Laraib A. Khan

Functional graphene nanoplatelet reinforced epoxy resin and polystyrene-based block copolymer nanocomposite

GRAPHICAL ABSTRACT ABSTRACT Amine-functionalized graphene nanoplatelet (GNP-A) was reinforced in a blend matrix of diglycidyl ether of bisphenol-A (DGEBA) and polystyrene-block-poly(ethylene-ran-butylene)-block-polystyrene (PSPEB) via facile solution approach. Diaminodiphenylmethane was employed as hardener. According to SEM, inclusion of pristine GNP enhanced surface roughness, however, autumn leaf like pattern was observed in amine-functional nanocomposite. For 0.1 wt.% pristine GNP loading Tmax was observed as 545°C, whereas GNP-A showed higher value (553°C). Glass transition temperature of amine-system was also higher (230°C) than pristine one (224°C). DGEBA/PSPEB/GNP-A 0.1 depicted semi-crystalline nature (12.6°and 19.8°). EMI shielding effectiveness of nanocomposite was sufficiently high i.e. ∼18.87-20.15 dB.

Modified graphene nanoplatelet and epoxy/block copolymer-based nanocomposite: physical characteristic and EMI shielding studies

Abstract In this research work, diglycidyl ether of bisphenol-A (DGEBA) and polystyrene-block-poly(ethylene-ran-butylene)-block-polystyrene (PSPEB) were blended and loaded with purified graphene nanoplatelet (GNP-P) and acid-functionalized graphene nanoplatelet (GNP-F). Solution mixing route was used for nanocomposite processing with diaminodiphenylmethane as a hardener. According to SEM, inclusion of functional GNP-F depicted fine morphology due to interfacial adhesion between functional nanofiller and blend. Sharp increase in ultimate tensile strength and toughness was observed for DGEBA/PSPEB/GNP-F 0.03–0.1 system, i.e. 60.4–64.5 MPa and 422.6–725.5 MPa, respectively. For 0.1 wt.% GNP-P loading, Tmax was observed as 547 °C; whereas, GNP-F showed higher value of 568 °C. Glass transition temperature of acid functional system was also higher (258 °C) than purified one (229 °C). DGEBA/PSPEB/GNP-F 0.1 depicted semi-crystalline nature (12.5° and 19.1°). EMI shielding effectiveness of nanocomposite was sufficiently high in the range of ~17.9–20.07 dB, i.e. desired for aerospace applications. Moreover, introduction of 0.1 wt.% functional graphene nanoplatelet enhanced the electrical conductivity up to 0.14 cm−1.

Effect of hygrothermal conditioning on the fracture toughness of carbon/epoxy composites cured in autoclave/Quickstep

The hygrothermal effect on the flexural, interfacial and glass transition behaviors of 977-2A carbon/epoxy composites cured in an autoclave and by using Quickstep were evaluated in the previous paper. This article concerns with the hygrothermal effect on the mode I and mode II delamination resistance of the samples cured in an autoclave and by Quickstep. It was observed that the mean initiation and propagation GC values (i.e. GIC and GIIC) of both autoclave and Quickstep 60 cured specimens were apparently reduced after hygrothermal conditioning; however, the data obtained from both autoclave and Quickstep 60 cured specimens in dry and wet states were not statistically significant. The scanning electron micrograph confirmed the enhancement of matrix ductility; however, no effect of this matrix ductility was observed in the GIC and GIIC data.

The drilling-induced failure mechanisms in T800/924C toughened carbon-epoxy composite materials

The process of drilling of toughened carbon fiber composite materials presents numerous problems during structural assembly. The extremely abrasive nature of carbon fibers along with the softer resin quickly dull sharp tools, split, tear, pullout, and push-in the fibers on the hole boundaries. The presence and growth of such flaws seriously impairs the structural stability, durability, and reliability particularly under fatigue loading. This research aims to investigate the failure modes, pattern, and sequence of damage mechanisms in toughened carbon-epoxy composite in relation to the drilling dynamics. The surface morphology of the damaged fibers in the sectioned holes was examined by scanning electron microscopy (SEM). The drill forces were determined by drill dynamometer to investigate the drilling thrust and torque. The photoelastic stress analysis was used to determine the strains around hole of the lowest ply. The most critical failure mode was found to be shear crimping of −45° fibers due to microbuckling. This resulted in formation of damage pits that were spaced apart periodically at an angle of 45° on hole boundaries. The through-the-thickness drilling forces caused delamination in the resin rich region of −45°/90° interlayer. The SEM, dynamometer, and photoelastic strain results were correlated to predict the onset of failure modes. The results have been explained in the light of analytical models based on fracture mechanics. Measures have been suggested for minimizing the damage on carbon-epoxy composite hole boundaries.

Mechanical Properties of Composites Made from Locally Manufactured Carbon Fabrics and the Composites Produced from Air-Textured Glass Yarns

Composite materials have a wide range of applications in structural components because of their high strength-to-weight and stiffness-to-weight ratios. However, the most crucial and common life-restricting crack growth mode in laminated composites i.e. delamination is of great concern. Air jet texturing was selected to provide a small amount of bulk to the glass yarn. The purpose was to provide more surface contact between the fibres and resin and also to increase the adhesion between the neighbouring layers. These were expected to enhance the resistance to delamination in the woven glass composites. The development and characterisation of core-and-effect textured glass yarns was presented in the previous paper. This paper describes the comparison of the mechanical properties of composites produced from air-textured glass yarns and the composites made from locally manufactured carbon fabrics. The tensile, flexure and inter-laminar shear strength (ILSS) were compared and it was observed that although glass fibres are inferior to carbon fibres in terms of mechanical properties however, the flexure strength and ILSS of glass based composites increases after texturing and were found closer to the properties of carbon based composites.