Papers by Author: Mohammad Bilal Khan

Abstract: The impregnation of the fiber with a resin system, the polymeric matrix with the interface needs to be properly cured so that the dimensional stability of the matrix and the composite is ensured. A modified epoxy resin matrix was obtained with a reactive toughening agent and anhydride as a curing agent. The mechanical properties of the modified epoxy matrix and its fiber reinforced composites were investigated systematically. The polymeric matrix possessed many good properties, including high strength, high elongation at break, low viscosity, long pot life at room temperature, and good water resistance. The special attentions are given to the matrix due to its low out gassing, low water absorption and radiation resistance. In addition, the fiber-reinforced composites showed a high strength conversion ratio of the fiber and good fatigue resistance. The dynamic and static of the composite material were studied by thermo gravimetric analysis (TGA), Differential Scanning Calorimetry (DSC) and Scanning Electron Microscopy (SEM) with EDX. The influences of processing technique such as curing and proper mixing on the mechanical and interfacial properties were determined. The results demonstrated that the modified epoxy resin matrix is very suitable for applications in products fabricated with fiber-reinforced composites.

Abstract: Mechanical and ballistics properties are a measure of the performance of AP/Al/HTPB composites. These properties are influenced by the characteristics of inorganic crystalline oxidizer and aluminum particles. This paper reports the effect of the particle size distribution on mechanical and burning properties of 87% solid loaded composites. Composites were fabricated by mixing the ingredients in the planetary mixer followed by curing at an elevated temperature for several days. Multimodal particle size distribution was used in which coarse to fine ratio was varied proportionally. The burning rate was measured using strand burner at various pressures. Mechanical properties of the composites were investigated by using tensile tester. Results revealed that tensile strength and the burning rate increased while elongation at maximum stress decreased with the increase in the quantity of fines oxidizer. Whereas the variation in the particle size of the aluminum do not have any pronounced effect on the burning as well as mechanical properties of the composite.

Abstract: The surface of Kevlar fibers is chemically modified by treatment with Phthalic anhydride (PA) and the effect is examined by SEM for the laser cut, three point bending and interlaminar shear delaminated surfaces. The surface modification improved the adhesion to epoxy resin that clearly leads to cohesive fracture as opposed to interfacial failure in the untreated specimen. SEM reveals marginal surface roughening of fibers without compromising their strength. The interface modification technique described in this paper is attractive thermodynamically as it does not compromise surface free energy of the polymer matrix or that of the fiber itself to enhance wetability.

Abstract: The output considerations: velocity, pressure, density, internal energy, temperature and L/D ratio of explosively formed projectiles (EFPs) were investigated. The internal energy of the EFPs was inversely proportional to the density of the liner material. The shock pressure generated and its fluctuations were highest for Fe and Ta liner materials respectively. The least pressure variations were observed for Cu along its axial direction with highest length to diameter (L/D) ratio to supports deeper penetration. The maximum difference between numerical simulation and experiment was 9.7 % for Cu EFP.

Abstract: Bioactive CNT reinforced hydroxyapatite nano-composite is synthesized by in-situ precipitation for use in load bearing orthopedic applications. Microwaves augment the synthesis, enhance the reaction rate, and institute energy savings. Heat and acid treated purified CNTs in microwaves are functionalized and dispersed in calcium nitrate tetrahydrate. Diammonium hydrogen phosphate is incorporated in calcium ion solution to furnish the required Ca:P ratio. Refluxing of the precursor solution is accomplished under microwaves. XRD shows the phase purity and crystallinity, FTIR spectroscopy indicates the fucntionalization of CNTs and SEM analysis depicts the nanoporous nanomorphology of synthesized powder. TGA measures the thermal endurance of product, showing good CNTs retention at high temperatures (1100°C) in nitrogen ambient, otherwise they get oxidized in air in that temperature range. CNT reinforced sintered biomaterial exhibits excellent consolidation and a Vicker hardness increment of 30%. The relation of between mechanical properties and sintering time is correlated by SEM.

Abstract: Polyurethanes with two different types of –OH backbones castor oil (CO) and hydroxyl terminated polybutadiene (HTPB) were synthesized by using moderately reactive iso-phorone diiscocayante (IPDI) as curing agent. IR spectroscopy and mechanical property evaluations were carried out to elucidate the structure-property relationship of the polymer. It was found that the polymer, intersegment bonding had significant effects on the ultimate tensile properties. The CO based polymer exhibited far better mechanical properties than that of HTPB based polymer. However, a reverse behavior was observed in the composites. Composite fabricated with HTPB based polymer matrix showed four times the tensile strength of CO based composite. SEM comparison of the fractured composites revealed better wetting and adhesion properties with HTPB. Dynamic mechanical testing results indentified a relationship between the viscoelastic parameters and frequency of the applied load.

Abstract: This work demonstrates the horizontal patterning/alignment of single wall nano tubes (SWNTs) using simple filtration method. In the quest of vertical alignment of SWNTs to fabricate the vertically aligned CNT-membrane, this horizontal patterns as observed by simple filtration technique has been achieved. These horizontal patterns are key arrangements sought in the electronic field and fabrication of CNT-nano composites of required characteristics. In this work SWNTs purified/oxidized treatment with nitric acid at 120-122°C. Oxidized SWNTs further reacted with Octadecyl amine at same temperature to make them significantly dispersible/soluble in solvents especially in Tetrahydrofuran (THF). These modified SWNTs dissolved in THF by sonication and uniform black color solution was obtained that did not settle upon prolonged time of standing. This solution is subsequently filtered through 0.2 micro porous PTFE filter using long neck sintered funnel for horizontal alignment. The inter tube gap between CNTs is initially filled by the precursor reactive vapor stream that is consolidated as a solid polymer through insitu polymerization. Transform Infrared (FTIR) analysis was performed to find the attached functional groups. Alignment of functionalized SWNTs collected on PTFE filter was analyzed by Field-emission scanning electron microscopy (FE-SEM). Ordered horizontal patterns were observed. The contemporary horizontal alignment techniques being used are tedious and need very special facilities. The current method is comparatively quite simple and large quantities of CNTs can be aligned to advantage.

Abstract: Cadmium selenide nanoparticles coated with zinc sulphide CdSe/ZnS were prepared using dual source method. The composites were fabricated by stabilizing chemically synthesized semiconductor CdSe/ZnS into Laurylmethacrylate (LMA) and ethyleneglycol dimethacrylate (EGDMA) matrices in the presence of tri-n-octylphosphine (TOP). CdSe/ZnS were dispersed in toluene as a compatible medium for the polymerization and cross-linking of poly Laurylmethacrylate (LMA) networks. Transparent, fluorescent and flexible nano composites (NCs) materials resulted. The nano size particles and polymer composites were characterized by XRD, TG-DTA, IR, TEM and SEM.

Abstract: The paper relates to high concentration particle doped composites based on thermosetting polymer systems in which the sequential addition of particles of certain size distribution is followed by curing and casting of the slurry to form a thermoset composite. Conventionally, at a threshold of beyond 90% of particles by weight of the polymer using triglyceride, the mechanical properties of the composite exhibit a sharp decline. The present research mitigates this behavior by incorporating a unique combination of cross-linking agents in the base polymer to impart exceptional mechanical properties to the composite. More specifically, the base polymer consists of butadiene, with triglyceride as cross-linking agent together with hydroxy-alkane as the chain extension precursors, when tune to the appropriate level of hard segment ratio in the polymer. An added advantage according to the present work resides in the analytical nature of butadiene pre-polymer as opposed to natural product; traditional composites based on natural sources are hampered by their inconsistent chemical composition and poor shelf life in the fabricated composite. The thermoset composite according the present research exhibits superior tensile strength (200-300 psi) properties using particle loading as high as 92% by weight of the fabricated composite as measured on a Tinius Olsen machine. Dynamic Mechanical Testing reveals interesting combination of storage and loss moduli in the fabricated specimens as a function of optimizing the thermal response of the viscoelastic composite to imposed vibration loading.

Abstract: Ablative composites are heat shielding, protective materials that are being used in aerospace industry to protect inner hardware and sensitive devices. The aero dynamic vehicles have to face high stresses, ultra high temperature and adverse conditions of air friction. It is required to develop the materials with light weight and high modulus. EPDM, being heat and ozone attack resistant is the best candidate for the preparation of ablative composites by introducing different heat sinks such as silica, glass fiber, carbon fiber, asbestos, carbon and their combinations have been studied in this work. The prepared materials were tested and it was found that visco elastic behavior of the composites affected by the addition of reinforcing filler (carbon, silica), semi-reinforcing filler (carbon fiber, glass fiber) and non-reinforcing filler (asbestos powder). Mechanical properties tested at different rates, revealed the improvement in tensile strength and % elongation in case of reinforcing and semi-reinforcing fillers but showed adverse effect in case of non-reinforcing fillers. Rheological investigations of these novel composites shows that moony viscosity of the materials containing glass fiber, carbon fiber, silica decreases in the order glass fiber > carbon fiber > silica.