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Magnesium phosphate cement (MPC) exhibits brittleness when utilized as a repair material for bridge decks. To address this issue, this study employs nano-TiO2 (NT) and a novel material (basalt fiber bar) as modifiers. A double-K fracture model is developed for the modified MPC to quantitatively evaluate the enhancement of fracture toughness induced by NT and basalt fiber bars. The cracking behavior and toughening mechanisms of the NT and basalt fiber bar reinforced MPC are investigated using extended finite element theory and composite material theory. Additionally, a formula is proposed to calculate the incremental fracture toughness of NT and basalt fiber bar reinforced MPC. The results indicated that NT and basalt fiber bar can effectively enhance the ultimate bending capacity of MPC. The improvement increases with the fiber volume fraction, and noticeable bending hardening occurs when the fiber content exceeds 2%. With the same fiber volume fraction, the peak load can be increased by up to 11.7% with the addition of NT. The crack initiation toughness of the NT group without basalt fiber bars is 58% higher than that of the CC group. The content and diameter of basalt fiber bar are critical parameters affecting the toughness of the NT and basalt fiber bar reinforced MPC.

Solid-state batteries are seen as key to the development of safer and higher-energy-density batteries, by limiting flammability and enabling the use of the lithium metal anode, respectively. Composite polymer–ceramic electrolytes are a possible solution for their realization, by benefiting from the combined mechanical properties of the polymer electrolyte and the thermal stability and high conductivity of the ceramic electrolyte. In this study we used different liquid electrolyte chemistries as models for the polymer electrolytes, and evaluated the effect of adding a variety of porous and dense ceramic electrolytes on the conductivity. All the results could be modelled with the effective medium theory, allowing prediction of the conductivity of electrolyte combinations. We unambiguously determined that highly conductive porous particles act as insulators in such systems, whereas dense particles act as conductors, thereby advancing our understanding of composite electrolyte conductivity. Solid-state electrolytes are key to the development of safer and higher-energy-density batteries. Using liquid electrolyte chemistries as models for polymer electrolytes, the effect of adding a variety of porous and dense ceramic electrolytes on the conductivity is now investigated.

The current work develops a size-dependent model to provide a comprehensive analysis of static stability in doubly curved micro-panels resting on an elastic foundation. The doubly curved panel is made of advanced composites which reinforced with carbon-based materials. A seven-unknown shear deformation theory in curvilinear coordinate is combined with a non-classical approach to obtain a suitable model to get an accurate result for mechanical performance of micro-size shells. To perform this aim, a virtual work of Hamilton statement is developed and then an analytical technique on the basis of double-Fourier series is implemented for the microshell with fully simply supported conditions in edges. Results show that, CNTs reinforced composite curved shells exhibit a hardening response under buckling. It is also showed that the greatest critical buckling load of the microshell is observed for the shell with spherical panel followed by elliptical, cylindrical, and hyperbolic panels, respectively. Moreover, change of CNTs weight fraction can significantly alter the static stability characteristics of CNTs reinforced composite curved size-dependent shells.

This work analyzes the impact of porosity on the static and dynamic behaviors of laminated composite shells using a novel high-order shear deformation theory. The employed model considers five unknown variables with a new sinusoidal shear function which provides precise distribution of transversal shear stresses through the thickness direction of the shell. The porosity can occur in the structure and can reduce their mechanical properties. For this purpose, three different porosity distributions in the thickness direction are considered in this investigation, the first model has the same percentage of the micro-void in the all thickness, the second one the percentage of the porosity is higher in the upper and lower surfaces contrary the third model the porosity percentage is maximum at the means axis. The governing differentials equations are derived using Hamilton’s principle and solved by Navier’s method. In the numerical results, transversal deflection, natural frequencies and axial and shear stresses are determined for laminated composite plates and shells with porosity, to verify the exactness and effectiveness of the new shell theory and to compare the results with those of the other solutions previously published.

Understanding and analysing the complex phenomena related to elastic wave propagation has been the subject of intense research for many years and has enabled application in numerous fields of technology, including structural health monitoring (SHM).

In this study, the nonlinear forced vibration response of fiber-reinforced laminated composite beams coated with functionally graded materials (FGMs) is investigated under the combined action of aero-thermoelastic loads and a concentrated harmonic excitation. The mathematical formulation is established using the Euler–Bernoulli beam theory, where von Kármán geometric nonlinearities are taken into account, along with the modified third-order piston theory to represent aerodynamic effects. By neglecting axial inertia, the resulting set of nonlinear governing equations is simplified into a single equation. This equation is discretized through the Galerkin procedure, yielding a nonlinear ordinary differential equation. An analytical solution is, then, obtained by applying the method of multiple time scales (MTS). Furthermore, a comprehensive parametric analysis is carried out to evaluate how factors such as the power-law index, stacking sequence, temperature field, load amplitude and position, free-stream velocity, and Mach number influence both the lateral dynamic deflection and the frequency response characteristics (FRCs) of the beams, offering useful guidelines for structural design optimization.

In this article, size-dependent vibrations and the stability of moving viscoelastic axially functionally graded (AFG) nanobeams were investigated numerically and analytically, aiming at the stability enhancement of translating nanosystems. Additionally, a parametric investigation is presented to elucidate the influence of various key factors such as axial gradation of the material, viscosity coefficient, and nonlocal parameter on the stability boundaries of the system. Material characteristics of the system vary smoothly along the axial direction based on a power-law distribution function. Laplace transformation in conjunction with the Galerkin discretization scheme was implemented to obtain the natural frequencies, dynamical configuration, divergence, and flutter instability thresholds of the system. Furthermore, the critical velocity of the system was evaluated analytically. Stability maps of the system were examined, and it can be concluded that the nonlocal effect in the system can be significantly dampened by fine-tuning of axial material distribution. It was demonstrated that AFG materials can profoundly enhance the stability and dynamical response of axially moving nanosystems in comparison to homogeneous materials. The results indicate that for low and high values of the nonlocal parameter, the power index plays an opposite role in the dynamical behavior of the system. Meanwhile, it was shown that the qualitative stability of axially moving nanobeams depends on the effect of viscoelastic properties in the system, while axial grading of material has a significant role in determining the critical velocity and natural frequencies of the system.

The carboxy groups abundantly and densely present on 2,2,6,6-tetramehylpiperidine-1-oxyl radical (TEMPO)-oxidized cellulose nanofibers (TEMPO-CNFs) have been chemically modified to prepare resin composites with high thermal dimensional stability. A primary-amine-terminated polyalkylene glycol (PAG) with number-average degree of polymerization of 2222 was reacted with the carboxy groups in the TEMPO-CNFs through amide bonds at PAG amidation degrees of 22%, 44%, and 76% of the carboxy groups in the TEMPO-CNFs by changing the reaction conditions. These surface PAG-amidated TEMPO-CNFs were nanodispersed in methyl ethyl ketone (MEK), mixed with the polyurethane acrylate monomer, and PAG-amidated TEMPO-CNF/polyacrylate resin composites were prepared by ultraviolet-light curing. When PAG-amidated TEMPO-CNFs with amidation degree of 44% were used, the tensile modulus and thermal dimensional stability of the PAG-amidated TEMPO-CNF/polyacrylate resin composite remarkably improved. This was because the TEMPO-CNF elements were homogeneously distributed in the polyacrylate resin matrix, which was confirmed by atomic force microscopy observation and percolation theory. In contrast, when epoxy resin was used as the composite matrix, the above PAG-amidated TEMPO-CNFs did not have high thermal dimensional stability. However, when a dual surface-modified TEMPO-CNF sample containing phenyl amides and PAG-ammonium/carboxylate salt structures at amidation and amine/carboxylate salt formation degrees of 80% and 6% of the carboxy groups in the TEMPO-CNFs, respectively, the thermal dimensional stability of the neat epoxy resin remarkably improved. Thus, the carboxy groups on the TEMPO-CNF surfaces have to be suitably modified, such as by PAG amide or phenyl amide/PAG-ammonium salt dual structures, depending on the matrix resin used. Graphic abstract

Triple-layered composite plates are created by joining three composite layers using shear connectors. These layers, which are assumed to be always in contact and able to move relatively to each other during deformation, could be the same or different in geometric dimensions and material. They are applied in various engineering fields such as ship-building, aircraft wing manufacturing, etc. However, there are only a few publications regarding the calculation of this kind of plate. This paper proposes novel equations, which utilize Mindlin’s theory and finite element modelling to simulate the forced vibration of triple-layered composite plates with layers connected by shear connectors subjected to a moving load. Moreover, a Matlab computation program is introduced to verify the reliability of the proposed equations, as well as the influence of some parameters, such as boundary conditions, the rigidity of the shear connector, thickness-to-length ratio, and the moving load velocity on the dynamic response of the composite plate.

This paper deals with an important issue, which is the influence of failure caused by the quality of matrix post-curing on the strength of complex and difficult materials of the “new generation” such as fibre composites, particularly with a polymer matrix. In recent years, significant advances in the field of adhesive materials chemistry have led to the constant development of bonding technology. The effectiveness of bonding depends, to a large extent, on the suitable selection of the adhesive and the use of appropriate surface treatment technology. It is difficult to imagine virtually any modern industry without adhesive joints, be it the aircraft, aerospace or automotive industries, which simultaneously highlights the great importance of adhesives and adhesive materials for the present-day economy. In modern technology, it is extremely important to obtain the right combination of modern construction materials. The statistical analysis of the components showed the complexity of the layered composite structure. The proposed model of the weakest micro-volume developed in this study indirectly reflects the experimentally based curing variables that affect the stresses of the components in the composite (laminate) structure. The strength of fibrous composite structures based on the Markov chain theory considers technological aspects during hardening. The model proposed in the paper was validated on the basis of examples from the literature and experimental data obtained in the research project. The numerical results are in good agreement with the literature database and measurement data. The presented model could be a novel method, which allows better insight into the curing process of epoxy resins.