نشریه علوم و فناوری کامپوزیت
سال نهم شماره 2 (پیاپی 32، تابستان 1401)

In this paper, the profile of the longitudinal and transverse sections of a submarine, which is located at a certain depth, based on the hydrodynamic pressure imposed on the submarine body by the fluid flow, from a structural point of view and considering the buckling resistance of the body under external pressure optimized. The calculation of hydrodynamic pressure has done using computational fluid dynamics analysis and body geometry optimization using ANSYS Workbench software. The pressure body of the submarine withstands almost the most pressure and hence it is considered to be made of polymer based composite material. Considering that the studied geometry and the type of loading (hydrodynamic load) in this article are complex, and analytical relationships for stress analysis are not available in this research, buckling is obtained using software calculations and by performing submarine stress analysis with the desired initial geometry, forces and stresses applied to the body have been calculated and hydrodynamically and structurally studied. Assuming 12 geometrical variables and minimizing weight and drag force as objective functions, by optimization methods, optimal longitudinal and transverse profile and this process is repeated until the desired values are reached. The results obtained in this article indicate that the use of non-circular shapes such as pseudo-ellipses in the design and construction of submarines can replace circular sections

According to the structure of sandwich panels, different failure modes occur during periodic loading in these structures. When the effect of these modes on each other is considered the predictions will be more accurate. In this research, a new tool presented with the help of the combination of USDFLD and UMAT subroutine in the Abaqus software to see the mutual fatigue effect of the face and the delamination between the face and the core using the existing models. This tool is used to fatigue analysis of a sandwich beam with a PVC core with different stiffness and AS4/3501-6 composite faces with [0]4, [90]4 layup. The delamination between the face and the core is analyzed by cohesive zone model and the face fatigue by an energy-based model simultaneously. The results showed that with the increase of the core stiffness, the delamination between the face and the core, caused by fatigue, begins later and moves towards the free edges of the plate. It was also observed that the failure mode that controls the life of this structure is the delamination between the face and the core. The results show the decrease in the growth rate of the damage parameter in the cohesive zone for specified element, increase of the crack growth rate and growth rate of the damage parameter in the face during loading.

In this paper, a developed micromechanical model to predict the effective electrical conductivity of polymer nanocomposites containing carbon nanotubes was presented. This model was based on mean field theory and considering the quantum tunneling phenomenon of electrons between nanofillers. Carbon nanotube was assumed to be cylindrical, which was covered by an interphase layer. Carbon nanotubes were randomly distributed and oriented inside the polymer matrix. The effect of various parameters such as the geometric dimensions of carbon nanotubes, their aspect ratio, the thickness of the interphase layer, the quantum tunneling of electrons, the conductivity of the polymer matrix, the conductivity of carbon nanotubes and the conductivity of the interphase layer on the effective conductivity of the nanocomposite were considered in the theoretical model. The presented model reproduced the electrical behavior of nanocomposites in the insulating region, the percolation region, and the metal region, as well as the sharp transition of conductivity or the beginning of percolation and the metal region in high volume fractions. The results showed that by increasing the size of carbon nanotubes in nanocomposite, the percolation threshold decreased. The conductivity values of the filler and the matrix, respectively, only affected the metal and insulation areas. Finally, the present model was used to reproduce the experimental reported data that the predicted results were in good agreement with the experimental data.

Composites are materials with at least two combined materials, one of which is added to the base material to increase its valuable properties. This study is also about one of the widely used composites called aluminum metal matrix composites (Al-MMC) and additional reinforcing materials, including Tin and Silicon carbide (SiC, Sn) particles. These composites have excellent features such as high hardness and strength and are lightweight, while they also pose low machinability. As a result, to improve the current conditions, this study was conducted with the approach of Al520 base composite machining and statistical analysis of the effect of cutting parameters on tool flank wear and surface quality after machining. Based on the investigations, it can be concluded that the defined cutting parameters had an excellent and good effect on tool flank wear. On the other hand, when studying the tool flank wear during the machining of such composites with reinforcing particles of SiC, Sn, the cutting speed always has the most significant effect, and the feed rate and lubrication method, as well as the amount of depth of cut, have the least effects on the flank wear size.

This paper investigates the mechanical performance and energy absorption capacity of bi-material three-dimensional lattice structures via experimental and numerical approaches. At first, fused deposition modeling was used to manufacture the outer part of the proposed three-dimensional lattice structure with TPU material. Using a syringe, epoxy resin is injected into the inner part of the manufactured lattice structure. Then, quasi-static compression tests were conducted to analyze the mechanical properties and energy absorption capacity of the bi-material three-dimensional lattice structure. As the nonlinear numerical study, the elasto-plasto-damage behavior was implemented in finite element analyses which track the nonlinear response of considered structures. This model is capable to investigate the differences in tensile and compressive properties of the materials as well. The comparison of the load-displacement curve of structures under compressive loading has been compared. The numerical models exhibit an acceptable prediction about the linear and nonlinear responses of the proposed three-dimensional lattice structure. The results reveal that not only does the use of hybrid structures provide more energy absorption and improve mechanical properties, but also the rational combination of two materials makes the bi-material three-dimensional lattice structure with the optimum energy absorption and stiffness, in comparison to those usual lattice structures with a single material.

Nanocomposites are widely used in dental restorative materials and medical equipment, among the most important of which, polymer-based nanocomposites can be mentioned. One of the most useful biocompatible polymers in this field is polymethylmethacrylate (PMMA). In the present study, the numerical analysis of the fatigue behavior of polymethyl methacrylate nanocomposite reinforced with hydroxyapatite nanoparticles has been investigated. For this purpose, standard samples of nanocomposite were made and their mechanical properties were investigated. To study the fatigue behavior and life cycle, a notched model was simulated in Abaqus and Fe-Safe software, and the data obtained from the tensile test were used as the mechanical properties of the material. By adding nanoparticles to the pure polymer, Young's modulus and tensile strength of the part, as well as the life cycle, were improved; However, it was observed that with the addition of more nanoparticles, the mechanical properties and the life cycle decreased slightly, which was caused by the accumulation of nanoparticles on the surface of the nanocomposite, which leads to a decrease in the strength of the samples.