Journal of Science and Technology of Composites
Year:2016 | Volume:3 | Issue:2|Papers Count:10

Shape Memory Alloys (SMAs) are a type of Shape Memory Materials (SMMs) which can recover large deformation and return to their primary shape by rising temperature. In this study, numerical simulation of thermo mechanical behavior of composites reinforced with shape memory alloys under static uniaxial loading was conducted. By inserting SMA wires inside the host composite the macro mechanical behavior of hybrid composite changed to a bilinear curve which is due to the phase transformation of SMA wires and nonlinear behavior of host composite. Simulated results are compared with available data in the literature.Validated model is used to evaluate the effect of various parameters as, wires pre-strain, temperature, interface conditions between SMA wires and Epoxy matrix on hybrid composite behavior. Also a theoretical method was developed to calculate the compressive and tensile strain induced in host composites and wires, after releasing of SMA wires. According to the results obtained, considering weak interface between SMAs wires and matrix improved simulation results rather than perfect bonding assumption. Pre-strained SMA wires would cause initial compressive stress in the host composite and its value will increased by increasing service temperature, however, it will increased interface separation of SMA and host materials, too.Therefore, in design of Shape memory alloys hybrid composites, optimum amount of applied pre-strain on SMA wires and working temperature should be selected.

Centrifugal casting is one of the methods which is used for producing bimetallic composite parts. This method runs both horizontal and vertical mode. Vertical mode, used in this work, is currently taken to produce casting parts with height to diameter ratio less than unity. In this study, aluminum melt with 1.5 and 2.5 melt-to-solid volume ratio was cast into 100°C preheated brass bush rotating at 800, 1600, and 2000 (rpm), respectively. In order to characterize the cast samples, possible phases and casting defects various equipment such as optical microscope (OM), scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDS) have been used. Flowing of Al melt, at centrifugal field, is possibly associated with surface oxide film rupture so that metallurgical bonding is attained. On the other hand, these oxide films flowing at the melt surface and inherent turbulence of this process may cause defects in the casting. It was noted that bimetal composites produced at 2000 rpm are subjected to more defects than the other. This article categorizes various defects seen and analyzes different effective parameters.

ABS (Acrylonitrile butadiene styrene) polymeric material is widely used in different industries. The increasing demand of ABS for different applications has required a thorough understanding of its fracture behavior. This paper investigates mixed-mode fracture behavior of ABS polymeric material based on experimental and numerical analyses. Experiments were conducted on modified Arcan set-up. By varying the loading angle from 0° to 90°, pure mode-I, pure mode-II and a wide range of mixed-mode data were obtained experimentally. Also, finite element analysis was carried out for different loading conditions in order to determine correction factors needed for fracture toughness calculations. In this study viscoelastic behavior was considered for ABS specimens. Therefore, it is expected that the values of stress intensity factors to be time (frequency) dependent. Consequently, based on correspondence principle and assuming linear elastic fracture mechanics, time dependent mixed-mode fracture toughness for ABS polymeric material was determined. Results indicated that in all loading conditions, values of fracture toughness decrease while time increases in stress relaxation test, until a specific time. Accordingly, it can be resulted that the minimum value of fracture toughness of ABS, which plays a crucial role in various applications, does not appear in the first instance of loading.

This paper presents a Novel method for fabricating of thin ceramic plates. Although achieving nearly full density, the commercial hot pressing machine have extremely high price and upkeep cost. The device presented in this paper have lower cost and for hot pressing, needs just an ordinary electrical furnace.Despite all this benefits, it can just form thin ceramic plates. In this paper, initially a brief description about ceramic matrix composites (CMCs) is presented and the effect of formed components and forming methods on its properties is discussed. Then the powder forming methods with advantages and disadvantages is presented. In the next step the device (expansional hot pressing device) and its working method is introduced. And finally this device is used for forming of a special ceramic matrix composite and the mechanical and microscopic properties of the formed part is examined and the method proves to be useful for forming CMCs.

Nanocomposite gears based on Polyamide 6/Polypropylene (PA6/PP 67/33) blend containing 2.5 to 10 phr of nano-CaCO3 and 5 phr of maleated polypropylene (PP-g-MAH) as compatibilizer were produced by injection molding. The morphology was studied using scanning electron microscopy. The wear and temperature of gears teeth as well as gears working lives were characterized by employing a gear test rig under two different output torques including 8.9 and 14.8 Nm. In all experiments, the teeth’s temperature and wear values for driver gear were higher as compared to those of driven gear. The incorporation of 2.5 and 5 phr nano-CaCO3, led to the reduction of temperature and wear rate of gears. The wear rates of gears containing 2.5 phr of nano-CaCO3, under the torque of 8.9 and 14.8 Nm, were 60 and 83% lower than those of neat PA6 gears respectively. The maximum gear life under the torque of 14.8 Nm (63000 revolutions) was observed in nanocomposite gears containing 2.5 phr of nano-CaCO3 which was nearly 200% higher than that of neat PA6 gears (21000 revolutions). The raise of Polymer based gears performances as a result of CaCO3 nanoparticles inclusion may be attributed to the improvements of gear teeth flexural, wear and heat resistances.

The impact behavior of steel– polyurea bi-layer panel is studied and the effect of nano clay addition to polyurea is investigated. Experimental and numerical analysis is used. Polymeric and nano polymeric bilayer specimens are fabricated and Simple tension test and drop impact test are carried out. Impactor acceleration for each test is recorded and compared with numerical one. Experimental results show that adding nano clay to polyurea will improve impact energy absorption and plastic deformation of bi-layer panel. nano clay with 1% weighting is added to soft part of the polyurea i.e. polyamine. Mechanical mixing and ultrasonic dispersion system is used for good dispersion of nano particles before mixing in polyamine.Experimental results show that elastic modulus is increased about 60% and elongation at break is decreased about 7% with nano clay addition. Also nano clay effects on bi-layer panel is studied with drop impact test and the results is verified with numerical analysis. It is shown that adding nano clay to polyurea as a reinforcement filler has increased the impact energy absorption about 3% and has decreased the maximum plastic deformation about 7 %. The experimental results show a good agreement with the numerical ones when compared together.

In the present paper, the effects of nanoclay and nano calcium carbonate on polypropylene nano composites micro hardness are assessed using Vickers test. Also, a 3D finite element model of Vickers test has been simulated by Abaqus code to compare to the experimental results. The Drucker-Prager yield criterion has been used to predict the polymeric composite plastic deformation. The Drucker-Prager parameters implemented in the numerical model are determined by a tension and a compression test separately. Two associative and non-associative plastic flow assumptions are considered and an appropriate dilation angle is derived by minimizing the error difference of experimental and the numerical results. Furthermore, micromechanical and macromechanical models are investigated to predict nanoparticles effect on the polypropylene microhardness. Although the results show that analytical models including Marsh and rule of mixture models have suitable accuracy (about 10% error), excellent results (less than 2% error) can be obtained by selecting appropriate dilation angle value in the numerical method. Moreover, experimental evidences show that adding nanoclay and nano calcium carbonate increases elastic modulus, tensile and compressive yield stress as well as microhardness of the polypropylene.

In this study, the effects of delamination size and location on vibration characteristics of laminated composite beams are investigated via analytical, finite element and experimental methods. In the analytical method, the delaminated beam is divided into four interconnected beams and the interaction of two subbeams at the location of delamination is simulated by both constrained and free mode models. The effect of bending-extension coupling is taken into account in the analytical formulation. In finite element method, modal analysis is performed on the delaminated composite beams with different delamination sizes and locations and various boundary conditions using commercial finite element software, ABAQUS. Both free and constrained mode models are simulated in the finite element model using suitable interactions, nonlinearities and friction conditions. Analytical and finite element results of both constrained and free mode models are compared for a symmetric cross-ply delaminated composite beam with various sizes and locations of delamination. Also, in order to investigate the effects of axial location of relatively small delamination on the first three natural frequencies, modal tests are done on glass/epoxy composites for various boundary conditions. Results show that analytical, finite element and experimental frequencies have good agreement with each other.

This work details an experimental investigation on understanding the effects of multi-walled carbon nanotubes (MWCNTs) on the tensile and flexural properties of basalt fiber (BF) /epoxy laminated composites. As a first step, the surface of MWCNTs was modified with a silane coupling agent namely 3-Glycidoxypropyltrimethoxysilane (3-GPTS). Fourier transform infrared (FT-IR) data confirmed the reaction mechanism between the silane compound and MWCNTs.3-GPTS/MWCNTs with various loadings (0, 0.1, 0.3 and 0.5 wt.%) were added to the epoxy resin via mechanical and ultra-sonication routes. The resultant mixtures were then utilized to fabricate MWCNT/woven BF/epoxy nanocomposites using hand-layup technique. Mechanical properties of the composites were investigated under tensile and flexural loadings.Also, a field-emission scanning electron microscope (FESEM) was used to study the distribution level of MWCNTs in the matrix as well as the fracture surfaces of the specimens. The results revealed that at filler loading 0.3 wt.% of 3-GPTS/MWCNTs, maximum improvements in tensile and flexural strengths and energy absorption of the BF/epoxy composites were obtained. Besides, the flexural and tensile moduli were enhanced continually by increasing the MWCNTs content. The microscopic investigations verified this subject that the addition of the 3-GPTS/MWCNTs to the matrix of BF/epoxy composite improves the BFmatrix interface yielding enhanced mechanical properties.

In this article, a new method for finite element modeling of planar multi-material structures, using only an input image, has been presented. This method which is implemented in a Matlab program is based on digital image processing technique. After importing a digital image by the user, the program automatically converts it into a binary format. The inner part and the boundary of the desired structure in the input image are recognized based on the difference between the colors of their pixels. These two regions are meshed separately by connecting their pixels to each other. The output of the program is a file in INP format which includes the coordinates of the nodes of the finite element model, their connections and the material of each part which has been defined by the user during the modeling process. The obtained results indicate the high accuracy of the method in the modeling of planar composite structures with complicated geometries in a very short time. Further, the results from the numerical analysis of the output model are in a good qualitative and quantitative agreement with the previous experimental data. The presented method in this article provides a strong background for future realistic modeling of planar composite structures.