Journal of Science and Technology of Composites
Year:2018 | Volume:5 | Issue:3 |Papers Count:16

Polypropylene has a poor toughness and impact strength. So, it needs to modification for some applications. Addition of elastomers to PP to enhance the toughness is a traditional way, but it causes to decrease of the modulus and tensile strength of products. In this research a hybrid composite system including PP, thermoplastic elastomer, nanoparticle and compatibilizer was prepared by melt mixing method. The interaction effect of nanoparticle, thermoplastic elastomer, and compatibilizer on the tensile and impact properties of composites were studied using the experimental design technique; response surface methodology. The results of microscopy analysis showed that the blends were two-phase, where thermoplastic elastomer was dispersed phase. The elastomeric particle size was in the range of 100-400 nm and by increasing the rubber content, rubber particle size increased. Nanosilica dispersed in the presence of compatibilizer had a particle size between 40-90 nm, while the lack of compatibilizer created some agglomerations of nanoparticles. As elastomer content increased, the strain of failure and impact strength of nanocomposites increased, while the Young modulus and tensile strength were decreased. Addition of nanosilica to the PP in the absence of compatibilizer lowered the tensile and impact strengths. While, addition of nanosilica along with compatibilizer improved the tensile modulus of blends. According to the experimental design results, some mathematical relations were presented to predict the mechanical properties. The optimal hybrid nanocomposite had significantly higher impact strength than pure PP while their moduli were in the same order.

The effects of functionalized graphene nanoplatelets (FGN) on the flexural properties of basalt fibers/epoxy composites were studied. The functionalization of graphene was performed by 3-Aminopropyltrimethoxysilane. Four nanocomposites with different weight percentages of FGN (0. 2, 0. 3, 0. 4 and 0. 5) were fabricated via hand lay-up method. Among these four, the nanocomposite reinforced by 0. 4 wt. % FGN showed the best flexural behavior. To investigate the effects of graphene as well as its functionalization, two other composites one without graphene and another reinforced by 0. 4 wt. % of unfunctionalized graphene nanoplatelets (UFGN) were also fabricated. In comparison to the sample without graphene, the nanocomposite with 0. 4 wt. % of FGN showed respectively 89. 6, 252. 6 and 44. 6 percent improvements in the flexural strength, flexural modulus and fracture energy, but the nanocomposite with 0. 4 wt. % UFGN showed respectively 26. 2 and 10. 8 percent decrease in the flexural strength and fracture energy, although had a slight increase of 3. 1 percent in the flexural modulus. These results indicated that functionalization facilitated the dispersion of graphene in the matrix and thus enhanced its interaction to both matrix and basalt fibers. According to the Fourier transform infrared spectroscopy results, the improvement in the flexural properties is related to the functional groups whose presence on the graphene platelets enhanced better adherence to the polymer’ s molecules and the basalt fibers. Furthermore, scanning electron microscopy observations of the fracture surfaces showed better polymer to fiber interfacial adhesion and thus caused toughening mechanisms such as crack deflection, graphene delamination and crack pining in the FGN containing samples.

Considering the importance of nanotechnology, especially nanofibers and nanocomposites; as its most eligible products and the vast applications of polyvinyl alcohol (PVA) and nanoclay ( modified organo-clay), the main objective of this work was study on effect of polymer blends (PVA as matrix) and nano-filler ( organo-clay as disperse phase) concentrations and electrospinning parameters, on morphology of resulted nanocomposite nanofibers. It is noteworthy that bead less nanofibers with even diameter distributions can make the final products application more valuable. In order to investigate the microstructure and morphology and the miscibility and chemical bonding of polyvinyl alcohol / organo-clay nanocomposite nanofibers, the scanning election microscope (SEM), and the Fourier transform infrared spectrometer (FTIR) were used, respectively. Also, the thermal gravimetric analysis (TGA) was employed to investigate thermal behavior of nanocomposite nanofiber samples. The X-Ray Diffraction (XRD) data demonstrated the exfoliation of organo-clay layers in poly vinylalcohol matrix and nanofibers nanocomposite were electrospun with diameter about 300 nm.

This paper presents a new analytical method for low velocity impact on sandwich plates with Fiber Metal Laminate (FML) face sheets subjected to static indentation of a blunt end cylindrical indenter. The sandwich plate was composed of laminated face sheets and a rigid– plastic core. The core-crushing strength in the vertical direction was assumed constant. In this method, using of principle of minimum potential energy and the use of energy-balance model between indenter and sandwich plate, contact unknown coefficients corresponding with Hertizian contact law are obtained. The elastic strain energy resulting from bending in the sandwich plate and external work due to indentation load are evaluated using an appropriate shape function for the sandwich plate deformation. The maximum contact force using two-degree-of-freedom (2DOF) spring-mass model was found through an iterative process. Limitation of using Hertzian contact law for sandwich plates is determined. The results are in good agreement with the experimental and numerical results. The results indicated that some of parameters such as the layer sequence, mass and velocity of impactor in a constant impact energy level and aspect ratio of sandwich plate are important factors affecting the dynamics response of the sandwich panel.

Using methods based on artificial intelligence to reduce the role of human interpretations in data analysis and obtaining the favorable results, in line with increasing the speed, reducing the errors and adjustment of the costs in the nondestructive evaluation and structural health monitoring is seriously concerned by researchers. In this study, the design and implementation of a structural health monitoring system is performed by the intelligent signal processing of the ultrasonic waves in order to identify and classify the three common defects in the composite plate-like structures. By creating three types of damages including delamination, crack and hole in the multi-layer composite plate made of glass fiber reinforced polymer and dividing it into 4 different zones, 9 piezoelectric transducers with dual role of actuator and sensor are attached with their network arrangement and the propagated signals in the four mentioned zones on the 12 paths in three different directions including 240 signals were stored. In the next step, extraction of the features from the signals is conducted by the advanced signal processing techniques such as wavelet transform and the findings have been used to train a neural network of advanced multilayer perceptron by back-propagation error method. The results show that the designed and trained neural network algorithm in this research is able to differentiate between the intact zone from the damaged ones. In addition, it has classified the types of current defects and damages in the structure with the acceptable efficiency (the average is about 80%), which can be generalized to the different conditions and configurations and unknown situations.

Polymer-based adhesives undergo creep deformation under constant loading due to their viscoelastic nature. The aim of this study was investigation of the effects of temperature level and stress-to-strength ratio on creep behavior of single lap joints (SLJs) manufactured with adhesive Araldite 2011. Static tensile tests were done on the samples at 40 and 50° C. Then, the tensile creep tests were done at 40 and 50° C and at stress-to-strength ratios of 0. 25 and 0. 35. With increasing the stress-to-strength ratio from 0. 25 to 0. 35 at 40° C, the creep displacement and the slope of the second creep stage were increased by 24% and 96. 7%, while at 50° C such increase reached to 14. 3% and 79. 9%, respectively. With increasing the temperature from 40 to 50° C, at the stress-to-strength ratio of 0. 25, the creep displacement was increased by 20. 6% and the slope of second creep stage increased by 49. 5%. Whereas, at the stress-to-strength ratio of 0. 35, changing the temperature from 40 to 50° C resulted an increase in the creep displacement by 11. 1% and the slope of second creep stage by 36. 6%.

Due to unique properties, composite cylindrical shells are used extensively in aviation, marine and automotive industry. In recent decades, several studies have been done to predict the critical buckling load of composite cylindrical shells without breakdown or failure. One of the most important non-destructive methods is Vibration Correlation Technique (VCT). The aim of this research is the prediction of the critical buckling load of composite cylindrical shells by using VCT. For this purpose, linear and nonlinear vibration analysis of composite cylindrical shells were performed in different compressive loads by using finite element software ABAQUS, firstly. In the next step, linear buckling critical load was determined by using Rayle-Ritz and numerical methods. Then, nonlinear critical buckling load of composite cylindrical shells was predicted by using VCT. To validate the results of VCT, five composite cylindrical shells were fabricated by using filament winding method with same conditions and axial compression test was done. Finally, the critical buckling load was measured experimentally. The results show that the difference between the critical buckling load of VCT with experimental buckling load is less than 3%. This subject implies that VCT is suitble for prediction of critical buckling load of composite cylindrical shells with very high accuracy.

In this study, the corrosion behavior of Fe-Ni-Cr composite coatings reinforced by SiC and carbon nanotube (CNT) has been investigated. In this regards, the electrodeposion processing has been done in a chloride bath in the presence of SiC nanoparticles and carbon nanotubes. The prepared coatings were characterized using X-ray diffraction (XRD) and field emission scanning electron microscopy (FESEM). The corrosion behavior of coatings was also examined in NaCl 3. 5% electrolyte by potentiostat analysis. The results showed that, the prepared amorphous-nanocrystalline Fe-Ni-Cr coating in lower current densities has higher corrosion behavior due to lower density of micro-cracks in coat. The annealing process and the crystallization of amorphous phase (at 250oC for 10 h) had the positive effects on corrosion resistance of prepared coats. The corrosion resistance of composite coatings was higher than alloyed coatings. In this condition, the highest corrosion resistance was achieved in the presence of SiC nanoparticle in the coats.

In this research, a uniform film of polypyrrole/CNT/cadmium oxide nanocomposite was produced to protect the austenitic stainless steel 304 against corrosion in 0. 5 molar hydrochloric acid medium. For this purpose, the chemical deposition method was used for CNT / CdO synthesis. Electrochemical synthesis method was used to coat the stainless steel and to find optimal coating conditions. Electrochemical impedance spectroscopy test was used to find the optimum amount of reinforcement nanocomposite. Optical microscope and scanning electron microscope (SEM) were used to study the morphology of coating. Results showed that the final nano composite had a remarkable corrosion resistance and the presence of CNT / CdO reduced the porosities in the final polymer film. Also coating results showed that the optimum amount of apply current density and pH for electropolymerization were 4mA/cm2 and 9 respectively. The 0. 5% weight-volumetric functionalized carbon nanotube with Cadmium Oxide was determined as optimum amount of nano composite reinforcement using a polypyrrole matrix. Polypyrrole Carbon nanotube/Cadmium Oxide nanocomposite coating on the surface of austenitic stainless steel 304 protected more than 92. 5% against corrosion in a 0. 5 M solution hydrochloric acid.

Aluminum-ceramic metal matrix composite is a class of modern engineering materials with interesting physical and mechanical properties. These composites are used widely in many industrial (aerospace, automobile, electronic and etc). In present study, alumina granules preforms with different size (20-100 μ m) were made and sintered at 1300° C and 1400° C for 2 h. Then the preforms were preheated at 700° C for 1h. Finally, molten Al was infiltrated into the preforms under load of 3 MPa by squeeze casting method. After composites making their microstructures were studied by SEM and optical microscope. The microstructure results showed that composite with higher sintering temperature has low porosities and well connected granules. Also, compressive strength, impact resistance and hardness of the composites were investigated. The results showed that sintering temperature improved compressive strength and hardness of the composites, but impact strength decreased. The strength and brittleness of the composites is higher for the composites with high sintering temperature.

In this study, mechanical properties of nano-composites based on epoxy reinforced with graphene nano-platelets and XNBR is investigated. Fillers were added to the epoxy matrix in 0, 0. 75 and 1. 5 wt. % levels for graphene nano-platelets and 0, 5 and 10 wt. % levels for XNBR. Samples were prepared by hand method and mechanical tests were performed in room temperature to determine tensile strength, tensile modulus, elongation at break and impact strength. FESEM images were used to determine the state of graphene nano-platelets dispersion. It was observed that graphene nano-platelets had well dispersion in 0. 75 wt. % but in high loading of them, aggregation was observed. Graphene nano-platelets decreased tensile strength and elongation. On the other hand, enhanced tensile modulus and impact strength by 20% and 23%, respectively. Adding XNBR declined tensile strength and modulus by ~18% and increased impact strength and elongation by considerable amount of 130% and 46%, respectively. Simultaneous presence of graphene nano-platelets and XNBR in epoxy matrix decreased tensile strength by ~10%. On the other hand, tensile modulus, elongation and impact strength increased by 6%, 29% and 143% compared to neat epoxy.

This research is on the energy absorption level in a metal-fiber laminate reinforced with a shape-memory-alloy and against low velocity impact. The parameters of the study are fiber angle, level of pre-strain and position of memory wires in a GLARE reinforced with 2 memory-wires, and a 200-J Charpy-Impact device was used to exert the impact. Moreover, we have focused on effects of changes in fiber's angel, the location of shape-memory wires and their pre-strain effect on energy absorption level of GLARE, which is reinforced with two shape-memorywires, against a Charpy-impact of 200 Jules. Taguchi method was used in designing of the experiments for this research and the investigated specimen were constructed based on L16 orthogonal array. During the usage of array, parameters of "fiber angel" and the "pre-strain level of shape-memory wires" were tested in 4levels as well as the parameter related to the location of shape-memory-wires, tested in 2levels. The scrutinized GLAREs were constructed of 16layers containing 3layers of aluminum. The analysis of variance was performed on extracted data to investigate the effect of changes in parameters on the energy absorption level of laminate-Charpy-impact. It was found that the changes in following parameters of pre-strain of shape-memory wires, fiber's angel and the location of these wires in laminate, have the influence of 39. 12%, 32. 13%, 4. 56%, respectively, on the energy absorption level of laminate. The variance analysis also proved that changes in energy absorption have confidence level of 92. 1%, 90. 6% and 71% respectively with the changes in aforementioned parameters.

Sandwich structures are used in applications that required a combination of high rigidity and low weight same as aerospace, marine and automotive. Large and/or complicated sandwich structures are often manufactured by connecting pre-fabricated sandwich panels by means of connections, adhesive or bolts. In present study, two types of metallic connections were used to join two sandwich panels with glass-epoxy face-sheets and aluminum honeycomb core. Connections have the same material and different geometries and were bonded to the sandwich structures using the same epoxy as used to manufacture the face-sheets. Two groups of specimens were made and tested under bending loading. Also, a finite element simulation using LS-DYNA were performed to predict the behavior of sandwich structures. A good compliance between numerical and experimental results was observed. The effects of increasing the length and the thickness of the connections on the maximum force and energy absorption were investigated to examine the influences of involved parameters on bending response of a sandwich plates.

In the present study the effect of change in thickness and material of the middle layer in fiber metal laminates (FMLs) with squared section on the energy absorption is investigated. In this work four types of specimens, based on the change in the material of the middle layer, were produced. In order to fabricate FML samples, Glass-epoxy, Carbon-epoxy, polyurethane foam and aluminum 2024 were utilized as the middle layer and aluminum 2024 for inner and outer layers, respectively. The specimens were then subjected to the compression test and their forcedisplacement curves were experimentally obtained. Additionally, the effect of the middle layer thickness on the energy abortion performance was studied by numerical simulation using Ls-Dyna explicit code. The numerical model was initially validated by experiment. In conclusion, it was found that the maximum and minimum efficiency were determined for the FML specimen made of Carbon-epoxy and foam, respectively. Moreover, by changing the middle layer thickness, it was numerically demonstrated that the specimen with three layers of the same thickness yields the best absorption energy capability.

In this paper the effect of hygrothermal conditions such as temperature and moisture on buckling of composite laminated plates is investigated. For this purpose, the effect of changing in material characteristics with changing in temperature and moisture on buckling capacity of plates with different end conditions and biaxial loading is evaluated. In addition, the effect of delamination of layers on buckling load of plate is studied in different situations. The finite strip method is used in present paper to calculate the critical load of plate considering first shear order deformation theory. In finite strip formulation for evaluating the displacement field of each strip, the trigonometric shape functions is used in longitudinal direction and the Hermitian and linear shape function is used for out of plate and in plane transverse direction, respectively. The place and dimension of delaminating layers is modeled by separating the adjacent elements and reconstructing the standard, geometric, force and mass matrices, so, the critical load of laminated plates is calculated in different situation. The results show that the amount of changing in critical load of laminated plate for different temperatures, moistures and delamination of layers.

Nanocomposites samples based on unplasticized polyvinyl chloride (UPVC) containing polymethyl methacrylate (PMMA) as toughener, graphene nano-platelets (GNP) as reinforcement and di-octylphthalate as plasticizer were prepared with different composition ratios (i. e. 80/20 and 90/10 containing 0, 0. 5, 1 and 2 phr GNP) using Haake internal mixer. Nanocomposite samples were analyzed using x-ray diffraction and scanning electron microscopy to investigate the mutual interactions between GNP and PMMA. Mechanical properties (Tensile modulus, elongation at break and impact resistance) of the prepared nanocomposites including tensile modulus, elongation at break and impact strength were also measured. Results showed that increasing nanographene platelets content increases tensile modulus where impact strength, tensile strength and elongation at break are decreased. At constant graphene contents, nanocomposites containing 20% PMMA show higher impact strength and tensile modulus. This was attributed to the higher mixing efficiency due to the interactions established between PMMA and GNP observed through FTIR and also higher miscibility of UPVC/PMMA pair besides the PMMA characteristics. Fracture surface of nanocomposites are significantly rough at the presence of nano-graphene which shows the torturous crack growth path.