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Journal articleHe L, Xu Y, Yang Z, et al., 2024,
Copper-decorated strategy based on defect-rich NH2-MIL-125(Ti) boosts efficient photocatalytic degradation of methyl mercaptan under sunlight
, Environmental Pollution, Vol: 344, ISSN: 0269-7491Photocatalysis has received significant attention as a technology that can solve environmental problems. Metal-organic frameworks are currently being used as novel photocatalysts but are still limited by the rapid recombination of photogenerated carriers, low photogenerated electron migration efficiency and poor solar light utilization rate. In this work, a novel photocatalyst was successfully constructed by introducing Cu species into thermal activated mixed-ligand NH2-MIL-125 (Ti) via defect engineering strategy. The constructed defect structure not only provided 3D-interconnected gas transfer channels, but also offered suitable space to accommodate introduced Cu species. For the most effective photocatalyst 0.2Cu/80%NH2-MIL-125 (300 °C) with optimized Cu content, the photocatalytic degradation rate of CH3SH achieved 4.65 times higher than that of pristine NH2-MIL-125 under visible light (λ > 420 nm). At the same time, it showed great degradation efficiency under natural sunlight, 100 ppm CH3SH was completely removed within 25 min in full solar light illumination. The improved catalytic efficiency is mainly due to the synergistic effect of the integrated Schottky junction and rich-defective NH2-MIL-125, which improved the bandgap and band position, and thus facilitated the separation and transfer of the photo-generated carriers. This work provided a facile way to integrate Schottky junctions and rich-defective MOFs with high stability. Due to its excellent degradation performance under sunlight, it also offered a prospective strategy for rational design of high-efficiency catalysts applied in environmental technologies.
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Journal articleHe L, Yang Z, Lu X, et al., 2023,
Defective UiO-66 by metal doping for highly efficient photocatalytic degradation of methyl mercaptan
, Journal of Environmental Chemical Engineering, Vol: 11, ISSN: 2213-3437Defective UiO-66 by metal doping exhibits considerable promise in the photocatalytic degradation of environmental contaminants, albeit how different metal doping affect formation of defects and its efficacy in the degradation of methyl mercaptan has yet to be comprehensively explored. In this study, a one-step solvothermal method was employed to successfully synthesize six distinct metal-doped UiO-66 with variations of defects by incorporating Ce, Al, Cu, Cr, Mg, and Fe. A systematic examination of the structural and photochemical attributes of these metal-doped UiO-66 materials was conducted through a series of characterisations. Metal doping creates defects in UiO-66, changes its colour and morphology and increases its specific surface area. Subsequently, the adsorption and photocatalytic degradation characteristics of these nanomaterials concerning methyl mercaptan were investigated. In comparison to pristine UiO-66, all metal-doped UiO-66 variants exhibited enhanced adsorption and photocatalytic degradation capabilities towards methyl mercaptan. Notably, among the prepared materials, FeUiO-66 demonstrated the most exceptional photocatalytic degradation performance, followed by CuUiO-66, AlUiO-66, CeUiO-66, CrUiO-66, and MgUiO-66 in that order. 1.0FeUiO-66 exhibiting the most remarkable performance, achieving a 99 % degradation of methyl mercaptan within 30 min. This represented a degradation rate 36.8 times higher than that of pure UiO-66, attributable to the incorporation of low-valence metals into the UiO-66 framework, resulting in the creation of oxygen vacancy defects. Furthermore, the presence of these metals facilitated electron transport, thereby enhancing the efficiency of photocatalytic degradation. This study underscores the potential of various metals-doped UiO-66 for adsorption and photocatalytic elimination of methyl mercaptan.
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Journal articleWu C, Ding Y, Almeida-Fernandes L, et al., 2023,
State-of-the-art review on the web crippling of pultruded GFRP profiles
, Thin Walled Structures, Vol: 192, ISSN: 0263-8231Web crippling involves the failure of pultruded glass fibre reinforced polymer (GFRP) profiles under transverse concentrated loading. The possible failure modes include web buckling, web crushing and web-flange junction failure, which are very different from those of metallic sections, which are isotropic and yield. This paper provides a comprehensive review of the up-to-date research advancement in web crippling of pultruded GFRP profiles from four perspectives. Firstly, the experimental results available in the literature are summarized and a database is tabulated. Secondly, the factors influencing failure modes and web crippling resistance are analysed, including loading conditions, section geometries, and material properties. Thirdly, recent advancement in numerical modelling is reviewed and paths for improvement are identified. Lastly, analytical models for predicting web crippling resistance are reviewed and their accuracy is assessed by comparing predictions with experimental results from the database. It is concluded that this research area is still in its early stages and more experiments need to be conducted, in a standardized and systematic manner; in addition, more detailed material properties should be characterized for a better interpretation of the failure mechanisms. Accurate and reliable analytical models covering all design cases are not yet available, and most existing analytical models still need to be validated with independent experimental data. Finally, the paper identifies key research gaps and proposes future research directions. This paper also provides a benchmark for the future development of design provisions regarding the web crippling of pultruded GFRP profiles.
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Journal articleTam L-H, Wu R, Minkeng MAN, et al., 2023,
Understanding creep behavior of carbon fiber/epoxy interface via molecular dynamics simulation
, Mechanics of Advanced Materials and Structures, Vol: 30, Pages: 4052-4064, ISSN: 1075-9417This work focuses on molecular creep behavior of carbon fiber/epoxy interface under sustained loads at different levels. Threshold stress and energy barrier for the onset of interfacial creep failure under peeling loads are found greater than those under shearing. Microstructural changes during creep show that the epoxy has a large and irreversible deformation under peeling loads, denoted as a yielding process in the peeling case. The yielding process in the peeling case dissipates the applied energy in the epoxy structure. Therefore, the interface shows a stronger resistance to the peeling and the shearing is more critical during composite failure.
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Journal articleTam L-H, Zhou A, Yu Z, et al., 2023,
Editorial: microstructures and mechanical properties of cement-based composites
, Materials, Vol: 16, ISSN: 1996-1944 -
Journal articleMa H, He L, Wu C, 2023,
Development of reactive MgO cement-silica fume-based strain-hardening engineered cementitious composite
, Journal of Materials in Civil Engineering, Vol: 35, ISSN: 0899-1561MgO-based cementitious materials have attracted increasing attentions due to their advantages of low energy consumption, fire resistance, and low CO2 emission. This study develops a new reactive MgO cement (RMC)-silica fume (SF) engineered cementitious composite (ECC). The effects of RMC∶SF mass ratio, fiber type, fiber content, and curing conditions on the mechanical properties and strain-hardening behavior of the RMC-SF ECC are investigated. The hydration characteristics of RMC-SF ECC under different curing conditions were studied through X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR) and scanning electron microscope (SEM) analysis. It was found that the RMC-SF ECC obtained a tensile strain capacity of 5.7%. Polyethylene (PE) fibers achieved higher compressive strength, and polyvinyl alcohol (PVA) fibers yielded better tensile strain capacity. A RMC-SF mass ratio of 1∶1 obtained a higher ductility under high temperature curing at 50°C. Although carbon dioxide curing improves the mechanical properties of RMC-SF ECC due to the formation of MgCO3, it greatly reduces its ductility. A large amount of brucite and M─ S─ H gels were generated under room temperature curing with plastic wrap.
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Journal articleWu C, Pan Y, Yan L, 2023,
Mechanical properties and durability of textile reinforced concrete (TRC) - a review
, Polymers, Vol: 15, ISSN: 2073-4360Textile reinforced concrete (TRC) is an innovative structure type of reinforced concrete in which the conventional steel reinforcement is replaced with fibre textile materials. The thin, cost-effective and lightweight nature enable TRC to be used to create different types of structural components for architectural and civil engineering applications. This paper presents a review of recent developments of TRC. In this review, firstly, the concept and the composition of TRC are discussed. Next, interfacial bond behaviour between fibre textile (dry and/saturated with polymer) and concrete was analysed considering the effects of polymer saturation, geometry and additives in polymer of the textile. Then, the mechanical properties (including static and dynamic properties) of TRC were reviewed. For static properties, the mechanical properties including compression, tension, flexural, shear and bond properties are discussed. For dynamic properties, the impact, seismic and cyclic properties were investigated. Furthermore, the durability of TRC under different environmental conditions, i.e., temperature/fire, humidity and wet–dry cycles, freeze–thaw, chemical and fatigue were discussed. Finally, typical engineering applications of TRC were presented. The research gaps which need to be addressed in the future for TRC research were identified as well. This review aims to present the recent advancement of TRC and inspire future research of this advanced material.
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Journal articleWu R, Wang XQ, Zhao D, et al., 2023,
Degradation of fiber/matrix interface under various environmental and loading conditions: insights from molecular simulations
, Construction and Building Materials, Vol: 390, ISSN: 0950-0618Fiber-reinforced polymer composites have been increasingly applied as reinforcing and load-bearing components in building constructions and civil infrastructures. Long-term exposure to changing environmental and loading conditions leads to composite degradation, which is highly related to degraded structure and properties of fiber/matrix interface and consequent interfacial debonding between fiber and matrix at nanoscale. By simulating interfacial structure and interactions with atomistic precision, molecular simulation allows for a high fidelity to interfacial variations as affected by environmental and loading conditions. In this paper, molecular investigations of interfacial degradation between fiber and matrix under various environmental and loading conditions are reviewed. Model construction of interfaces formed by different fibers and matrixes and simulation of various environmental and loading conditions are firstly introduced. Afterwards, mechanical and adhesion properties of molecular interfaces obtained from deformation simulations are presented. Meanwhile, interfacial degradations under various environmental and loading conditions are discussed and underlying mechanisms are revealed. Further discussions on modeling and simulation of molecular interface are proposed for future investigations. Overall, this work reviews previous molecular investigations of interfacial degradation of composites under different environmental and loading conditions, which contributes to evaluation of interfacial behaviors of composite materials during long-term service life.
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Journal articleWu C, Hou J-A, Liu H, et al., 2023,
Understanding moisture effect on nonlinear vibrations of epoxy thin film via a multiscale simulation
, Journal of Sound and Vibration, Vol: 553, ISSN: 0022-460XEpoxy thin films have been widely used in microelectromechanical systems, aerospace and civil engineering, which are exposed to external excitations in wet environment that lead to severe nonlinear vibration. In this paper, a multiscale simulation consisting of molecular simulation and meshless simulation is adopted to study moisture effect on nonlinear vibrations of epoxy thin film. In molecular simulations, the cross-linked epoxy molecules with moisture content from 0.0 to 4.0 wt% are constructed. It is measured that mechanical properties of epoxy molecules show an initial enhancement with moisture content from 0.0 to 1.0 wt%, and a subsequent decrease when moisture content increases to 4.0 wt%. With molecular simulation results as inputs, meshless simulations are carried out to investigate epoxy vibration behaviors, where vibration equations of epoxy thin films with investigated moisture contents are constructed and solved. It is determined that fundamental frequencies of epoxy thin films show a similar trend as the variation of mechanical properties. Meanwhile, the level of nonlinear frequency ratio decreases in 1.0 wt% case and subsequently increases up to 4.0 wt%. The vibration behaviors of epoxy thin film as revealed in this work contribute to the prediction of vibration behaviors of epoxy-based applications in wet environment.
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Journal articleTam L-H, Minkeng MAN, Lau D, et al., 2023,
Molecular interfacial shearing creep behavior of carbon fiber/epoxy matrix interface under moisture condition
, Engineering Fracture Mechanics, Vol: 282, ISSN: 0013-7944During the intended service-life, carbon fiber-reinforced polymer (CFRP) composite is inevitably exposed to moisture and external loading conditions. Here, molecular simulation is used to investigate the moisture effect on interfacial creep responses of carbon fiber/epoxy matrix interface subjected to sustained loading. The molecular model is constructed by bonding epoxy molecule on top of graphite sheets representing the fiber outer-layer. In wet case, water molecules are added inside interface, and graphite sheets are subjected to different shearing load levels to simulate external loadings. Compared with dry case, the threshold stress and energy barrier for the onset of creep failure decrease by 19.8–20.0% and 18.5%, respectively. Strain and stress evolution associated with configurational changes show that shearing deformation is larger and interfacial sliding occurs faster in wet case. It is found that water molecules aggregated near fiber surface and around epoxy functional groups interrupt the molecular interactions and degrade the bonding properties and mechanical responses of fiber/matrix interface, which accelerates the interfacial sliding and debonding process under shearing loading, and hence the interfacial resistance to shearing loading is significantly reduced in wet case. This study provides molecular insights into interfacial degradation under moisture and sustained loading conditions, which form the basis for predicting the interfacial degradation of CFRP composites during the intended service-life.
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Journal articleWu C, Ding Y, He L, et al., 2023,
Web crippling of pultruded GFRP built-up sections
, Thin Walled Structures, Vol: 185, ISSN: 0263-8231Web crippling is a critical premature failure of pultruded glass fiber reinforced polymer (GFRP) composites. One solution is to combine several sections to form a built-up section to carry the web crippling load. However, there is no existing study on the web crippling behavior of built-up sections under transverse loading. This paper presents an experimental and analytical study on the web crippling behavior of built-up I-shaped sections. The I-shaped sections were made by connecting two single channel sections back-to-back. Two connections methods were used including adhesive bonding and mechanical bolting. The bolt arrangements including number of bolt rows in the longitudinal direction, bolt spacing were varied to understand their effects on the web crippling behavior. The built-up sections were tested under two loading conditions of ITF and ETF, and the failure modes, load–displacement curves, and web crippling capacities were reported. Finally a section integrity enhancement coefficient was introduced in the analytical model to predict the web crippling capacity of built-up I-shaped sections and the predictions agreed well with the experimental results. This study contributes to the understanding of web crippling behavior of built-up sections made with pultruded GFRP sections.
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Journal articleWu C, Yu Y-Z, Tam L-H, et al., 2023,
Effects of bondline defects on the bond behaviour of CFRP-steel double strap joints
, Composite Structures, Vol: 308, ISSN: 0263-8223Adhesive bonding is used frequently for the applications of carbon fiber-reinforced polymer (CFRP) composites in steel structures such as strengthening or joining. However, the bondline defects are inevitable and could negatively affect the bond behaviour between CFRP and steel. Thus, the bondline defects represent a critical hazard and require careful assessment. This paper presents an experimental and numerical study on the effects of bondline defects on the bond behaviour of CFRP-steel double strap joints. The variables include the defect size (up to 35% of the bonded area), number (up to 45) and locations in the bondline. Multiple defects with mixed sizes are considered in a numerical analysis to investigate the effect of the defect number in more detail. It is found that the bondline defects lead to a reduction in the joint capacity. The highest reduction in capacity (36%) is observed when multiple small-sized defects are presented in the bondline. With the increment of the defect area, the failure mode becomes a combination of steel-adhesive interface debonding and CFRP delamination. A design framework is proposed based on the experimental and numerical results for the conservative prediction of the joint capacity with consideration of bondline defects.
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Journal articleFame CM, He L, Tam L-H, et al., 2023,
Fatigue damage tolerance of adhesively bonded pultruded GFRP double-strap joints with adhesion defects
, Journal of Composites for Construction, Vol: 27, ISSN: 1090-0268This paper reports an investigation on the damage tolerance of adhesively bonded pultruded glass fiber–reinforced polymer (GFRP) joints under fatigue loading. Double-strap joints with and without bondline defects were subjected to constant amplitude fatigue loading. The study investigated the effects of the defect location, size, and number on the fatigue performance of the joints (i.e., failure mode, fatigue life). Results showed that the failure mode was a combination of delamination and adhesive fiber–reinforced polymer (FRP) interface debonding at the defect vicinities. The fatigue life of the joints was significantly reduced (up to 90%) when the defect was at the overlap end. A defect size larger than 10% of the total bonded area could yield a substantial reduction in fatigue life. Small defects (less than 10% of the total bonded area) could yield a reduction in fatigue life of up to 73% when their number exceeded four. The joint exhibited better damage tolerance under static than fatigue loading conditions.
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Journal articleYu Y-Z, Tam L-H, Wu C, 2023,
A universal solution of the bond behaviour between CFRP-steel double strap joints considering steel yielding
, Composite Structures, Vol: 304, ISSN: 0263-8223Steel structures strengthened with CFRP (carbon fiber-reinforced polymer) composite may encounter extreme load such as earthquake or impact which may cause steel yielding and plasticity. But very limited investigations exist on the effect of steel yielding on the bond behaviour between CFRP and steel. This paper presents a comprehensive study on the effect of steel yielding on the bond behaviour of CFRP-steel double strap joints. Firstly, a stress-based analytical model is established for the analysis of the ultimate load and failure initiation position of the double strap joints. This is a universal model which is able to analyse elastic joint as well as plastic joint with steel yielding. Then a series of tensile tests with double strap joints is carried out and the experimental results are used to validate the proposed analytical model. Finally, a parametric analysis is performed using the analytical model and an additional numerical method in which the debonding between steel and CFRP strips is simulated by a cohesive approach. The parametric analysis considers both geometrical and material variables. It can be concluded that the steel yielding has a significant effect on the bond behaviour of CFRP-steel double strap joints, including ultimate load, stress and strain distributions of CFRP, steel and adhesive, and debonding initiation position of the joint. Based on the experimental and analytical results, criteria are proposed for the determination of effective bond length and yielding bond length, debonding initiation position and ultimate load of CFRP-steel joints.
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Journal articleWu C, Zhang Z, He L, et al., 2023,
Experimental study on the static and fatigue performances of GFRP-timber bolted connections
, Composite Structures, Vol: 304, ISSN: 0263-8223Steel plate connection is popular in modern timber structures. However, the steel plate may be subjected to corrosion issue due to the presence of moisture in timbers. This paper proposes to replace steel plate with glass fiber reinforced polymer (GFRP) plate for connecting timber elements, so that the durability of the timber structure is expected to be improved. An experimental study is presented on the static and fatigue performances of the proposed GFRP-timber bolted connections. Variables including bolt diameter, number of bolt rows, number of bolt columns were selected to understand their effects on the static and fatigue behaviours of the connections. Failure modes, load–displacement curves, static bearing capacities, fatigue lives, stiffness degradations of the GFRP-timber bolted connections were reported. The residue bearing capacities of the connections were tested after the fatigue loading tests to assess the fatigue effect on the connection static behaviour. This study contributes to the understanding of the mechanical behaviour of GFRP-timber bolted connections.
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