Anwarul Haque

Magnetite-embedded cellulose fibers prepared from ionic liquid

A dry-jet wet spinning process for making magnetically active cellulose fibers has been developed using the ionic liquid (IL) 1-ethyl-3-methylimidazolium chloride ([C2mim]Cl). Cellulose from different sources with various degrees of polymerization (DP) was used for making fibers by first dissolving the cellulose in the IL, dispersing particles of magnetite in the solution, and then coagulating the fibers in a water bath under appropriate spinning conditions. The variation of fiber properties with cellulose source and concentration of magnetite is discussed. Fiber texture was found to be related to overall magnetite concentration, cellulose concentration, and molecular weight in the spinning solution. In general, it was found that increasing DP and/or cellulose concentration resulted in more robust fibers, and conversely the addition of magnetite particles weakened the overall mechanical properties.

Characterization and Modeling of the Effect of Environmental Degradation on Interlaminar Shear Strength of Carbon/Epoxy Composites

Accelerated ageing experiments have been conducted to address durability issues of carbon/epoxy composites to be used for emerging facilities and infrastructure, such as, bridges and buildings, in different climatic zones. The degradation of carbon/epoxy composites under UV, hygrothermal exposure, and applied tensile stress has been investigated. The tests were designed to capture the synergistic effects of field exposure and extreme temperatures, viz., hot/dry, hot/wet, cold/dry, and cold/wet conditions. Short beam shear tests (SBST) were performed for the determination of interlaminar shear strength (ILSS) of conditioned composite specimens. The hot/dry samples showed increased strength, while the hot/wet ones showed a decrease in strength. It is conjectured that conditioning at 90 °C possibly contributed to an increase in the ILSS from post curing. For the hot/wet samples (90 °C, immersed in water) the results indicate that strength degradation due to moisture-induced hydrolysis overshadowed the post-curing effect. The samples subjected to shear stress under hot conditions (90 °C) showed a higher ILSS, possibly due to improved crosslink density arising from post-cure. There is insignificant variation in the ILSS of UV treated and the UV untreated control samples. All the SBST test data reported in this work are from tests performed at room temperature and ambient humidity after environmental ageing. A two-dimensional cohesive layer constitutive model with a prescribed traction-separation law constructed from the basic principles of continuum mechanics, taking into account hygrothermal mechanisms that are likely to occur within a cohesive bi-material interface, such as between adjacent plies in a laminate, was applied to simulate interlaminar failure in the SBST specimens, using Finite Element Analysis (FEA). A phenomenological predictive model was developed using the finite element results.

Environmental Degradation of Interlaminar Shear Strength in Carbon/Epoxy Composites

The effect of environmental and loading conditions on the degradation of Interlaminar Shear Strength (ILSS) of the carbon-epoxy composite specimens was studied. The hygrothermal conditions capture the synergistic effects of field exposure and extreme temperatures. A short beam shear test (SBST) was performed to determine the Interlaminar Shear Strength (ILSS) of environmentally aged composite specimens in accordance with ASTM D2344-84. Initially, a standard two-dimensional cohesive layer constitutive model was employed in order to simulate the experiment using an in-house FEA code (NOVA-3D). Numerical instabilities, encountered using the standard cohesive layer model, were overcome by incorporating viscoelastic regularization in the constitutive equations of the cohesive layer. This modification also enabled the analysis to continue beyond the point of peak failure load. The model was able to accurately simulate the load vs. displacement behavior of most of the SBST samples aged under various hygrothermal and synergistically applied stress conditions. Further, the effect of displacement rate on the ILSS of specimens was studied using NOVA-3D. The model indicated a strong dependence of viscoelastic cohesive strength on the displacement rate. Regrettably, the predicted rate dependence could not be verified experimentally.

Structures and Characterization of Organoclay-Epoxy-Vinylester Nanocomposites

The field of polymer-clay nanocomposites has attracted considerable attention as a method of enhancing polymer properties and extending their utility. Layered silicates dispersed as a reinforcing phase in a polymer matrix are one of the most important forms of such inorganic-organic nanocomposites, making them the subject of intense research. We have recently prepared several thermoset-based nanocomposites with improved thermal and mechanical properties. This paper is primarily focused in studying the effects of nano clay particles such as montmorillonite on improving mechanical and thermal properties of the polymer matrix composite. Epoxy and vinyl ester nanocomposites were prepared by adding different weight percentages (0.5%, 1%, 2%, 5% and 10%) of montmorillonite nano clay particles to epoxy and vinyl ester matrices. The results show significant improvements in mechanical and thermal properties of the nanostructured materials with low loading of organo silicates. Thermal property measurement includes dynamic mechanical analysis (DMA). Mechanical properties such as flexural strength and flexural modulus of polymer matrix were improved in nano structured materials owing to their unique phase morphology and improved interfacial interactions. Molecular dispersion of the layered silicate within the cross-linked matrix was verified using Wide Angle X-Ray Diffraction (WAXD) and Transmission Electron Microscopy (TEM) revealing the intercalated nanocomposites were formed.Copyright

Tensile properties, void contents, dispersion and fracture behaviour of 3D printed carbon nanofiber reinforced composites:

In this paper, additive manufacturing technology has been used in processing carbon nanofiber (CNF) reinforced thermoplastic composites through fused deposition modeling (FDM). The effects of nanofiber concentrations, nozzle geometries on void contents, and tensile properties of FDM printed nanocomposites have been studied. The contact angles and void geometries have been characterized as a function of bead spreading orientations. Such measurements were carried out using micrographs of optical and scanning electron microscopy (SEM) examinations. The dispersion and orientation of nanofiber in polylactic acid (PLA) matrix have been studied using transmission electron microscopy observations. Finally, the fracture surfaces of both neat PLA and CNF/PLA nanocomposites have been investigated in order to understand the failure mechanism. The results show improved modulus, strength, and strain up to elastic limit in CNF/PLA nanocomposites in comparison to neat PLA matrix. The square nozzle geometry shows increased tensile strength and reduced void geometry in comparison to circular shaped nozzle. Three types of voids such as inter-bead, intra-bead, and interfacial bead were observed with total voids ranging from 24% to 30% with circular nozzle. The level of void content is reduced to about 7% for square nozzle. Contact angles and bead orientation play an important role in forming void contents. CNF/PLA nanocomposites exhibit decreased contact angle and higher void contents in comparison to neat PLA resin. Transmission electron microscopy study of CNF/PLA nanocomposites show uniform dispersion of carbon nanofibers with aligned orientation in both composite filament and three-dimensional printed specimen. Fractured surfaces of CNF/PLA nanocomposites show fiber pullout mechanism and comparatively coarse surface topography indicating higher fractured energy than neat polylactic acid resin.

DEVELOPMENT OF HIGH-STRENGTH AND HIGHLY DUCTILE HYPO-EUTECTIC Al-Si ALLOYS BY NANO-REFINING THE CONSTITUENT PHASES

Among the structural light weight materials, Al-Si alloys can be the most widely used Al-alloys for aerospace and automotive applications. Our recent experiments using Ba additions of 1-3wt% into the melt of hypo- and hyper-eutectic Al-Si alloys have shown considerable promise in terms of both Si refinement of nano-scale (verified with both by SEM and TEM studies) and limited mechanical testing. The preliminary experiments indicate that the solidification conditions together with the new hypothesis of Si refinement can besuccessfully used with permanent mold casting. Recent permanent mold casting of such Al-8%Si-1.8%Ba hypo-eutectic Al-Si alloys have resulted cast alloys that without any further processing revealed a microstructure in which eutectic silicon assumes nano-fibrous morphology and where the primary aluminium phase shows dendrites of very fine size. The alloys in as cast conditions exhibit UTS values of around 172 Mpa and ductility values of about 15%.