Mechanics of Composite Materials最新文献

Lignocellulose fillers, like cotton stalks, provide a stiffness that enhances the mechanical properties of composites. However, finding an appropriate filler loading for optimizing the mechanical performance of biocomposites remains a challenge, as there are disparities in the optimum filler loadings found in previous studies concerning the use of cotton stalk as a filler in biocomposite manufacturing. Therefore, the need for further investigations is of prime importance. Cotton-stalk-filler-reinforced high-density polyethylene (CS/HDPE) biocomposites were fabricated with different weight proportions (10-50 wt%) of the cotton stalk filler with particle size distributions 425 to 53 μm. The biocomposites were prepared using an extrusion process with a twin-screw extruder followed by compression molding in an electrically heated platen press. Results showed that the composite reinforced with 50 wt% filler gave the optimum values of tensile and flexural moduli.

The low-cycle fatigue behavior of woven intraply carbon/Kevlar reinforced epoxy hybrid composites below ambient temperatures at 0, –5, and –10°C was investigated. Samples of woven intraply carbon/Kevlar reinforced hybrid composites were fabricated by means of vacuum infusion technique and tested for stress-controlled constant amplitude fatigue tests at stress ratio of 1 and 10 Hz within stress range of 60 to 90% of its tensile strength. The correlation between the elastic modulus and strength with the fatigue performance was established. Fatigue results showed linearized fatigue curves with larger scatter observed at –5 and –10°C. Using the maximum likelihood estimation (MLE), the life degradation rate at sub-zero temperature decreased from 5.2 to ~ 3% of its ultimate tensile strength. An inverse correlation between the degradation rate and the tensile strength was observed. In addition, surface temperatures were monitored during the fatigue cycles, and it was found that self-heating was significantly influenced by the fiber structures and its stiffening properties. At lower temperature, the heat generation also found to be influenced by the tensile modulus but did not affect the material fatigue properties.

The experimental and numerical studies of carbon composite sandwich panels with stiffened polyurethane (PU) foam core were carried out. A novel concept of stiffening the panels by co-bonding to skin was introduced. The stiffening of PU core was conceptualized using carbon composite by wrapping and skin/facesheet was co-bonded. Four different sandwich panel configurations such as plain, longitudinal stiffening, transverse stiffening, and stiffening in both directions were manufactured. To explore the suitability of this novel concept for structural applications, the bending behavior of panels were investigated under three-point bend tests. A three-dimensional finite element model incorporating stiffness degradation concept was developed in ANSYS to understand the fundamental behavior of configured panels. Experimental and numerical results showed failure patterns like shear in foam core, indentation in composite skin and bulge/lift-off of outer composite stiffener. Comparative study of results showed that oriented stiffened sandwich panels have superior mechanical characteristics with 75% increase in the load-bearing capacity and 29% reduction in displacement. The failure patterns were envisaged through microscopy and computer-based tomography techniques.

The energy dissipation and stress-strain characteristics, and characteristic stresses, namely the crack initiation σ_ci , dilatancy σ_cd , and peak σ_f stresses, of polypropylene fiber-reinforced recycled concrete under uniaxial compression were studied. According to the research results, the crack initiation and peak stresses of the specimen with single-blend polypropylene coarse fiber (No. 3) and the specimens with mixed-blend coarse and fine polypropylene fibers (No. 4 and No. 5) are higher than those of the specimen with single-blend fine fiber and plain concrete. The analysis of the energy characteristics and failure mechanism of polypropylene fiber-reinforced recycled concrete during loading based on the principle of energy conservation showed that the total strain energy, elastic strain energy, and dissipation energy absorbed per unit volume increase with the blending of polypropylene fiber. The strain energy and elastic strain energy of coarse aggregates with a 5-10 to 10-20 mm coarse aggregate size ratios of 5:5 are higher than those of 4:6 and 6:4. It was found that the continuous blending of polypropylene fiber increases the elastic strain energy, causing the point at which the dissipation energy exceeds the elastic strain energy move further and further back. The position where the dissipation energy exceeds the elastic strain energy can be used to evaluate the blending effect of polypropylene fiber. The further back the position, the better the blending effect.

Within the framework of the nonlocal strain gradient and the Euler–Bernoulli beam theories, a model of electrostatically actuated functionally graded (FG) microbeams is developed taking into account the intermolecular interaction forces in it. In addition to the electrostatic forces resulting from the applied DC voltage between a fixed substrate and the FG microbeam, the Casimir and van der Waals forces were also considered. The governing equation of motion of FG microbeams was derived by employing the Hamilton principle. Utilizing the Galerkin and the equivalent linearization methods, an analytical solution was obtained for the nonlinear vibration problem with zero initial conditions. To validate the accuracy of the results obtained, our solution was compared with the numerical and analytic solutions published in the literature.

A promising mathematical model is considered for studying the aeroelastic stability of sandwich shells supported by an internal hollow elastic cylinder and annular ribs. Using the relations derived, the influence of thickness of the inner hollow cylinder, the length of the shell, and the shear modulus of core on the critical air flow speed leading to the occurrence of flutter was studied. Based on the calculations performed, recommendations were developed for choosing parameters of the sandwich composite structure considered. The mathematical model presented makes it possible to expand the range of topical scientific and applied problems that can be solved in the field of aeroelastic stability of sandwich shells.

The problem of forced bending vibrations of a plane rod with a finite-length fastening section under the action of an external transverse force at its free end was solved. The classical Kirchhoff–Love model in the classical geometrically nonlinear approximation was used to describe the deformation process of the free part of the rod. The deformation of its fixed part was described by the Timoshenko refined shear model that takes into account transverse strains. The conditions of kinematic conjugation of the free and fixed parts of the rod were formulated. The equations of motion, the corresponding boundary conditions, and the force conditions of conjugation of the rod parts were obtained using the Hamilton–Ostrogradsky variational principle. An exact analytical solution of the problem of forced vibrations of a rod under the action of a harmonic transverse force at the free end of the unfastened part of the rod was deduced. Numerical experiments were carried out to study the resonant vibrations of rods made of unidirectional fiber composite. The effect of a noticeable increase of the amplitudes of transverse vibrations of the ends of the cantilever parts of the rods studied due to transverse contraction of the fixed section was revealed. Taking into account the transverse contraction caused an almost twofold reduction of the maximum transverse shear stresses in the fixed part of the duralumin rod.

The main, well-known scientific results were obtained by outstanding scientist Yu. N. Rabotnov in the field of creep theory, hereditary elasticity, damage mechanics, technical theory of shells. However, in the last years of his life, the academician Yu. N. Rabotnov was keen on some problems in the field of mechanics of fiber-reinforced composite materials. He proposed new, original strength criteria, simplified methods for ply-by-ply calculation of composite laminates. One of Yu. N. Rabotnov’s scientific passions were connected with description of specific fracture modes of layered fibrous composites having the types of delamination and splitting. On the base of energy fracture criterion, it’s possible to estimate the scale effect of strength – the dependence of critical stresses on the absolute sizes of composite members. Such models of specific fracture modes make it possible to estimate the danger of such technological defects as thin polymeric film between composite layers.

The aim of the present study is to use beech wood flour (WF) and expanded ethylene vinyl acetate (EVA) copolymer industrial waste to develop a sustainable composite and its production method for further engineering use. Polyamide (PA) powder waste obtained after multiple selective laser sintering (SLS) thermal cycles was used to increase the strength and adhesion between the waste composite components. The morphological, mechanical, and thermal properties of the EVA/WF composites were characterised along with their interfacial wetting and water absorption properties. Optical and electron microscopy investigations revealed that the composites prepared have homogeneous dispersion and good interfacial adhesion between EVA and wood. The addition of SLS waste PA powder increases the strength and stiffness of the composite developed. The composite with 40 wt% WF exhibited the best water absorption, mechanical properties, and processability among the various compositions. The sustainable composite proposed can replace commercially available materials, which helps to save resources and reduce waste.

A new analytical study for nonlinear buckling and postbuckling behavior of porous functionally graded material (FGM) circular plates and shallow spherical caps resting on nonlinear elastic foundation was carried put using the nonlinear Reddy’s higher-order shear deformation theory (HSDT). The spherical caps/circular plates under thermo-mechanical loadings were considered, and the nonlinear elastic foundation was used to model the behavior of hardening and softening foundations. The total potential energy expressions of caps/plates were established, and the Ritz energy method was applied. The analytical expressions of load-deflection relationships were obtained. The critical buckling loads and postbuckling behavior of shells/plates were determined and analyzed. The remarkable influences of geometrical parameters, material parameters, and nonlinear foundation stiffnesses on the nonlinear static stability behavior of caps and circular plates were noted.