Mechanics of Composite Materials最新文献

A composite resin containing eggshell particles for the additive manufacturing according to the stereolithography (SLA) printing technology was studied. First, the viscosity properties of the eggshell-particle-reinforced resin were determined. Then, the effect of particle wt% on the hardness, tensile, and compressive behaviors of the composite specimens were investigated. Besides, the optical microscopy images of unreinforced and reinforced 3D printed composites were scrutinized. The cross-sections of the composite were analyzed by the energy dispersion spectrometry and optical and scanning electron microscopes (EDS/SEM) in order to examine its structure in detail. To analyze the damping properties and the elastic modulus determined in tension and free vibration tests were also carried out.

A numerical analysis of the vibration problem for the annular plates from functionally graded graphene-platelets-reinforced composites (FG-GPLRC) was carried out. Since the amount of reinforcing platelets was different in different layers of the plates, they had a stratified structure. Based on Mindlin’s theory of moderately thick plates, the differential quadrature method (DQM) was used to study their fundamental frequencies. The first five calculated natural frequencies showed that this method gives results rather well agreeing with data reported in the scientific literature. The natural frequencies of the composite annular plates were studied considering their different geometric parameters: ratios of their external dimensions, GPL weight fractions, GPL distribution patterns, and GPL dimension ratios.

The finite element analysis based on microstructure of SiCp (silicon carbide particulates) reinforced aluminum matrix composites to evaluate the dynamic mechanical response and damage behavior was carried out. The effects of strain rate, reinforcement content and reinforcement size on the stress-strain state of SiCp reinforced aluminum matrix composites and the damage mechanism were analyzed. The results show that the strain rate sensitivity of the composites is obvious, and this trend is promoted with the increase of SiCp content and the decrease of reinforcement size. The damage such as particle breakage and interface debonding was predicted, and the influence of reinforcement size on the damage mechanism was analyzed. It is found that the defects of the composites with smaller reinforcement particle size are mainly SiCp/Al interface debonding, while SiCp cracks and interface debonding are more likely to coexist in the composites with larger reinforcement size.

This study focuses on the mechanical properties of different thermoplastic polymers that have been processed by fused filament fabrication, including basic (PLA, PC, PA, ABS, PP, CPE, PET-G), industrial (PEI, PEKK), and with added functionality (thermochromic, electrostatic discharge, electrically conductive). Analysis of the porosity of specimens was performed by X-ray microtomography and optical microscopy of a fractured surface, both giving similar results. During printing, a non-equilibrium polymer macromolecular structure was created. The stiffness and strength of the printed specimens were impacted by the stabilization of the macromolecular structure over time. The maximum values were reached for amorphous materials after 24 hours and for semi-crystalline materials after 160 hours. Tensile properties of “as-received” filaments, extruded mono-fibers, and unidirectional printed specimens were compared. In most cases, the elastic modulus of “as-received” filaments was lower than that of the extruded mono-fibers by 12% on average. Loading rate significantly affects both elastic modulus and strength, confirming the essential contribution of the viscoelastic component to the whole deformability of polymers. The elastic modulus and strength increased by 20 and 80%, respectively. The effects of layer thickness and nozzle diameter on mechanical properties were investigated. The compatibility of different polymer types for hybrid structures was evaluated in the adhesion tests. Tests showed that adhesion at hybrid PLA contact is only slightly affected by the presence of colourant additives in one of the parts. However, approx. 10 times adhesion reduction was observed when one of the parts contained conductive particles.

Different methods can be applied to strengthen the weakened structure in perforated composite plates. A comparison of the four reinforcement models around the hole (ring, daisy, square and ellipse) under pure tension, pure shear, and combined (both tensile and shear loads) loadings was presented using Tsai-Wu failure criteria and calculations by finite element method (FEM). Before FEM analysis, tensile tests were performed with 12 tensile- and 6 shear-test specimens made of woven carbon fiber epoxy prepreg. During the tests of shear-test specimens, the strain distribution was obtained using the digital image correlation (DIC) method. Finite element verification was performed with both the applied force-deformation curve determined in the tensile test and the strain distribution obtained by the DIC technique. It was observed that four different reinforcement models, which have 38% volume of the created lightening hole, provide at least by 30% strength improvement to the unreinforced structure under tensile and shear loadings. Under combined loadings, according to the tensile/shear load ratio, the reinforcement types provide improvements at different rates.

Piezoelectric polymer poly(vinylidene fluoride) (PVDF) is extensively used as sensor and actuator devices owing their excellent piezoelectric and pyroelectric properties. However, the melting point of PVDF is relatively low and the service temperature of PVDF is up to 100°C. This restricts the use of PVDF in high temperature applications. This can be improved by adding appropriate fillers to the PVDF. In the present study, a composite of PVDF-Onium salt was developed and characterized to improve the thermal efficiency of PVDF for high temperature applications. In order to investigate the presence of β-phase, which is necessary for sensor applications, X-ray diffraction, scanning electron microscopy, differential scanning calorimetry, Raman and infrared spectra, and dielectric test were used to characterize PVDF-Onium salt composite films made using the solvent cast method. The melting point of PVDF-Onium salt composite was found to be higher (175°C) as compared to the PVDF polymer alone (168.2°C) which has been discussed in detail. The PVDF-Onium salt composite sensors were further tested for dynamic strain sensing application for the first time. The modes of cantilever beam vibrations and the impact loading effects were recorded in order to assess the performance of these sensors.

In the first part of the article [1], a physically and geometrically nonlinear boundary-value problem, that describes the compression of a fiber-reinforced plastic rod with [0]_s layup, was formulated. The rod had a rectangular cross-section and thin elastic side tabs. The boundary-value problem was reduced to a system of integral-algebraic equilibrium equations containing Volterra integral operators of the second type. To find its numerical solution, the method of finite sums in the variant of integrating matrices was used. The advantage of the method is the possibility of a strong local thickening of the computational grid in the region of large gradients of solutions. Based on the algorithm constructed, an application software package was developed. The results of computational experiments showed that the test specimens under compression according to one of the most commonly used test schemes predominantly failed when the localized transverse shear stresses reached their ultimate values. Failure was also possible according to the shear buckling mode in stress concentration zones. The identification of such modes was possible by using a proposed refined geometrically and physically nonlinear deformation model built in the quadratic approximation with account of transverse shear strains and transverse compression. To verify the numerical method developed, physical experiments were carried out on unidirectional carbon-fiber-reinforced specimens with [0]_s layup. They showed a good agreement between the theoretical and experimental results of the research.

The flexural response of imperfect advanced (functionally graded) composite plates was considered by using an integral-quasi-3D shear deformation (quasi-3D-HSDT) model. The impact of transverse and normal strains was integrated. The present formulation has four displacement variables-unknowns only. The defect in the material composition is taken into consideration based on the power law gradation. The four differential governing equations are extracted with the help of the virtual work principle (VWP) and Navier’s method. A range of numerical results were presented in the table and graphs forms to reveal the impact of the inhomogeneity parameter, the imperfection, the dimensions and geometric ratios on the static (flexure) response of imperfect advanced composite plates. The work most significant accomplishment was the presentation of a simple theoretical model based on a problem with the material makeup of functionally graded materials.

Biological structures, such as mantis shrimp crustacean, provide a rich source of inspiration for constructing high-performance materials with an excellent mechanical strength and impact resistance. Therefore, helicoidal structures inspired by mantis shrimp were investigated to explore the static and dynamic properties. The firstorder shear deformation theory of plates was used to describe the displacement field of laminated helicoidal composite plates. By the finite-element analysis (FEA), the bending and vibrations of bio-inspired composite plates were studied numerically using the ANSYS mechanical analysis software and the parametric design language APDL. Three classical orientations (unidirectional, cross-ply, and quasi-isotropic) and two helicoidal (linear and Fibonacci) orientations were considered. The “SHELL281” finite element of the APDL tool was exploited to solve the problem numerically with three integration points in each direction. The model proposed was verified, and its parametric studies were performed to clear up the effects of fiber orientation, slenderness ratio, and elasticity ratio on the static and free vibrations of a Bouligand composite plate. Results showed that the composite material had extraordinary mechanical properties, which is highly important for their unlimited applications in military industry and civil engineering.

A plane contact problem on the interaction of a rigid stamp with a poroelastic strip lying on a Winkler base was investigated. The deformation of the strip was modeled based on the equations of the Cowin–Nunziato poroelastic bodies theory. It was assumed that the base of the stamp has a flat or parabolic shape and there is no friction in the contact zone. With the help of the Fourier integral transformation, the problems stated were reduced to an integral equation for an unknown contact stress, which was solved with the use of the collocation and the asymptotic methods. The values of contact stresses, sizes of the contact area in the case of a parabolic stamp and the relative deformation of the surface outside the stamp were determined. A comparative analysis of the studied quantities for various values of the poroelastic strip parameters and the coefficient of subgrade resistance of the Winkler base was carried out. Numerical results are presented in the form of tables and graphs.