The continuum damage mechanics (CDM) approach is widely used to model damage in polymer matrix composite materials which are represented using the homogenized properties of the fiber and matrix constituents. CDM simplifies the problem of accounting for a large number of defects in a material by considering the homogenized effect of the defects as a change in constitutive properties of the material. However, recent investigations of textile composites have shown that CDM inaccurately predicts the direction of damage zone growth for some composite architectures which fail under shear load, tending to predict failure transverse to the fibers. This behavior is fundamentally attributable to the fact that shear failure in textiles results in large (tow-scale) matrix cracks, while CDM is intended to model distributed micro-cracks. It is shown that when CDM is used to model shear failure in anisotropic continua, material anisotropy tends to cause CDM to predict failure contrary to what is expected for these structures. An approach is presented that may allow CDM to better predict damage growth for shear failure in composites by encouraging the creation of an intial damage zone with sufficient directional bias to overcome the effect of material anisotropy.

Ever since the discovery of carbon nano materials like carbon nanotube (CNT) and graphene, this class of materials has gained significant attention due to their exotic properties. The principle idea of my present research project is to understand the novel improvements induced in polymer matrices with inclusion of the nanofillers. This thesis is thematically divided into three parts. In the first part we introduce principle materials that we use for preparation of composites. Methods of nanofiller preparation and different nanocomposites as previously reported in literature are discussed to formulate the basis of our study. Different dispersion techniques are discussed which facilitate uniform nanofiller distribution. A variety of experimental methods are described which were employed to investigate the structure and properties of the composites. In the second part we discuss in details polyamide-12 (PA12) composites using CNT and graphene as fillers. A marked improvement is recorded in the toughness of the films with incorporation of CNT, dispersed in PA12 using a surfactant. Electrical percolation is also achieved in the otherwise insulating matrix. With PA-12 fibers we explored the effect of fiber processing and CNT incorporation in the mechanical properties. Extensive wide angle x-ray diffraction was carried out to interpret the structural modifications brought about by CNT in the matrix. The final part of the thesis deals with a thermosetting polymer, epoxy composites. CNT, Graphene and also a mixture of the two nanofillers were used as reinforcing agents. Appreciable improvement was recorded in the mechanical properties, electrical and thermal conductivity of the composites. Detailed optical and electron microscopy was carried out to get a vivid idea of the micro-structure and dispersion. The presented work demonstrates the significant ability of carbon nanofillers to reinforce polymer matrices enhancing their mechanical, electrical and thermal properties and opening a wide horizon for a variety of applications.

<p><font face="Times New Roman" size="4"><font face="Times New Roman" size="4"> <p align="left">The aim of this study is to investigate the repair bond strength of composite resin following micromechanical and chemical means of retention in improving the repair of composite resin specimens.</p> </font></font></p>

Lapping pad will be worn during lapping process. Therefore, the quality of the work piece and the material removal ability will be lower. First, in this paper, it propose a intermittently nickel-electroplating lap-ping pad in lapping process : At first, plate a layer of nickel on copper plate and used it to be lapping pad. Replate the lapping pad to restore the working ability when the working ability of lapping pad decreased be-cause of wear. Secondary, it propose another restore method : composite electroplating on grinder in process. When grinding by using Ni-SiC composite coating pad, it is used to restore the pad by Ni-SiC composite electroplating at the same time. At first, the influence of load and rotation speed on mate-rial removal are investigated in this study. It is found that the material removal increased as the rotation speed of lapping pad and load increased. It is also found that the roughness of sin-tering SiC decreased as the load increased at a constant rotational speed. And at constant load , the influence of rotation speed on roughness of sintering SiC is unapparent. The ability decay of material removal of lap-ping pad is as time as go by. It can complete restore the wore lap-ping pad to unwear state by replating 15 minutes with 2.5 cur-rent density. The restored pad¡¦s behavior of material removal and roughness is the same as a new one¡¦s. The material removal of sintering SiC of composite electro-plating on grinder in process by using Ni-SiC composite coating is bigger than the material removal of sintering SiC of lapping by nickel-electroplating lapping pad. The material removal increase to 1.7 ~ 3.8 times in 90 minutes at the same load and rotation speed. And the material removal and time are linearly depend. It is investigated that the working ability of grinding disk can be maintain constant. It is also found that the material removal increased as the rotation speed of lapping pad and load in-creased.

Sandwich composites with polymer foam core are currently used in load-bearing components in buildings and naval structures due to their high strength to weight and stiffness to weight ratios, excellent thermal insulation, and ease of manufacturing. During their service time, sandwich composites are exposed to various external mechanical and hygro-thermal stimuli. It is known that the constituent properties of the sandwich composites are greatly influenced by the temperature and moisture fields. For example extreme temperature changes and humid environmental conditions can significantly degrade the stiffness and strength of the polymer foam core. This study analyzes the effect of moisture diffusion on the deformation of viscoelastic sandwich composites, which are composed of orthotropic fiber-reinforced laminated skins and viscoelastic polymeric foam core. It is assumed that the elastic and time-dependent (transient) moduli at any particular location in the foam core depend on the moisture concentration at that location. Sequentially coupled analyses of moisture diffusion and deformation are performed to predict overall performance of the studied viscoelastic sandwich systems. A time and moisture dependent constitutive model is used for the polymer foam core. A time-integration algorithm is developed to link this constitutive model to finite element (FE) analyses framework. The overall time-dependent responses of the sandwich composites subject to moisture diffusion are analyzed using 2D plane strain and 3D continuum elements. A 23% increase in the transverse deformation of the viscoelastic sandwich beam is observed due to the moisture degradation. Experimental data and analytical models available in the literature are used to verify the results obtained from the FE code. Parametric studies on the effects of different diffusivity ratios of skin and core materials on stress, strain and displacement fields have been analyzed. At the initial times the effect of moisture on the field variables is found to be most pronounced in the case with the highest diffusivity ratio. Contributions of moisture dependent elastic and the time-dependent moduli to the overall stress, strain and displacement field have been studied. The structural analysis of the sandwich composite under combined moisture diffusion and mechanical loading for two kinds of problems using FE method is performed to complete the study.

This study analyzes the thermo-mechanical response of a composite cylinder made up of two layers of linear isotropic viscoelastic materials that belong to the class of non-Thermorheologically Simple Material. The effect of time-varying temperature field due to unsteady heat conduction phenomenon is analyzed on the short term and long term material response in terms of stress, strain and displacement fields. The material properties of the two layers of the composite cylinder at any given location and time are assumed to depend on the temperature at that location at that given instant of time. Sequentially coupled analyses of heat conduction and deformation of viscoelastic composite cylinder is carried out to obtain the overall response. The stress and strain field developed in the composite cylinder is evaluated as the discontinuity in hoop stress and radial strain at the interface of the two layers caused due to mismatch in material properties may lead to delamination if it exceeds critical value. Analytical solution for the stress, strain and displacement fields of the viscoelastic composite cylinder is developed from the corresponding solution of linear elasticity problem by using the Correspondence Principle. The analytical solution for determining the temperature dependent stress, strain and displacement fields is further developed by incorporating the temperature dependence on the material properties and modeling the material as non-TSM. To analyze more complex geometry with general loading and boundary conditions, Finite Element(FE) analysis of the composite cylinder is performed and the results of analytical and FE method are found to be in good agreement. Parametric studies are carried out to understand the effect of change in material parameters namely the Prony coefficients in the transient creep compliance, characteristic of creep time in transient creep compliance and the instantaneous elastic compliance, on the overall response of the composite cylinder. The effect of different temperature dependent functions of the material properties, namely linear temperature variation and quadratic polynomial variation on the overall material response is also analyzed. It is observed that the effect of change in elastic properties significantly increases the jump in hoop stress and radial strain. It is also observed that when the materials are highly dependent on temperature the jump in radial strain and hoop stress increases significantly. The radial displacement also increases by a significant amount in both the cases.

The continuum damage mechanics (CDM) approach is widely used to model damage in polymer matrix composite materials which are represented using the homogenized properties of the fiber and matrix constituents. CDM simplifies the problem of accounting for a large number of defects in a material by considering the homogenized effect of the defects as a change in constitutive properties of the material. However, recent investigations of textile composites have shown that CDM inaccurately predicts the direction of damage zone growth for some composite architectures which fail under shear load, tending to predict failure transverse to the fibers. This behavior is fundamentally attributable to the fact that shear failure in textiles results in large (tow-scale) matrix cracks, while CDM is intended to model distributed micro-cracks. It is shown that when CDM is used to model shear failure in anisotropic continua, material anisotropy tends to cause CDM to predict failure contrary to what is expected for these structures. An approach is presented that may allow CDM to better predict damage growth for shear failure in composites by encouraging the creation of an intial damage zone with sufficient directional bias to overcome the effect of material anisotropy.

Nanoscaled-Al2O3 particles reinforced 1050 Aluminum composites by FSP were successfully fabricated in this study. The grain size of 1050 aluminum was obviously refined to about 0.5£gm by friction stir process(FSP), and there was a tendency that grain size decreased with increasing of Al2O3 content, where grain size of 0.84£gm was achieved with 24.7vol% of Al2O3. Nanoscaled-Al2O3 particles reinforced 1050 Al alloy by FSP revealed an excellent strengthening effect and excellent ductileity, Where hardness and UTS of the composite with 24.7vol% nanoscaled-Al2O3 particles were increased up to Hv113 and 310MPa respectively. The tensile result showed a 400% of increase in UTS comparing to the pure Al after FSP.

Electromagnetic shielding materials for plastic packaging in laser modules application were studied experimentally. Bipheny1, Nylon and LCP mixed with Al-powder, Al-flake, carbon-fibers and steel-fibers was fabricated and measured in shielding effectiveness(SE) for EMI. Compression molding, double-screw extrusion and injection molding were used for fabrication. We examed the mechanical properties and shielding effectiveness of these compounds. The SE of conductive plastics was measured to be 40dB at 30MHz and 60dB at 1GHz for carbon-fiber and plastic mixture. The experiment result indicates that introducting conductive carbon fiber fillers into plastics will produce conductive composites having an excellent SE to reduce EMI. With these excellent SEs, such conductive carbon fiber fillers into plastics are suitable for use in low-cost laser modules.

Abstract In this paper, the mechanical properties of carbon-fiber reinforced polyether-ether ketone (PEEK) with and lay-up subject to impact and temperature reaction have been investigated.The drop-weight impact tests were performed by a 4mm diameter semi spherical nosed projectile. Incident impact height adopts 0.8m and 1.6m incident height. After impact testing, the static tension tests were performed to measure the ultimate strengths and elastic modulus at 25¢J¡B75¢J¡B125¢J¡B145¢J,so that the effects of stacking sequence and the damage mechanism subjected impact at elevated temperature was obtained. By the parametric study and research , there are very important results as follow: The destructive crack of AS4/PEEK laminates subject to impact were arised from the tension sides toward the pressure sides, and the lay-up was more serious than the lay-up. Although more excellent ultimate strength than the lay-up, the must be quantities of decay When the incident height increase as well as elevated temperature. Keywords: Composite, Impact, Temperature, Strength, Elastic Modulus, Fracture.