•Large amplitude vibration of FG-GPLRC annular plates is investigated.•A DQM-based iterative method is developed to obtain the nonlinear frequencies.•Dispersing more GPLs within outer layers ...decreases the nonlinear frequency ratio.•The GPL geometry has little influence on the nonlinear vibration behaviour.
This paper investigates the large amplitude vibration of functionally graded nanocomposite multilayer annular plates reinforced with graphene platelets (GPLs) in thermal environments. It is assumed that the GPL concentration varies from layer to layer across the plate thickness but remains constant in each individual GPL-reinforced composite (GPLRC) layer, whose elastic modulus is estimated by the modified Halpin-Tsai micromechanics model. Within the framework of first-order shear deformation theory and von Kármán geometric nonlinearity, the governing equations are derived by using the Hamilton’s principle and then solve by the differential quadrature method together with an iterative scheme. Numerical results are presented to show the influences of GPL geometry, distribution pattern and concentration, plate geometry, boundary conditions, as well as temperature rise on the nonlinear vibration behaviour of functionally graded GPLRC annular plates. It is found that dispersing more GPLs within the outer layers substantially decreases the nonlinear frequency ratio, while the effect of GPL geometry is insignificant.
Zeolitic imidazole frameworks (ZIFs) offer rich platforms for rational design and construction of high‐performance nonprecious‐metal oxygen reduction reaction (ORR) catalysts owing to their ...flexibility, hierarchical porous structures, and high surface area. Herein, an Fe, Cu‐coordinated ZIF‐derived carbon framework (Cu@Fe‐N‐C) with a well‐defined morphology of truncated rhombic dodecahedron is facilely prepared by introducing Fe2+ and Cu2+ during the growth of ZIF‐8, followed by pyrolysis. The obtained Cu@Fe‐N‐C, with bimetallic active sites, large surface area, high nitrogen doping level, and conductive carbon frameworks, exhibits excellent ORR performance. It displays 50 mV higher half‐wave potential (0.892 V) than that of Pt catalysts in an alkaline medium and comparable performance to Pt catalysts in an acidic medium. In addition, it also has excellent durability and methanol resistance ability in both acidic and alkaline solutions, which makes it one of the best Pt‐free catalysts reported to date for ORR. Impressively, when being employed as a cathode catalyst in zinc–air batteries, Cu@Fe‐N‐C presents a higher peak power density of 92 mW cm−2 than that of Pt/C (74 mW cm−2) as well as excellent durability.
Fe, Cu‐coordinated zeolitic imidazole framework–derived carbon framework shows a superior oxygen reduction reaction performance with a half‐wave potential of 0.892 V, 50 mV higher than Pt/C, and excellent stability, resulting from bimetallic active sites, high active N content, and the mesoporous architecture. When employed as cathode catalyst, it also displays a good Zn–air battery performance.
The cellulose microfibril in the wood cell wall possesses a functionally graded structure, the biomechanical contribution of which is unclear. At the molecular scale, we analyze the heterogeneous ...crystallinity of the microfibril and characterize its stiffness gradient with the help of molecular dynamics. The determined stiffness profile is then upscaled to the cell wall level, based on which a shear-lag analytical model is developed to reveal the load transfer mechanism in the cell wall. We find that the presence of the stiffness gradient can significantly alleviate the stress concentration on the interface by reducing the interfacial shear stress up to 70%. The analysis on the debonding procedure shows profoundly enhanced debonding resistance of the cell wall due to the graded structure. Moreover, we identify a novel “dual debonding” mode, meaning that the debonding initiates and propagates in both the edge and inner regions of the interface until the two debonded regions join each other, which is much more complex than the edge debonding mode exhibited by the conventional fiber-reinforced composites. The stress alleviating effect, together with the special debonding mode, profoundly postpones the interfacial debonding of the material, leading to a significantly enhanced debonding resistance. A discussion on the structural profile of the microfibril shows that the special “dual debonding” mode can only be achieved with specific stiffness gradients. In all, we believe our work helps to unravel the biomechanical role of the microfibril in the wood cell wall, and builds the theoretical foundation for tailoring the bio-inspired composites reinforced by functionally graded fibers.
•The graded stiffness profile of the microfibril is characterized by molecular simulations.•The graded structure is found to greatly alleviate the interfacial shear stress.•A novel “dual debonding” mode is identified in the cell wall.
•A CDM-based approach incorporating debris layer evolution is developed.•The approach is implemented in finite element analysis of fretting fatigue.•The wear profile, debris layer and fretting ...fatigue lifetime are predicted.•The effects of debris layer on the prediction results are evaluated.
A continuum damage mechanics (CDM)-based approach is proposed to investigate fretting wear and fretting fatigue behavior of Ti-6Al-4V with the consideration of debris layer evolution. An elastic-plastic-damage model is developed to calculate the stress, strain, and fatigue damage fields. The debris layer and its thickness evolution are considered in a friction energy-based wear model. Both models are implemented in a finite element package to predict the fretting wear profile and fatigue lifetime. It is found that the numerical approach with the consideration of debris layer provides more accurate predictions than that without debris layer. The effects of debris layer evolution on the fretting fatigue lifetime, wear profile, contact pressure and subsurface stress are evaluated.
A thermomechanical model is developed to predict the temperature, degree of crystallization, residual stress, and strain in the selective laser sintering process for polymeric powder. Especially, a ...transient heat transfer model is used to calculate the temperature evolution. An elastic–viscoplastic model is developed to describe the temperature- and time-dependent stress–strain behavior of polymeric materials with crystallization-induced strain being included. A crystallization model is used to predict the relative crystallization degree during the cooling process. The sintering process and cooling process of polyamide 12 are simulated using the developed model. The melt pool depth and the deformation of the printed parts are validated by the experimental results. The evolutions of the temperature, relative degree of crystallization, strain, and stress are evaluated. The effects of the cooling rate on the strain and stress evolutions are discussed.
Dynamic stability of microbeams made of functionally graded materials (FGMs) is investigated in this paper based on the modified couple stress theory and Timoshenko beam theory. This non-classical ...Timoshenko beam model contains a material length scale parameter and can interpret the size effect. The material properties of FGM microbeams are assumed to vary in the thickness direction and are estimated though Mori–Tanaka homogenization technique. The higher-order governing equations and boundary conditions are derived by using the Hamilton’s principle. The differential quadrature (DQ) method is employed to convert the governing differential equations into a linear system of Mathieu–Hill equations from which the boundary points on the unstable regions are determined by Bolotin’s method. Free vibration and static buckling are also discussed as subset problems. A parametric study is conducted to investigate the influences of the length scale parameter, gradient index and length-to-thickness ratio on the dynamic stability characteristics of FGM microbeams with hinged–hinged and clamped–clamped end supports. Results show that the size effect on the dynamic stability characteristics is significant only when the thickness of beam has a similar value to the material length scale parameter.
This paper investigates the thermo-electro-mechanical vibration of the rectangular piezoelectric nanoplate under various boundary conditions based on the nonlocal theory and the Mindlin plate theory. ...It is assumed that the piezoelectric nanoplate is subjected to a biaxial force, an external electric voltage and a uniform temperature rise. The Hamilton's principle is employed to derive the governing equations and boundary conditions, which are then discretized by using the differential quadrature (DQ) method to determine the natural frequencies and mode shapes. The detailed parametric study is conducted to examine the effect of the nonlocal parameter, thermo-electro-mechanical loadings, boundary conditions, aspect ratio and side-to-thickness ratio on the vibration behaviors.
The effect of nonlocal parameter μ on the fundamental mode shape of the electric potential ϕ⁎ of the CCCC piezoelectric nanoplate. Display omitted
•The natural frequencies are quite sensitive to the mechanical loading and electric loading.•The natural frequency is not sensitive to the thermal loading.•The nonlocal parameter has distinguished effect on mode shapes for CCCC and CCSS nanoplates.
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