---

The influence of maleic anhydride-polypropylene (MAPP) (0, 2, 3 and 5%) as a compatibilizer on the wettability of polypropylene/wood flour/glass fiber hybrid composites was studied by using the contact angle determination technique. Sample slats with a cross section of 10×70 mm were made by a twin screw extruder. Specimens were conditioned at room temperature and the angles between the water droplets and surfaces of the hybrid composites were measured. Results revealed that the wettability of the composites was significantly decreased as the MAPP was increased to 3%. However, no significant decreasing effect was observed at MAPP contents above 3%.

---

Nanostructured (Al-8wt%Zn-3wt%Mg) alloy was synthesized by simultaneous fracture and cold welding mechanisms in mechanical alloying with initial elemental powders and subsequently, this alloy was applied as matrix to fabricate Al/Short glass fiber nanocomposite in 1, 3 and 5 percent of glass fibers. The resulting powders were consolidated under 400 MPa at 380 °C in cylindrical die to produce consolidated nanocomposites. Relative density of samples reduced with increasing the percentage of glass fibers and this trend was more intense from 3 to 5 percent. Also compressive strength and hardness were investigated for these samples in different percent of glass fiber. The results showed that strength and hardness were enhanced with increasing glass fiber but decrease of mechanical properties was observed in 5 percent due to reducing in relative density. Compressive strength was compared between nanocomposite with pure Al and Al alloy matrix, and results show more reinforcement in Al based sample.

---

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.

---

In recent years a high attention has been conducted to the structural application of wood plastic composites (WPCs). Regarding that the WPCs have lower mechanical strengths, fiber reinforcements have been applied for strengthening the WPCs. Hybrid wood plastic composites (HWPCs) include two types of reinforcements of glass fibers and wood flours that are added to a polymeric matrix. WPC pallets as an example can exploit the mechanical strength of HWPCs. In previous work, wood plastic composite was reinforced by continuous glass fibers by a unique extrusion process. Embedding the continuous glass fibers in WPC matrix resulted in significant improvements in mechanical properties such as tensile and impact strengths. In this paper, a model has been proposed to predict the tensile strength and modulus of the WPCs reinforced with unidirectional glass fibers. The methodology applied in this research considers the WPC as matrix and the glass fibers as reinforcements. Since WPC matrix is brittle, the rule of mixtures corresponding to the brittle matrix composites was used to predict the tensile strength. Results indicated that the predicted tensile properties were in good agreement with experimental data. The obtained mean errors between the experimental and theoretical results for tensile strength and modulus were 9.5% and 8.6% respectively.

---

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.

---

In this paper, the effect of processing temperature on the elastic and viscoelastic properties including storage modulus, loss modulus and damping value of PVC/plain weave fiberglass composites laminates was investigated. For this, composite samples with [0/90]10 lay ups were produced in three different temperatures including 160 ᵒC, 200 ᵒC and 230 ᵒC using film stacking procedure. Firstly, the flexural strength and modulus of the samples were measured using three points bending test according to ASTM D790-07 standard. Then, viscoelastic properties of the samples were measured in the temperature range of 25 ᵒC up to 220 ᵒC using Dynamic Mechanical Thermal Analysis (DMTA) and the effect of temperature on the viscoelastic properties was studied. Also, the effect of fiber/ matrix impregnation quality on the thermal and dynamic properties of the samples was evaluated using optical microscope images. It was concluded that the temperature of 230 ᵒC is proper to achieve high quality impregnation, according to both DMTA and three points bending test. Also, it was seen that increase of processing temperature up to 230 ᵒC increases the storage modulus; however, processing temperature doesn’t affect the glass transition temperature of the samples.

---

This research investigated experimentally the effect of useing of 3D fiberglass fabric in the energy absorption in glass fiber metal laminate composite made by vacuum assisted resin transfer molding (VARTM) method. The prepared GLARE is made of two or three Aluminum 2024 facing sheets and E glass/epoxy as nano composite core. Composite core section for samples of glass fiber plain weave has been composed of plain weave glass fiber 200 g⁄m^2 , 3D fiberglass fabric samples consists of 3D fiberglass fabric to thickness of 5 mm, resin R510 and hardner H515. All panels fabricated using VARTM method in section glass fiber plain weave in fiber volume fraction of 71%. Low velocity impact tests were conducted using by drop weight device at the impact energy of 50 and 80 j. The results of the low velocity impact experiments show that the amount of resistance of impact plain weave samples in comparison to the 3D fabric in various energy levels is more and better. In applications where weight is an effective agent component, the weight of glass fiber plain weave base samples is less than 3D fiberglass fabric samples.

---

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.

---

This study investigates the effect of steel fibers and its hybrid form with glass fiber on the properties of cement composites. The studied mechanical properties included compressive strength and flexural strength, and the energy absorption rate of the specimens was determined by the flexural toughness. In the mixtures, Portland cement and calcium aluminate have been used as bonding agents the mixes containing 2% steel fiber (% of total volume of the mixture), 2% AR Glass fiber, and hybrid of these fibers were made of glass fiber (2% steel fibers and 2% glass fiber), the length of these fibers was 25 mm. The compressive strength test was performed at the age of 1, 7, 28 and 90 days. Speciments made with calcium aluminate cement had higher compressive strength due to quick formation of microstructure compared to Portland cement mixtures, so that 90-day compressive strength of Portland cement mix was lower compared to the 1-day compressive strength of Calcium aluminate concrete. Incorporating 2% steel fibers also had a slightly enhancing effect on compressive strength. Flexural strength test was carried out at 28 and 90 days. The steel fibers create appropriate mechanical bond with the cementitious matrix, and the ultimate flexural strength was about 2 times higher than non-fibers specimen, due to the congrated geometry of the steel fibers. Substituting glass fiber also increased the ultimate flexural strength due to the high aspect ratio glass fibers and the well formed Interfacial transition zone (ITZ). The hybridization of the aforementioned fibers with steel fibers increases the bending strength due to the synergistic effect. The energy absorption content of the cementitious mix measured by flexural toughness index shows that this energy absorption content increases with the hybridization of the glass and steel fibers, so that the hybrid specimen made with Portland cement had a flexural toughness of 34.4 Nm. The glass fiber increased the toughness due to its excellent energy absorption. The steel fibers in the mixed increased the area under the flexural loading cureve and prevent the mixture from being destroyed by the first crack. In the shrinkage test results the control specimen with the two types of cements did not differ significantly, but the addition of 2% of the fibers (steel fiber and glass fiber) reduced shrinkage by their limiting effect on length change and propagation of micro cracks. When the percentage of glass fiber become higher, similar to the hybrid mix, the shrinkage was reduced further. This experiment was performed uo to 270 days and it was observed that the shrinkage of the hybrid specimen made with Calcium aluminate cement reduced by 65.5% compared to the plain concrete. In this study, the RCMT was carried out at 90 days. The results indicate that the penetration rate of the hybrid specimens and the glass fiber mixtures were lower than those of the steel fibers incorporated mixed. Also, in comparing two types of calcium aluminate cement and Portland cement, specimen made with calcium aluminate cement, the chloride ion penetration was lower than those made with Portland cement due to the improved Interfacial transition zone (ITZ) and less porosity of this type of cement.   

---

In this research, vinyl ester matrix composite coatings reinforced by E-glass fibers, Nano TiO_2, and Carbon Nanofiber were prepared by hand lay-up method and their mechanical properties were investigated. The mechanical properties of fiber-reinforced composites were investigated by the tensile, impact, hardness, shear test, and wear tests. Scanning electron microscopy was employed in order to study the fracture surface of the prepared samples. The results of the tensile test showed that the presence of the E-glass fibers in the vinyl ester matrix increases the strength about 4 times and the elongation about 8 times. There was no change in the fiber-reinforced composite strength by reinforcing the composite with nanoparticles of TiO₂ and carbon Nanofiber, but the elongation of the fiber-reinforced composite increased by 1.6 times. Impact resistance of fiber-reinforced composite and fiber-reinforced nanocomposite relative to vinyl ester resin increased about 20 and 29 times. The presence of glass fiber and Nanoparticles in the vinyl ester matrix increases the hardness of the samples about 1.5 to 2 times. The results of the adhesion test demonstrated that the presence of nanoparticles in fiber-reinforced nanocomposite improves adhesion to concrete surfaces. Also, the results of the wear test showed that the presence of glass fiber in the matrix of vinyl ester reduces wear resistance and the presence of Nanoparticles in fiber-reinforced nanocomposite improves wear resistance of the fiber-reinforced composite.

---

Digital Shearography is one of the new methods of non-destructive testing based on the laser beam which is used to measure the surface displacement derivatives. In this method, relying on the interference of two laser waves reflected from the object surface, the displacement gradient of the deformed sample can be measured directly. So that it is possible to evaluate the industrial parts in a non-contact and full-field way with a high speed and accuracy. One of the significant advantages of this method is the ability to detect subsurface defects in various materials, including composites. In this paper, samples with subsurface cracks made of composite materials reinforced with glass fibers and carbon fibers have been inspected by Digital Shearography testing. Also, the optimal values ​​of each main parameter such as shear distance and loading size for each material have been obtained using the Taguchi experiment design. The results show that for each type of material there is an optimal amount of loading amount and shear distance, which if applied, the best test results are obtained.