Aramid fibers are well-known for their excellent tensile properties and low density but are limited in composite applications due to their inert surface which leads to poor interfacial properties. ...One method that has shown promise in recent years is the application of nanoscale reinforcements to the surface of the fibers to improve mechanical interaction with the matrix. With aramid fibers, it is ideal to perform an interfacial reinforcement utilizing the dense hydrogen bonding which is responsible for the fibers strength. Here, it is demonstrated that recently developed aramid nanofibers (ANFs) can adsorb onto the surface of macroscale aramid fibers to enhance the interfacial properties through mechanical interlocking with the matrix. A simple and rapid dip-coating process is used to deposit the ANFs on the aramid fiber surface. These ANFs bond with the fiber through physisorption and hydrogen bonding, yielding a 70.27% increase in interfacial shear strength and a 25.6% increase in short beam shear strength in composites prepared by dip-coating unidirectional tape into a solution of ANFs. Notably, the interfacial gains are made while fully preserving the strength of the aramid fiber following the treatment, therefore ensuring in-plane properties of the composite are maintained. This work shows that the introduction of an ANF interphase may present a novel and convenient method to improve the interfacial strength of aramid reinforced composites, enabling cost-effective and simplified production of stronger structural materials.
Graphene reinforced metal matrix composites (MMCs) have received extensive research interests as promising structural materials in developing lightweight structures. The mechanical performance of ...such composites, however, is considerably hindered by weak van der Waal (vdW) interaction between graphene and metal matrix. The present work shows that this challenging issue can be effectively alleviated by the use of chemically functionalized graphene fillers with mechanically induced wrinkles. Our extensive molecular dynamics (MD) simulations on graphene reinforced copper (Cu) composite manifest that the presence of shear-induced wrinkles and chemical modification of graphene using functional groups can significantly increase its surface roughness, enhance the vdW interaction and consequently lead to higher interfacial shear strength (IFSS) between graphene and Cu matrix. Compared with its counterpart functionalized with hydrogen, graphene functionalized with alkyl (methyl, ethyl, propyl, and butyl) offers better interfacial interactions with Cu matrix because these functional groups are longer than hydrogen functional group and can be embedded deeper into the matrix.
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Continuous fibre reinforced thermoplastic composites (CFRTPCs) are becoming more significant in industrial applications due to their inherit advantages such as excellent mechanical performance, ...potential use in lightweight structures and being recyclable. Fused deposition modelling (FDM) is a promising additive manufacturing technology and an alternative to conventional processes for the fabrication of CFRTPCs due to its ability to build functional parts having complex geometries. However, a major concern affecting the efficient use of 3D printed composites is their weak interlaminar bonding performance compared to conventional pre-preg composites. The aim of this study is to evaluate the effect of layer thickness and fibre volume content on the interlaminar bonding performance of 3D printed continuous carbon, glass and Kevlar® fibre reinforced nylon composites manufactured by FDM technique. Short beam shear tests were carried out to determine interlaminar shear strength (ILSS). SEM images and cross-sectional micrographs were examined to assess failure mechanics of the different configurations.
It was observed that the effect of layer thickness of nylon samples on the interlaminar shear performance was marginally significance. ILSS values decrease as layer thickness increase due to higher porosity. In addition, continuous fibre reinforced samples show higher ILSS values than unreinforced ones but, conversely, the level of increase in ILSS is moderate with continued increase in fibre content, particularly in the case of Kevlar® fibre. Carbon fibre reinforced composites exhibit the best interlaminar shear performance with higher stiffness. On the other hand, Kevlar® fibre reinforced composites have the lowest interlaminar shear performance due to poor wettability of Kevlar® fibre bundles by the nylon, leading to extensive delamination. Finally, the results obtained demonstrate that it is still a challenge to increase shear performance of 3D printed composites with respect to common pre-preg materials. Nevertheless, ILSS values exhibited by 3D printed composites are significantly higher than the usual 3D printed thermoplastics.
•The effect of process parameters on the ILSS performance of continuous fibre reinforced composites is investigated.•Short beam shear tests are performed to obtain interlaminar shear strength (ILSS).•In the case of nylon samples, ILSS values decrease as layer thickness increases due to higher porosity.•Reinforced samples show higher ILSS values than nylon ones, but the level of increase is moderate with fibre content.•Carbon fibre reinforced samples exhibit the best interlaminar shear performance with higher stiffness.
Graphene has been widely used as new generation reinforcing nanofiller to achieve significantly improved mechanical properties in composites. However, its reinforcing effect has been considerably ...affected by the poor interfacial strength between graphene and the matrix. By using molecular dynamics simulations, the present work explores an effective route to improve the interfacial shear strength (ISS) of graphene sheets through the introduction of mechanically induced wrinkles that are formed by applying shear/compressive strains to graphene. The slide-out tests of a wrinkled graphene sliding over the graphene substrate show that the strain-induced wrinkles in graphene slider gives rise to larger surface roughness which leads to stronger interfacial interactions between graphene layers and consequently, significant improvement in ISS. Compared with compression induced wrinkles, shear induced wrinkles are found to be much more effective in enhancing ISS. Our results indicate that applying mechanical pre-strain, in particular, shear strain to graphene is a very useful strategy to improve its reinforcing effect in composites.
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•Wrinkles are designed by applying shear/compressive strain to graphene sheet.•The characteristics of wrinkles including amplitude/half-wavelength, roughness and ratio of interaction area are analyzed.•Shear/compressive strain-induced wrinkles effectively improve the interfacial shear strength between graphene sheets.•Shear-induced wrinkle is more effective in enhancing the interfacial shear strength than the compression-induced one.
This study adopts the Bayesian neural network (BNN) integrated with a strong non-linear fitting capability and uncertainty, which has not previously been used in geotechnical engineering, to propose ...a modelling strategy in developing prediction models for soil properties. The compression index C
c
and undrained shear strength s
u
of clays are selected as examples. Variational inference (VI) and Monte Carlo dropout (MCD), two theoretical frameworks for solving and approximating BNN, respectively, are employed and compared. The results indicate that the BNN focused on identifying patterns in datasets, and the predicted C
c
and s
u
show excellent agreement with the actual values. The reliability of the predicted results using BNN is high in the area of dense datasets. In contrast, the BNN demonstrates low reliability in the predicted result in the area of sparse datasets. Additionally, a novel parametric analysis method in combination with the cumulative distribution function is proposed. The analysis results indicate that the BNN-based models are capable of capturing the relationships of input parameters to the C
c
and s
u
. BNN, with its strong prediction capability and reliable evaluation, therefore, shows great potential to be applied in geotechnical design.
The microstructure, interfacial characteristics, shear behavior, tensile properties and fracture morphologies of stainless steel clad plates fabricated by vacuum hot rolling at different rolling ...reduction ratios of 20%, 40%, 70%, 90% and 93.75% are investigated using optical microscope (OM), ultra-depth microscope, scanning electron microscope (SEM), electron probe microanalysis (EPMA) and universal testing in detail. With the increasing rolling reduction ratio, the refinement degree of microstructure is increased, while the thicknesses of interface alloy element diffusion zones including the decarburized, carburized layers and martensite zone are decreased. Due to the different interface bonding status, the shear fracture of clad plate rolled at a low reduction ratio of 40% is located at interface, while clad plates with high reduction ratios of 70% and 90% fracture at the decarburized layers. Therefore, interface shear strength is sharply and then slightly increased. Moreover, the interface bonding strength, tensile strength and interface deformation coordination are increased, while fracture elongation is increased firstly and then decreased with the increasing rolling reduction ratio, which are attributed to the competing mechanisms of grain refinement, work hardening, interface strengthening and intergranular cracks of carburized layer. Overall, the interfacial bonding mechanism can be related to the Mn-Si oxide inclusions rupture, alloying elements diffusion, phase transition and severe plastic deformation at high rolling temperature.
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•Reduced delamination and intergranular cracks can enhance deformation coordination.•Ruptured Mn-Si oxide inclusions can promote interface diffusion and bonding.•Clad plates hot-rolled at 90% obtain the highest tensile ductility.•Martensite zone thickness is gradually decreased with the rolling reduction ratio.
•Water absorption of FRP included a Fick's diffusion and deterioration responses.•Linear relationship between mechanical properties and bonding water was established.•Mechanical properties decreased ...owing to resin plasticization and interface debonding.•Long-term life prediction was conducted to provide an application guideline of FRP.
The hygrothermal aging of fiber reinforced polymer (FRP) composite rod served as bridge cables played a key role on the long-term service performances. In the present paper, two types of pultruded carbon/glass fiber reinforced epoxy hybrid composite rods, one with uniformly dispersed carbon and glass fibers, and the other with glass fiber shell and carbon fiber core, were investigated on the water uptake and interface shear strength. The aging condition was immersion in deionized water at 40 °C, 60 °C and 80 °C. Interface shear strength degradation mechanism was revealed by thermal analysis and microstructure analysis. It was found that the water absorption of two types of hybrid rods represented the two-stage behavior. For the rod of uniform fiber dispersion, more water uptake in the second stage occurred compared to that of the shell/core rod, which was attributed to the resin rich area and interface debonding of fiber/resin. Long-term hygrothermal exposure led to a remarkable degradation in the interfacial shear strength of the rods, up to 17.5% ∼ 42.1%. The resin plasticization and interface debonding were the main factors contributed to the strength degradation. Based on the Arrhenius equation, the long-term life prediction of the interfacial shear strength under two typical bridge service environments was conducted to the design guideline of hybrid rods in the bridge engineering.
Many of the world reserves of fossil fuels are located at various water depths in fine-grained sediment under the seabed. The fine-grained sediment contains relatively large biogas bubbles, which has ...been posing challenges to the stability of offshore foundations supporting oil and gas platforms. Although fine-grained gassy soil was found to exhibit different undrained shear strengths (c.sub.u) by altering the initial pore pressure, u.sub.i (relevant to water depth), systematic studies concerning the effect of u.sub.i on undrained shear behaviours of the soil are still lacking. This study reports a series of undrained triaxial tests aiming to compare and investigate the responses of reconstituted fine-grained gassy soil with the same consolidation pressure (p'.sub.c), but at a wide range of varying u.sub.i (0-1000 kPa). The shearing-induced excess pore pressure (DELTAu) in the gassy specimens highly depends on u.sub.i. It can be either smaller than that of the saturated specimen with the same p'.sub.c (due to partial dissipation of Au into relatively large bubbles at low u.sub.i) or larger than that of the saturated specimen (related to collapse of relatively small bubbles at high u.sub.i). Consequently, the presence of bubbles had beneficially increased c.sub.u at relatively low u.sub.i (u.sub.i/p'.sub.c < 0.6), and vice versa. The critical stress ratio of the reconstituted fine-grained gassy soil, however, did not appear to be altered by u.sub.i.
•The anti-rutting efforts focus on improving the rheological properties of asphalt.•Semi-flexible and cool asphalt pavements can help reduce rutting depth.•The applicability of wheel tracking test ...was systematically analyzed.•It is unnecessary to perform rutting tests at a rather high temperature.•Multiple-stress mode should be considered in performing laboratory rutting test.
Permanent deformation, mainly referring to rutting, is one of the main distress modes of asphalt pavement. Exploring effective methods to mitigate the rutting distress is of great significance for providing a long-life and safe road. The rutting solutions were first reviewed. It was found that the efforts from academic and engineering industries focused on enhancing the rheological properties of asphalt binder by adding modifying powder, fiber or mixture into binder or mixture, as well as strengthening aggregate interlock and applying novel pavement structure. Semi-flexible asphalt pavement was suggested to be a promising method to fight the rutting distress, because it has a high mechanical property without scarifying the flexibility of asphalt pavement. In order to consider the influence of temperature on rutting occurrence, cool asphalt pavements, especially heat-transfer induced structures, were reviewed and deemed to be a new strategy for reducing rutting susceptibility of asphalt pavement. In order to evaluate the effectiveness of above rutting solutions, many tests, such as multi-stress creep recovery test for asphalt binder and wheel tracking test for asphalt mixture, were reviewed. By linking the reported results of wheel tracking test with high-temperature rutting mechanism it was advised to develop a test method that could reproduce the real field pavement environment, including multiple stress mode, temperature gradient control system and pavement structure, to assess the rutting response of asphalt mixture. This review is expected to provide an overall insight on the existing rutting solutions and test methods, and recommend future studying areas relevant to rutting distress.
An effective and easily-handled strategy for enhancing the interfacial adhesion of CF/PEEK-titanium hybrid laminates was proposed, which was achieved by introducing micro-nano layers with ...multi-walled carbon nanotube (MWCNT) networks between titanium and PEEK layers via electrophoretic deposition. The optimal deposition condition was explored by setting different concentrations of MWCNTs and times of deposition. Short beam shear tests were conducted at room temperature to characterize the interlaminar shear strength of the hybrid laminates. The results showed that the optimum parameters of deposition were 0.75 mg/mL of MWCNTs concentration and 90 s of deposition time, leading to a 47.8% increase of interlaminar shear strength compared with the sandblasted-only case. The mechanisms for enhancement were explained by micromorphology, apparent contact angle, and roughness analyses, which could be utilized to guide the preparation of CF/PEEK-Ti hybrid laminates with interfacial reinforcement by MWCNTs. Besides, multiple failure modes occurred at the metal-composites interface including a mixed mode of interfacial and cohesive failures, and a large amount of PEEK and carbon fibers remaining on the surface of titanium sheet proved the excellent interlaminar properties of the hybrid laminates.
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