Shaik Jeelani

Enhancement of strength and stiffness of Nylon 6 filaments through carbon nanotubes reinforcement

We report a method to fabricate carbon nanotube reinforced Nylon filaments through an extrusion process. In this process, Nylon 6 and multiwalled carbon nanotubes (MWCNT) are first dry mixed and then extruded in the form of continuous filaments by a single screw extrusion method. Thermo gravimetric analysis (TGA) and differential scanning calorimetry (DSC) studies have indicated that there is a moderate increase in Tg without a discernible shift in the melting endotherm. Tensile tests on single filaments have demonstrated that Young’s modulus and strength of the nanophased filaments have increased by 220% and 164%, respectively with the addition of only 1wt.% MWCNTs. SEM studies and micromechanics based calculations have shown that the alignment of MWCNTs in the filaments, and high interfacial shear strength between the matrix and the nanotube reinforcement was responsible for such a dramatic improvement in properties.

MANUFACTURING AND CHARACTERIZATION OF CARBON NANOTUBE/POLYETHYLENE COMPOSITES

The present study describes a method to fabricate polymer matrix nanocomposites by reinforcing multi-walled carbon nanotubes through an extrusion process. Linear low density polyethylene (LLDPE) powder and multi-walled carbon nanotubes (CNTs) are first dry mixed and extruded in the form of filaments by a single screw extrusion process. After extrusion, the filament is partially cooled by chilled air, dried, and continuously wound in a spool. The filaments are then laid in roving, stacked in a unidirectional fashion, and consolidated in a compression molding machine to come up with laminated composites. Thermo gravimetric analysis (TGA) has been performed to compare the thermal stability of as-fabricated composites with the neat polymer. The TGA result shows that the extruded composites are thermally more stable than their neat counterparts. The crystalline nature of CNTs and of as-fabricated composites were identified by X-ray diffraction (XRD) studies. The XRD results indicate that the nanocomposite materials are more crystalline than the neat systems, and the differential scanning calorimetry studies also confirmed the same trend. The scanning electron microscopy result showed that the sizes of extruded neat and nanophased filaments were about 117 and 73 µm, respectively. Tensile coupons from the consolidated panels were then extracted both in longitudinal (0◦) and in transverse (90◦) directions and tested in a Minimat Tester. It was found that with the addition of 2% by weight of CNTs in LLDPE, the tensile strength and modulus of the composite has increased by about 34 and 38%, respectively. The (0◦ )a nd (90 ◦) coupons have also demonstrated that there are directional effects in the tensile response, which is believed to have been caused by the alignment of CNTs during the extrusion process. It is our understanding that such improvement in properties is because of the increase in crystallinity of the polymer due to CNT infusion, and also due to the alignment of CNTs in the extrusion direction in the nanocomposites.

Studies on impact damage resistance of affordable stitched woven carbon/epoxy composite laminates

This paper discusses the response of seven layer plain and satin weave carbon fabric reinforced composites fabricated using low-cost Vacuum Assisted Resin Infusion Molding (VARIM) process under low-velocity impact loading. Both stitched and unstitched laminates were tested at energy levels ranging 5-50 J using an instrumented drop-weight machine. A 3-cord Kevlar thread was used to stitch the laminate in two orthogonal grid patterns each at a 6 mm pitch: one with 25.4 mm and the other with 12.7 mm grid. Damage due to impact loading was evaluated through ultrasonic nondestructive evaluation (NDE). Results of the study showed the effectiveness of stitching in containing the damage size with 12.7 mm grid stitch samples exhibiting the least damage. Further, satin weave fabric composites exhibit better impact resistance as compared to plain weave fabric composites.

Sonochemical effect on size reduction of CaCO3 nanoparticles derived from waste eggshells.

A novel combination of mechanochemical and sonochemical techniques was developed to produce high-surface-area, bio-based calcium carbonate (CaCO3) nanoparticles from eggshells. Size reduction of eggshell achieved via mechanochemical and followed by sonochemical method. First, eggshells were cleaned and ground, then ball milled in wet condition using polypropylene glycol for ten hours to produce fine particles. The ball milled eggshell particles were then irradiated with a high intensity ultrasonic horn (Ti-horn, 20 kHz, and 100 W/cm(2)) in the presence of N,N-dimethylformamide (DMF); decahydronaphthalene (Decalin); or tetrahydrofuran (THF). The ultrasonic irradiation times varied from 1 to 5 h. Transmission electron microscopic (TEM) studies showed that the resultant particle shapes and sizes were different from each solvent. The sonochemical effect of DMF is more pronounced and the particles were irregular platelets of ~10 nm. The BET surface area (43.687 m(2)/g) of these nanoparticles is much higher than that of other nanoparticles derived from eggshells.

Low Velocity Impact Response of Resin Infusion Molded Foam Filled Honeycomb Sandwich Composites

In this study the low-velocity impact and post-impact response of low-cost resin infusion molded sandwich composites utilizing a foam filled honeycomb core with graphite and S2-glass fabric facesheets (skins) has been investigated. The foam filled honeycomb core provides combined advantages of the traditional foam core and honeycomb sandwich composites in that it possesses high shear and bending stiffness, and cell wall stability. The low velocity impact response of 101.6 mm x 101.6 mm sandwich plates is studied at five energy levels representative of damage initiation and propagation. The low velocity damage is correlated to ultrasonic C-scan images, vibration resonance frequency and optical microscopy observations. The results indicate that the damage tolerance is enhanced by the foam filled honeycomb core and that load required to initiate damage is independent of the facesheet type for any specific core/facesheet thickness. The sandwich composites with S2-glass facesheets are found to possess more damage tolerance as compared to the graphite facesheets.

Sonochemical synthesis and rheological properties of shear thickening silica dispersions.

A sonochemical method has been developed to synthesize shear thickening fluid. This shear thickening fluid (STF) is composed of hard silicon dioxide nanoparticles and polyethylene glycol (PEG) liquid polymer. The combination of flow-able and hard components at a particular composition, results a material with remarkable rheological properties that is suitable for liquid body armor applications. In the present study nine types of STFs have been synthesized with two different types of silica nanoparticles (15 nm and 200 nm) and polyethylene glycol at various weight fractions using a high intensity ultrasonic irradiation. The resultant STF samples were tested for their rheological and thermal properties. The advantages and disadvantages of this process have been discussed.

Residual Stress Distribution in Machining Annealed 18 Percent Nickel Maraging Steel

A novel electrolytic etching technique is used to determine the residual stress distribution in the machining of annealed 18 percent nickel maraging steel. Ring shaped specimens were machined under unlubricated orthogonal conditions with carbide cutting tools having wear lands of 0.125, 0.25, and 0.5 mm length at cutting speeds ranging between 0.05 and 1.60 ms−1 . The results of the investigation show that the residual stresses are tensile at the machined surface and decrease with an increase in depth beneath the machined surface. The maximum (near surface) residual stress and depth of the severely stressed region increase with an increase in cutting speed and tool wear land length. The results are interpreted in terms of the variations in the amount of surface region deformation produced by changes in cutting conditions.

Subsurface plastic deformation in machining 6Al-2Sn-4Zr-2Mo titanium alloy

Abstract The effect of cutting speed and tool geometry on the plastic deformation in the surface region of 6242 titanium alloy machined orthogonally under lubricated and unlubricated conditions is determined using the grid technique and metallography. The results show that the magnitude of the plastic deformation in the surface region and the depth of the work-hardened layer increase with an increase in the cutting speed or the tool wear land length. The presence of the lubricant in the cutting region results in a considerable reduction in the subsurface damage.

Strain rate effects on sandwich core materials: An experimental and analytical investigation

Abstract Poly-vinyl chloride (PVC) based closed-cell foams were tested at different strain rate under compression loading ranging from 130s–1750 s −1 using a modified Split Hopkinson Pressure Bar (SHPB) apparatus, consisting of polycarbonate bars. Foams with different density and microstructure were examined. The attainment of stress equilibrium within the specimen at various strain rates was examined. It was found that the stress equilibrium was reached early at lower strain rate as compared to higher strain rate. Both the peak stress and absorbed energy were found to be dependent on foam density and strain rate, although foam density was found to be a more dominating factor. A model based on unit cell geometry of the closed-cell foam was also developed to predict the absorbed energy at high strain rate. The proposed model is found to be promising in predicting the energy absorption during high strain rate loading.

Effects of stress ratio on fatigue life of carbon-carbon composites

Cyclic loading causes cumulative damage and therefore degrades the inelastic properties of composite materials. Present work investigates the damage development under tension-tension fatique, and the effect of stress ratio on the fatigue life of carbon-carbon (CC) composites at room temperature at a frequency of 3 Hz. The fatigue damage has been identified through ultrasonic non-destructive technique, optical microscopy and scanning electron microscopy. From the S-N curve it has been observed that the endurance strength of CC composite is quite high; approximately 85% of the ultimate tensile strength. The fatigue life of CC composites has also been observed to increase with the stress ratio. Matrix cracks, filament splitting within the yarns, complete delamination and the nucleation of the interfacial flaws have been identified as the failure mechanisms during the fatigue tests. On the other hand, the failure modes during the static test were found to be complete fiber fracture accompanied by partial delamination. A statistical fatigue life distribution for carbon-carbon composites has also been presented in this paper.