Abstract
The implementation of low-cost transition-metal complexes in CO
2
reduction reaction (CO
2
RR) is hampered by poor mechanistic understanding. Herein, a carbon-supported copper ...bis-(terpyridine) complex enabling facile kilogram-scale production of the catalyst is developed. We directly observe an intriguing baton-relay-like mechanism of active sites transfer by employing a widely accessible operando Raman/Fourier-transform infrared spectroscopy analysis coupled with density functional theory computations. Our analyses reveal that the first protonation step involves Cu-N bond breakage before the *COOH intermediate forms exclusively at the central N site, followed by an N-to-Cu active site transfer. This unique active site transfer features energetically favorable *CO formation on Cu sites, low-barrier CO desorption and reversible catalyst regeneration, endowing the catalyst with a CO selectively of 99.5 %, 80 h stability, and a turn-over efficiency of 9.4 s
−1
at −0.6 V vs. the reversible hydrogen electrode in an H-type cell configuration. We expect that the approach and findings presented here may accelerate future mechanistic studies of next-generation CO
2
RR electrocatalysts.
Machining of carbon fiber-reinforced polymers (CFRP) still remains a difficult procedure in the whole manufacturing process. One of the reasons is the cutting mechanism varies during machining, ...causing the inconsistency of surface integrity. This study intends to investigate the continuous variation of cutting mechanism and the induced cutting responses and damages. A novel experiment, with square and circular workpieces involved in cutting, was designed. A three-dimension micro-scale cutting simulation model was built. The experiment and simulation were combined to analyze the evolution and the correlation of cutting forces, machined surface roughness, sub-surface damage and the burr formation. The effects of rake angle and tool edge radius on chip formation and sub-surface damage were also presented. The conclusions are helpful to understand the damages generation during machining of CFRP.
Interference-fit is getting increasing attentions in the aerospace field owing to its excellent enhancement on the sealing and fatigue life of composites assembly, but the severe damage around the ...hole caused by installation is still a huge challenge. In this paper, a three-dimensional anisotropic non-linear progressive damage model based on continuum damage mechanics was developed to reveal the damage mechanism of carbon fiber reinforced plastic (CFRP) composites interference bolting with sleeve. The proposed model adopted strain-based failure criteria and non-linear damage evolution law to predict damage initiation and propagation of composite laminates. A cohesive model taking into account the traction-separation constitutive response was employed to capture the delamination behavior between the composite plies. The elastoplastic model was utilized to characterize the sleeve's deformation behavior. Numerical simulations of different installation modes are performed and compared with experiments. The inserting load, damage modes and damage positions predicted by the proposed model agree well with the experimental results. Moreover, it is also verified that the interference installation of sleeved fasteners can remarkably reduce the intra-laminar damage and avoid the inter-laminar delamination of composite laminates compared to the conventional bolt.
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•A 3D anisotropic non-linear PDM was developed to reveal the damage mechanism of composites interference bolting with sleeve.•The model adopted strain-based failure criteria and non-linear damage evolution law to predict damage of composites.•Interference installation experiments were conducted to verify the damage behavior of composites under different modes.
Drilling-countersinking (DC) machining is one of the most popular methods for making holes with countersink in modern industry. In DC machining process of carbon fiber reinforced plastics ...(CFRP)-aluminum (Al) stacks, the force caused by each cutting edge in different materials is changing all the time and will affect the quality of holes. This paper focused on the cutting force for DC machining of CFRP-Al stacks, developed a novel cutting force model, which can represent the dynamic cutting force at any time of the DC process. The whole DC process is divided into six different states which contain drilling, reaming, and countersinking in different materials. Forces on different cutting edges are modeled on the base of the microscopic oblique cutting theory. And the dynamic cutting forces of every moment in the six-state DC machining process are integrated on base of the integral limits analysis and equivalent fiber orientation. Experiments with different cutting parameters are developed to analyze the dynamic cutting force of CFRP-Al stacks. The trend of cutting forces according to different machining parameters is similar, and the influence of different cutting edge on the cutting force will change in different state according to the result of both experiment and proposed model. The values of cutting force getting from the experiments can match with the results of dynamic model well, despite the fact that gaps between different materials will affect the change of cutting force.
This paper presents a mechanistic model for prediction of fluctuating thrust force and torque during drilling of unidirectional carbon fiber–reinforced polymer (UD-CFRP). A micro-scale model ...consisting of fiber, matrix, and fiber-matrix interface is proposed to simulate the orthogonal cutting behavior for the entire range of fiber orientation. Based on the FE model, a detailed energy analysis is conducted to quantify the various energy-absorbing mechanisms. The relationship between the percentage of each mechanism and factors such as depth of cut, tool rake angle, and fiber orientation is revealed. Afterwards, force coefficients related to these factors are obtained based on the orthogonal cutting database and used to calculate the instantaneous thrust forces and torque generated on the cutting lips, which are divided into a continuous set of infinitesimal elements conducting orthogonal cutting. Orthogonal cutting and drilling experiments with various machining parameters have been performed to validate the proposed FE and mechanistic models. Good correlation between the experimental and predicted results is found and thus the model is capable of predicting the fluctuation of thrust forces and torque for the whole drilling process.
This paper reports the modeling method and outcomes of mechanical performance and damage evolution of single-lap bolted composite interference-fit joints under extreme temperatures. The anisotropic ...continuum damage model involving thermal effects is established on continuum damage mechanics which integrates the shear nonlinearity constitutive relations characterized by Romberg-Osgood equation. The temperature-induced modification of thermal strains and material properties is incorporated in stress-strain analysis, extended 3D failure criteria and exponential damage evolution rules. The proposed model is calibrated and employed to simulate behavior of composite joints in interference fitting, bolt preloading, thermal and bearing loading processes, during which the influence of interference-fit sizes, preload levels, laminate layups and service temperatures is thoroughly investigated. The predicated interfacial behavior, bearing response and failure modes are in good agreement with experimental tests. The numerical model is even capable of reflecting some non-intuitive experimental findings such as residual stress relaxation and matrix softening at elevated temperatures.
The T800 Carbon fiber reinforced polymer/plastic (CFRP) has been increasingly used for its considerable specific strength/modules to manufacture the primary load-carrying structures in aerospace ...industry. The abrasive carbon fibers can cause rapid tool wear in CFRP drilling, which deteriorate the quality of hole wall and result in unpredictable decrease of bearing capacity. In order to effectively reduce the tool wear, a cooling method namely external cooling lubrication (ECL) is applied in this study by using two different lubricants (Boelube 70104 and Castrol Syntilo 9828). The results show that Boelube 70104 lubricant exhibits the maximum flank wear (VB) reduction (34.5%) as compared to dry drilling after drilling 30 holes. And, the maximum CER reduction (57.4%) is obtained by using Castrol Syntilo 9828 lubricant. Different from previous researches, the maximum thrust force of drilling process using ECL presents obvious decrease as compared to dry drilling. And, the value of surface roughness (Ra) exhibits an obvious decrease when using Boelube 70104 lubricant. Two main different mechanisms for Ra decrease namely reducing surface cavity at FCA of 90° <
θ
< 180° and reducing saw-tooth surfaces at FCA of 0° <
θ
< 90° are separately observed for Boelube 70104 and Castrol Syntilo 9828 separately.
Large-sized thin-walled composite structure has been widely used in aircraft due to favorable strength-to-weight ratio and stiffness-to-weight ratio. The deformation has great influence on assembly ...quality of aircraft. So, deformation prediction is essential for guaranteeing the assembly quality. The structure with complicated geometry is difficult to discretize into regular quadrilateral or hexahedron. However, the above types of element are required when using the available conventional laminate shell and continuum laminate shell elements in the commercial software. To cope with this issue, an efficient trans-scale and multi-stage approach is proposed to predict deformation of large-sized thin-walled composite structure in this paper. Firstly, the large-sized composite is divided into several sub-regions based on its lay-ups. Multi-scale homogenizations were adopted to compute the macroscale material properties of each sub-region. Then, deformation analysis on the homogenized model is conducted. During simulation, micro-stress distribution in each element is investigated by stress projection. Damage analysis was conducted with failure criteria. An assembly experiment was conducted to validate the proposed model. The numerical results are in agreement with the experiment. Deformation behaviors of composite panel under different working pressures of 0.03 MPa and 0.09 MPa are evaluated.
In this article, an Adaptive Hamiltonian-Based Energy Control (AHBEC) with a built-in integrator is introduced for the Proton-Exchange Membrane Fuel Cell (PEMFC) hybrid power-conversion system. The ...presented additional built-in integrator is based on the Lyapunov and Hamiltonian functions. Unlike previous works, the control strategy proposed in this article aims to regulate the output current of the PEMFC stack, i.e., to provide sufficient power support to the load, and the integrator is built into the control loop in order to eliminate the steady-state current error caused by external disturbances and model parameter uncertainties. The large-signal stability of the whole system is demonstrated by selecting a suitable Lyapunov-candidate function. An experimental setup is constructed in the laboratory to verify the proposed control strategy. The experimental results demonstrate the robustness and effectiveness of the designed energy-control approach.
A novel virtual material layer model based on the fractal theory was proposed to predict the natural frequencies of carbon fiber reinforced plastic composite bolted joints. Rough contact surfaces of ...composite bolted joints are modeled with this new proposed approach. Numerical and experimental modal analyses were conducted to validate the effectiveness of the proposed model. A good consistence is noted between the numerical and experimental results. To demonstrate the necessity of accurately modeling the rough contact surfaces in the prediction of natural frequencies, virtual material layer model was compared with the widely used traditional model based on the Master-Slave contact algorithm and experiments, respectively. Results show that the proposed model has a better agreement with experiments than the widely used traditional model (the prediction accuracy is raised by 8.77% when the pre-tightening torque is 0.5 N∙m). Real contact area ratio A* of three different virtual material layers were calculated. Value of A* were discussed with dimensionless load P*, fractal dimension D and fractal roughness G. This work provides a new efficient way for accurately modeling the rough contact surfaces and predicting the natural frequencies of composite bolted joints, which can be used to help engineers in the dynamic design of composite materials.
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