our theoretical framework. In the constituent phases of the sandwich plates, the core is assumed to be isotropic, and the faces are assumed to be orthotropic, so the model can be applied to sandwich plates with composite faces. Next, the solution is compared with different results in the literatures, and the finite element computations is then carried out as a standard for measuring the accuracy. It is shown that the present solution leads to better accuracy after considering the transverse shear effect. Despite the global buckling mode is also involved in this unified solution, the emphasis of this study is on the wrinkling (short-wave) mode; the authors have shown that the transverse shear effect is particularly apparent in those short-wave modes. In the end, we determine a boundary where the shear effect will produce a non-negligible influence to the critical buckling of sandwich plates.

More and more attention has been paid to the synthesis and characterization of self-emulsifying sizing agents without organic solvent due to the demand of environment-friendless. Herein, self-emulsifying amphiphilic epoxy sizing agents with different hydrophilic-hydrophobic ratios were synthesized and used to enhance interfacial adhesion between carbon fibre (CF) and epoxy resin (EP). The effects of hydrophilic-hydrophobic ratio on the characteristics of sizing agent emulsion, the wettability and morphology of sized CFs, the monofilament CF tensile strength and the interfacial shear strength (IFSS) of CF/EP were investigated. The results showed that the emulsions were mono-dispersed nanospheres and the particle size was increased with the hydrophobic groups increasing. High thermal stability with negligible weight loss unless well above 300℃ was obtained for all the emulsions. The sized CFs by the emulsions of high hydrophobic ratio (9:1 and 19:1) exhibited more favorable wettability. The CF surface defects were healed and the roughness was reduced mildly by sizing treatment. The IFSS showed a growing trend with the hydrophobic groups increasing and was significantly enhanced by 96 % as the hydrophilic-hydrophobic ratio was 19:1. The improvement of IFSS benefited mainly from the strong interphase due to the excellent film-forming property, favorable wettability and mechanical interlocking.

Highly porous, bendable laterally compressed graphene foam (cGF)/acrylonitrile butadiene styrene (ABS) composites are developed by dip coating of ABS on dense cellular-structured, freestanding cGFs. Electrical conductivities of the cGF/ABS composites are enhanced to 6.5 S/cm, higher than that of GF/ABS composites. An electromagnetic interference shielding effectiveness (SE) of 42.4 dB and a specific SE (SSE) of 300.7 dB·cm3/g are delivered, shielding 99.99% incident electromagnetic radiations. Compared with isotropic and fragile graphene foam (GF)/ABS composites, the cGF/ABS composites with 75% compression degree of GFs exhibit a distinctive two-layer structure which endows them with strong and bendable performances to a maximum wrapping angle of 50°. Synergistic effects of the unique two layer morphology, the balance between the thicknesses of two layers, the bending direction, and the compressively strong porous structure contributed to the highly bendable properties of 75%-cGF/ABS composites.

The lamella number and interlamellar spacing are crucial structural parameters in determining mechanical properties of layered nanocomposites, while they are rarely discussed. Herein, we investigate effects of the two parameters on mechanical properties of copper/nickel (Cu/Ni) nano-laminated composites (NLCs) under uniaxial tension using molecular dynamic simulation. The Cu/Ni NLCs with one single Ni laminate exhibit the largest enhancement in Young’s modulus (E = 121 GPa) and yield strength (σz = 9.8 GPa), attributing to the stronger texture of Ni and interfacial blocking effect on the motion of dislocations. With different Ni layer spacing, the shockley dislocations form a crescent slip plane and enter the Cu matrices along the 45° direction with respect to the Ni laminate. According to the evolution of dislocation length, the flow stress shows a negative relationship with the mean dislocation length. The peak yield strength coincides with the stage of sudden increase of the total dislocation length, indicating decreased mechanical properties with increased dislocation length. These findings provide fundamental relationships between nanoscale laminated structure and macroscopic mechanical properties of Cu/Ni composites, shedding new lights on the rational design of NLCs with enhanced mechanical performances.

Aramid fiber (AF) reinforced by polyamide (PA) composites are excepted to have good interfacial matching due to their similar chemical interactions of hydrogen bonding. Thus, polarizing optical microscope (POM), transverse fiber bundle (TFB) test, and droplet micro-debonding technique were respectively performed to characterize interfacial crystallization, adhesion and shear behaviors of AF/PA6 composites with different thermal treatments. Both interface adhesion and AF fibrillation are enhanced with decreasing cooling rate or increasing annealing temperature due to the increased interfacial transcrystallization interaction. However, fast cooled interface also presents a high interfacial shear strength (IFSS) due to favorable normal residual stress. The apparent IFSS is believed to be a result of competition between crystallization enhancing interfacial interaction, interfacial mismatching aggravating debonding, and an uncertain residual stress positive or negative for load transfer. TFB failure mechanism including AF fibrillation and kinking are schematically presented. Fibrillation strength of AF is found to follow Weibull distribution evaluated by droplet micro-debonding technique.

The low compressive strength of fiber-reinforced polymer (FRP) composites has been one of the critical problems limiting their applications. The compressive damage behaviors of FRP composites are much more complicated than their tensile failure behaviors, usually including different modes, such as delamination and kink-band instability, thereby throwing a great challenge to increase the compressive strength of FRP composites by maneuvering the compressive damage mode. However, limited numerical and experimental studies exist on the compression damage mode control and design. In this study, we examined the competition mechanism between the two major compression damage modes, delamination and kink band, by simulations through finite element method and identified the interlaminar strength and yield strength of the polymer matrix as the crucial factors regulating the damage modes. Accordingly, we established a strategy of designing two material parameters to effectively regulate the compressive damage mode and increase the compressive strength of FRP composites. Furthermore, a series of experiments were conducted to validate the design strategy. The experimental results revealed that tuning the interlaminar strength and yield strength of the polymer matrix could effectively maneuver the compression damage modes and their conversion, and the optimal compressive strength of FPR composites could be achieved when the two damage modes coincide. This study would not only further our understanding of the compressive behaviors of FRP composites but also provide valuable guidelines for their compressive strength enhancement and design.

Polyaryletherketone with Cardo (PEK-C) was used as matrix additive, film and particle interleaves to improve the fracture toughness of carbon fibre epoxy matrix composites. The toughening efficiency and mechanism of the three methods were studied. The PEK-C film interlayer was more efficient and stable in the interlaminar toughening. The flexural strength was not compromised with the incorporation of PEK-C due to the limited addition. The enhanced interlaminar toughening was mainly attributed to the two-phase structure of micrometer scale formed by PEK-C “peel” and the rounded epoxy matrix wrapped by PEK-C. The nanoscale sea-island substructure in the rounded epoxy matrix was observed by atomic force microscopy (AFM), which might be also correlated with the toughness improvement.

A study on lateral disturbance, which is regarded as a factor that causes imperfect loading, is presented herein. The rationale behind the study is that fiber misalignment has always been regarded as the cause of an imperfect structure. The main purpose of this paper is to establish that even for a perfect structure, lateral disturbance can cause compression instability in a composite. In this paper, a novel numerical model has been established, in which the lateral disturbance effect is applied to a long fiber with perfect alignment to study the compressive instability behavior. The numerical results show that even in the case of perfect structure, lateral disturbance is still the key factor that causes compressive bucking of a composite. In our experiments, the lateral disturbance is observed in-suit from the deformation of the unidirectional (UD) composite using the digital image correction (DIC) technology. Finally, a theoretical prediction model of the compressive strength of fibre reinforced polymers (FRPs) and the effects of lateral disturbance and loading path dependency on compressive behavior of the FRP are also discussed. These results can provide a more comprehensive understanding for the instability mechanism and the compressive strength of FRPs composite.

The buckling behavior of a face layer debonded locally from the core of a sandwich panel is analyzed by considering a Euler beam on Winkler foundation with debonds subjected to in-plane compression. Exact closed form solutions of the buckling load and mode shape are obtained, and corresponding numerical results are given to illustrate the solution. Results indicate that the wrinkling wavelength of the perfectly bonded face layer can be used as an appropriate characteristic length for normalizing the debond length of a relatively long face layer. The effects of length and location of debonds and the end constraints of the face layer on the load carrying capacity are discussed. Interactive effects due to two debonds and the overlapping of debond faces are also studied. A master curve based on a classical solution is developed by employing the new normalization of the debond length. A modification to the usual Winkler foundation constants is made for an isotropic core, and it agrees very well with published results of a finite element analysis.

A wrinkling model for sandwich panels in compression is developed with the assumption of a continuous isotropic linear elastic core. Wrinkling stresses for the three modes, defined in a well-known book by H.G. Allen, are expressed by a unified, single expression. The expression depends linearly on a case parameter η defined to specify the three cases of wrinkling: η=0 for single-sided face wrinkling (case 1), η=1 for in-phase wrinkling (case 2), and η=–1 for out-of-phase wrinkling (case 3). It is shown that the stresses in all three cases are almost identical for short wavelength wrinkling and can be expressed by a single simplified analytical expression; however, they may differ significantly in moderate and long wavelength wrinkling, and for these cases they are given by simplified analytical expressions. It is proved that the in-phase wrinkling stress is the lowest among the three cases. Based on the analysis, conducted limitations of the commonly used Winkler and two-parameter models are discussed. Finally, engineering design procedures are recommended for the wrinkling effect in sandwich panels under compression.