Micro-reinforced composite structure

There are many applications where the physical properties of a textile substrate are combined with the electrical and shielding properties of polypyrrole. Thus polypyrrole-coated fabrics show excellent dissipation properties. In this way industrial uniforms where explosion-proof conditions or shielding fi om micro-waves are necessary can be fabricated, as well as the use of polypyrrole-coated filters where static charges could cause the explosion of flammable solvents. Other important applications are related to military equipment, as radar-absorbing sheets. The microwave response of those fabrics seems to be ideal for camouflage nets that avoid visual, near-infrared and radar detection. Textile fabrics have also applications in fiber-reinforced composite structures of different resins. 

Thermal residual stresses are inherent to fibre reinforced composites due to the heterogeneity of the thermo-mechanical properties of their two constituents. Such stresses build up when composite structures are cooled down from the processing temperature to the test temperature. Residual stresses will be present on both a fibre-matrix scale (micro-scale), and on a ply-to-ply scale (macro-scale) in laminates built up from layers with different orientations. It is recognised that these stresses should be taken into account in any stress analysis. 

It is now well established that the extent of reinforcement highly depends on the filler characteristics, especially surface characteristics and morphology. In addition, the dispersion of the nanofillers is considered to be one of the most important determining factors of physical properties of the polymer composites. Therefore, it is desirable to investigate metal oxide filled micro/nano-composites of NR for the structural analysis by XRD and morphology by TEM, SEM, FE-SEM and AFM. 

The neat polyester resin showed very low water uptake due to the three dimensionally cross-linked network structure after curing. The -OH group in the chain end of polyester and oxygen of the ester linkage influences the formation of hydrogen bonds. However it absorbs 0.05 mol% of water due to the presence of micro cracks and also due to the hydrophihc nature of polyester. The fiber-reinforced composites absorb water very rapidly at the initial stage and later a saturation level is attained, and there is no further increase in water absorption. As the flber content increased the water absorption also increased due to the hydrophilic nature of the fiber [101]. 

During the last two decades micro/nanocellulose-reinforced composites have been the subject of intensive research and a number of review papers have appeared covering this work [14, 17, 19, 24, 53, 173,174], Nanocellulose either in CNC or NFC form will result in varying reinforcement of nanocomposites. Also, different types of nanocellulose can be used in various forms of reinforcement, including distributed reinforcements, planar reinforcements, or continuous networked structures. 

P.A. Annis and T.W. Quigley, Jr., in Micro-structural Characterisation of Fibre-Reinforced Composites, edited by J. Summerscales (CRC Press, Boca Raton, 1998), p. 17. 

When modeling the fiber/matrix micro-structure, in order to study wear and failure mechanisms in real fiber-reinforced composites, an FE macro/micro contact model (introducing the displacement coupling technique) is much more suitable than using an equivalent macro-model. As a result, the calculated contact, stress, and strain results are significantly closer to the real conditions. 

Fiber-reinforced composite materials are composed of dispersed fibrous materials (e.g. glass, Kevlar, PET, flax, hemp, sisal, etc.) set within a continuous polymer matrix. The primary benefit of fiber-reinforced composites over traditional engineering materials comes from their impressive strength-to-weight ratio and the ability to design the micro-structure so as to optimize their macro-stmctural properties. These advantageous properties were first exploited by the space and aerospace industries. 

In this seetion we go through the details of micro-macro modeling of a random fiber-reinforced composite. The material is assumed to be macroscopically isotropic, but it is micro-structurally anisotropic as a result of the presence of fibers in a random arrangement at that scale. 

Defining the micro-structure. The fiber-reinforced composite which serves as the model problem consists of a polymer matrix containing thin, randomly orientated, natural fiber reinforcements. Needle-punching is used to entangle the fibers, which are then bonded into the matrix. This process results in a thin, flat composite which is used as the outer layers in a laminate, which sandwich honeycomb filler. 

Standard multi-scale methodologies as presented in this review Chapter have developed significantly over the last 15 years. The method is able to describe the large deformation response of inelastic media with complex micro-structure, but certain key limitations exist. One such limitation is the description of shells or plates with complex micro-structure which cannot be captured in a layered-wise composite shell approach. Clearly a large munber of fiber-reinforced composite products fall into this category. This limitation exists as conventional first-order approximations can t pass second-order information, such as macroscopic deformation gradients (e.g. in bending), to the RVE boundaries. This information is required in shell theory. 

Perfluorinated membranes reinforced with woven PTFE, such as Nafion 324 or Nafion 417, are used in many industrial electrochemical processes. Unfortunately, the relatively coarse weave of the woven PTFE reinforcement results in membranes that are much too thick for high electrochemical performance. Some non-woven PTFE/perfluorinated ionomer composite membranes have been formulated for ion transport studies and for investigation of other properties relevant to chlor-alkaU and fuel cell applications. Advancements in materials and processing technology have resulted in the introduction of PTFE/perfluorinated ionomer composite membranes claimed by Gore and Associates, Inc. under the Gore Select trademark. Most types of ion exchange membranes contain some type of reinforcement because they are weak and tend to swell substantially as they incorporate a solvent onto their structure. This reinforcement can be a macro reinforcement or a micro reinforcement . 

Chu, C.Y. and Singh, J.P. Mechanical properties and micro structure of Si3N4-whisker-reinforced Si3N4 matrix composites , Ceram. Eng. Sci. Proc., 11 [7—8] (1990) 709-720. 

This paper presents results from a study of assemblies composed of glass fibre reinforced epoxy composites. First, tests performed to produce mixed mode fracture envelopes are presented. Then results from tests on lap shear and L-stiffener specimens are given. These enabled failure mechanisms to be examined in more detail using an image analysis technique to quantify local strain fields. Finally the application of a fracture-mechanics-based analysis to predict the failure loads of top-hat stiffeners with and without implanted bond-line defects is described. Correlation between test results and predictions is reasonable, but special attention is needed to account for size effects and micro-structural variations induced by the assembly process. 

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