Explore the vast range of titles available.

The stiffness and vibration characteristics of the face sheets strongly influence the mechanical performance of sandwich beams. Reinforcing these layers with advanced nanomaterials has been demonstrated to enhance stiffness and effectively suppress vibrations. Recently, graphene-based metamaterials have attracted attention due to their exceptional mechanical properties and tunable behavior, enabling the design of lightweight, high-stiffness, and vibration-resistant structures for critical engineering applications. This work presents a benchmark study for the vibration behavior of a sandwich beam composed of composite face sheets reinforced with graphene platelets (GPL) and graphene origami auxetic metamaterials (GOAM), as well as porous or tetra-chiral aesthetic cores, in which it exhibits a zero Poisson’s ratio. The innovations of this work include the investigation of graphene origami auxetic metamaterials as reinforcement and a comparison of their effect with that of graphene platelets on the vibrations of a sandwich structure. Another innovation of this work is the investigation of two types of sinusoidal displacement fields and their comparison in terms of effect on the vibrations of sandwich structures. In addition, another novelty of the present study is the comparison of six sandwich structures with various cores and reinforcements in the face sheet. Hamilton’s principle is used to derive the governing equations of motion, which are then developed using displacement fields based on two types of sinusoidal shear deformation theories. Also, these equations are solved using trigonometric functions for various boundary conditions, such as clamped and simply supported at two ends. Various porosity patterns are considered in the study, although reinforcement is only used for the face sheets. A thorough parametric analysis shows how the Young’s modulus of the reinforcing material, wave number, length, and width of graphene platelets, temperature change, porosity type and distribution, core-to-face thickness ratio, and aspect ratio impact the natural frequencies. The findings show that fundamental natural frequencies decline as aspect ratio, porosity, and core-to-face thickness ratio increase. In contrast, distribution 2 of porous core generates greater frequencies than the 1 and 3 patterns. An increase in temperature and the folding degree (HGR) of graphene origami auxetic metamaterials reduces natural frequencies, while this result is observed for the weight% of GOAM nanoparticles (WGOAM ). Predicted frequencies are demonstrated to be significantly impacted by the difference between the two sinusoidal displacement fields. These findings indicate that graphene origami auxetic metamaterials, with their tunable Young’s modulus controlled by folding degree and temperature, can enable smart, adaptive, and high-performance sandwich structures, offering transformative potential for vibration-resistant and lightweight applications. These results demonstrate the importance of nanomaterial reinforcement and well-designed porosity in enhancing the dynamic performance of sandwich beams, providing valuable insights for creating lightweight, highly stiff, and vibration-resistant structures in civil, automotive, and aerospace engineering applications.HighlightsVibration analysis of a sandwich beam based on two types of sinusoidal shear deformation theories is studied.Based on a micromechanical model including Halpin-Tsai and the rule of mixture, GPL as reinforcement is considered.The GOAM as reinforcement by considering the folding degree (HGR), weight fraction, and temperature is investigated.Three types of porous core with distributions 1, 2, and 3 are employed.A tetra-chiral aesthetic material with zero Poisson’s ratio for the core of a sandwich beam is used.

In the present study, we analyze the nonlinear forced vibration of thin-walled metal foam cylindrical shells reinforced with functionally graded graphene platelets. Attention is focused on the 1:1:1:2 internal resonances, which is detected to exist in this novel nanocomposite structure. Three kinds of porosity distribution and different kinds of graphene platelet distribution are considered. The equations of motion and the compatibility equation are deduced according to the Donnell’s nonlinear shell theory. The stress function is introduced, and then, the four-degree-of-freedom nonlinear ordinary differential equations (ODEs) are obtained via the Galerkin method. The numerical analysis of nonlinear forced vibration responses is presented by using the pseudo-arclength continuation technique. The present results are validated by comparison with those in existing literature for special cases. Results demonstrate that the amplitude–frequency relations of the system are very complex due to the 1:1:1:2 internal resonances. Porosity distribution and graphene platelet (GPL) distribution influence obviously the nonlinear behavior of the shells. We also found that the inclusion of graphene platelets in the shells weakens the nonlinear coupling effect. Moreover, the effects of the porosity coefficient and GPL weight fraction on the nonlinear dynamical response are strongly related to the porosity distribution as well as graphene platelet distribution.

Epoxy nanocomposites reinforced with various grades of multilayer graphene nanoplatelets (GNPs) are manufactured and tested. The effects of size, surface area, and concentration of GNP, as well as alternating current (AC) frequency on the electrical and dielectric properties of epoxy nanocomposites are experimentally investigated. GNPs with larger size and surface area are always beneficial to increase the electrical conductivity of the composites. However, their effects on the dielectric constant are highly dependent on GNP concentration and AC frequency. At lower GNP concentration, the dielectric constant increases proportionally with the increase in GNP size, while decreasing as the AC frequency increases. At higher GNP concentration in epoxy, the dielectric constant first increases with the increase of the GNP size, but decreases thereafter. This trend is also observed for varying the processed GNP surface area on the dielectric constant. Moreover, the variations of the electrical conductivity and dielectric constant with the GNP concentration and AC frequency are then correlated with the measured interfiller spacing and GNP diameter.

The primary resonance and nonlinear vibrations of the functionally graded graphene platelet (FGGP)-reinforced rotating pretwisted composite blade under combined the external and multiple parametric excitations are investigated with three different distribution patterns. The FGGP-reinforced rotating pretwisted composite blade is simplified to the rotating pretwisted composite cantilever plate reinforced by the functionally graded graphene platelet. It is novel to simplify the leakage of the airflow in the tip clearance to the non-uniform axial excitation. The rotating speed of the steady state adding a small periodic perturbation is considered. The aerodynamic load subjecting to the surface of the plate is simulated as the transverse excitation. Utilizing the first-order shear deformation theory, von Karman nonlinear geometric relationship, Lagrange equation and mode functions satisfying the boundary conditions, three-degree-of-freedom nonlinear ordinary differential equations of motion are derived for the FGGP-reinforced rotating pretwisted composite cantilever plate under combined the external and multiple parametric excitations. The primary resonance and nonlinear dynamic behaviors of the FGGP-reinforced rotating pretwisted composite cantilever plate are analyzed by Runge–Kutta method. The amplitude–frequency response curves, force–frequency response curves, bifurcation diagrams, maximum Lyapunov exponent, phase portraits, waveforms and Poincare map are obtained to investigate the nonlinear dynamic responses of the FGGP-reinforced rotating pretwisted composite cantilever plate under combined the external and multiple parametric excitations.

Investigated in this paper is the nonlinear forced vibration response of axially moving graphene platelet-reinforced metal foams (GPLRMF) conical shells. According to Reddy’s high-order shear deformation theory and von Karman’s geometric nonlinearity, the governing equations with highly nonlinear terms for the GPLRMF conical shells are obtained and discretized by Galerkin principle. Subsequently, considering the simply supported boundary condition, the multiple scale method is employed to determine the amplitude-frequency response curves of GPLRMF conical shells. Numerical analyses are performed to verify the correctness of present method. In the end, the effects of porosity distribution form, graphene platelets (GPLs) distribution pattern, damping coefficient, porosity coefficient, coning angle, GPLs weight fraction, geometrical dimensions and the position of the external load, axially moving velocity as well as pre-stressing force on the nonlinear-forced vibration response curves of the GPLRMF conical shells are presented.

Technological development in latent heat storage (LHS) systems is essential for energy security and energy management for both renewable and non-renewable sources. In this article, numerical analyses on a shell-and-tube-based LHS system with coupled thermal enhancement through extended fins and nano-additives are conducted to propose optimal combinations for guaranteed higher discharging rate, enthalpy capacity and thermal distribution. Transient numerical simulations of fourteen scenarios with varied combinations are investigated in three-dimensional computational models. The shell-and-tube includes paraffin as phase change material (PCM), longitudinal, radial and wire-wound fins and graphene nano-platelets (GNP) as extended fins and nano-additives, respectively. The extended fins have demonstrated better effectiveness than nano-additives. For instance, the discharging durations for paraffin with longitudinal, radial and wire-wound fins are shortened by 88.76%, 95.13% and 96.44% as compared to 39.33% for paraffin with 2.5% GNP. The combined strengths of extended fins and nano-additives have indicated further enhancement in neutralising the insulative resistance and stratification of paraffin. However, the increase in volume fraction from 1% to 3% and 5% is rather detrimental to the total enthalpy capacity. Hence, the novel designed wire-wound fins with both base paraffin and paraffin with 1% GNP are proposed as optimal candidates owing to their significantly higher heat transfer potentials. The proposed novel designed configuration can retrieve 11.15 MJ of thermal enthalpy in 1.08 h as compared to 44.5 h for paraffin in a conventional shell-and-tube without fins. In addition, the proposed novel designed LHS systems have prolonged service life with zero maintenance and flexible scalability to meet both medium and large-scale energy storage demands.

In this study, a nonlinear energy sink (NES) is used to suppress the nonlinear aeroelastic response of graphene platelet reinforced composite (GPLRC) lattice sandwich plates in a supersonic airflow for the first time. The face sheets and lattice core trusses of lattice sandwich plates were reinforced with graphene platelets (GPLs). The effective elastic modulus of the GPLRC was solved using the Halpin–Tsai micromechanical model, and Poisson's ratio, mass density, and coefficient of thermal expansion were calculated using the rule of mixtures. Kirchhoff plate and first-order shear deformation theories were used separately to model the face sheets and lattice core layer of the structure. The nonlinear strain–displacement relationship was derived using the von Karman large-deformation theory. The aerodynamic load was simulated using the piston theory. The motion equations of the supported GPLRC lattice sandwich plates with an NES under supersonic flow were derived using the Lagrange equation and the assumed mode method. The nonlinear aeroelastic responses of the GPLRC lattice sandwich plate system coupled with an NES were solved using Newmark direct integration combined with the Newton–Raphson iteration technique. Finally, a detailed study of the effects of the NES on the suppression of the flutter behavior of GPLRC lattice sandwich plates was carried out. The results showed that within specific mass, damping, and nonlinear stiffness ranges, the NES could effectively suppress the nonlinear aeroelastic response of the GPLRC lattice sandwich plates.

Due to the harsh service environment and multiple loads, studying the nonlinear vibration characteristics of rotating blades under complex loads is necessary. The new axial force model assumed as a combined force including the non-uniform aerodynamic force in the tip clearance and blade-casing local rubbing force is proposed for the first time in this paper. The nonlinear analysis of a rotating pre-twisted composite blade reinforced with functionally graded graphene platelet (FGGP) is investigated under axial and transverse excitations. The blade is treated as FGGP-reinforced rotating twisted cantilever plate. The transverse excitation caused by subsonic airflow is derived by using the vortex lattice method. The blade-casing local rubbing and non-uniform axial force dynamic change when the blade is rotating. Based on von-Karman nonlinear geometric assumptions and Lagrange equation, the governing equations of motion for the FGGP-reinforced rotating twisted plate are derived. The averaged equations under the case of primary resonance and 1:2 internal resonance are obtained by the multiple scale method. Comparisons of frequencies and modes in the present method are carried out. The results are in good agreement with other literature. The amplitude–frequency and amplitude–force curves, bifurcations, and chaotic motions of the FGGP-reinforced rotating twisted cantilever plate under axial and transverse excitations are discussed. The results show that the nonlinear vibrations are complex when 1:2 internal resonance and primary resonance of the FGGP-reinforced rotating twisted composite blade occur. The amplitude of the blade is higher with the bigger axial force. At the same time, with the increase of axial force and incoming flow speed, the motion of the blade changes from periodic to chaotic. The interesting phenomena of inverse period-doubling bifurcations are found.

The present work pays attention to the primary resonance of axially moving graphene-reinforced mental foam (GPLRMF) cylindrical shells with geometric imperfection. Porosities and graphene platelets (GPLs) are uniformly or non-uniformly distributed along the thickness direction of the cylindrical shell. Considering the influences of initial geometric imperfection and axial velocity, the equivalent elastic modulus is calculated by Halpin–Tsai model, and the equivalent density and Poisson’s ratio are described by the mixture rule. Using the energy principle, the nonlinear equations of motion are derived. Considering two different boundary conditions, the nonlinear primary resonance response is obtained using the modified Lindstedt Poincare (MLP) method. The results indicate that the MLP method can effectively overcome the limitation of traditional perturbation method. In the end, we study the effects of the GPLs distribution patterns, GPLs weight fraction, the porosity coefficient, axial velocity, initial geometric imperfection, and the prestressing force on the resonance problems. It can be found that the presence of initial geometric imperfection can alter the frequency response curve from the characteristics of the hard spring to the soft spring.

Graphene platelets were chemically modified in a reflux reaction with stearic and oleic acids. Examination of the surface features of the graphene platelets before and after modification by infrared spectroscopy and ultraviolet–visible spectrophotometer revealed that the modification led to an improvement in the dispersion of graphene platelets in base oil. The tribological behavior of the lubricating oil containing modified graphene platelets (MGP) was further investigated using a four-ball machine. The results indicated that the oil containing only 0.075 wt% of MGP clearly improved the wear resistance and load-carrying capacity of the machine. Scanning electron microscopy and energy dispersive spectrometer performed to analyze the wear scar surfaces after friction confirmed that the outstanding lubrication performance of MGP could be attributed to their small size and extremely thin laminated structure, which allow the MGP to easily enter the contact area, thereby preventing the rough surfaces from coming into direct contact.