نشریه علوم و فناوری کامپوزیت
سال دهم شماره 2 (پیاپی 36، تابستان 1402)

In this paper, the free vibrations of multi-layered composite cylindrical shells with rectangular cutout are analyzed analytically. Cylindrical shell equilibrium equations are derived based on classical shell theory (CST) and using Newton's method. Boundary conditions of the two-headed shell are considered simply supported. According to the boundary conditions, the displacement components are written as double Fourier series expansions. Relationships of the strain-displacement and curvature displacement are considered based on Love’s approximation theory. Modeling of the cutout by distribution function (Heaviside) is considered based on the equilibrium equations of the composite cylindrical shell. In order to obtain the natural frequency of the rectangular cutout composite cylindrical shell, the equations of motion have been solved using the Galerkin method. For validation, firstly, the results of the composite cylindrical shell have been compared with the Abaqus finite element software and the Previous literature in this field, that there is a good match between them. Finally, the effect of the geometrical parameters of the composite cylindrical shell with cutout, such as the length, radius, thickness and layering of the cylindrical shell, as well as the dimensions, direction and location of the cutout, on the natural frequency of the structure was investigated, that the results show that with increasing The dimensions of the cutout increase the reduction of the natural frequency of the structure.

The production of parts using 3D printing, which is a type of additive manufacturing, is expanding at a faster rate. This technology can produce complex geometries by depositing melting polymer material layer by layer. Polylactic acid (PLA) is one of the most widely used materials in this technology due to its good properties such as biodegradability and bio-compatibility, and parts manufactured with PLA are being used in various engineering applications. The strength of these layer-by-layer parts depends on the printing parameters such as the infill density, the orientation of the printed fibers, the speed and temperature of the print, the distance between the fibers, etc. Also, the presence of grooves in engineering parts, especially printed polymer layer-by-layer parts, can significantly affect the mechanical behavior of these materials. In this research, the strength of short grooved beam parts with three different geometries (U, V, key hole) printed with PLA material under quasi-static bending loading is investigated experimentally and statistically. The amount of load and fracture energy of the samples are measured and also the sensitivity to the geometry of the groove in the tested parts is evaluated. Fisher's test is used for pairwise comparison of the grooves' strength. The results of this research show that the groove with an angled corner is the weakest, while the circular groove has a higher resistance, and this resistance increases when the radius of the circle is increased.

Polymer matrix composites are one of the most widely used types of composites due to their lightness, and special strength and stiffness. Fibers-reinforced composites are the most important composites, and basalt fibers are one of the important types of mineral fibers that are used in the matrix of polymers. In this research, the effect of addition of silica fume particles (which has not been used in fibers reinforced polymer composites) on the mechanical properties of basalt fibers-epoxy composites under bending and tensile loadings was studied. The silica fume particles are surface modified with silane and then with different percentages (2, 4 and 6 wt.%) were distributed inside the epoxy matrix using a mechanical stirrer and ultrasonic waves. Hand lay-up method was used to make composite samples. The results of this research showed that with the addition of silica fume particles, the greatest improvement in the properties of the tensile strength and modulus, as well as the bending strength and modulus of the sample containing 4 wt.% silica fume is 22, 34, 27 and 40% respectively in compared to the sample without silica fume. On the other hand, the results of mechanical tests and microstructural examination after failure showed that the improvement of the interface between the fibers and the matrix as a result of the proper distribution of these particles inside the matrix has a significant effect on improving the mechanical properties. Also, the unfavorable distribution of these particles leads to the loss of mechanical properties under different loadings.

Man always tries to get inspiration from nature and create new structures. One of these new structures is cellular and lattice structures, which have attracted the attention of researchers due to their low weight and appropriate compressive strength. In this article, inspired by nature and the structures in it, these structures have been investigated and modeled on creatures such as turtles, snails and sea shells. For this purpose, two models of each pattern were designed and made of Petg material using the additive method. The samples were subjected to the test of two consecutive impacts with the impact weight of 2.2 Kg and at two heights of 5 cm and 10 cm. The results showed that the highest and the lowest impact force at a height of 5cm respectively correspond to one of the samples taken from a turtle and one of the samples taken from a snail with a ratio of 325% and at a height of 10 cm, respectively, it corresponds to one of the turtle samples and snail samples, with a ratio of 200%. The highest and lowest displacement in the maximum force resulting from the impact is at a height of 5 cm, respectively, related to one sample taken from a snail and a turtle with a ratio of 252%, and at a height of 10 cm, respectively, it corresponds to one of the snail samples and turtle samples, with a ratio of 238%

One of the most important applications of nanomaterials in polymer resins is to achieve high fracture toughness even in small volume fractions of filler nanoparticles. Such performance is related to energy released through damage mechanisms that occur at the nano scale. Among these mechanisms, nanoparticle surface separation is more important. In the present work, considering the hierarchical structure of nanocomposites, it has been tried to investigate the effect of debonding of graphene nanoparticles from the surrounding resin on the fracture toughness of the first mode of the presented epoxy/graphene nanocomposite using a multi-scale method. Therefore, a representative volume element has been selected and using the data available in the experimental works of other researchers, the effect of several parameters such as Young's modulus, weight fraction and dimensions of nanographene was investigated. Finally, it was observed that the fracture toughness has a direct relationship with the Young's modulus of the nanocomposite. Also, the smaller the dimensions of the nanoparticles used, the greater the improvement in the fracture toughness.

Nowadays, much attention has been paid to metal matrix composites due to their unique features and extensive applications in numerous manufacturing sectors such as automotive, aerospace and energy. Aluminium metal matrix composites (Al-MMCs) are among the most highly used MMCs. The unique features of Al-MMCs are high hardness and high resistance-to-weight ratio. Moreover, the main drawbacks are the low machinability, high and rapid tool wear, and complications in the surface quality in machining operations. Limited studies reported using cooling methods, such as cryogenic strategies, on the surface quality when machining Al-MMCs. Therefore, the effects of cutting parameters and cryogenic cooling method on the surface quality of A356-10%SiC have been studied in this study. According to the performed analysis, it was observed that cryogenic cooling parameters and cutting speed had negligible statistical effects on the average surface roughness (Ra) of the tested material with R2 of 65%, which resembles a weak relationship between studied parameters and Ra. Nevertheless, the cryogenic pressure had the most significant effects on the variation of Ra amongst cutting and lubrication parameters.