breaking strain. [18] 4) The creasing in thin foils during fabrication and operations pose another challenge. [19] 5) The rigid and metallic foil-based absorbers will be difficult to mount on surfaces with complex geometry and curved contours. 6) The integrity of these absorbers with variety of underlying surfaces made of metals and polymers have not been established yet. To overcome some of these issues, flexible optical absorbers are developed using nanocomposites or thin metal foils as base substrate. [9,20] More recently, Zeranska-Chudek et al. has reported the flexible absorber based on grapheme/ polydimethylsiloxane (PDMS) nanocomposite with an average absorption of 95% in 400-1600 nm wavelength range. [21] The lower absorption capacity and narrow operating range is again a critical issue with this absorber. [22,23] Unavailability of an absorber which can meet all these functional requirements naturally leads to a fundamental question that how we can fabricate a near perfect flexible absorber which can overcome these issues. Here we report the fabrication of a novel flexible absorber (flexorb) with an absorbing capacity of >99% in the whole UV-vis-NIR broadband region using a simple and economical process. Apart from absorbing capacity, the mechanical integrity of flexible absorber with different types of underlying surfaces is an important parameter in order to qualify them for a variety of applications. A unified study which deals with the absorbing capacity and mechanical integrity of flexible absorbers has not been carried out to the best of author's knowledge and has been thoroughly performed in the current work. The use of PDMS as base matrix material ensures the flexibility as well as integrity of multifunctional absorber with different types of surfaces. Texturing and addition of ZnO, Fe, and carbon nanotubes (CNTs) as reinforcing fillers increases the photonic path length through multiple scattering of incident light and hence augments the absorbing capacity of PDMS. Additionally, the presence of CNTs helps to achieve impedance matching and thus significantly reduces the reflection of incident beam at absorber-surrounding interface. All these factors combined in a synergistic way and results in a near perfect absorption of incident light in the broader wavelength range of 300-2000 nm. Moreover, the flexorb shows multifunctional behavior in the sense that it can avoid environmental assisted degradation due to its observed hydrophobic and self-cleaning characteristics. In addition the improved Synthesis of a near perfect absorber is required for many technologically challenging areas. Most of the existing super absorbers are rigid and usually exploit the light in the visible range only leaving a significant part of available energy in the solar spectrum unutilized. Here the synthesis of a multifunctional flexible absorber (flexorb) with an ultrahigh absorbing capacity of >99% in the whole UV-vis-NIR region is reported. Flexorb is fabricated by texturing the polydimethylsiloxane matrix reinforced by Z...

Towards developing a constitutive model for describing the flow and fracture behaviour of engineering materials under higher strain rates, studying the deformation fields in uniform and localized deformation regime using the high strain rate tensile tests is of technical importance. To this end, high strain rate tensile tests have been carried out on flat tensile specimen of reduced activation ferritic-martensitic (RAFM) steel at different loading rates varying from 5 m/s to 14 m/s. The strain fields at uniform and localized deformation regime have been mapped by Digital Image Correlation (DIC) technique. For carrying out the DIC, high speed images of the specimen surface have been captured in-situ by high speed camera, synchronized with the loaddisplacement data acquisition system. The stress-strain fields thus obtained in this study would be an appropriate input to numerical analysis to characterize the flow and fracture behaviour of RAFM steels.

Experimental investigations are carried out to quantify the effect of carbon nanotubes (CNTs) addition on the actuation performance of polydimethylsiloxane (PDMS) based soft dielectric elastomer actuator (DEA). The actuation ability of pure PDMS and CNT/PDMS composite samples is compared in unimorph configuration. Comparative analysis of experimental results shows that incorporation of optimum CNT concentration (0.05 wt%) significantly enhances the tip displacement (two times) and efficiency (three times) of pure PDMS based DEA. Increasing the CNT concentration beyond optimum level degrades the tip displacement and efficiency of bend actuator. The experimental results are well supported by the theoretical analysis and finite element simulations. Moreover, experimental and numerical findings are combined to establish microstructure-property relationship of DEA. It is shown that at optimum CNT concentration, the induced Maxwell stress compensates for the increase in stiffness of DEA. However, the enhanced stiffness and agglomeration beyond optimum CNT loading results in lower tip displacement.

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Finite element (FE) simulations are performed to investigate the effect of fiber induced anisotropy on the notch behavior in hyperelastic skin type materials. The modified anisotropic (MA) model is used to define the constitutive behavior in FE simulations through Abaqus user defined material model UMAT. A parametric study is carried out to examine the effect of fiber orientation, notch root radius and sample geometry on the stress field ahead of the notch tip. A non-dimensional parameter  is defined to characterize the combined effect of J energy and average anisotropic energy (aniso)avg on the notch behavior. It is shown that fibre orientation significantly influences the stress state and J-integral at the notch. The findings of the present study will be helpful in determining optimal constitution and orientation of skin grafts at locations of high stress and complex geometries, such as corner of eyes and lips etc.

Flexible near perfect optical absorbers have many applications in the field of photovoltaic, energy harvesting and defence technologies. Even though flexible absorber coatings can be easily applied on the curved surfaces with complex geometry, the experimental realization of such absorbers having high absorption capacity in the broadband range is a challenging task. Here, we report the design and fabrication of a polydimethylsiloxane (PDMS) based optically graded thin (total thickness - 750 μm) assembly which shows near perfect absorption (95%) in the wavelength range of 300 to 2000 nm. The observed high absorbing capacity may be attributed to the presence of multiscale feature size in optically graded assembly which leads to efficient light trapping and multiple scattering of incident beam. The multilayer assembly comprises layers of PDMS reinforced with iron, zinc oxide (ZnO) and carbon nanotubes (CNTs). In addition to this, detailed fracture mechanism of fabricated absorber is studied. Moreover, contact angle study of fabricated thin film structure reveals that it is not only a near perfect absorber but also hydrophobic in nature. The ease of fabrication process combined with the excellent properties shown by the multilayer flexible assembly makes it an attractive option for industrial applications.

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