Thèses sur le sujet « Glass Nano-composites »

In the first part of this dissertation, glass fiber reinforced/unreinforced polyamide 6 (PA6) and polyamide 66 (PA66) were compounded with three different flame retardants, which were melamine cyanurate, red phosphorus and brominated epoxy with antimony trioxide, by using an industrial scale twin screw extruder. Then, to investigate flame retardancy of these specimens, UL-94, Limiting Oxygen Index (LOI) and Mass Loss Cone Calorimeter (MLC) tests were carried out. In addition to flammability tests, thermogravimetric analysis (TGA) and tensile testing were performed. Results of the tensile tests were evaluated by relating them with fiber length distributions and fracture surface morphologies under scanning electron microscope (SEM). Incorporation of melamine cyanurate (MCA) to PA6 led to some increase in LOI value and minor reductions in Peak Heat Release Rate (PHRR) value. However, it failed to improve UL-94 rating. Moreover, poor compatibility of MCA with PA6 matrix caused significant reductions in tensile strength. Brominated epoxy in combination with antimony trioxide (Br/Sb) was compounded with both glass fiber reinforced PA6 and PA66. Br/Sb synergism was found to impart excellent flammability reductions in LOI value and UL-94 as V-0 rating. Effectiveness of Br/Sb flame retardant was also proven by the MLC measurements, which showed excessive reductions in PHRR and Total Heat Evolved (THE) values. On the other hand, Br/Sb shifted the degradation temperature 100°
C lower and decreased the tensile strength value, due to poor fiber-matrix adhesion and decreased fiber lengths. Red phosphorus (RP), when introduced to glass fiber reinforced PA66 induced V-0 rating in UL-94 together with significant increase in LOI value, and major decrease in PHRR. Degradation temperature was 20°
C lower while mechanical properties were kept at acceptable values compared to neat glass fiber reinforced PA66. In the second part of this dissertation, to investigate synergistic flame retardancy of nanoclays
glass fiber reinforced PA6 was compounded by certain nanoclay and an organo-phosphorus flame retardant (OP), which contains aluminum phosphinate, melamine polyphosphate and zinc borate, in a laboratory scale twin screw extruder. Exfoliated clay structure of the nanocomposites was assessed by X-Ray Diffraction (XRD) and Transmission Electron Microscopy (TEM), while thermal stability and combustion behaviors were evaluated by TGA, LOI, UL-94 and MLC. Replacement of a certain fraction of the flame retardant with nanoclay was found to significantly reduce PHRR and THE values, and delay the ignition. Moreover, remarkable improvements were obtained in LOI values along with maintained UL-94 ratings. Residue characterization by ATR-FTIR and SEM ascribed the enhanced flame retardancy of nanocomposite specimens to the formation of a glassy boron-aluminum phosphate barrier reinforced by clay layers at the nanoscale.

Polymer-bioglass composites are favourable materials for bone repair. However, early failure in the interface of components is a common problem in physical mixtures. The aim of this project was to address the issue of phase separation by creating a hybrid material in which the polymer is bonded to bioglass. Synthetic non-biodegradable poly(methyl methacrylate) (PMMA) and natural biodegradable chitosan were selected as two types of polymers for fabrication of hybrid with bioglass. PMMA and chitosan were functionalised with appropriate silane coupling agents and covalently bonded to bioglass. The polymer and bioglass were then co-condensed during sol-gel method to form hybrid. The results of molecular scale analyses demonstrated that at optimum condition (0.1 coupling agent:MMA mol ratio, 60:40 vol% polymer:bioglass), the covalent bond between PMMA and bioglass occurred and resulted in the fabrication of hybrid. The presence of nano-scale interaction resulted in improved physico-chemical and biological properties compared with physical mixtures and bioglass. Furthermore, by manipulating process parameters such as replacing tetrahydrofuran with ethanol, increasing the temperature to 70 °C and adding sodium bicarbonate as catalyst, the gelation time was reduced and a more condensed structure was produced. The chitosan-bioglass hybrid was optimized for the volume ratio of chitosan:bioglass and coupling agent. Furthermore, a new method was developed for the creation of porosity in polymer-bioglass composites in which sodium bicarbonate was used as a gas foaming agent and a biocompatible alternative for the commonly used hydrofluoric acid during sol-gel method. In conclusion, the presence of nano-scale interaction significantly improved the physico-chemical properties of polymer-bioglass hybrids via promoting the homogenous distribution of phases. These hybrids open an avenue for the applications of polymers-bioglass composites for bone replacement and tissue engineering.

Le Poly Vinyl Alcohol (PVA) a été associé aux verres élaborés dans un système quaternaire (BG) 46S6 par les procédés cités (fusion, sol-gel et sacffolds). Différents paramètres intervenant dans les synthèses des verres bioactifs ont été étudiés, nous citons à titre d’exemple : la température, le pH, la taille des particules, le rapport Polymère / verres, la microstructure, la porosité et la biodégradation. Les caractéristiques thermiques des verres élaborés ont été également déterminées après chaque synthèse par analyse thermique différentielle (DSC/TG, DTA/TG). Ainsi, la température de fusion, la température de transition vitreuse et la température de cristallisation ont été élucidées. Ces caractéristiques thermiques changent lorsque la composition chimique du verre est modifiée. A ce titre, les compositions chimiques ont été étudiées par Fluorescence (XRF) et Inductively Coupled Plasma-Opticale Emission Spectroscopy (ICP-OES) après chaque synthèse pour s’assurer de la pureté des verres bioactifs élaborés et destinés à des applications médicales. Plusieurs techniques physico chimiques d’analyses (DRX, MEB, MET, FT-IR, XRF, ICPOES) ont été mises en oeuvre pour déterminer les propriétés physico chimiques de nos verres bioactifs avant et après expérimentations « in vitro ». Le nano composite Polymère-Verres scaffolds que nous avons obtenu présente des particules de tailles comprises entre 40 et 61 nm et une porosité d’environ 85%. La biodégradation des verres scaffolds décroît lorsque la teneur en verre scaffolds dans le nano composite croît. Les expérimentations « in vitro » montrent qu’après immersion de ces nano composites dans un liquide physiologique synthétique (SBF), une couche d’apatite (phosphate de calcium) se forme à leur surface. L’épaisseur de la couche formée dépend clairement de la taille des particules et du rapport polymère / verre scaffolds
The aim of the present work is the preparation of Bioactive Glass (BG) 46S6 by different techniques. Fabrication of composite scaffolds by using of Poly Vinyl Alcohol (PVA) and quaternary BG (two methods melting and sol-gel) with different ratios to the prepared scaffolds was carried out. Different factor affecting the final properties of the prepared composite scaffolds were investigated in this study, such as; temperature of treatment, BG particle size, polymer/glass ratio, microstructure, porosity, biodegradation, bioactivity, and drug release. The thermal behavior of the prepared bioactive glass by sol-gel and melting techniques were identified using Differential Scanning Calorimetric/Thermo Gravimetric (DSC/TG) or Differential Thermal Analysis/Thermo Gravimetric (DTA /TG). The elemental composition of the prepared bioactive glasses was determined by X-rays Fluorescence (XRF) to confirm that the prepared bioactive glasses have the same elemental compositions and high purity for biomedical applications. The particle size of the prepared bioactive glass was determined by Transmission Electron Microscopic (TEM). Nano-bioactive glass could be obtained by modified sol-gel and the obtained particle size ranged between 40 to 61 nm. The prepared bioactive glass by both applied methods has the same amorphous phase and all identified groups as well as. The porous scaffold has 85% porosity with a slight decrease by increasing the glass contents. The degradation rate decreased by increasing of glass content in the prepared scaffolds. The bioactivity of the prepared composite scaffolds was evaluated by XRD, FTIR, SEM coupled with EDX and Inductively Coupled Plasma-Optical Emission Spectroscopic (ICP-OES). It has been observed that after soaking in Simulated Body Fluid (SBF), there was an apatite layer formed on the surface of the prepared samples with different thickness depending on the glass particle size and polymer/glass ratio

碩士
逢甲大學
纖維與複合材料學系
104
In this study, the use of nano-silica on bisphenol A epoxy resin to toughen and prepare different nano silica content of the modified resin system. Then hand laminated prepared a quantitative basis weight and fiber content of the prepreg resin material. By using differential scanning thermal analyzer (DSC) and rheometer find hardening resin systems and processing conditions of temperature and then to a hot press method to make glass fiber cloth laminate. And its effect of different proportions of nano-silica glass transition temperature of the substrate of the position (Tg) and viscosity, followed by use of materials testing machine to test the toughness of DCB destroy Discussion (Double Cantilever Beam test) and impact properties, and finally and SEM image of fracture surface were analyzed after the DCB test. The results show: glass transition temperature of the resin material in position 118 ± 2 °c, not by the addition of various amounts of nano silica caused significant impact; fig SEM observation of fracture surface from DCB test after the damage occurred during discovery crack path deflection, crack pinning, micro-cracks and peeling failure mechanism proved to add nano-silica composites can absorb leaving more destructive energy, when the silica content is 6wt% when, GIC will be from 0.56 kJ / m2 upgraded to 1.05kJ / m2. Increased by 46.67%; impact damage from 40.14 kJ / m2 increased to 51.27 kJ / m2, increased by 27.73%.

碩士
逢甲大學
纖維與複合材料學系
102
An optimized synthesis of nanometer silica particles by sol-gel method take advantage of Tetraethoxysilane (TEOS). Preparation of nano-silica / epoxy mixed solution thorugh ultrasonication and mechanical agitation. Using differential scanning calorimetry (DSC) to explore the effect of different nano-silica added proportions on glass transition temperature (Tg) of resin system. Glass fabric/nano-silica/epoxy composite laminates made by hand lay-up and hot pressing method. The purpose of this study is to evaluate the reinforced role of nano-silica on the mechanical properties and the interlaminar fracture behaviour of fibre reinforced toughened epoxy. Flexural test, short-beam test and fracture toughness test (Double Cantilever Beam test) were performed to evaluate mechanical performance. Based on the experimental results showed that glass transition temperature (Tg) of resin system does not significantly influenced by adding with different amounts of nano-silica. Flexural strength and flexural modulus increased with increasing of nano-silica added amounts. The flexural strength and flexural modulus of the composites enhance 9.98% and 13.74%, respectively, with silica particles added 8 wt.% loading. Compared to the neat epoxy, the interlaminar shear strength of silica composites increased of 16.31% for 12 wt.% silica loading. The mode I fracture toughness of laminates also exhibt increased with increasing of nano-silica weight fraction. The GIC value enhance 55.7% with adding 12 wt.% nano-silica weight fraction. According to observ the photos of SEM after DCB tested specimen showed that including crack pinning, crack deflection, particle pull-up and microcracks etc. failure modes on the fracture surface. It demonstrates the composite materials could absorb more energy and causes the GIC increased when added nano-silica into epoxy system.

In the present investigation molecular dynamics (MD) simulations of nano-indentation on Zr50Cu50, Zr50Cu30Al20 metallic glasses (MGs) and Zr50Cu50, Zr50Cu30Al20 glass matrix composites (GMCs) with 14%, 30% and 50% crystalline volume fraction have been studied. Nano-indentation tests are conducted at varying strain rates (2.5 × 109 s-1, 2.5× 1010 s-1, 1.25 × 1011 s-1 and 2.5 × 1011 s-1) and temperatures (100K, 300K and 500K) to investigate the deformation behaviour and response on the mechanical properties such as yield point, maximum load, and hardness through load-displacement plots. Also, the effect of crystallite distribution (single-spherical and multi-spherical) and shape (spherical and cylindrical) on the load-displacement response have been studied. Structural analysis during deformation has been done by centro-symmetry parameter (CSP) studies. It is found that all curves have linear elastic behaviour and non-linear plastic behaviour with load varying linearly with displacement of the indenter following Hertz’s contact theory in the elastic region. After the first “pop in” or initiation of plastic deformation, serrations are observed to be irregularly spaced in amorphous alloys because of their short range order arrangement of atoms. With compared to that of MGs. This may be due to delay in load transfer from amorphous phase to crystallites which can be observed in the atomic position snapshots of CSP studies. The increase of temperature leads to the decrease in the yield point and maximum loads in MG and GMCs. This may be due to the fact that atoms are displaced far away and so the interatomic interaction force decreases causing softening of the alloy. Studies on the effect of crystallite distribution show that single-crystallite (14%) reinforced composite exhibits higher strength as compared to multi-spherical crystallite composite (14%). Also, studies on the shape of the crystallite reveal that composite reinforced with cylindrical shaped crystallites (14%) offer better strength than that of the composite with spherical crystallites (14%). From this study, it can be concluded that GMCs have better strength compared to MGs. Zr50Cu50 with 30 % crystalline volume fraction has better strength and in case of Zr50Cu30Al20 GMC with 50% crystalline volume fraction exhibits superior properties.

碩士
淡江大學
化學學系碩士班
102
This research has been developed a series of hydrophilic PU resin materials for the treatments of anti-fogging glass and hydrophilic PET textile, respectively. Anti-fogging Glass: A PEG-1000 containing NCO-terminated PU prepolymer is prepared and it reacted further with 3-aminopropyl triethoxy-silane, APTES (consists silane and amino function group), and a silane-terminated PU oligomer is resulted after TBT (for nano-TiO2 via sol-gel process) is added at pH=5 for 65 oC/6 hr. A silane-terminated hydrophilic PU oligomer is applied on an anti-fogging glass. The glass anti-fog effect will stand for more than 10 minutes and also remain excellent adhesion (cross-cut passes 4 B) after dipping in boiling water for 10minutes or in alcohol for 1 hr . Hydrophilic Textile treatment: A mixture of nano-TiO2 (TBT via sol-gel process) and hydrophilic (PEG-1000) group-containing UV-curable aqueous PU resin(UV-WPU) has been prepared for breathable textile treatment. A PET textile has been treated with UV-WPU by dipping process and then cured by UV-radiation. A hydrophilic PET textile has resulted and that demonstrated by its water diffusion area and water absorption. And PET textile still is hydrophilic after 20 water washing cycles (AATCC method). Due to UV-curing process creates IPN (interpenetrating polymeric networks) of hydrophilic UV-WPU between textile fibers that enhancing water washing durability.

碩士
逢甲大學
纖維與複合材料學系
105
Epoxy resin was brittle after hardening into a three-dimensional network structure. The force would produce cracks, and growth rapidly. So it need to improve the toughness and mechanical properties by modification. In this time, the epoxy resin was modified by adding chain extending agent and different proportions of nano-silica. And using DSC to examine the effect of modifiers on the glass transition temperature (Tg). The mechanical properties of epoxy resin /glass fabric composite laminate were investigated by Mode I fracture toughness, Mode II fracture toughness, flexural properties and interlaminar shear strength (ILSS). The Zeta Potential Analyzer was used to understand the different of nano- silica’s particle size. And the Field Emission Emission Scanning Electron Microscope (FE-SEM) to observe the failure morphology on the fracture surface of after fracture toughness test. With the high speed mixer and three-roll miller which can reduce the phenomenon of nano-silica agglomeration. Based on the DSC determined showed that glass transition temperature of cured resin system decreased with increasing of the chain extending agent. Because the soft chain caused by the increase in free volume. And when the nano-silica added in to the resin system, it would increasing the glass transition temperature. The flexure properties and ILSS all showed the same trend like glass transition temperature. The Mode I and Mode II fracture toughness of laminate enhance 55.7 % and 47 % with content 5 wt% of chain extending agent and 8 wt% of nano-silica. According to the FE-SEM observation found that with the increase of toughening agent, the broke section would become roughly.

Transparent glass-ceramics have been of industrial interest because of their multifarious applications. These are becoming increasingly important because of the flexibility that is associated with this route of fabricating intricate sizes and shapes as per the requirement. A number of glass-ceramics, based on well known ferroelectric crystalline phases (LiNbO3, LaBGeO5, SrBi2Nb2O9, Bi2WO6 etc.) were fabricated and their polar and electro-optic properties were reported. Keeping the potential applications of transparent glass-nano/microcrystal composites in view, attempts were made to fabricate SrBi2B2O7 and CaBi2B2O7 glasses and glass-nano/microcrystal composites. An attempt has been made to employ strontium bismuth borate SrBi2B2O7 (SBBO) as a reactive host glass matrix for growing the nanocrystals of ferroelectric oxides belonging to the Aurivillius family. The in situ nucleation and growth of SrBi2Nb2O9 (SBN) nanocrystals in a reactive SrBi2B2O7-Nb2O5 system and its influence on various physical (dielectric, pyroelectric and optical) properties were investigated. The strategy has been to visualize the formation of nanocrystalline SrBi2Nb2O9 as a result of the simple chemical reaction between glassy SrBi2B2O7 and Nb2O5. Indeed at lower concentrations of Nb2O5 transparent glasses were obtained which upon heat-treatment at appropriate temperatures yielded nanocrystalline SrBi2Nb2O9 phase in a transparent glass matrix. Textured SrBi2Nb2O9 ceramics were obtained by quenching the melts of SrBi2B2O7-Nb2O5 in equimolar ratio and their physical properties were studied. A strong anisotropy in physical properties (which are akin to single crystals) were demonstrated in the textured ceramics.

Transparent glass-ceramics have been of industrial interest because of their multifarious applications. These are becoming increasingly important because of the flexibility that is associated with this route of fabricating intricate sizes and shapes as per the requirement. A number of glass-ceramics, based on well known ferroelectric crystalline phases (LiNbO3, LaBGeO5, SrBi2Nb2O9, Bi2WO6 etc.) were fabricated and their polar and electro-optic properties were reported. Keeping the potential applications of transparent glass-nano/microcrystal composites in view, attempts were made to fabricate SrBi2B2O7 and CaBi2B2O7 glasses and glass-nano/microcrystal composites. An attempt has been made to employ strontium bismuth borate SrBi2B2O7 (SBBO) as a reactive host glass matrix for growing the nanocrystals of ferroelectric oxides belonging to the Aurivillius family. The in situ nucleation and growth of SrBi2Nb2O9 (SBN) nanocrystals in a reactive SrBi2B2O7-Nb2O5 system and its influence on various physical (dielectric, pyroelectric and optical) properties were investigated. The strategy has been to visualize the formation of nanocrystalline SrBi2Nb2O9 as a result of the simple chemical reaction between glassy SrBi2B2O7 and Nb2O5. Indeed at lower concentrations of Nb2O5 transparent glasses were obtained which upon heat-treatment at appropriate temperatures yielded nanocrystalline SrBi2Nb2O9 phase in a transparent glass matrix. Textured SrBi2Nb2O9 ceramics were obtained by quenching the melts of SrBi2B2O7-Nb2O5 in equimolar ratio and their physical properties were studied. A strong anisotropy in physical properties (which are akin to single crystals) were demonstrated in the textured ceramics.

Transparent glasses embedded with TTB structured ferroelectric nano/micro crystals (K3Li2Nb5O15, Ba5Li2Ti2Nb8O30) were fabricated in various tellurite and borate based glass matrices and characterized for their physical properties. Nanocrystals of K3Li2Nb5O15 were successfully grown inside tellurite glass matrix via conventional heat-treatment route. Eventhough, tellurite glasses preferentially crystallize only on the surface, bulk uniform crystallization was achieved in the (100-x) TeO2 - x(1.5K2O-Li2O-2.5Nb2O5) system. Heat capacity studies revealed them to be thermodynamically less fragile than any other tellurite glasses ever reported in the literature. Pyroelectric and ferroelectric effects as well as second harmonic generation were demonstrated for the heat treated (glass nanocrystal composites) samples in this system. The conventional method of melt-quenching of constituent oxides could not yield Ba5Li2Ti2Nb8O30 crystallites. So, Ba5Li2Ti2Nb8O30 microcrystals were successfully formed in tellurite glass matrix by mixing pre-reacted Ba5Li2Ti2Nb8O30 ceramic powders with TeO2. The glass transition temperature was found to be the highest ever reported and this system was kinetically strong based on the fragility parameter. Dielectric studies revealed a frequency and temperature independent nature of the dielectric constant and very low dielectric loss. The SHG measurement which was carried out as a function of temperature demonstrated the incidence of blue second harmonic generation in the microcrystals present in the glass matrix. Ba5Li2Ti2Nb8O30 nanocrystals were successfully crystallized in the transparent glass system (100-x)Li2B4O7 – x(Ba5Li2Ti2Nb8O30). Dielectric constant increased while the dielectric loss decreased with the increase in Ba5Li2Ti2Nb8O30 content. Nuclear magnetic resonance spectroscopic studies were carried out to have an insight into the structure of this system. Transmission studies and refractive index measurements were performed and various optical parameters were calculated. Dielectric and transport properties were studied for the glasses and glass nano/microcrystal composites of all the systems reported in this thesis. Li+ ion was found to be responsible for conduction in all these systems. Evolution of self-organized nanopatterns of K3Li2Nb5O15 crystals has been demonstrated in the glass system (100-x) TeO2 - x(1.5K2O-Li2O-2.5Nb2O5) by excimer laser irradiation. The second harmonic signal observed by the Maker fringe technique has been attributed to the presence of well-aligned nano-sized grating structures in the glass system. Glasses belonging to the systems TeO2-K3Li2Nb5O15, TeO2-Ba5Li2Ti2Nb8O30 and V2Te2O9 undergo spinodal decomposition on exposing to KrF pulsed excimer laser. The spinodally phase separated structures were observed on all the surfaces of the samples. Ring shaped patterns were observed on several locations of the samples at higher frequency of laser pulses probably owing to the shock waves produced by the high intense laser beam. Line shaped patterns were found to originate on the sample surfaces when irradiated for longer periods.

Transparent glasses embedded with TTB structured ferroelectric nano/micro crystals (K3Li2Nb5O15, Ba5Li2Ti2Nb8O30) were fabricated in various tellurite and borate based glass matrices and characterized for their physical properties. Nanocrystals of K3Li2Nb5O15 were successfully grown inside tellurite glass matrix via conventional heat-treatment route. Eventhough, tellurite glasses preferentially crystallize only on the surface, bulk uniform crystallization was achieved in the (100-x) TeO2 - x(1.5K2O-Li2O-2.5Nb2O5) system. Heat capacity studies revealed them to be thermodynamically less fragile than any other tellurite glasses ever reported in the literature. Pyroelectric and ferroelectric effects as well as second harmonic generation were demonstrated for the heat treated (glass nanocrystal composites) samples in this system. The conventional method of melt-quenching of constituent oxides could not yield Ba5Li2Ti2Nb8O30 crystallites. So, Ba5Li2Ti2Nb8O30 microcrystals were successfully formed in tellurite glass matrix by mixing pre-reacted Ba5Li2Ti2Nb8O30 ceramic powders with TeO2. The glass transition temperature was found to be the highest ever reported and this system was kinetically strong based on the fragility parameter. Dielectric studies revealed a frequency and temperature independent nature of the dielectric constant and very low dielectric loss. The SHG measurement which was carried out as a function of temperature demonstrated the incidence of blue second harmonic generation in the microcrystals present in the glass matrix. Ba5Li2Ti2Nb8O30 nanocrystals were successfully crystallized in the transparent glass system (100-x)Li2B4O7 – x(Ba5Li2Ti2Nb8O30). Dielectric constant increased while the dielectric loss decreased with the increase in Ba5Li2Ti2Nb8O30 content. Nuclear magnetic resonance spectroscopic studies were carried out to have an insight into the structure of this system. Transmission studies and refractive index measurements were performed and various optical parameters were calculated. Dielectric and transport properties were studied for the glasses and glass nano/microcrystal composites of all the systems reported in this thesis. Li+ ion was found to be responsible for conduction in all these systems. Evolution of self-organized nanopatterns of K3Li2Nb5O15 crystals has been demonstrated in the glass system (100-x) TeO2 - x(1.5K2O-Li2O-2.5Nb2O5) by excimer laser irradiation. The second harmonic signal observed by the Maker fringe technique has been attributed to the presence of well-aligned nano-sized grating structures in the glass system. Glasses belonging to the systems TeO2-K3Li2Nb5O15, TeO2-Ba5Li2Ti2Nb8O30 and V2Te2O9 undergo spinodal decomposition on exposing to KrF pulsed excimer laser. The spinodally phase separated structures were observed on all the surfaces of the samples. Ring shaped patterns were observed on several locations of the samples at higher frequency of laser pulses probably owing to the shock waves produced by the high intense laser beam. Line shaped patterns were found to originate on the sample surfaces when irradiated for longer periods.

Molecular dynamics (MD) simulations are carried out for cyclic nano-indentation on sintered metal (Al)-metallic glass (Cu66Zr34) reinforced composites termed as composite-I and on sintered alloy(Al-4%Cu)-metallic glass (Cu66Zr34)termed as composite-II to measure the hardness, stiffness and reduced young modulus.I ndenter radius, and indentation speed effects on the load-displacement behavior, hardness, stiffness, and young modulus has been studied. Depth-sensing cycling nano-indentation is studied to assess depth-dependent plastic deformation of the composite at room temperature. The results showed that the plastic deformation continued to take place and the continuous displacement increased as the number of indentation increased. We have found that composite-II sample shows high mechanical properties like hardness, stiffness and reduced young modulus than composite-I.But, there was reduction in the plasticity of the composite-II to enhance other mechanical properties such as Hardness and stiffness.Furthermore, the initial hardness is seen to slightly increase with increase in indenter radius, indentation speed and alloying element. After each cyclic nano-indentation, the loading curve overlapped with the previous unloading curve and had a small displacement after each reloading cycle. From the first loading-unloading cycle, plastic deformation continued to take place and the continuous displacement increased as the number of indentations increased. The stiffness was seen to remain constant for a constant cycle and increased with increase in number of cycles and was seen to remain constant after few cycles.

Many material properties depend on specific details of microstructure and both optimal material performance and material reliability often correlate directly to microstructure. In nano- and micro-systems, the material's microstructure has a characteristic length scale that approaches that of the device in which it is used. Fundamental understanding and prediction of material behavior in nano- and micro-systems depend critically on methods for computing the effect of microstructure. Methods for including the physics and spatial attributes of microstructures are presented for a number of materials applications in devices. The research in our group includes applications of computation of macroscopic response of material microstructures, the development of methods for calculating microstructural evolution, and the morphological stability of structures. In this review, research highlights are presented for particular methods for computing the response in: 1) rechargeable lithium ion battery microstructures, 2) photonic composites with anisotropic particulate morphologies, 3) crack deflection in partially devitrified metallic glasses.
Singapore-MIT Alliance (SMA)

The ability to fundamentally understand how changes in the molecular architecture and reinforcement at the molecular and nano-scale effect the mechanical and thermal behavior of glassy thermosets is of considerable interest. A series of epoxy-based networks with controlled molecular weight between crosslinks and backbone stiffness are utilized to identify characteristics that govern yield behavior. Two parameters, the glass transition temperature, Tg, and cohesive energy density, Ec, are identified to describe changes in network stiffness and strength, respectively. The parameters are incorporated into a model that describes yielding over a range of stress states, strain rates, and temperatures. The same epoxy network is used to explore the effects of backbone stiffness and crosslink density on the strain hardening modulus and fracture. It is found the strain hardening modulus is directly related to the crosslink density of the network similar to a traditional rubber. The backbone stiffness appears to have no effect on several post-yield phenomena. A class of compounds labeled molecular fortifiers are then incorporated into the model epoxy network. Two phosphorus-based compounds, one that is included as a free additive and another that is covalently bound to the network, are shown to improve a range of mechanical, physical, and thermal properties. The covalently bound fortifier increases the crosslink density through specific physical bonding interactions and alters the characteristics of the network. In addition several sulfur and a carbon-based compound are investigated as possible molecular fortifiers. The phhysical interactions in the interphase region are found to be enhanced in nano-clay composites that contain fortifiers. These interactions lead to improved mechanical and thermal characteristics over composites utilizing commercially modified nano-clays.