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This article presents a theoretical analysis on the multiple equilibria of pinned functionally graded porous graphene platelet reinforced composite (FGP-GPLRC) circular arches subjected to a half-span distributed radial load. The effective material properties of the arch with different porosity distribution modes are approximated via a modified Halpin–Tsai micromechanical model. The decoupled neutral-plane-based governing equations are then built in the framework of the principle of minimum potential energy, from which analytical solutions for the radial displacement at an arbitrary point on the arch axis are derived. Utilizing a perturbation method, the possible buckling modes are discussed. The complete buckling evolution process of bending moment and vertical displacement are followed, meanwhile the critical geometrical parameters that control buckling behaviors switching are identified. To validate the presented analytical solutions, Finite element (FE) analysis is carried out. An in-depth parameter analysis is performed subsequently to evaluate the fluences of porosity distributions, GPL weight fraction, and porosity coefficient on the multiple equilibria path of arches. It was found that the pinned FGP-GPLRC arches could buckle only in a limit point mode under a half-span distributed radial load. When λ ≥ 8.36 , the multiple equilibria phenomenon occurs and the external force corresponding to inflexion point vanishes. [ABSTRACT FROM AUTHOR]

This paper introduces a novel numerical method for investigating the dynamic stability of a flutter panel exposed to a supersonic gas flow and a fluctuating axial excitation force. Initially, the system equation of motion was derived using Lagrange’s equation, where the first two modes are coupled Mathieu–Hill equations with damping, constituting a system of linear second-order differential equations with periodically variable coefficients. Subsequently, a new numerical method was proposed to analyze the dynamic stability of coupled Mathieu–Hill equations with damping. This method involves breaking down an arbitrary parametric load into discrete segments to approximate the variable excitation function using a step function. The system responses of each segment are then accumulated in matrix form. The proposed numerical method proves particularly effective for dynamic systems whose parameters cannot be treated as small. In practical application, the method allows the construction of instability regions corresponding to natural frequencies, subharmonics, and combination frequencies. Dynamic stability diagrams were generated based on dynamic pressure ratio, air/panel density ratio, Mach number, panel thickness—length ratio, and excitation frequency. The results demonstrated general agreement with those obtained through Hsu’s perturbation method, however, our numerical results have proven more accurate. The paper concludes by offering suggestions for suppressing panel flutter through appropriate parameter combinations. [ABSTRACT FROM AUTHOR]

This article investigates the out-of-plane buckling of functionally graded porous I-shaped circular arches with graphene platelets reinforcements in a uniform temperature field. The accurate expressions of the prebuckling internal forces owing to thermal expansion are derived. The theoretical out-of-plane buckling temperature difference is obtained by the Ritz technique and is verified by finite element results. Notably, with the asymmetrical distribution of pores along the height of the section, the monosymmetry parameter is considered in the out-of-plane buckling energy equation. The effects of graphene platelets weight fraction, porosity coefficient, and porosity distribution patterns on buckling temperature difference are analyzed in detailed. [ABSTRACT FROM AUTHOR]

Using oyster shell powder (OSP) to prepare magnesium phosphate cement (MPC) not only reduces the pollution caused by the wasted oyster shell disposal, but also benefits the development of more environmentally friendly cement. The effect of OSP on the hydration and strength development of MPC was studied. An axial compression experiment including 45 cuboid specimens was executed to investigate the compressive strength, failure mode, stress–strain relationship, and energy absorption of MPC mixing with different mass contents (0% to 12%) of OSP over the curing times of 7, 14, and 28 days. Scanning electron microscopy, X-ray diffraction and energy dispersive spectroscopy were utilized for measuring the variation of MPC microstructure and hydration products caused by OSP. Results indicated that a new reactant CaHPO4·2H2O was formed, which optimized matrix strength. The substitution of OSP could reduce the cost of MPC by 2–9% without decreasing the strength. Compared with MPC without OSP, the compressive strength of the specimen with 3% OSP is increased by 6%. However, with the continuous increase of OSP, the compressive strength gradually decreases. Similarly, the elastic modulus of MPC increases first and then decreases with the increase of OSP. [ABSTRACT FROM AUTHOR]

Microplastics and nanoplastics are emerging pollutants of concern in the aquatic environment that are causing increasing global environmental and human health problems. Although there has been extensive research on microplastics and nanoplastics, little has been said about the differences in their behavior in the aquatic environment, and many studies have considered them as the same class of hazardous materials; but in fact, microplastics and nanoplastics should be considered as two different types of environmentally hazardous materials. In this review, we propose that microplastics and nanoplastics behave in the aquatic environment in a size-dependent manner and should be distinguished. And we systematically analyzed the differences in the behavior of microplastics and nanoplastics in the aquatic environment in terms of five aspects: 1) distribution behavior; 2) adsorption behavior; 3) reaction with natural colloids; 4) aging and leaching behavior; 5) interaction with organisms. This paper has been written to draw academic attention to the different behaviors of microplastics and nanoplastics in the aquatic environment in order to distinguish between their effects on humans and the environment., Competing Interests: The authors declare no competing financial interest., (© 2024 The Authors. Co-published by Research Center for Eco-Environmental Sciences, Chinese Academy of Sciences, and American Chemical Society.)