H.N. Narasimha Murthy

Seawater Durability of Epoxy / Vinyl Ester Reinforced With Glass / Carbon Composites

Seawater aging response was investigated in marine-grade glass/epoxy, glass/vinyl ester, carbon/epoxy and carbon/vinyl ester composites with respect to water uptake, interlaminar shear strength, flexural strength, tensile strength, and tensile fracture surface observations. The reduction of mechanical properties was found to be higher in the initial stages which showed saturation in the longer durations of seawater immersion. The flexural strength and ultimate tensile strength (UTS) dropped by about 35% and 27% for glass/epoxy, 22% and 15% for glass/vinyl ester, 48% and 34% for carbon/epoxy 28%, and 21% carbon/vinyl ester composites respectively. The water uptake behavior of epoxy-based composites was inferior to that of the vinyl system.

Low-Velocity Impact Response of Polyurethane Foam Composite Sandwich Structures:

Low-velocity instrumented impact tests were carried out on sandwich panels made of glass fiber-reinforced plastic facesheets and polyurethane foam core. The tests were carried out using a drop weight instrumented impact tester, connected to a data acquisition system. Four different types of sandwich samples using polyester/e-glass and epoxy/e-glass facesheet materials and polyurethane foam were considered for investigation. Two different face sheet materials were chosen to experimentally examine the effect of their elastic modulus on the impact response of the sandwich structures. The data acquisition system records the impact data such as impact force, penetration time and depth of penetration, and plots impact force versus depth of penetration and penetration time versus depth of penetration curves. From the recorded data the impact parameters such as maximum impact force, penetration time and depth of penetration versus impact energy were plotted to study the impact behavior. The results show that higher impact energy is required to break the epoxy/e-glass facesheet and backsheet sandwich specimens than other types of specimens examined. The impact damage caused to the facesheet, the core and the backsheet were thoroughly studied experimentally and the extent of damage caused to the facesheets and the core were also compared by finite element analyses.

Study of mechanical properties of epoxy/glass/nanoclay hybrid composites

The objective of this research was to study the mechanical properties of epoxy/glass/nanoclay hybrid composites. Nanomer 1.30E nanoclay (0—6 wt%) was initially dispersed into epoxy using ultrasonication and the hybrid nanocomposite was fabricated using hand lay-up technique. Mechanical properties such as ultimate tensile strength, Young’s modulus, flexural strength, flexural modulus, interlaminar shear strength, and microhardness of the hybrid composites increased with increase in nanoclay loading up to 5 wt%. Glass transition temperature increased marginally at 2 wt% nanoclay loading and the same decreased for further addition of the filler. The tensile-fractured specimens were studied to examine the mode of failure using scanning electron microscope.

The Processing and Characterization of MWCNT/Epoxy and CB/Epoxy Nanocomposites Using Twin Screw Extrusion

This paper presents results of the processing of nanocomposites based on epoxy and nanofillers, namely multiwalled carbon nanotubes (up to 10 wt%) and carbon black (up to 15 wt%). The twin screw extruded nanocomposites showed increases in electrical and thermal conductivities, tensile strength, microhardness and glass transition temperature. Electrical conductivity increased on the order of 1011 at 10 wt% of nanotubes loading and at 15 wt% of carbon black. Greater increases in thermal and mechanical properties were observed in cases of nanotube-dispersed composites more so than others. SEM and AFM were used to examine the dispersion of the fillers.

Buckling Response of Stitched Polyurethane Foam Composite Sandwich Structures

Edgewise compression (buckling) tests were performed on unstitched and stitched sandwich specimens made of glass/epoxy face-sheets and polyurethane foam core. The buckling characteristics of the specimens with through-the-thickness stitches and the influence of strain rate on buckling were investigated. Ultimate load carrying capacity of the specimens was determined. Modes and causes of failure along with their relation to the buckling properties were identified. The effect of stitch row spacing on the instability preceding the crush failure was investigated using finite element analyses, which were found to explain the fracture and debonding phenomena accurately. The average sustained critical compression load increased with reduced stitch row spacing and the total buckling load decreased with decrease in strain rate, as revealed by the buckling experimental studies.

Development and Characterization of Electrocodeposited Nickel-Based Composites Coatings

The objective of the article is to study the development and characterization of composite coatings using nickel-tungsten carbide (Ni-WC), nickel-silicon carbide (Ni-SiC), nickel-carbon black (Ni-CB), and nickel-carbon nanotube (Ni-CNT) materials using electrocodeposition technique by varying the composition of reinforcements. The electrochemical parameters such as current density, bath temperature, and pH of the solution were maintained at constant levels for all the coating configurations. The composition of the coating and its proportion were studied using x-ray diffraction and energy dispersive x-ray spectroscopy, respectively. Mechanical properties such as ultimate tensile strength and microhardness were studied. Morphology of the coatings and fracture surfaces were studied using scanning electron microscope. Improvement in mechanical properties of composite coatings was found due to the reduction in crystalline size of the composites coatings. Although loading of carbon nanotube was the least, it also shows good mechanical properties along with Ni-WC composite coatings.

Fatigue studies of polyurethane sandwich structures

The fatigue characteristics of polyurethane foam-cored (PUF) composite sandwich structures were investigated using three-point bending tests carried out according to ASTM C 393. Three types of specimens (epoxy/glass-PUF-epoxy/glass, polyester/glass-PUF-polyester/glass, and epoxy/glass-PUF-polyester/glass) were considered for investigation. Experimental results indicate that degradation of stiffness occurs due to debonding and sliding between the skin and the foam during fatigue cycles. Epoxy/glass-PUF-epoxy/glass sandwich structures exhibit higher bending strength along with higher stiffness degradation than the other two types of sandwich panels, due to higher initial fatigue loading. The lowest fatigue properties have been obtained for the polyester/glass-PUF-polyester/glass sandwich panel specimens. Better performance of the epoxy/glass-PUF-epoxy/glass sandwich panels is most likely due to the superior properties of the outer thin skins. Most of the specimens fail within the foam region and not at the skin level. This situation is possibly due to debonding between the foam and the skin. The fatigue damage development in the foam and skin has been investigated using scanning electron microscopy.

The Effect of the Addition of Acrylonitrile-Butadiene Styrene on the Mechanical Properties of Bismaleimide/Carbon Composites

The objective of the work was to investigate the effect of addition of various weight percentages of Acrylonitrile-Butadiene-Styrene in to Bismaleimide resin on mechanical properties. Matrix material and their blends were characterized for viscosity and glass transition temperature. Modified and unmodified carbon composites were prepared and tested for tensile, flexural and impact strengths. Tensile (11%) and impact properties (29%) were found to be highest at 6% weight of ABS. In the case of flexural strength was found to be increasing with increase of ABS. The morphology of the BMI modified resin systems were also studied by scanning electron microscopy.

The influence of montmorillonite on mechanical, thermal and fire retardation properties of vinylester/glass composites

This paper presents the influence of dispersing montmorillonite in 2 to 8 wt% in vinylester on the mechanical, thermal and fire retardation behaviour of vinylester/glass composites. X-ray diffraction and transmission electron microscopy results of montmorillonite/vinylester showed exfoliation of montmorillonite up to 4 wt% loading. Glass transition temperature (Tg) and microhardness of montmorillonite/vinylester increased with increase in montmorillonite loading. Tensile strength, interlaminar shear strength, flexural strength, impact strength and fatigue life of vinylester/glass increased by the addition of 4 wt% montmorillonite. Thermogravimetric analysis showed decrease in thermal degradation in 4 wt%/montmorillonite/vinylester compared to 2 wt%/montmorillonite/vinylester. Horizontal and vertical burning rates of vinylester/glass decreased with the addition of montmorillonite. Limiting oxygen index increased by 18% and 25% with the addition of 8 wt% montmorillonite to vinylester and vinylester/glass respectively. Scanning electron microscopy was used to study montmorillonite, vinylester and glass fibre interfacial strengths and the fatigue damage mechanism.

Influence of Solvents on the MWCNT/Adhesive Grade Epoxy Nanocomposites Preparation

In this article, the effect of two solvents, namely dimethyl formamide (DMF) and N-methyl pyrrolidone (NMP), on the dispersion effectiveness and the resulting electrical and mechanical properties of multi-walled carbonanotubes (MNCNT) filled structural adhesive grade epoxy nanocomposites was studied. The solvents were used mainly to reduce the viscosity of the resin system to effectively disperse the nanofiller. The dispersion was carried out under vacuum using high energy sonic waves. SEM was undertaken to study the dispersion effectiveness. Electrical resistivity, tensile properties, and glass transition of the nanocomposites were studied. Between DMF and NMP, the former proved better in terms of dispersion effectiveness and the resulting electrical and mechanical properties of the nanocomposites. Addition of MWCNT into AV138M resulted in an increase in glass transition temperature irrespective of the solvent used and in both cases percolation threshold was found with respect to reduction in electrical resistivity of the nanocomposites. Less agglomeration and hence better interaction between CNT and epoxy was observed in the samples prepared using DMF compared with that using NMP.