Abrar H. Baluch

Influence of chemically and plasma-functionalized carbon nanotubes on high-performance polymeric nanocomposites

This investigation highlights different surface functionalization processes of multi-walled carbon nanotubes (MWCNTs) and their effects on mechanical properties of polyetherimide nanocomposite. Surfaces of MWCNTs were modified by chemical process and by low-pressure plasma process. There is a significant change in physicochemical characteristics of MWCNTs after chemical and low plasma treatment evident from scanning electron microscopy, transmission electron microscopy, and X-ray photoelectron spectroscopy studies. Due to surface modification of CNTs, there is a significant change in surface morphology and increase in oxygen functionalities such as C=O, C–O, and COOH especially evident in low-pressure plasma treatment; however, differential scanning calorimeter and thermogravimetric analysis studies reveal that thermal properties of the composite do not alter as such. There is a significant increase in mechanical properties of high-performance polymeric nanocomposites when surface-functionalized MWCNTs are dispersed in polymeric matrix; however, surface characteristics of the composite remain almost unchanged evident from contact angle and surface energy studies.

Effect of velocity variation on carbon/epoxy composite damage behavior

In this paper, the damage mechanism for carbon fiber-reinforced polymers composites was studied from low- to high-velocity impact for different velocity ranges. Initially, the composites were manufactured by using CU125NS prepreg in quasi-isotropic 16 layers pattern [0/±45/90]2s in autoclave by adopting standard procedures. Specimens were also exposed to the simulated LEO environment and 0.42% total mass loss occurred due to out-gassing. Afterwards, the specimens were impacted with Al2017-T4 spherical projectiles of 5.56 mm in diameter, 0.25 g in weight for different velocities ranging from 500 m/s to 2200 m/s. With the impact velocity increase, the energy absorption was found to increase in the composite specimens, while the ratio of energy absorbed to total impact energy remains the same on average. Mainly, the fiber breakage and matrix fracture play a critical role in energy absorption, but delamination contribution also found increasing trend with the increase of impactor velocity. Afterwards, C-SCAN analyses were conducted to investigate the damage patterns, and it was found that the damage area increased with higher velocities. The delamination contribution increased on average by 12.7% for the velocity range of 2200 m/s in comparison to that for 502 m/s. On the basis of these findings, it was concluded that the contribution of fiber breakage, matrix fracture and delamination towards the damage mechanism of composites is greater for higher velocities.

Behavior of composite structures orientations towards their failure and damage

In this paper, carbon/epoxy composites were employed as a potential candidate for spacecraft structural shielding along with the new concept of geometric configurations according to the threat severity to maximize the impactor energy absorption to improve performance. Carbon/epoxy composites of quasi-isotropic 16 layers [0/ ± 45/90]2s were manufactured using an autoclave, and the specimens were exposed to a low Earth orbit environment, which produced an average total mass loss of 0.42%, mainly due to outgassing. Al2017-T4 spherical projectiles with a diameter of 5.56 mm weight of 0.25 g were used as the impactor in the velocity range of 1500 ± 500 m/s. Earlier experimentations showed the superiority of obliquity towards energy absorption for single bumpers. Double bumpers with one 45° obliquity at 100 mm standoff absorbed 14% more specific energy than double bumpers with one at 30°; both of them were found to be superior to normal–normal bumpers by 40% and 30% on average, respectively. By CSCAN, it was also found that oblique impact on the first bumper resulted in less damage on the rear bumper and resulted in the superiority of the proposed geometric configurations, which enabled enhanced protection and designs according to threat severity.

Effect of atmospheric pressure plasma treatment for repair of polymer matrix composite for aerospace applications

This paper investigates the repair of polymer matrix composites and validates the repair by static testing. Scarf repair is carried out on the laminates and cured under vacuum. It is observed that 80% of tensile strength is recovered due to this process. Therefore, this investigation highlights the significance of atmospheric pressure plasma treatment on repair of graphite epoxy laminate. It is observed that the surface energy of graphite epoxy laminate has improved significantly due to atmospheric pressure plasma treatment. Atmospheric pressure plasma treatment results in noteworthy increase in oxygen functionalities as detected by X-ray photoelectron spectroscopy, as well as surface roughness as detected by atomic force microscopy. The improvement in adhesion properties is correlated with lap shear strength of adhesive bonded joints and mode of failure has been analyzed by scanning electron microscopy. The plasma-treated laminates, when used for repair, provided an additional 12% in the tensile strength and thereby retaining a strength increase up to 92%.

High Velocity Impact Characteristics of Shear Thickening Fluid Impregnated Kevlar Fabric

The development of high performance fabrics have advanced body armor technology and improved ballistic performance while maintaining flexibility. Utilization of the shear thickening phenomenon exhibited by Shear Thickening Fluids (STF) has allowed further enhancement without hindering flexibility of the fabric through a process of impregnation. The effect of STF impregnation on the ballistic performance of fabrics has been studied for impact velocities below 700 m/s. Studies of STF-impregnated fabrics for high velocity impacts, which would provide a transition to significantly higher velocity ranges, are lacking. This study aims to investigate the effect of STF impregnation on the high velocity impact characteristics of Kevlar fabric by effectively dispersing silica nanoparticles in a suspension, impregnating Kevlar fabrics, and performing high velocity impact experiments with projectile velocities in the range of 1 km/s to compare the post impact characteristics between neat Kevlar and impregnated Kevlar fabrics. 100 nm diameter silica nanoparticles were dispersed using a homogenizer and sonicator in a solution of polyethylene glycol (PEG) and diluted with methanol for effective impregnation to Kevlar fabric, and the methanol was evaporated in a heat oven. High velocity impact of STF-impregnated Kevlar fabric revealed differences in the post impact rear formation compared to neat Kevlar.