نشریه علوم و فناوری کامپوزیت
سال هشتم شماره 4 (پیاپی 30، زمستان 1400)

In recent decades, the use of metal matrix composites and functionally graded materials for achieving a combination of mechanical and physical properties has increased. In this research, an in-situ centrifugal casting method was used to make the samples. The primary composite used in this method was Al-15wt.% Mg2Si. In situ prepared functionally graded samples were successfully manufactured at 1000, 1300, and 1700 rpm rotational speeds. Optical microscopy was used to examine the microstructure of the samples, and a Vickers hardness tester was used to examine the mechanical properties. The cross-section of the fabricated samples was divided into two parts, the reinforced and the matrix parts. Porosity increased as a destructive parameter in the reinforced area. The hardness increased as the volume fraction of particles in the reinforced area was increased. Also, hardness increased in the chilled zone due to the fine-grains and trapped particles in that area. Solutionizing heat treatment was performed for the fabricated samples. By observing the microstructure, there was no change in the placement trend of the primary particles, but the morphology of the primary and eutectic Mg2Si particles were changed. Hardness increased after heat treatment while its gradient did not change.

Cement protector sheath as a factor of durability and stability in oil and gas wellbore structure plays a vital role in the continuous sustainable production from hydrocarbon reservoirs. In order to enhance the mechanical properties of cement protector sheath, this research has focused on the use of carbon nanotubes due to their proven excellent mechanical properties. Although this idea has previously been an exciting topic for research in the development of cement and concrete, In this regard, as research innovation, to overcome the non-uniform distribution challenges of organic carbon nanotubes in the cement aqueous base medium, an advanced technique for making emulsion nano polymers was handled to disperse the nanoparticle cores in the polymer matrix. According to the findings of this work, carbon nanotubes disperse effectively in polymer emulsions, and polymer latex disperses well in the aqueous base of cement, allowing for a wide dispersion of nanoparticles to benefit from their maximal surface performance and mechanical properties. Non-agglomeration of nanoparticles in the cement structure has led to the use of the highest reactive and physical surface of these nanoparticles, which has significantly strengthened the mechanical properties of cement mass after hardening. The experimental results significantly increase the Young modulus to 580% From 4.12 GPa for the benchmark sample compared to 28 GPa for the modified sample with 4%W of the nanopolymer. The optimized samples in slurry form also provide good rheological properties for pumping capability and sufficient hydrostatic pressure to control the wellbore pressure.

Despite the unique superior properties of balsa such as reasonable price and excellent mechanical properties, the hydrophilicity and high sensitivity of this material to moisture absorption have posed a serious challenge to its increasing use in the construction of advanced marine structures. If moisture can penetrate into the composite skins, the balsa core sandwich structures will absorb a lot of water and compromise its structural integrity. In this study, to improve the mechanical properties and the environmental resistance of sandwich structures with balsa core against the moist environmental conditions, the idea of using fiber metal laminates instead of polymer composite skins has been proposed. For this purpose, sandwich structures with balsa core and two types of composite skins made of glass fiber/epoxy and fiber metal laminate were subjected to environmental and mechanical tests. The most important results obtained from the 100-day aging test in water show that the maximum water absorption in sandwich specimens with glass fiber/epoxy composite and fiber metal laminate skins having sealed edges and artificial damage is 106.71% and 83.32%, respectively. In addition, by evaluating the flexural and buckling behavior of two types of sandwich structures, before and after the moisture aging process, it was found that the reduction of flexural load, flexural stiffness and maximum buckling load due to moisture aging in sandwich specimens with glass fiber/epoxy composite skin with sealed edges were 23.43%, 23.15% and 36.14%, respectively, and for specimens with fiber metal laminate skin were much less, and 13.57%, 11.06% and 16.14%, respectively.

The main of this paper is to determine the tensile properties of natural flexible composites. In order to fabricate the composites, the cotton fibers and the latex were used as the reinforcement and matrix, respectively. At the first step, the latex samples were manufactured and tested under tensile loading. In the next step, using the cotton fiber the latex was reinforced and then tested under tensile loading. In addition, the NiTi shape memory alloy (SMA) wire was used to improve the tensile properties of the pure latex and the cotton/latex laminated composites. Therefore, one, two or three NiTi wires were used in the pure latex and cotton/epoxy composites samples. The results of experimental study displayed that in the presence of cotton fiber, the ultimate tensile strength of pure latex was increased from 0.93 to 13.51 MPa. Moreover, it was observed that due to adding one, two or three NiTi wires, the ultimate strength of the pure latex was enhanced almost 70, 500 and 800%, respectively. However, the ultimate tensile strength of the cotton/epoxy laminated composites in the presence of one, two and three NiTi wires was increased almost 2, 20 and 40%, respectively. In addition, comparison of the current research results with the other researchers’ investigations manifests that the cotton/epoxy composites reinforced by NiTi wire, the tensile strength of this flexible material is greater than the tensile strength of natural and artificial leathers.

In this paper, the addition of silicon carbide (SiC) nanoparticles to polyamide 6 (PA6) / acrylonitrile-butadiene rubber (NBR) blends was performed by friction stir process. In order to achieve optimal mechanical responses of tensile strength and elongation at break, response surface methodology (RSM) was used to optimize the process parameters of rotational speed (ω), traverse speed (V) and material parameter as silicon carbide nanoparticles (S) content. The validation of the mechanical results was done with compare the microstructure of nanocomposite samples by scanning electron microscopy (SEM). Using mathematical models, the results showed that tensile strength and elongation at break are increased by increasing the rotational speed from 800 rpm to 1200 rpm when the values of silicon carbide content and traverse speed are constant. By selecting the rotational speed of 1200 rpm, traversed speed of 20 mm/min, and 2.784 wt.% of SiC process and material parameters, the maximum tensile strength, and elongation at break can be achieved. Observation of scanning electron microscopy images confirmed that the changes in mechanical properties are related to the changes in the elastomeric phase of NBR.

PTFE-based composites are widely used as sealing materials. These composite materials are industrially manufactured and supplied with various reinforcements. Despite the desirable properties of commercial seals, these materials are generally not capable of sealing in specific working conditions and require the design and construction of PTFE-based composite with new reinforcements. In this study, Inconel 625 alloy powder was used as a reinforcing phase to make the PTFE-based composite. The effect of weight percentage of reinforcement on mechanical and tribological properties of composites has been investigated. In addition, the molecular dynamics simulation was used to investigate the composite wear. Addition of Inconel 625 significantly improves PTFE wear resistance. Addition of Inconel 625 reinforcing phase to PTFE matrix changes the PTFE wear mechanism from fatigue to adhesive type. Molecular dynamics simulation studies have shown that this is due to the high interaction energy at the junction of PTFE and Inconel 625, which does not allow PTFE to be easily separated from the sample. Among the developed composites, PTFE-reinforced composite with 50% by weight Inconel 625 had the best combination in terms of hardness (70 shore D) and specific wear rate (4/710-4 mm3 / Nm). The manufacturing method is easy to use and the manufactured samples are capable of industrial production.

Self-healing materials can be used as one of the types of smart materials in recovering and repairing equipment and preventing breakdown and fracture of tools. There are several ways to increase the efficiency and repeatability of the self-healing process, one of which is to combine self-healing microcapsules with shape memory alloys. Although several laboratory studies have been performed in this field, this method has not been given the attention it deserves. In this study, an attempt has been made to evaluate the performance of this compound using the finite element simulation method. For this purpose, used glass microcapsule and Ni-Ti SMA within the concrete matrix. After examining the results, the effect of shape memory alloy wires on increasing the maximum fracture stress was quite obvious. By adding two shape memory wires, the fracture tension has increased from 1.93 MPa to 2.08 MPa. Also, the most important effect is to close the crack opening distance in such a way that using two shape memory wires, the distance of the crack opening has decreased from 5 μm to 0.008 μm. Then, the effect of radius of memory alloy wires and thickness ratio and volume fraction of microcapsules on ultimate fracture stress and self-healing performance was investigated. Finally, the effect of interface strength on microcapsule fracture and ultimate fracture stress is evaluated.

Reactive composites are a new group of composite materials consisting of two or more materials that cannot ignite or explode in the Environmental conditions, but can release a lot of energy due to shock and severe impact loads. This study aimed to investigate the effect of milling time on the microstructure, thermal and mechanical properties of the Al-Ni composite. For this purpose, the Al-Ni compound with a 2:1 Al:Ni molar ratio was milled for 0.5, 1, 2, 4 and 6 hours in attrition mill and mixed. Then the samples were cold press and sintered at 400 ˚C under argon atmosphere for one hour. The microstructure of samples was analyzed by field emission scanning electron microscope (FESEM) and XRD. To investigation of thermal properties DSC and DTA analysis and for mechanical properties compression test and Hopkinson test were used. The DSC analysis results showed that by increasing the milling time, the reaction start temperature decreased from 650.34 °C in the sample milled to 0.5 hour to 645.84 °C the sample milled to 6 hour and the reaction heat (enthalpy) decreased from 26.87 J/g to 14.84 J/g. The results of compression and Hopkinson tests of samples after 6 hours milling time showed 21 and 42 percent increase in compressive strength, respectively compared to samples after 0.5 hours milling time. Also, the results showed that the compressive strength increased by changing the strain rate from 0.01 s-1 (in the pressure test) to 1000 s-1 (in the Hopkinson test).

In this paper, the free vibrations of a three-layer sandwich plate with magneto-rheological fluid (MR) core as a smart structure using Trigonometric Shear Deformation Theory (TSDPT) are investigated. The equations of motion are obtained using the Hamilton principle and solved using the Galerkin residual weight method. The complex shear modulus of the MR material in the pre-yield region was described by complex modulus approach as a function of magnetic field intensity. Primary attention is focused on the effects of magnetic field magnitude, geometric aspect ratio, and MR core layer thickness on the dynamic characteristics of the sandwich plate. When an electric field is applied, the damping of the system is more effective. After validation of the present study with the available results in the literature, the effects of the natural frequencies and loss factors on the dynamic behavior of the sandwich plate are examined and discussed. The results show that increasing the intensity of the magnetic field increases the frequency and depreciation coefficient of each mode. Furthermore, increasing the thickness of the fluid has a direct effect on increasing the depreciation coefficient and decreasing the frequency. With the increasing use of smart structures, it is hoped that the findings of this study will make engineering applications more effective.

This paper has been presented according to the importance of crack bridging in mixed mode I/II delamination of laminated composites and it is aimed to understand the physics of crack bridging. Firstly, the most important micro-mechanisms involved during fiber bridging are introduced. To do this, interlaminar fracture tests have been performed on composite specimens. Also, the fracture surfaces and the damage zone on the edge of the specimens have been observed using a scanning electron microscope (SEM). In the following, due to the complexity of the existing bridging models and the difficulty of determining their various parameters, a novel approximate method has been presented. In this method, which is based on a more complex physics-based model, the bridging laws are extracted by preserving the physics of the problem and considering simple approximations. The main advantage of the proposed method is the achievement of bridging laws using simpler relationships with fewer required parameters. Finally, the validity of the method has been evaluated through a comparison of the traction-separation behavior predicted by the proposed approximate bridging laws with the experimental traction-separation curves in different mode mixities.

In this study, the vibration of a composite cylindrical shell in the presence of a longitudinal and circumferential crack was investigated. The governing equations were derived based on the first-order shear deformation theory and could be converted to Donnell’s, Love’s, and Sanders’ theories by selecting proper parameters. A multi-domain generalized differential quadrature method was used to solve the problem. In this technique, a physical domain was decomposed into several elements. Then, a generalized differential quadrature method was employed to discretize the governing equations, boundary conditions at shell edges, and the compatibility conditions at the interface boundaries of adjacent elements in both longitudinal and circumferential directions. Assembling these discretized equations led to a system of algebraic equations, which could be solved through an eigenvalue solution to calculate the natural frequency of the shell. This procedure was coded in Matlab environment. Numerical results obtained by the presented method were compared with Abaqus results and those available in the literature. After verifying the accuracy and precision of the proposed method, it was employed to study the effect of different parameters on the vibrational behavior of cracked composite shells. The obtained results can be used as a benchmark for further studies.

Impact resistance and energy absorption of thermosetting composites not only due to the inherence brittleness of the matrix, but also reinforcing the matrix with other composite components due to agglomerated phases, weak interfacial interaction at the absence of functionalization and coupling agents and thus weak interfacial load transfer could result in more deteriorated thermosetting composites energy absorption behavior. One important geometrical quantity is the effective aspect ratio (AR) of fillers. In this study, hybrid microcomposites of natural kenaf fiber/polyester was prepared through a direct mixing technique using nominal fibers ARs of 160, 250 and 320. To evaluate the synergistic effects, micro-particles of carbon black (CB) at the loading of 0 to 8 wt% were added to specimens with kenaf wt% of 5. The results demonstrated the direct influence of AR and wt% of fibers on the impact resistance with up to 203% improvement. The synergistic effect of CBs on the reference sample containing 5 wt% of fibers of 0.5 and 1 cm and 5 wt% led to 108% increase in the impact resistance in the case of 0.5 cm long fibers; however, at longer fibers the addition of CB resulted in the decrease in impact resistance and no significant changes in absorbed energy. The observed 28 and 65% enhancement in the absorbed energy of behavior of samples filled 5wt% of CB and 5 wt% of kenaf with the length of 0.5 cm compared to neat polyester and the reference kenaf/polyester parts, respectively, confirmed the synergistic effect of CBs and kenaf.