نشریه علوم و فناوری کامپوزیت
سال پنجم شماره 1 (پیاپی 15، بهار 1397)

This paper investigates the ultimate strength analysis of imperfect composite plates under both in-plane compressive load and lateral pressure using Ritz method. In this study, the first order shear deformation plate theory has been applied and the small deflection theory is also considered therefore the obtained results for thin plates could be a little bit off however the results for relatively thick plates are more reliable. The formulations are based on the concept of the principle of minimum potential energy. The laminates are simply supported at the loaded ends as well as the unloaded edges. The in-plane lateral expansion is allowed for all edges however they are kept straight. To investigate the failure analysis, Hashin failure criterion has been applied and also two different models for degradation of stiffness has been used. The first model is complete-ply stiffness degradation model that apply the degradation of properties to the whole ply, and the second is regional stiffness degradation model which degrade the properties of that region. The instantaneous degradation of material properties is used for failed ply or region of failed ply. In addition to find the first and last ply failure loads, the number of failed plies and coordinates of failure points in first and last plies has been obtained. Finally, the results obtained by the proposed method have been validated by results available in the literature.

One of the most important, most accurate and the best of views to projectile impact and penetration phenomena in the composite target is the models related to energy discussion. In this paper previous works have been studied and it has been tried to verify and complete them. In the experimental study for the accuracy of model a reservoir of glass/epoxy is done under projectile impact and penetration of spherical pellets at different speeds. This model can investigate the ability or inability of projectile exit from the target and predict the remaining energy during passing through the target, by comparison the total energy of projectile with energy absorption mechanism, Also it is estimated the contribution of each mechanism to absorb energy at different speeds by this model. As well as ballistic velocity of projectile is estimated when it impacts to a composite target with good accuracy. This model has considered the most mechanism of energy absorption and it has been tried to add new mechanism of energy absorption; includes energy absorbed from the shift of the top cone under the projectile, energy absorbed by deformation of elastic – plastic primary fiber and energy absorbed from the friction make between the projectile and composite targets; and expresses the best and most accurate model of energy absorption. Finally, the results of this model have been compared with the results of FEM performed by ANSYS module LS.DYNA.

Glass/epoxy prepregs are widely used in composite industry. Although they have significant advantages, the brittleness nature of its epoxy matrix produces some difficulties. In this paper the effect of liquid carboxyl-terminated butadiene-acrylonitrile rubber (CTBN) and a flexible diamine (Jeffamine D-400) curing agent on epoxy prepregs based on diglycidyl ether of bisphenol-A (DGEBA) resin and dicyandiamide (Dicy) reinforced with glass fiber were studied. For this purpose, after preparing the resin formulation and its impregnation with glass fiber or preparing the prepreg samples, the effect of CTBN and Jeffamine on epoxy/glass prepregs properties like resin flow, lap shear strength (LSS) and interlaminar shear strength (ILSS) were studied. Volatile content, resin content and pre-curing of prepared prepregs are characterized. Results show that in all samples the amount of resin content, volatile content and pre-curing were nearly the same and adding different amounts of CTBN or Jeffamine do not changed the resin flow. By adding 20 phr of liquid rubber, LSS does not changed but, adding the Jeffamine up to 20% increased the LSS by 8% and adding Jeffamine up to 40% does not changed this property. By adding the CTBN by 5 phr, the ILSS increased by 7.7% and in all Jeffamine samples the ILSS varied from 4.6 MPa for 100% Dicy to 2.0 MPa for sample containing 60% of Jeffamine and 2.6 MPa for 100% of Jeffamine content.

Nowadays due to water shortage, the use of treated wastewater as sustainable solution has been considered by industrial units; especially in industrial cooling units and boilers. However the use of treated wastewater also has its own problems such as corrosion of metal parts that they are often made of carbon steel. Therefore different methods such as coating have been considered by the industrial user of treated wastewater in order to reduce corrosion. So in this study, SiO2/TiO2 Ceramic Nano composite coatings was put on Carbon Steel plates by Sol-Gel method and by dipping process for 100 seconds and microstructure and properties of produced ceramic coatings were investigated. The results showed that ceramic Nano composite coatings improved corrosion properties of Carbon Steel. In order to improve the properties and performance of the coating, the molar ratio of components and factors affecting performance of coating were evaluated till optimum coating with Nano structure and highest level of corrosion protection is provided. To evaluate the performance of coatings for corrosion protection, polarization curves and to determine the surface morphology, scanning electron microscope was used. In order to study the bonds type and functional groups in the optimal sol, infrared spectrum was used. The optimum corrosion protection coatings were studied in 3.5% sodium chloride solution. The results showed that the ceramic optimal deposited coating provides effective protection for the surface of Carbon Steel against corrosion in 3.5% sodium chloride solution.

Carbon fiber reinforced composites because of suitable mechanical and physical properties are used in numerous industrial applications. Drilling is a common method to connect fiber reinforced material structures. Fiber reinforced composite laminates in machining operations, especially in drilling which is subjected to stress concentration, tend to be delaminated. Delamination phenomena is extremely under the influence of factors like tool and workpiece geometry and material as well as machining parameters. In this research, by using Taguchi experiment design method, an experimental study conducted on drilling of carbon fiber reinforced composite with tungsten carbide tool to investigate amount of delamination. Discussed parameters include predrilling, rotational speed, feed rate, tool diameter and workpiece thickness. According to conducted experiments, observed that predrilling, rotational speed increment and feed rate decrement cause delamination damage reduction and hole quality improvement. Also using drilling tool with smaller diameter and utilization of thinner composite cause delamination reduction. As for achieved results, in Minitab software, Analysis of Variance(ANOVA) carried out to examine hole quality and effectiveness of each parameter. Among examined parameters, workpiece thickness has the most effect on the amount of delamination. Optimized parameters to reduce the delamination also obtained.

In this paper, the performance of some glass/vinylester composite laminates was examined. Using 3D FE models for the specimens and progressive failure analysis of the models, an accurate simulation of the contact between the composite beam and the supports was implemented. Also the influence of material and geometric non-linearity on the flexural load carrying behavior of the beams was investigated. At the first, the tension experiments were conducted for observation of the progressive failure behavior in the composite laminates and verification of the failure model. In the following, by implementing the three-point-bending tests and then simulation of the composite beam specimens, varaition of the flexural modulus was investigated by the aid of comparing the load-deflection curves obtained by the experiments and the FE models. For prediction of the failure, the strain-based failure criteria were used rather than the stress-based failure criteria. Since the failure strains were identical for tensile and bending specimens, variation of the flexural modulus led in variation of the flexural strength. As variation of the flexural modulus was considered dependent on the performance of the polymeric phase of the composite laminates, this variation was attributed to the performance of the 90˚ layers.

The A356 is a cast alloy which consist of aluminum, silicon and magnesium. This alloy has good strangth and ductility with excellent casting properties, high corrosion resistance and good fluidity. This alloy is wiedly used in the automotive industry, aircraft, defense industry and especially the automotive industry as a substitution of steel components. Poor wear resistance of the alloys is major limitation for their use. Friction stir processing (FSP) is a recognized surfacing technique as it overcomes the problems of fusion route surface modification methods. In this study, friction stir processing was utilized to incorporate TiO2 and graphite particles into the matrix of an A356 alloy to form surface hybrid nanocomposite. For fabrication of nanocomposite a constant tool rotation rate of 900 rpm and travel speed of 60 mm/min with a tool tilt angle of 3 degree was used. Keeping in view of the requirement for improving wear resistance of A356 alloy, friction stir processing was attempted for surface modification with TiO2 and graphite powders. SEM, metallography, hardness, nanoindentation and pin-on-disc wear testing were used for characterizing the surface of nanocomposite. Microstructural analysis showed a uniform distribution of reinforcement particles inside the nugget zone. The surface nanocomposite results in enhanced properties in mechanical properties and wear resistance compared to the behavior of the base metal. Addition of solid lubricant graphite improve tribological properties of the nanocomposite.

In this research trunk fibers of date palm tree were utilized as the reinforcement for epoxy matrix composites. Composite samples were produced using the fibers with the cut length of 1, 2 and 3 cm and with three levels of fiber volume percentage (FVP) by the hand molding method and were subjected to tensile and three-point bending tests. The results showed that fiber length, in the range of the research parameters, didn’t have a significant effect on the tensile and flexural properties. In general, adding date palm fibers (DPFs) didn’t improve tensile strength compared with the pure matrix, which may be due to week bonds between fibers and matrix and existence of structural defects in the samples. A fairly good agreement was observed between theoretical tensile moduli calculated using Tsai-Pagano model and experimental values. The results of bending test showed that adding 7.5 volume percent of DPFs leads to the improvement in flexural strength of the composites, however, in the higher FVP (10.7) it decreases which is due to the increase in fibers volume and thus less penetration of resin into them and deterioration of structural integrity of the samples. Moreover, by adding DPFs to epoxy the tensile modulus of the composite increased. This increase was observed in samples containing 7.5 and 10.7 FVP with a maximum value of 3.7 GPa in 7.5 FVP (105% enhancement).

Given the demand for high strength, light materials in today's industry, fabrication methods implemented for manufacturing parts have become increasingly important. Hot Metal Gas Forming (HMGF) is a novel process that enhances the strength of the parts, while reducing total weight and fabrication time, due to the elimination of auxiliary processes such as welding. High temperatures are not feasible in hydroforming given the presence of water/oil in the forming process; however, there is no temperature limit in HMGF as the working fluid is gas. Drawing on Taguchi methods of experimental design, first, the axial feed and the internal pressure were evaluated at different temperatures (350, 400, 450 °C) and at three levels in terms of lowest thinning. The evaluation was performed through finite element simulation and the resulting optimum conditions were experimentally applied in bulge forming of a double-walled composite Al6063-AZ80 tube. The results of Taguchi methods and finite element simulation show that bulge forming of the tube at 400 °C with an internal pressure of 55 bar and axial feed of 4 mm is optimal for the HMGF process. Experiments were successfully performed under these conditions and showed good agreement with simulation results with a maximum difference of 5.49% in thickness reduction compared to simulations.

Sandwich structures are made of two thin skin with high mechanical properties and a thick core that have weak strength. Due to high strength and stiffness to weight down, sandwich plate are used too much in engineering structures such as ship hulls, turbines, etc. In this paper, the effect of skin/core debonding on the dynamic response of sandwich structures with composite skins and a PVC foam core is investigated experimentally and also numerically. The separation size affects strongly on the natural frequency so that with a reduction in structural stiffness due to the separation zone between the upper skin and the core occurs, the natural frequencies decreases. Increase the length and depth of separation reduces the local stiffness and thereby reduces the natural frequency of the structure. The composite skins are bonded to the foam using VIP (Vacume Infusion Process) method because of VIP method can make more qualify specimens. In order to validate the obtained results, the results of modal test and also the effect of separation length on the natural frequencies and mode shapes in ABAQUS software are used.The results show good agreement between the numerical and experimental tests respectively

Fiber- metal laminates (FMLs) are new type of hybrid composites based on thin metal layers, such as aluminum or titanium alloys, and prepreg composite material, such as glass fiber reinforced epoxy resin. FML represents good mechanical property and less weight than traditional aluminum layers. This paper presents experimental and numerical investigations on high velocity impact response of fiber- metal laminates based on prepreg woven glass fiber and 2024-T3 aluminum alloy. After lay- up and curing of samples, in order to assessment of ballistic impact behavior, tests on FMLs and 2024-T3 aluminum layers, were undertaken using a light gas gun at velocities up to 90 m/s. The results of experimental works indicate that FMLs based on prepreg woven glass fiber have higher specific perforation energy than the aluminum samples. Numerical simulations were performed by the finite element software, ABAQUS, using tensile and shear failure for damage criteria. Good agreement was observed between the numerical and experimental data.

In this study, the effect of surface modified graphene nanoplatelets (GNPs) by silane on the high velocity impact behavior of basalt fiber epoxy nanocomposites was evaluated experimentally. The pristine and silane modified GNPs of 0, 0.3 and 0.5 weight percentages were employed for reinforcing basalt fiber- epoxy nanocomposites and the surface modification procedure of GNPs were confirmed using Fourier transform infrared (FT-IR) spectroscopy. Results from the high velocity impact tests proved that utilizing silane modified GNPs had a considerable influence on the mechanical performance of the basalt fiber reinforced polymer nanocomposites. in the 0.3 wt.% GNPs sample, the impact limit velocity and absorbed energy respectively improved by 11 and 23 %, Compared with the 0 wt.% GNPs sample,but in the 0.5 wt.% sample, agglomeration of GNPs caused reduction in the mechanical properties. Electron microscopy investigations revealed that load transfer between the polymer matrix and the reinforcing fibers was greatly affected by the addition of GNPs in enhancing the mechanical response of the nanocomposites.

Using fabrics as reinforcement of composites considerably leads to improve some of mechanical properties. One of the important mechanical properties is resistance to impact forces. Therefore, in the present study, the impact behavior of composites reinforced with weft-knitted spacer fabrics has been studied. Due to the out of plane nature of impact force , the through-the-thickness reinforcement of composite play a key rule in undergoing the impact forces. Weft-knitted spacer fabrics are adequate structures to reinforce through-the thickness of composite due to the existence of spacer yarns. In this study, at first, principle of low velocity impact behavior of composites was studied. Then, a semi-empirical model was generated to predict the impact behavior of composites considering the structural parameters of weft-knitted spacer fabrics as reinforcement of composites. In order to validate the proposed model, weft-knitted spacer fabrics with different types of spacer yarn's orientation were produced and used as reinforcement of composites. The low-velocity impact test was carried out on the prepared samples. A good correlation was found between theoretical and experimental results.

Several advantages such as low cost, availability of renewable natural resources and high stiffness are main reasons to pay attention to wood plastic composites. In this work, the blends of high density polyethylene (HDPE), polypropylene (PP) and recycled poly (ethylene terephthalate) (rPET) with maleated polyethylene (MAPE) and maleated polypropylene (MAPP) as the compatibilizer were used as the matrix of the wood-plastic composites (WPCs). WPCs has been prepared through an extrusion technology in two-step. In the first step, the bland of matrix (PP/HDPE/rPET) has been prepared, and in second step, the wood flour was added to polymer matrix to produce wood plastic granules. Wood plastic granules were converted to test samples through injection molding technology. The effects of rPET, wood flour and compatibilizer content on the mechanical properties (tensile strength, flexural strength, tensile modulus, elongation at break point and impact energy), density and water absorption resistance of WPCs were investigated. The results showed that the tensile modulus, density and water absorption of WPCs increased with rPET and wood flour, and impact strength and elongation at break point decreased. Tensile and flexural strength increased with rPET, whiles the strength significantly did not change with wood flour. Mechanical properties (elongation, impact energy, tensile modulus and flexural and tensile strength) and water absorption resistant improved with compatibilizer content. SEM images showed that rPET converted to micro fiber in matrix after second step of the extrusion.

Nowadays polymeric nanocomposite foams have attracted the attentions in both academic and industrial communities due to their advantages. Foams with open-cell structures have high ability to absorb sound, water, impact and moisture. The cell wall thickness can be used as a parameter to evaluate the approaches for achieving open-cell structures. In this study the structural and mechanical properties of polypropylene/nano Fe2O3 nanocomposite foams were investigated in batch foaming process using CO2 gas as blowing agent. Nano Fe2O3 content, foaming temperature and foaming time were considered as variable parameters. Design of experiments using L9 orthogonal array of Taguchi approach was used for studying cell wall thickness and specific impact strength. The signal to noise ratio and analysis of variance were carried out. The scanning electron microscope results showed that appropriate microcellular structures with cell density of 109 and 1010 cell/cm3 were achieved. The results indicated that foaming temperature was the most effective parameter on the properties of nanocomposite foams. Decreasing foaming temperature leads to decreasing cell wall thickness and increasing specific impact strength. Also, the results illuminated that specific impact strength was enhanced almost 20% by increasing 4 wt% of nano Fe2O3.

Carbon/epoxy composites have been used frequently in several structures due to their incredible ratio of strengths to weights. In this regard, investigation and classification of damages in composite structures are essential to prevent any probable happenings and to enhance the reliability. Such failures can be generally categorized into 4 groups, including matrix cracking, fiber breakage, debonding of fibers from the matrix, and the delamination. One of the new methods for detection of defects in composites is to utilize the acoustic emission approach. Accordingly, the aim of this article is to investigate and classify the different types of failure mechanisms in open-hole laminate composite specimens under tensile loading using acoustic emission. First, an open-hole specimen was examined under tensile loading based on ASME standards. Then, elastic waves due to failures in the specimen were recorded by wide-band acoustic emission sensors. Two methods have been utilized to detect the failure percent, including Pocket wavelet transform and Fuzzy clustering approaches. Results from these methods were compared to micro-structure images by the scanning electron microscopy. Results showed that about 50% of damages corresponds to debonding, about 30% comes from matrix cracking, and 20% is relevant to fiber breakage. In addition, the difference between two considered methods was 7%. Obtained results in this research indicated the appropriate efficiency of the acoustic emission approach to detect the type of failures and their percent in laminate composites.