Mechanics of Composite Materials最新文献

The damage stages of the ballistic impact effect on both thin and thick laminated composites were investigated. Thin and thick laminated composite plates were produced with unsymmetrical cross-ply [0/90], [–45/+45], and [30/60] layups consisting of 16 and 50 unidirectional layers, respectively. Ballistic tests of the composite plates were carried out by means of a single-stage gas gun system at different velocities in the range from 447 to 861 m/s. The thin composite plates were more damaged than the thick plates at ballistic tests with the same velocity. Relatively small strains were observed at low-velocity impact while the projectile rebounded in all thick specimens. All thick plate specimens, except the plates with [–45/+45] layup, were perforated at high velocity impacts. Tests showed an increase in the shear stress between layers with increasing projectile velocity.

The mechanical properties of both polymethyl methacrylate (PMMA) and polyethylene terephthate (PET) were examined in tensile and three-point bending tests, as well as their bond and interlayer shear strengths were assessed. The results obtained were employed in computer simulation of mechanical loading of temporary removable complete dentures (TRCDs). It was shown that the variations of the elastic moduli of the dental materials studied did not exceed 15.6%; the ultimate strength of PET was higher than that of PMMA by ~2.2 times in tension and by ~1.9 times in bending. Elongation at break was greater for the PET specimens than those for the PMMA ones by ~2.3 times in tension and by ~3.1 times in bending. Computer simulation has shown that when the load was applied at the angle of 90°, the tooth fractured in all cases. Stresses were much lower in the denture base concerning the critical levels. Therefore, the adhesion conditions considered did not affect the pattern of their failure, and the critical load was the same for both denture base materials. When the load was applied to canines at the angle of 45°, the critical load was below the specified level of 100 N in the PMMA denture base due to the peculiarities of TRCD design and the lower strength of PMMA. When both canines and incisors were loaded at the angle of 45°, the PET denture base could withstand the greater critical load than the PMMA one. Both mechanical tests and computer simulation results enabled to conclude that PET is the prospect denture base material for the manufacture of TRCDs and dental orthopedic treatment.

The growing demand for unmanned aerial vehicles (UAVs) in the wide range of commercial applications has necessitated engineers to develop lightweight and economical models that are simple to manufacture. This study focuses on the analysis of UAV wing a unconventionally manufactured medium altitude long endurance (MALE) by performing transient and static fluid structure interaction analysis. The wing was made of an expanded polystyrene (EPS) foam core reinforced by a glass and carbon fiber-reinforced polymer composite. The current study utilizes the one-way fluid-structure interaction technique to obtain the pressure profile from a computational fluid dynamics study, which then is used as a load boundary condition for the static and dynamic structural analyses of an EPS-reinforced composite wing to observe its failure characteristics under loading conditions. Modeling the composite laminate was conducted in the ANSYS Composite PrePost module with varying ply orientations to obtain an optimum configuration. The topology optimization of the wing core led to a 30.5% reduction in its overall weight, offering an economical and feasible solution for manufacturing UAVs on small and medium scales.

A systematic analytical study of the mathematical properties of the previously constructed nonlinear model of the shear flow of thixotropic viscoelastic-plastic media, which takes into account the mutual influence of the deformation process and structure evolution, is carried out. A set of two nonlinear differential equations describing shear at a constant rate and stress relaxation was obtained. Assuming six material parameters and an (increasing) material function that control the model are arbitrary, the basic properties of the families of stress-strain curves at constant strain rates, stress relaxation curves (Part 2) and creep curves (Part 3) generated by the model, and the features of the evolution of the structuredness under these types of loading were analytically studied. The dependences of these curves on time, shear rate, stress level, initial strain and initial structuredness of material (for example, degree of physical crosslinking), as well as on material parameters and function governing the model, were studied. Several indicators of the model applicability are found, which are convenient to check with experimental data. It was examined what effects typical for viscoelastic-plastic media can be described by the model and what unusual effects (properties) are generated by structuredness changes in comparison to typical stress-strain, relaxation and creep curves of structurally stable materials. The analysis proved the ability of the model to describe behavior of not only liquid-like viscoelastoplastic media, but also solid-like (thickening, hardening, hardened) media: the effects of creep, relaxation, recovery, a number of typical properties of experimental relaxation curves, creep and stress-strain curves at a constant rate, strain rate and strain hardening, flow under constant stress, etc. The first part of the article is devoted to formulation of the model and preparation of basis for the second part: the proof of the uniqueness and stability of the equilibrium point of the nonlinear equations set, analytical study of the equilibrium point dependence on all material parameters, possible types of phase portraits and the properties of integral and phase curves of the model.

The dynamic behavior of a sandwich beam with a porous core and carbon nanotube-reinforced polymer facesheets subjected to a moving mass on simple supports was investigated using the quasi-3D theory of shear deformation. The system of equations was determined using the energy technique. In order to solve the equations of motion, the analytical Navier’s approach in the space domain and the numerical Newmark’s method in the time domain were employed. Additionally, the natural frequencies of the free vibrations of beam were studied and evaluated. To validate the accuracy of the results obtained, comparisons were made with existing responses for specific circumstances reported in the literature. The effect of various parameters such as carbon nanotube volume percentage, porosity coefficient and distribution pattern, ratio of geometric and dimensional parameters, speed of moving mass, and facesheet-to-core thickness ratio on the dynamic response, critical speed of moving mass, and natural frequency of the sandwich beam with a porous core and nanocomposite surfaces were investigated. The results showed that by increasing the core porosity, the natural frequencies and critical speeds were increased. Because the intrinsic holes in the core structure get bigger, the stiffness and mass of the beam decrease. However, the effect of the mass reduction is greater than the effect of the stiffness reduction, so the frequency and critical speed of the system are increased.

The bending analysis of isotropic, laminated composite and cylindrical sandwich shells was carried out using a higher order shear deformation theory which incorporates undetermined integral in the displacement field. The model proposed involves only four variables. Moreover, unlike the conventional FSDTs, the shear correction factor is not necessary. The Hamilton’s principle and the Navier’s method are employed to determine and solve the equations of motion. The present analytical model was compared with other higher-order theories in the literature. In addition, finite element analysis methods were designed to calculate displacements and stresses of shells. Shells are subjected to uniform loads. Results are given for shallow and deep shells and thick to thin. According to the analysis, kinematics, based on the indeterminate integral component, are very effective and enable researchers to investigate laminated plates and shells more accurately than traditional models.

The mechanical behavior of composites, made of an epoxy resin matrix reinforced by 30 and 40% of a satin cloth from long Alfa, sisal and hybrid Alfa/sisal fibers was studied. The fibers are obtained by extraction with elimination of binders such as pectins and lignin. For each type of fibers, appropriate and optimal chemical and thermal treatments were conducted within NaOH solution, to enhance both the fiber surface quality and the interfacial bonding between fibers and matrix. Fourier transform infrared (FTIR), scanning electron microscopy (SEM), and chemical decomposition of treated and untreated fibers lead to prove the treatment efficiency. The thermogravimetric (TGA) and differential thermogravimetric (DTG) analyses showed better thermal stability. Differential scanning calorimetry (DSC) made it possible to quantify the enthalpy changes which showed an increase in the amount of heat as a function of the increase in weight fraction of natural fibers. The endothermic reaction of the composites studied containing 30 wt% fiber reinforcement was less than that containing 40 wt% fiber reinforcement. The composite materials were produced by vacuum assisted resin transfer molding (VARTM) method due to hydrophilic nature of the fibers. The results of static tests were compared to those of pure epoxy resin. It showed a significant increase for 40 wt% woven A1lfa/epoxy of about 333, 113, and 81% in tension, 3-points bending and compression tests respectively. SEM morphology analysis revealed good interfacial adhesion between the treated fibers and the matrix.

Fiber-reinforced composite materials are increasingly used in oil and gas transmission, and joints are the areas prone to failure in pipelines. Damage evolution in the adhesive joints connecting pipes made for basalt-fiber-reinforced polymers (BFRPs) was analyzed. First, finite-element models for three types of adhesive joints (single-lap, sleeve, and scarf ones) were developed. Second, an optimal cohesive zone model (CZM) for the adhesive layer was developed based on the inverse analysis of the results of debonding experiments. Finally, the damage evolution in the adhesive joints was analyzed under internal pressure, tension, bending, and torque, and their pipeline loading capacities were evaluated. Results showed that the single-lap joint exhibited the highest ultimate load-carrying capacity at a unit overlapping length, followed by the sleeve joint, but the scarf joint had the lowest unit ultimate load. For sleeve and scarf joints, the presence of a gap or a weak interface between two pipe adherends led to a reduction in their load-carrying capacity. These findings provide a basis for the design of the composite pipe joints.

Dynamic behavior of hybrid composite shallow shell panels was analyzed utilizing a high-order shear deformation theory (HOSDT) in conjunction with the finite-element method (FEM). To enhance the suitability of plant-fiber composites and to use them as substitutes for pure synthetic-fiber composites, the hybridization of banana-epoxy and glass-epoxy composites was performed, and different sets of hybrid composites were prepared by altering the layers of glass and banana fibers. The elastic constants of these composites were evaluated experimentally and utilized in the further numerical investigation. Simultaneously, a mathematical formulation was developed based on a HOSDT and the FEM. The governing equation of a transient analysis was derived using the Hamilton’s principle and Newmark’s direct integration scheme to get responses in the time domain. First, the consistency of the present model was checked via an element convergence test, and the accuracy of the model was established by comparing the transient responses obtained from the current model with those of published data. Afterwards, different parametric investigations were carried out to explore the influence of the curvature ratio, shell geometry, hybridization, end conditions, and loading rate on the time-dependent responses of the composites.

A comparison of one-dimensional (1D) and three-dimensional (3D) models for simulating free vibrations of axially functionally graded material (AFGM) beams with non-uniform cross-sections was carried out. Both models were constructed using ABAQUS and the eigenvalue problem was solved to determine the natural frequencies and their corresponding mode shapes. User-defined material model subroutines (UMAT) were developed using 1D beam or 3D hexagonal graded finite elements to implement material gradients into appropriate finite element models. The performance of both models was evaluated using data for beams with non-uniform cross-sections and material gradation profiles for which natural frequencies were available in the literature. The accuracy and effectiveness of each modeling approach proposed were estimated by comparing the results obtained. Generally, distinctions between the 1D and 3D models become more pronounced as the geometric complexity and material inhomogeneity of AFGM beams increases, especially for high-frequency modes.