An Experimental Study on Energy Absorption Behavior of Polyurethane Foams

This article is concerned with a study on the energy absorption behavior of polyurethane (PU) foams such as flexible high resilience (HR), flexible viscoelastic (VE) and semi-rigid (SR) foams as a function of the overall foam density. Foam samples were prepared in the form of cubes by mixing appropriate polyol and isocyanate compounds produced by Huntsman International India Pvt. Ltd. in varying proportions leading to a range of densities for each type of foam. The cubical samples were tested under compressive load in a standard UTM. Based on the measured load-displacement behaviors, variations of peak load and energy-absorption attributes with respect to density are plotted for each type of foam and the possible existence of an optimum foam density is shown.

Energy absorption behaviours of CSM-based GFRC plates with hemispherical features

In the present study, the mechanical behaviour of CSM (chopped strand mat)-based GFRC (glass fibre-reinforced composite) plates with single and multiple hemispheres under compressive loads has been investigated both experimentally and numerically. The basic stress-strain behaviours arc identified with quasi-static tests on two-ply coupon laminates and short cylinders, and these are followed up with compressive tests in a UTM (universal testing machine) on single- and multiple-hemisphere plates. The ability of an explicit LS-DYNA solver in predicting the complex material behaviour of composite hemispheres, including failure, is demonstrated. The relevance and scalability of the present class of structural components as `force-multipliers' and `energy-multipliers' have been justified by virtue of findings that as the number of hemispheres in a panel increased from one to four, peak load and average absorbed energy rose by factors of approximately four and six, respectively. The performance of a composite hemisphere has been compared to similar-sized steel and aluminium hemispheres, and the former is found to be of distinctly higher specific energy than the steel specimen. A simulation-based study has also been carried out on a composite 2 x 2-hemisphere panel under impact loads and its behaviour approaching that of an ideal energy absorber has been predicted. In summary, the present investigation has established the efficacy of composite plates with hemispherical force multipliers as potential energy-absorbing countermeasures and the suitability of CAE (computer-aided engineering) for their design.

Tailoring energy absorption capacity of CNT forests through application of electric field

This study examines the effect of electric field on energy absorption capacity of carbon nanotube forests (CNTFs), comprising of vertically aligned multiwalled carbon nanotubes, under both quasistatic (strain rate, (epsilon) over dot = 10(-3) s(-1)) and dynamic ((epsilon) over dot = similar to 10(3) s(-1)) loading conditions. Under quasistatic condition, the CNTFs were cyclically loaded and unloaded while electric field was applied along the length of carbon nanotube (CNT) either throughout the loading cycle or explicitly during either the loading or the unloading segment. The energy absorbed per cycle by CNTF increased monotonically with electric field when the field was applied only during the loading segment: A 7 fold increase in the energy absorption capacity was registered at an electric field of 1 kV/m whereas no significant change in it was noted for other schemes of electro-mechanical loading. The energy absorption capacity of CNTF under dynamic loading condition also increased monotonically with electric field; however, relative to the quasistatic condition, less pronounced effect was observed. This intriguing strain rate dependent effect of electric field on energy absorption capacity of CNTF is explained in terms of electric field induced strengthening of CNTF, originating from the time dependent electric field induced polarization of CNT. (C) 2015 Elsevier Ltd. All rights reserved.

Evaluating shock absorption behavior of small-sized systems under programmable electric field

A simple ball-drop impact tester is developed for studying the dynamic response of hierarchical, complex, small-sized systems and materials. The developed algorithm and set-up have provisions for applying programmable potential difference along the height of a test specimen during an impact loading; this enables us to conduct experiments on various materials and smart structures whose mechanical behavior is sensitive to electric field. The software-hardware system allows not only acquisition of dynamic force-time data at very fast sampling rate (up to 2 x 10(6) samples/s), but also application of a pre-set potential difference (up to +/- 10 V) across a test specimen for a duration determined by feedback from the force-time data. We illustrate the functioning of the set-up by studying the effect of electric field on the energy absorption capability of carbon nanotube foams of 5 x 5 x 1.2 mm(3) size under impact conditions. (C) 2014 AIP Publishing LLC.

Polycrystalline Lead Tin Chalcogenide Thin Film Grown by Spray Pyrolysis

PbSnS2 thin film has been prepared for the first time by spray pyrolysis technique on FTO substrate at 570K. The preliminary optical and structural characteristics of the film have been reported. The optical studies showed that the value of the fundamental absorption edge lies at 1.47eV and a low energy absorption band tail has been observed. The prepared film is p- type electrical conductivity, polycrystalline in nature and has an orthorhombic crystal structure. The value of an average grain size of the film is 350Å.

On the utility of an instrumented impact set-up to characterise the response of discontinuous buffer strips in carbon–epoxy systems in dry and wet conditions

The use of an instrumented impact test set-up to evaluate the influence of water ingress on the impact response of a carbon–epoxy (C–E) laminated composite system containing discontinuous buffer strips (BS) has been examined. The data on the BS-free C–E sample in dry conditions are used as reference to compare with the data derived from those immersed in water. The work demonstrated the utility of an instrumented impact test set-up in characterising the response, first owing to the architectural difference due to introduction of buffer strips and then due to the presence of an additional phase in the form of water ingressed into the sample. The presence of water was found to enhance the energy absorption characteristics of the C–E system with BS insertions. It was also noticed that with an increasing number of BS layer insertions, the load–time plots displayed characteristic changes. The ductility indices (DI) were found to display a lower value for the water immersed samples compared to the dry ones.

Synthesis and Characterization of Carbon Nanotube-Polymer Multilayer Structures

We develop lightweight, multilayer materials composed of alternating layers of poly dimethyl siloxane (PDMS) polymer and vertically aligned carbon nanotube (CNT) arrays, and characterize their mechanical response in compression. The CNT arrays used In the assembly are synthesized with graded mechanical properties along their thickness, and their use enables the creation of multilayer structures with low density (0.12-0.28 g/cm(3)). We test the mechanical response of structures composed of different numbers of CNT layers partially embedded in PDMS polymer, under quasi-static and dynamic loading. The resulting materials exhibit a hierarchical, fibrous structure with unique mechanical properties: They can sustain large compressive deformations (up to similar to 0.8 strain) with a nearly complete recovery and present strain localization in selected sections of the materials. Energy absorption, as determined by the hysteresis observed In stress-strain curves, is found to be at least 3 orders of magnitude larger than that of natural and synthetic cellular materials of comparable density. Conductive bucky paper Is Included within the polymer interlayers. This allows the measurement of resistance variation as a function of applied stress, showing strong correlation with the observed strain localization In compression.

Thermo-mechanical stability of a cellular assembly of carbon nanotubes in air

Carbon nanotubes (CNT) in bulk form offer outstanding structural and functional properties, and are shown to remain viscoelastic over a wide temperature range (77-1273 K) under inert conditions. We examine the quasi-static and dynamic compressive mechanical response of these cellular CNT materials in ambient air up to a temperature of 773 K. In uniaxial quasi-static compression, several displacement bursts are noted at large strains. These are results of the slippage and zipping of the CNT, and lead to significant mechanical energy absorption. Results of the dynamic mechanical analysis experiments show no degradation in storage modulus and loss coefficient for up to 20 h at 673 K. Hence, these stable cellular CNT structures can be utilized up to a maximum temperature of 673 K in air, which is much higher than the best polymers. (C) 2012 Elsevier Ltd. All rights reserved.

A STUDY INTO THE BEHAVIOR OF AN ALUMINUM FOAM UNDER COMPRESSION

The characterization of a closed-cell aluminum foam with the trade name Alporas is carried out here under compression loading for a nominal cross-head speed of 1 mm/min. Foam samples in the form of cubes are tested in a UTM and the average stress-strain behavior is obtained which clearly displays a plateau strength of approximately 2 MPa. It is noted that the specific energy absorption capacity of the foam can be high despite its low strength which makes it attractive as a material for certain energy-absorbing countermeasures. The mechanical behavior of the present Alporas foam is simulated using cellular (i.e. so-called microstructure-based) and solid element-based finite element models. The efficacy of the cellular approach is shown, perhaps for the first time in published literature, in terms of prediction of both stress-strain response and inclined fold formation during axial crush under compression loading. Keeping in mind future applications under impact loads, limited results are presented when foam samples are subjected to low velocity impact in a drop-weight test set-up.

Influence of magnetic field on the compressive behavior of carbon nanotube with magnetic nanoparticles

Carbon nanotubes (CNT) in their cellular like micro-structure have presented an excellent mechanical energy absorption capacity. Although, several efforts have been progressed to modify the CNT structure for further enhancing their energy absorption capacity but yet no report has revealed the effect of magnetic field on the mechanical behavior of as-grown CNT mat that contains magnetic iron nanoparticles in the form of decorated nanoparticles on the surface or filled inside core of the CNT. We report a significant impact of the presence of magnetic content that modifies the mechanical behavior of the entangled CNT mat in the presence of an external magnetic field. The energy absorption capacity doubles when magnetic field was applied in the radial direction of the CNT mat under uniaxial compression. (C) 2013 AIP Publishing LLC.

A borane-bithiophene-BODIPY triad: intriguing tricolor emission and selective fluorescence response towards fluoride ions

The structure and photophysical properties of a new triad (borane-bithiophene-BODIPY) 1 have been investigated. Triad 1 exhibits unprecedented tricolour emission when excited at the borane centred high energy absorption band and also acts as a selective fluorescent and colorimetric sensor for fluoride ions with ratiometric response. The experimental results are supported by computational studies.

Laser receptive polyelectrolyte thin films doped with biosynthesized silver nanoparticles for antibacterial coatings and drug delivery applications

We report a simple method to fabricate multifunctional polyelectrolyte thin films to load and deliver the therapeutic drugs. The multilayer thin films were assembled by the electrostatic adsorption of poly (allylamine hydrochloride) (PAH) and dextran sulfate (DS). The silver nanoparticles (Ag NPs) biosynthesized from novel Hybanthus enneaspermus leaf extract as the reducing agent were successfully incorporated into the film. The biosynthesized Ag NPs showed excellent antimicrobial activity against the range of enteropathogens, which could be significantly enhanced when used with commercial antibiotics. The assembled silver nano composite multilayer films showed rupture and deformation when they are exposed to laser. The Ag NPs act as an energy absorption center, locally heat up the film and rupture it under laser treatment. The antibacterial drug, moxifloxacin hydrochloride (MH) was successfully loaded into the multilayer films. The total amount of MH release observed was about 63% which increased to 85% when subjected to laser light exposure. Thus, the polyelectrolyte thin film reported in our study has significant potential in the field of remote activated drug delivery, antibacterial coatings and wound dressings. (C) 2013 Elsevier B.V. All rights reserved.

Effect of fluid medium on mechanical behavior of carbon nanotube foam

This study reports the constitutive response and energy absorption capabilities of fluid-impregnated carbon nanotube (CNT) foams under compressive loading as a function of fluid viscosity and loading rates. At all strain rates tested, we observe two characteristic regimes: below a critical value, increasing fluid viscosity increases the load bearing and energy absorption capacities; after a critical value of the fluid's viscosity, we observe a rapid decrease in the systems' mechanical performance. For a given fluid viscosity, the load bearing capacity of the structure slightly decreases with strain rate. A phenomenological model, accounting for fluid-CNT interaction, is developed to explain the observed mechanical behavior. (C) 2014 AIP Publishing LLC.

Magnetic field induced tailoring of mechanical behavior of fluid filled micro porous carbon nanotube foam

Compressive loading of the carbon nanotube (CNT) has attracted much attention due to its entangled cellular like structure (CNT foam). This report investigates the mechanical behavior of magnetorheological fluid impregnated micro porous CNT foam that has not been realized before at this scale. Compressive behavior of CNT foam is found to greatly depend on the variation in both fluid viscosity as well as magnetic field intensity. Moreover, maximum achieved stress and energy absorption in CNT foam followed a power law behavior with the magnetic field intensity. Magnetic field induced movement of both CNT and iron oxide particles along the field direction is shown to dominate compressive behavior of CNT foam over highly attractive van der Waals forces between individual CNT. Therefore, this study demonstrates a method for tailoring the mechanical behavior of the fluid impregnated CNT foam. (C) 2014 AIP Publishing LLC.