Nanoshearing - Collective carbon nanotube micromechanics

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Development and validation of a novel data analysis procedure for spherical nanoindentation

This dissertation presents a novel approach for converting the raw load-displacement data measured in spherical nanoindentation, from indentation depths as small as a few nanometers,into much more meaningful indentation stress-strain curves. This new method entails a new definition of the indentation strain, a new procedure for establishing the effective zero-load and zero-displacement point in the raw dataset, and the use of the continuous stiffness measurement (CSM) data. The concepts presented here have been validated by finite element models as well as by the analyses of experimental measurements obtained on isotropic metallic samples of aluminum and tungsten. It is demonstrated that these new methods produce indentation stressstrain curves that accurately capture the loading and unloading elastic moduli, the indentation yield points, as well as the post-yield characteristics in the tested samples. A further development of this approach, without the need for the CSM – an option available only on a limited number of machines – is also outlined.Subsequent validation of this approach on a wide range of material samples including metals, carbon nanotubes (CNTs), ceramics and bone – confirms the ongoing success andversatility of this technique. In particular, the success of these data analysis techniques has been demonstrated in correlating the elastic moduli measured in loading and unloading segments, and explaining several of the surface preparation artifacts typically encountered in nanoindentation measurements in metals. In an extension of this technique to anisotropic polycrystalline samples, a judicious combination of the results from Orientation Imaging Microscopy (OIM) and nanoindentation were used to estimate, for the first time, the changes in slip resistance in deformed grains of anisotropic metallic samples of Fe-3%Si steel at a micron length scale. These results also represent the experimental validation of Vlassak and Nix’s theory1 for nanoindentation in anisotropic solids and the first report of experimentally measured nanoindentation yield strengths in anisotropic crystallographic solids as a function of crystal lattice orientation.Similar studies on dense CNT brushes, with ~10 times higher density than CNT brushes produced by other methods, demonstrate the higher modulus (~17-20 GPa) and orders ofmagnitude higher resistance to buckling in these dense CNT brushes than vapor phase deposited CNT brushes or carbon walls. This work also demonstrates the viscoelastic behavior, caused by the increased influence of the van der Waals’ forces in these highly dense CNT brushes, showing their promise for energy-absorbing coatings. Even in a complex hierarchical materials system like bone, this indentation analyses technique has been able to elucidate trends in elastic, yield and post-yield indentation behavior at the lamellar level in the femora (thigh bone) of two different inbred mouse strains, A/J and B6, to the corresponding structural information measured using Raman Spectroscopy at similar micron (lamellar) length scales. Thus bone with a higher mineral-to-matrix ratio is shown to demonstrate a trend towards a higher local modulus and yield strength and the B6 mouse strain exhibits a trend towards lower modulus and yield values than the more mineralized A/J strain. An extension of the above study to indentation testing of bone in the ‘wet’ or hydrated conditions (which represents more closely bone’s naturally hydrated invivo environment), demonstrates a novel approach to characterize bone’s dynamic mechanical behavior under contact loading. Bone having a higher collagen content or a lower mineral-tomatrix ratio was found to demonstrate a trend towards a higher viscoelastic response – confirming the trends shown in the dry bone results. In summary, the success of the analyses techniques demonstrated in this dissertation constitute a crucial first step in the formulation of a rigorous framework for establishing structure-property linkages in various materials models at the submicron length scale.Ph.D., Materials Science and Engineering -- Drexel University, 200

Studying grain boundary regions in polycrystalline materials using spherical nano-indentation and orientation imaging microscopy

In this article, we report on the application of our spherical nanoindentation data analysis protocols to study the mechanical response of grain boundary regions in as-cast and 30% deformed polycrystalline Fe-3%Si steel. In particular, we demonstrate that it is possible to investigate the role of grain boundaries in the mechanical deformation of polycrystalline samples by systematically studying the changes in the indentation stress-strain curves as a function of the distance from the grain boundary. Such datasets, when combined with the local crystal lattice orientation information obtained using orientation imaging microscopy, open new avenues for characterizing the mechanical behavior of grain boundaries based on their misorientation angle, dislocation density content near the boundary, and their propensity for dislocation source/sink behavio

Probing nanoscale damage gradients in irradiated materials with spherical nanoindentation

We discuss applications of spherical nanoindentation stress-strain curves in characterizing the local mechanical behavior of materials with modified surfaces. Using ion-irradiation on tungsten as a specific example, we show that a simple variation of the indenter size (radius) can identify the depth of the radiation-induced-damage zone, as well as quantify the behavior of the damaged zone itself. Using corresponding local structure information from electron backscatter diffraction (EBSD) and transmission electron microscopy (TEM) we look at (a) the elastic response, elasto-plastic transition, and onset of plasticity in ion-irradiated tungsten under indentation, and compare their relative mechanical behavior to the unirradiated state, (b) correlating these changes to the different grain orientations in tungsten as a function of (c) irradiation from different sources (such as He, W, and He+W)

SOIL EROSION MAPPING OF WATERSHED IN MIRZAPUR DISTRICT USING RUSLE MODEL IN GIS ENVIRONMENT

Soil erosion is one of the serious issues threatening the environment. It is a growing problem especially in areas of agricultural activity where soil erosion not only leads to de-creased agricultural productivity but also reduces water availability. This leads to drastic degradation of the agricultural lands. So there is a need to take up conservation and management measures which can be applied to check further soil erosion. Universal Soil Loss Equation (USLE) is the most popular empirically based model used globally for erosion prediction and control. Remote sensing and GIS techniques have become valuable tools for the digitization of the input data and genereation of maps. In the present study, RUSLE model has been adopted to estimate the soil erosion in the Khajuri watershed of Uttar Pradesh, India. This model involves calculation of parameters including runoff-rainfall erosivity factor (R), soil erodability Factor (K), topographic factor  (LS), cropping management factor (C), and support practice factor (P). Layer wise thematic maps of each of these factors were generated using GIS platform using various data sources and data preparation methods. The results of the study indicate that the annual average soil loss within the watershed is about  t/ha/yr (metric ton per hectare per year)

Viscoelasticity and high buckling stress of dense carbon nanotube brushes

We report on the mechanical behavior of a dense brush of small-diameter (1–3 nm) non-catalytic multiwall (2–4 walls) carbon nanotubes (CNTs), with ~10 times higher density than CNT brushes produced by other methods. Under compression with spherical indenters of different radii, these highly dense CNT brushes exhibit a higher modulus (~17–20 GPa) and orders of magnitude higher resistance to buckling than vapor phase deposited CNT brushes or carbon walls. We also demonstrate the viscoelastic behavior, caused by the increased influence of the van der Waals’ forces in these highly dense CNT brushes, showing their promise for energy-absorbing coatings

Comparative Analysis of Lunge Techniques: Forward, Reverse, Walking Lunge

The study aims to find the basis for the efficiency of lunge and risk of injury by comparing mechanical variables in various lunges (forward lunge, reverse lunge, and walking lunge). Four participants who were familiar with the three lunge movements were recruited to achieve the purpose of the study. The resultant hip joint moment, resultant knee joint moment, and resultant knee joint force were analyzed during the three lunge movements. Eight muscle of lower extremity were also analyzed using EMG. In conclusion, reverse lunge movement was found to be favorable in achieving the primary goal of lunge exercise, which is the development of gluteus maximus and quadriceps femoris, as it resulted in higher agonist muscle activities with relatively low momentary maximum knee shearing force compared to the other lunge techniques

Compressive response of vertically aligned carbon nanotube films gleaned from in situ flat-punch indentations

We report the mechanical behavior of vertically aligned carbon nanotube films, grown on Si substrates using atmospheric pressure chemical vapor deposition, subjected to in situ large displacement (up to 70 μm) flat-punch indentations. We observed three distinct regimes in their indentation stress–strain curves: (i) a short elastic regime, followed by (ii) a sudden instability, which resulted in a substantial rapid displacement burst manifested by an instantaneous vertical shearing of the material directly underneath the indenter tip by as much as 30 μm, and (iii) a positively sloped plateau for displacements between 10 and 70 μm. In situ nanomechanical indentation experiments revealed that the shear strain was accommodated by an array of coiled carbon nanotube “microrollers,” providing a low-friction path for the vertical displacement. Mechanical response and concurrent deformation morphologies are discussed in the foam-like deformation framework with a particular emphasis on boundary conditions

Nanomechanical testing of silica nanospheres for levitated optomechanics experiments

Optically-levitated dielectric particles can serve as ultra-sensitive detectors of feeble forces and torques, as tools for use in quantum information science, and as a testbed for quantum coherence in macroscopic systems. Knowledge of the structural and optical properties of the particles is important for calibrating the sensitivity of such experiments. Here we report the results of nanomechanical testing of silica nanospheres and investigate an annealing approach which can produce closer to bulk-like behavior in the samples in terms of their elastic moduli. These results, combined with our experimental investigations of optical trap lifetimes in high vacuum at high trapping-laser intensity for both annealed and as-grown nanospheres, were used to provide a theoretical analysis of the effects of porosity and non-sphericity in the samples, identifying possible mechanisms of trapping instabilities for nanospheres with non-bulk-silica-like properties.Comment: 10 pages, 7 figure