Ram Mohan

Static and Fatigue Behavior of Epoxy/Fiberglass Composites Hybridized with Alumina Nanoparticles

Advanced composites are hybridized by the integration of alumina nanoparticles into the matrix and onto the fabric surface. Alumina was pre-dispersed by sonication. Pre-processing of alumina was carried out by resin modification or fiber modification, prior to the consolidation into composite laminates. Alumina nano-particles were also functionalized by silane coupling agent tris-2-metoxyethoxy vinyl silane (T2MEVS). Vacuum assisted resin transfer molding (VARTM) was used to fabricate the composite panels for mechanical performance evaluation and characterization. Material property characterization for tensile, fatigue life and inter-laminar fracture toughness were determined for these hybrid composites and compared with the traditional fiber—matrix composite system as a baseline. Experimental characterization indicated that mode-I fracture toughness was significantly improved with the inclusion of alumina nanoparticles as well as by the functionalization of alumina nano-particles. However, the influences on the tensile behavior and tension/tension un-notched fatigue behavior in [0/90] configuration were not significant. In applications that involve only tension/tension fatigue loading, hybrid composites with nano-particulate inclusions can provide improved delamination failure characteristics without impacting the fatigue life and tensile behavior significantly.

Computational Modeling of Peptide–Aptamer Binding

Evolution is the progressive process that holds each living creature in its grasp. From strands of DNA evolution shapes life with response to our ever-changing environment and time. It is the continued study of this most primitive process that has led to the advancement of modern biology. The success and failure in the reading, processing, replication, and expression of genetic code and its resulting biomolecules keep the delicate balance of life. Investigations into these fundamental processes continue to make headlines as science continues to explore smaller scale interactions with increasing complexity. New applications and advanced understanding of DNA, RNA, peptides, and proteins are pushing technology and science forward and together. Today the addition of computers and advances in science has led to the fields of computational biology and chemistry. Through these computational advances it is now possible not only to quantify the end results but also visualize, analyze, and fully understand mechanisms by gaining deeper insights. The biomolecular motion that exists governing the physical and chemical phenomena can now be analyzed with the advent of computational modeling. Ever-increasing computational power combined with efficient algorithms and components are further expanding the fidelity and scope of such modeling and simulations. This chapter discusses computational methods that apply biological processes, in particular computational modeling of peptide-aptamer binding.

A composite manufacturing process simulation environment (COMPOSE) utilizing parallel processing and object-oriented techniques

Liquid composite molding, based on resin transfer molding (RTM), vacuum-assisted resin transfer molding, and its variants, have been increasingly used in new composite material developments for both land and air military vehicle applications. New processes have high risks in cost, time, quality, and reproducibility depending on their stage of maturity. Various defense initiatives have identified physical process modeling and simulations as a viable technology to provide the required technical base to promote composite affordability and provide for process maturation. The Composite Manufacturing Process Simulation Environment (COMPOSE) was developed to model the RTM process. COMPOSE utilizes parallel processing methods on massively parallel machines so that large complicated geometries and models can be analyzed. The object-oriented design methods used in COMPOSE allow code reuse and faster software development cycles.

Computational modeling of shear deformation and failure of nanoscale hydrated calcium silicate hydrate in cement paste: Calcium silicate hydrate Jennite

Calcium silicate hydrate Jennite is a molecular structure commonly accepted as a representation of the complex calcium silicate hydrate gel formed during the hydration of typical Portland cement. In this paper, the behavior of nanoscale calcium silicate hydrate Jennite under shear deformation was investigated using molecular dynamics simulations. Computational samples representing the nanoscale structure of calcium silicate hydrate Jennite were subjected to shear deformation in order to investigate not only their mechanical properties but also their deformation behavior. The simulation results indicated that the nanoscale calcium silicate hydrate Jennite under shear deformation displays a linear elastic behavior up to shear stress of approximately 1.0 GPa, and shear deformation of about 0.08 radians, after which point yielding and plastic deformation occurs. The shear modulus determined from the simulations was 11.2 ± 0.7 GPa. The deformation-induced displacements in molecular structures were analyzed dividing the system in regions representing calcium oxide layers. The displacement/deformation of the layers of calcium oxide forming the structure of nanoscale calcium silicate hydrate Jennite was analyzed. The non-linear stress–strain behavior in the molecular structure was attributed to a non-linear increase in the displacement due to sliding of the calcium oxide layers on top of each other with higher shearing. These results support the idea that by controlling the chemical reactions, the tailored morphologies can be used to increase the interlinking between the calcium oxide layers, thus minimizing the shearing of the layers and leading to molecular structures that can withstand larger deformation and have improved failure behavior.

Effect of Sintering Temperature on Mechanical Properties of Electrospun Silica Nanofibers

Mechanical Properties of materials depend upon the crystal structure, presence of dislocations and slip planes in the unit cells. Nano-structures due to its nano scale size are expected to have defect free unit cells and hence posses very good mechanical properties. Electrospinning provides simple and cost effective means to produce nanofibers on a mass scale. These electrospun nanofibers could be subsequently used in woven composites to improve interlaminar properties. This paper addresses manufacturing of silica nanofibers by electrospinning and effect of sintering temperature on properties of these fibers. Electrospinning produces nanofibers by stretching liquid droplet emanating from spinnerate under the combined action of Columbic forces due to applied voltage and repulsion of charged ions. When the formed electrospun silica nanofibers are sintered at different temperatures, there is variation SiO2 content due to evaporation of solvents. This results into variation in the mechanical properties of electrospun silica nanofibers based on the sintering temperature. Differential Scanning Calorimetric (DSC) studies are carried out to relate variation in SiO2 content with sintering temperature. The mechanical properties of these electrospun fibers under various sintering temperatures are ascertained by evaluating their performance of composite laminates with electrospun interlaminate layers.© 2008 ASME

Predictive Mechanical Properties of EPON 862 (DGEBF) cross-linked with Curing Agent W (DETDA) and SWCNT using MD Simulations - Effect of Carbon Vacancy Defects

Molecular Dynamics (MD) simulations are a viable alternative to experimental methods to obtain mechanical properties of EPON 862-DETDA-SWCNTcomposites. This paper investigates the effect of SWCNT carbon vacancy defects on the Young’s modulus of the EPON 862-DETDA-SWCNT composite using MD simulations performed via Accelrys. For a composite with 7-12 weight% SWCNT, 2 carbon vacancy defects in the SWCNT is found to reduce the Young’s Modulus by 13-18%, while 4 carbon vacancy defects in the SWCNT reduced the Young’s Modulus of the composite by 21-30%. This clearly indicates that carbon vacancy defects are one potential cause of disparity, and lower Young’s modulus values of Epoxy-SWCNT composites cited in the literature.

Effect of Electrospun Fibers on the Interlaminar Properties of Woven Composites

Failure by delamination of composite laminates due to low velocity impact damages is critical because of the subsurface nature of delamination. Traditional methods such as stitching and Zpinning, while improving interlaminar properties in woven composites, lead to a reduction of the inplane properties. To alleviate these problems, use of Tetra Ethyl Orthosilicate (TEOS) nano fibers manufactured using electrospinning technique in fiber Glass-Epon composite laminates is investigated for their potential to improve the interlaminar properties. Electrospun coated fiber glass woven mats are impregnated with epoxy resin using Heated-Vaccum Assisted Resin Transfer Moulding (H-VARTM) process. The interlaminar properties of the nano engineered hybrid composites obtained using ASTM Double Cantilever Beam (DCB) tests and short beam shear tests are compared with those without the presence of electrospun fiber layers, to study their influence. The short beam shear tests revealed a 20% improvement due to presence of TEOS interlaminar electrospun nanofibers. It is also noteworthy that fibers cured at different temperature levels had variation in performance as observed in MSBS test results.

Effect of Current Density and Magnetic Field on the Growth and Morphology of Nickel Nanowires

One-dimensional nanostructures due to their unique properties and applications have generated special interests in MEMS and NEMS applications. There have been numerous methods developed to synthesize such 1D nanostructures. One of the most prominent methods is the electrodeposition into the channels in a porous material. It has been found that applied external magnetic field could improve and direct the growth of one-dimensional nanostructures in certain crystallographic directions. However, the nature and behavior of such structures and the influence of the synthesis parameters are yet to be fully understood. Our present work investigates the effect of the current density along with external magnetic field intensity on the growth direction of the one-dimensional Nickel nanowires. In the present study, Ni nanowires are grown using the electrodeposition assisted anodic alumina template method. The grown nanowires are characterized using XRD to determine the crystallographic properties. SEM was then used to characterize the morphology of the grown structures, while EDS was employed to study the composition. Present results clearly indicate that the morphological and crystallographic properties of synthesized nanowires are influenced by the applied current density and magnetic field intensity. Further studies employing Focused Ion Beam to prepare TEM sample are required to investigate the atomic arrangement of the synthesized Ni nanowires to further conform the present SEM and XRD findings.

Tensile and Flexural Deformation of Nickel Nanowires via Molecular Dynamics Simulations

Metallic nanowires show great potential for applications in minimization of electronic devices due to their extraordinary mechanical strength and electrical properties. Their desirable property characteristics with the smallest dimensions for efficient transport of electrons show potential for use as interconnects and critical devices in nanoelectronics and nano-optoelectronics (Chen, et al., 2006). These metallic nanowires also show potential for applications in electronic packaging, nanoelectronic and nano mechanical devices. A significant issue in the application of these metallic nanowires is their structural strength and stability under mechanical and thermal loading conditions. The deformation behavior of these nanowires under different mechanical loads (for e.g., tensile, bending) is poorly known. Experimental investigations of these behaviors are impractical due to their size and the complications of applying these loading conditions via nano load cells within high resolution microscope systems. Computational techniques based on molecular dynamics (MD) simulations of the representative atomistic configuration of the metallic nanowires provide an effective means of understanding the mechanical deformation behavior of these nanowires. In this chapter, we discuss the tensile and flexural dynamic deformation behavior of the Nickel (Ni) nanowires due to tensile loading and flexural bending via molecular dynamics simulations. The tensile and flexural deformation behaviors based on the atomistic model configurations of Nickel nanowires are analyzed. The stress-strain constitutive behavior, tensile strength and the Young’s modulus for various Ni nanowire configurations are investigated and presented. The natural frequency of the flexural deformation of these nanowires via molecular dynamics simulations is obtained and analyzed. The simulation of the deformation behavior in metallic nanowires modeled as atomistic systems at finite temperatures is a dynamic process and is conducted using classical molecular dynamics. Focusing on the mechanical behavior of nanowires, it is known that the properties of material configurations at nanometer dimensions can be rather different from those of the bulk material. In the past decades, the rapid progress of miniaturization of electronic devices and nanoscale measurement systems has aroused an interest in nanometer scale materials such as nanowires (Ju, 2004) (Liang, 2003) (Park, 2005) (Silva et. al., 2004), (Silva, 10

Molecular Dynamics Simulations of Flexural Deformation of Nickel Nanowires

We study the flexural dynamic deformation behavior of nickel (Ni) nanowire beams due to flexural bending via molecular dynamics simulations. Molecular model configurations of Nickel nanowires are analyzed. The deformational vibration frequencies obtained from molecular dynamics simulations are compared with the natural frequencies based on classical beam theory. The tensile deformation behavior under various strain rates of the Ni nanowires are also analyzed to obtain the required Youngs Modulus for such comparisons. The frequency of flexural vibration obtained from molecular dynamics simulation was found to be independent of the magnitude of loading for the two boundary conditions studied. This is consistent with the classical beam theory. The magnitude of frequency based on the continuum classical beam theory was about an order higher compared to the frequency computed from the time displacement data obtained from the molecular dynamics simulations. These computational simulations provide an effective means of understanding the mechanical deformation and structural stability of the metallic nanowires.