فهرست مطالب karim shelesh-nezhad

Hypothesis: 

The effect of incorporation of carbon black nanoparticles (CB) and nano-precipitated calcium carbonate (NPCC) on wear behavior, thermal behavior and morphology in polyacetal (POM)-based nanocomposite gears has been studied. Polyacetal is one of the widely used engineering materials for manufacturing the gears. Nevertheless, heat resistance and relatively low crack impact strength and sensitivity to UV are the major disadvantage of POM. Adding carbon black nanoparticles into the polyacetal can simultaneously increase the tensile strength and toughness and increase the UV resistance of the polyacetal. In addition, the presence of NPCC in the POM/CB can lead to improvements in CB dispersibility, increase of wear and thermal resistance.

POM/CB/NPCC nanocomposite gears containing 0.42% (by wt) carbon black and different fractions (1.5%, 3% and 4.5% all by wts) of NPCC were produced by utilizing a twin-screw extruder and injection molding machine. Morphology and nanostructure were investigated by applying scanning electron microscopy. The gear performance of nanocomposites was examined by applying a gear test rig. Gear tests were performed in the mode constant loading. The temperature and wear of the gears were evaluated in the gear tests. 

The simultaneous addition of both types of nanoparticles to polyacetal led to a reduction in the amount of wear by 58% compared to pure polyacetal. The temperature of the gear surface, in the same number of revolutions, was reduced using CB and NPCC nanoparticles. The decrease in the temperature of the nanocomposite tooth surface compared to pure POM was attributed to the increase in storage modulus and improvement in elastic behavior, decrease in damping ratio, as well as decrease in friction coefficient and increase in heat transfer in presence of nanoparticles. The use of 4.5% (by wt) of NPCC nanoparticles caused cracks and expansion of wear and material flow in the gear pitch zone.

Acrylonitrile-butadiene-styrene (ABS) polymer owing to its relatively good mechanical properties is broadly used in the production of plastic products. However, ABS low fluidity prevents molding of thin-walled products. In this study, poly (butylene terephthalate) (PBT) was applied into ABS to enhance fluidity. In addition, carbon nanotubes utilized to promote mechanical performances. ABS/PBT blends of three different weight percentages (90/10, 80/20, 70/30) and nanocomposites based on ABS/PBT (80/20) blend containing 0.1, 0.3 and 0.5 wt. % of carbon nanotubes were prepared by employing a twin-screw extruder and an injection molding machine. The mechanical properties including tensile, flexural and impact resistance along with morphology and fluidity of different samples were investigated. The presence of 10, 20 and 30 wt.% PBT in ABS elevated the melt flow index as much as 25, 58 and 78% respectively as compared to pure ABS. The inclusion of PBT enhanced tensile and flexural strengths but reduced notched impact resistance. The existence of carbon nanotubes in ABS/PBT improved mechanical properties. The highest tensile strength was observed in nanocomposite containing 0.5 wt.% carbon nanotubes. The maximum flexural strength and impact resistance were observed in nanocomposite containing 0.3 wt.% carbon nanotubes. SEM studies showed the significant effect of CNT inclusion on the fracture morphology of nanocomposite samples.

Acrylonitrile butadiene styrene (ABS) has comparatively good mechanical properties, but its low fluidity limits the injection molding of thin parts. In this research, acrylonitrile butadiene styrene/thermoplastic polyurethane (ABS/TPU) blends and ABS/TPU nanocomposites containing multi-walled carbon nanotubes (MWCNT) were produced by employing a twin-screw extruder and injection molding. The morphology of fracture surfaces was studied by scanning electron microscopy. The tensile, flexural and impact properties as well as melt fluidity of different specimens were evaluated. The addition of TPU to ABS substantially increased the melt flow index (MFI), but decreased the mechanical properties. The presence of carbon nanotubes in ABS/TPU blend improved mechanical properties and expanded the plastic deformation of fractured surfaces. The maximum tensile and flexural strengths were obtained by applying 0.3 and 0.5 wt.% MWCNT, respectively. The notched impact strength in nanocomposite containing 0.1 wt.% CNT showed about 95% increase in comparison with ABS/TPU blends. The appropriate dispersion of carbon nanotubes and their adhesion to polymer matrix were considered as the most important factors in improving mechanical properties.

In recent years, numerous investigations have been conducted on self-healing process using vascular network in composites. Since the vascular network in the composites leads to a decrease in virgin tensile properties, it is important to determine the optimal design of the vascular network in order to achieve minimum tensile properties loss. In this research, experimental and numerical studies on the effect of hollow glass fiber (HGF) presence and orientation on tensile behavior in epoxy/glass fiber composite are carried out. The orientations of HGFs were selected at three levels of 0, 45 and 90°, and the distance of HGFs was kept at 200 μm. The experimental results indicated that the presence of blank HGFs in composite lowered the tensile strength. The lowest decrease in tensile strength was observed in the composite containing HGF at angle of 45°. The presence and failure of HGFs in composite specimens were studied using scanning electron microscopy. Next, three-dimensional simulations of composite containing vascular HGF were performed using ABAQUS software and representative volume element (RVE). To simulate the interface of HGFs and epoxy matrix, a combination of cohesive zone and Columb’s friction models was used. A good agreement between FEM and experimental results for tensile strength of different specimens was observed. Next, the healing performance for composite containing self-healing HGFs at angle of 45° was investigated.

In this study, the effect of vascular self-healing orientation on tensile strength and healing efficiency of epoxy-glass composite has been experimentally studied. Hollow glass fiber (HGF) of 450±10 μm diameter and 50%-55% hollowness was produced by using an extruder. Following, the HGFs were filled with healing components, and subsequently employed as vascular healing system in composite laminate. The orientations of HGFs were selected at three levels of 0, 45 and 90°. The distance of HGFs was kept at 200 μm. The virgin, damaged and healed specimens were characterized in term of tensile behavior and subsequently the healing efficiency was studied. The results of tensile tests indicated that the presence of blank HGFs in composite lowered the tensile strength as high as 17, 14 and 21% for HGFs angles of 0, 45 and 90°, respectively. As a damage, a strain of 1.2% was initiated in the tensile specimen and afterward the self-healing process was accomplished at temperature of 70 ˚C for a time period of 48 hours. Subsequently, the healing efficiency was measured by tensile testing. The results indicated that the best orientation of the filled HGFs was 45°, where the healing efficiency was equal to 42%. The morphology of fractured HGFs and healed zones was studied by employing scanning electron microscopy.

In this research, thermoplastic polyurethane (TPU) and clay nanoparticles were incorporated into poly (butylene terephthalate) (PBT) to improve the impact and tensile properties. The PBT/TPU (90/10, 80/20 and 70/30) samples were prepared by melt mixing using a co-rotating twin-screw extruder followed by injection molding. At the next stage, clay nanoparticles of different weight fractions were added to the PBT/TPU (80/20) blend in the same way to prepare nanocomposite samples. SEM images illustrated good compatibility between TPU and PBT. To characterize the dispersion of clay layers in the polymer matrix, wide-angle X-ray diffraction (WAXD) inspections were performed. The results of the mechanical assessments showed that the addition of TPU to PBT significantly increased the impact strength but decreased the tensile strength and modulus. Incorporating clay nanoparticles into the PBT/TPU blend noticeably improved the tensile properties of PBT/TPU-based nanocomposites. A balance of the tensile and impact properties was found in the PBT/TPU/clay (80/20/3) nanocomposite system.

The tensile properties of multiscale, hybrid, thermoplastic-based nanocomposites reinforced with nano-CaCO3 particles and micro–short glass fibers (SGF) were predicted by a two-step, three-dimensionalmodel using ANSYS finite element (FE) software. Cylindrical and cuboid representative volume elements were generated to obtain the effective behavior of the multiscale hybrid composites. In the first step, the mechanical performance of co-polypropylene/CaCO3 nanocomposite was analyzed. The thickness of the interphase layer around the nanoparticles was estimated by using differential scanning calorimetry data. In the second step, the nanocomposite (co-polypropylene/CaCO3) was considered as an effective matrix, and then the effect of micro-SGF inclusion on the corresponding effective matrix was evaluated. The FE and experimental stress-strain curves of multiscale, hybrid composites were compared at different weight fractions of the nanoparticle. The proposed two-step method can easily predict the tensile properties of multiscale, hybrid, thermoplastic-based nanocomposites.

Nanocomposites based on polyoxymethylene (POM)، containing 1. 5 to 9 wt% of CaCO3 nanoparticles، were prepared by melt compounding، using a co-rotating twin screw extruder، followed by injection molding process. The thermal behavior، mechanical properties as well as morphology were characterized. The inclusion of CaCO3 nanoparticles into POM slightly affected the melt flow index. The differential scanning calorimetry (DSC) results indicated that the incorporation of CaCO3 nanoparticles has nucleating effect and can raise the temperature and the degree of crystallinity. The results of shrinkage assessments revealed that crystal nucleation and filling effects of CaCO3 nanoparticles have counter effects on thermal contractions. Incorporation of the CaCO3 nanoparticles into POM improved tensile and flexural properties as well as the impact resistance at the same time. The maximum tensile strength، tensile modulus، flexural strength، flexural modulus and impact strength were achieved in the order given by applying 1. 5، 6، 3، 6، 3 wt% of CaCO3 nanoparticles، which corresponded to 13، 40، 33، 15 and 20% higher than those of pure POM. The notable improvements of tensile، flexural and impact properties as a result of incorporating 3 wt% of CaCO3 nanoparticles were attributed to the nucleation and crystallinity enhancements as well as relatively uniform dispersion of CaCO3 nanoparticles in POM matrix. The morphology studies indicated that CaCO3 nanoparticles inclusion can alter the fracture mechanism from brittle-to-ductile-brittle، a sharp transition from ductile-to-brittle fracture observed in POM/CaCO3 nanocomposite.

Nanocomposites 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 prepared by melt compounding followed by injection molding. The mechanical properties, water absorption, as well as shrinkage behavior were characterized and the morphology was studied using scanning electron microscopy. The presence of PP, PP-g-MAH and nano-CaCO3 lowered the amount of water absorption as high as 72 wt%. Morphology analysis indicated that the addition of PP-g-MAH can significantly improve the adhesion between PA6 and PP phases. The incorporation of PP-g-MAH led to 24% increase in flexural and impact strength, 27% rise in tensile strength and approximately 100% increase in elongation-at-break. The addition of nano-CaCO3 particles increased the impact resistance and flexural strength. The results of experiments indicated that the maximum flexural strength was achieved by adding 5 phr of nano-CaCO3 which was 16% greater than pure PA6, and the maximum impact strength was attained by adding 7.5 phr of nano-CaCO3 which was 29% superior compared to pure PA6. The incorporation of 10 phr of nano- CaCO3 particles led to filler agglomeration and, consequently, the impact strength was dramatically dropped. Dimensional characterization of molded samples revealed that the incorporation of PP-g-MAH can raise the shrinkage, but the addition of nano- CaCO3 has not had any considerable effect on the shrinkage of nanocomposites.