---

In this research,nanocomposite coatings based on epoxy containing pristine graphene oxide and starch-modified graphene oxide are prepared and characterized by Fourier transfer infrared spectroscopy, andtheir crosslinking behavior is studied using nonisothermal differential scanning calorimetry.These nanocomposites, because of having platelet-like nanomaterials inside and their organic origin, can be applied as coating on metal surface in diverse industries.The reason behind using starch was its natural basis and abundance of hydroxyl groups in its structure which can take part in crosslinking reaction with epoxide. Neat epoxy systems having amine curing agent, and nanocomposites containing epoxy, amine curing agent, andpristine or starch-modified graphene oxide nanosheets were cure at different heating rates to assess their curing behavior. Change in hearing rate of test caused change in onset and peak temperature of the exotherm curves and consequently heat of reaction changed. It was observed that the presence of the graphene oxide nanosheets hindered the crosslinking reactions, while surface modification of them with starch natural polymer compensated for such a hindrance via catalytic role of starch, and increased crosslink density of system. 

---

In this study, three different size (100-300-500 µm) of the rubber powder (waste tire) were used in the formulation of epoxy- phenolic adhesive. Rubber powder was modified with grafting method by acrylamide monomer. In order to prevent any loss in properties such as modulus and strength of the adhesive, which is due to the addition of rubber powder to the adhesive, the micro particles of silica were used in formulation of epoxy- phenolic adhesive.  The experiment was designed by Taguchi method, and in the experiment, the effect of the composition of rubber powder, size of rubber powder, composition of silica filler and phenolic resin on mechanical and thermal properties of epoxy adhesives were investigated. To study the mechanical properties of adhesives and adhesion properties, dumbbell-shaped specimens and single edge lap bonds that have been made of metal (stainless steel) to composite (epoxy resin / carbon fiber) were prepared and subjected to tensile test. Thermal stability and interfacial interaction between epoxy and filler in adhesive formulation were explored by thermogravimetric analysis and Fourier transform infrared spectroscopy analyses, respectively.  Tensile test results showed that for lap- joint bonding with the addition of each factor in its optimal level into epoxy adhesive, strength, modulus and toughness increase by 7.5%, 27.56% and 114% respectively in comparison with  the samples bonded with the neat  epoxy adhesive. A significant increase was obtained in thermal stability for formulated adhesive samples compared with neat epoxy adhesive.
 
 

---

The aim of this project is the design and optimization of the formulation of epoxy adhesives for bonding metal to composite parts . This joints are most widely used in the aerospace industry to reduce stress concentration at a point. Joints for single edge joining include stainless steel metal with commercial code 316L and composite epoxy resin / carbon fiber. In this study, the effect of three types of additives: filler (alumina micro-particles), nylon 6.6 and phenolic resin (type of resin) on the mechanical and thermal properties of epoxy adhesive have been investigated. Tensile test results showed that increasing alumina fillers increases the tensile strength and overlap shear adhesive samples, respectively, in single lap joint dumbbells and elderly. The test showed that increasing the amount of nylon 6.6 When is slightly higher due to a sharp drop in tensile strength and overlap shear, respectively, in both cases is dog bone and single lap joint adhesives. This limit depends on the capacity epoxy ring to absorb amide hydrogens. The test for thermal properties (TGA) showed that increasing the amount of phenolic thermal stability is improved. High-temperature tensile test of appropriateness is also increasing impact of phenolic resin. Finally, the adhesive properties built with the similar adhesive (UHU) were compared. Results showed superiority in single lap joint metal to composite adhesive is made in the study.

---

Research subject: In this research we studied the anti-corrosion properties of epoxy coating containing anti-corrosion pigment zinc phosphate with hydrophobic nano silica with different percentage also for determine the optimal conditions for preparation of nanocomposite Taguchi experimental design method was used.
 
Research approach: Anti-corrosion properties of epoxy coating under the influence of very important factors such as the percentage of nano silica, anticorrosive pigment and pigment to resin ratio according to model L9 taguchi method was studied and analyzed. Anti-corrosion properties of epoxy coatings were studied by electrochemical impedance spectroscopy test (EIS) in 3/5% NaCl aqueous solution and salt fog test (salt spray). To investigate the distribution of nano silica particles in epoxy resin were analyzed by transmion electron microscope (TEM) and scanning electron microscope (SEM). The results show that using from zinc phosphate and nano-silica was able to improve the corrosion resistances.
 
Main results:Results shows that addition of zinc phosphate and nano silica to epoxy resin caused a decrease in number of blisters and corrosion products after exposure to corrosion test based on the results in Nyquist and Bode plots, also the similarity in results was observed for the epoxy coating loaded according to the optimum conditions with 8% zinc phosphate, 3% nano silica and pigment to resin ratio of one according to salt spary. The significance levels of the experimental parameters, which indicate how the factors affect the compressive addition of zinc phosphate and nano silica to epoxy resin, were determined by using variance (Anova) method.

---

Abstract
Research subject: In this research, epoxy modification was successfully performed by polyurethane and its effect on abrasion and adhesion properties have been investigated. The most important concern in the blending of these polymers was the formation of gels upon exposure of epoxy resin and isocyanate in polyurethane.
Research approach: One solution to overcome this problem is to control the chemical activity of Isocyanate. Therefore to reduce the chemical activity of isocyanate and prevent gel formation due to the combination of epoxy and polyurethane, first polyurethane prepolymer containing 3.58 wt.% NCO was prepared by mixing poly tetra methylene glycol 2000 (PTMG 2000) and toluene di isocyanate (2,4-TDI); and then by adding 20 wt.% of it to the epoxy resin, the curing process was completed by using dimethyl thio-toluene di amine (DMTDA) as a common curing agent and also specific heat treatment.
Main results: Fourier transformation infrared spectroscopy results showed that the modification process has been successful by elimination of the peaks related to epoxide and isocyanate groups in the prepared sample in addition to the formation of a broad peak related to secondary hydroxyl group (C-O) due to the opening of epoxide rings. Pull off tests also confirmed increasing adhesion to carbon steel substrate as a result of secondary hydroxyl generation through this blending. Although, the Persoz hardness of modified epoxy decreased by 5%, but with a 17-fold reduction of elastic modulus (as per tensile test result), abrasion resistance improved 6 times according to abrasion test. Finally, joining of the cavities to each other is introduced as the abrasion mechanism by considering the field emission- scanning electron microscope images.

---

Syntactic foams are a kind of composite; consist of polymeric matrix and hollow micro-balloons. They have high strength to weight ratio if it compare to the neat matrix material. In this paper epoxy resin as matrix and ceramic micro-balloons are used and 36 kinds of syntactic foam were fabricated to investigate the effect of preparation factors such as: mixing speed, mixing time, mixing sequence and extracting bubbles by a vacuum oven on the mechanical properties. Also, two undesirable events like micro-balloon flotation in matrix and porosity are investigated as they affect the foam`s strength. The results show that the speed and sequence of mixing are not effective seriously. However the time needed for mixing would be changed for different volume percent of micro-balloons. It should be noted that as flotation and porosity increases the compression strength decreases. Using the vacuum pressure before molding may decrease the matrix porosity for above 40% micro-balloon volume fraction syntactic foams. Converse to previous, using the vacuum pressure for below 40% micro-balloon volume fraction syntactic foams would increase the floatation and decreases the compression strength.

---

Epoxy / ceramic micro balloon syntactic foams are used in marine and automobile industries because of their high specific strength and capability of absorbing energy. In this paper, the neat epoxy and 9 series of syntactic foams with 3 kinds of ceramic micro balloon with different diameters and crush strength in different volume fractions (20%, 40% & 60%) were fabricated. Effect of varying these parameters on the mechanical properties of syntactic foams is investigated. Besides of all, the effect of different loading rate is investigated, too. All of the samples were tested in 10-1, 10-2 and 10-3 strain rates. The results indicate that with increasing the strain rate from quasi-static to moderate rates, the strength of foams became more. Also the results show that the syntactic foam with bigger micro balloon was weak in compression. In syntactic foams of low volume fraction the size effects is more. On the other hand, with increasing the volume fraction, the crush strength of micro balloon is become effective. Plateau stress and absorbed energy results show these facts obviously. With increasing the strain rate, the strength is increased considerably.

---

Recently, great attention has been focused on epoxy polymers in different industrial and scientific activities, owing to superior mechanical properties and their stability in different environmental conditions. In this study, the molecular dynamics method was used to study the structure of cross-linked epoxy polymers and predict glass their transition temperature (Tg). The epoxy polymer with a certain degree of cross linking was constructed through the previously proposed cross linking procedure. A temperature cycle (300-600 K) with a constant rate was then applied to the cross-linked epoxy, and a rough estimate of the glass transition region was obtained through mean squared displacement curves. Thereafter, variation of density in terms of temperature was utilized to precisely calculate Tg. The estimated Tg was found to be in good agreement with experimental observations. Radial distribution function was finally used to investigate the effects of temperature and cross linking on the local structure of simulated polymer.

---

In the present study, central composite algorithm was used in order to model and optimize the mechanical behavior of “glass fiber reinforced epoxy composite - structural steel “connections. Initial tests showed that the polymer curing variables play a significant role as key process parameters in producing strong and reliable connections. After conducting Thermal Gravimeteric Analysis on polymer, by selecting curing time and curing temperature as input variables, the parameters were coded and each of them was studied in five levels. In order to estimate the desirable response and provide appropriate models, thirteen tests were conducted systematically. In order to assess the accuracy and to validate the proposed model, analysis of variance was performed successfully. The effect of curing time and curing temperature on the connection’s strength quality was studied utilizing two-dimensional graphs. Utilizing this approach the optimal bonding process variables was achieved at 40°C and 180 min for curing temperature and curing time respectively. Finally, the results obtained from micro structural characterization and fractography analyses of joints by Optical and Scanning Electron Microscope were in good agreement with the results achieved by the developed model.

---

The aim of this article is to investigate the effects of Nylon nanofiber in carbon- epoxy composites properties under double cantilever beam test by Non-destructive Acoustic Emission testing. In order to increase tougher of carbon- epoxy composite, Nylon nanofibers were placed in to the midplane interface of carbon- epoxy laminates. In order to better identification of the effects of Nylon nanofibers and more accurate clustering of Acoustic emission parameters were used combining of k-means algorithm and Genetic algorithm for clustering. Acoustic emission descriptors like Amplitude, Duration, Count, Acoustic Energy and Rise time were used in order to survey identification of effects of nanofibers. The results of clustering of Acoustic emission signals that obtained from carbon- epoxy composite and carbon- epoxy nanomodified composite shows that the presence of Nylon nanofibers increase the tougher of carbon- epoxy composite and delayed damage mechanisms. This method of clustering is a good fit between acoustic signals and damage mechanisms and time of events. Cumulative events of Acoustic emission Amplitude obtained from damage mechanisms of both composite are in the same range and Acoustic emission duration of carbon-epoxy is more than carbon-epoxy nanomodified composite.

---

Purpose of this study is to identify effects of hybrid fibers in composites properties which has reinforced by carbon and basalt fibers and also effects of hybrid composite in Acoustic Emission (AE) behavior under four point bending test by non-destructive AE testing. One of the main problems for failure mechanisms identification by AE method is discrimination of events due to different types of damage which occurs during loading of composite material. Fuzzy C- means clustering algorithm is a tool which is used in this paper to separate acoustic events. The results show that the method of clustering provides a better correlation between the acoustic signals, damage mechanisms and also time of these mechanisms. For analyzing the AE signals, some of the descriptors like amplitude, duration, count, acoustic energy and rise time were used to identify the micro mechanisms of failure. In the first steps of the hybrid composite loading, it is noisier than the last steps and it shows the progressive damage mechanisms. Scanning Electron Microscope (SEM) observation was verified the results of tests and analysis.

---

The purpose of the present research is to investigate effects of long multiwall carbon nanotubes (MWCNTs) on mechanical properties of epoxy resin and unidirectional glass fiber reinforced laminated polymeric composites. Therefore, mechanical properties of polymer (pristine resin), 0.5 wt.% MWCNT/epoxy nano-composites, E-glass/epoxy laminated composites and 0.5 wt.% MWCNT/E-glass/epoxy laminated nano-composites were evaluated. The tensile, flexural and shear moduli and strengths of epoxy polymer and nano-composites were experimentally characterized. Next, the longitudinal and transverse tensile stiffness and strength, also in-plane shear and flexural moduli and the strength of glass fiber laminated composites and glass fiber laminated nano-composites were determined. The experiment results of tensile specimens of laminated nano-composites reveal that the presence of the long MWCNTs improves the bounding properties of fibers in adjacent plies and postpones the failure mechanisms like fiber fracture under tension or edge delamination under shear loading conditions. It can be concluded that the improvement of mechanical properties in laminated composites are more significant than those of the pure epoxy with addition of long multiwall carbon nanotubes. For instance, the longitudinal tensile strength and shear strength of laminated nanocomposites increased by 34% and 26% in comparison with laminated composites, respectively.

---

Cracks in composite structures are the most common damages. For example, cracks in thickness direction (translaminar fracture) would be due to inadvertent impact of the projectile with the aerospace structures. Most of studies, so far, aimed at studying the interlaminar crack propagation and emergence of the delamination phenomenon. In this paper, in an attempt to study the translaminar crack propagation of composites, test specimens were prepared in the form of butterfly from a woven glass-epoxy composite by hand layup and the autoclave process. Experimental fracture tests were performed in the first mode, mixed-mode and the pure second mode by changing the loading angle, using a specially developed fixture, based on Arcan. Load versus displacement curves were obtained. Using critical loads of the tests and the dimensionless stress intensity factors, obtained from the finite element analysis by ABAQUS software, translaminar fracture toughness of the composite was determined. As the result, it can be seen that the opening mode translaminar fracture toughness is larger than the shearing mode toughness. This means that translaminar cracked specimen is tougher in tensile loading condition and weaker in shear. Finite element analysis was performed using effective elastic properties of the glass epoxy composite obtained from a homogenized woven composite model based on micromechanics. The effect of laminate thickness on the translaminar fracture toughness behavior of the glass epoxy composite has been studied.

---

In this paper, the mechanical behavior of the Graphene Oxide (GO)/ epoxy nanocomposites has been investigated under different strain rates. To reach this goal, GO nano sheets were synthesized through Hummers method (a chemical method) and then GO/epoxy nanocomposite was prepared using the solution-based method. Standard specimens test were made from nanocomposite. In order to study the static and dynamic behavior of material, the static pressure test and the split pressure hopkinson bar test were performed on the specimens, respectively. The results showed that the stiffness and the strength of epoxy increase with adding GO to it. It was found that the behavior of epoxy is dependent on the strain rate so intense that its dynamic strength is more than static one about 50%. Furthermore, the effect of GO in low strain rates is more than high strain rates such that adding 0.3% weight ratio of GO increase the strength of epoxy by nearly 20% and 5% in 0.01 s^(-1) and 1100 s^(-1) of strain rates, respectively. In addition, the comparison of Scanning Electron Microscopy (SEM) images from the fracture surfaces of neat epoxy and its composite showed that the surface toughness of nanocomposite is more than epoxy’s.

---

Today, composite materials have extensive use in aerospace automotive and defense industries compared to metals, because of their high strength to weight ratio and good corrosive resistance. Machining of these materials regard to their composite structure is complicated. Achieve optimal machining conditions, depending on the needs, according to the type of fiber and resin used in composites, need proper analysis and careful investigation. In this study, composite pipes made of glass-epoxy to a thickness of 5 millimeters, which are often used in the body of Aerospace structures, produced by hand lay-up and their surface roughness after turning process is measured. In order to obtain the minimum roughness in the turning process, tool type in two modes, and cutting speed, feed rate, and depth of cut are studied at three different levels. So Taguchi experimental design method and experimental test samples on roughness the results analysis and performed by minitab software. Finally, concluded that the minimum value of the surface roughness is obtained by tools with chip-breaking levels, cutting speed 100 m/min, feed rate 0.05 mm/rev, and the depth of cut 1.5 mm.

---

In the case of presence of deep micro-cracks within the composite structures, they must be replaced. The self-healing phenomenon which is inspired from the biological systems such as vascular networks in plants or capillary networks in animals, is an appropriate strategy to control the defects and micro-cracks. In the present research, by taking accounts the advantages of self-healing concept, an attempt has been made to control the micro-cracks and damages which were created in composite structures. To do so, series of micro glass tubes were employed to provide a self-healing system. These micro-tubes were filled with epoxy resin/anhydride hardener as a healing agent. When the structure is subjected to loading conditions, some damages or micro-cracks are created. In this situation, the micro glass tubes will rupture and the healing agent flows in the damage area, leading to the elimination of the defects over a time span. The aim of this study is to find out the appropriate self-healing material volume fraction and healing time to obtain an efficient healing. For this purpose, glass micro-tubes containing various healing agent loadings of 0.75, 1.65 and 2.5 vol.% were incorporated in epoxy-carbon fibers composites and the tensile behavior of the specimens were assessed during different time span from defect creation. The highest tensile strength recovery of 89% was observed for the specimen with 1.65 vol.% healing agent. Also the results show presence of micro tube decrease the fracture strain and over the time span fracture strain recovered.

---

In this research work, the self-healing behavior of epoxy matrix composite which reinforced by hollow glass fibers as self-healing container was investigated. For doing this, in first step, the hollow glass fibers were filled with the epoxy resin and hardener by creating a partial vacuum. Then, the filled hollow glass fibers with different percent of 1, 3 and 5 vol.% were embedded in the epoxy matrix. In the next step, by applying press, the destruction was created in these composites. Then, these destructed composites were healed at ambient temperature at different times of 2, 4, 7 and 14 days. Then, for accessing to the optimum healing time and percentage of hollow fibers in composite, the flexural test was applied in these composites. In the final step, the mechanical properties of composite with the optimum healing time and percentage of reinforcement were evaluated via tensile, flexural and impact exams. The obtained results show that the optimum percentage of hollow fibers and time for healing process are 3 vol.% and 7 days. Also, the healing efficiency of composite in optimum conditions (3 vol.% hollow fibers and 7 days healing time) at tensile, flexural and impact exams were approximately 77, 54 and 92 % respectively.

---

Large and/or complicated sandwich structures are often manufactured by connecting pre-fabricated sandwich panels by means of connections, adhesive or bolts. In nearly all sandwich constructions certain types of joints have to be used for assembly but little is known about their mechanical behavior. This paper deals with the investigation of the behavior of two aluminum joints with different geometries under low velocity impact tests. These two joints are used to connecting sandwich panels with glass-epoxy skins and aluminum honeycomb core. The joints and sandwich panels are connected by means of epoxy resin. After construction of the specimens, low velocity impact tests were performed on the specimens. Finite element analysis were used to simulate the behavior of sandwich panels with connection. Verification of the numerical results was performed by comparing the numerical and experimental results. There was a good compliance between numerical and experimental results. Also, the effect of increasing the length and the thickness of the connections on the behavior of the sandwich panel was done through a parametric study using the FEM model.

---

---