Fiber mechanical requirements

Proper characterization of composite interfaces, whether it is for chemical, physical or mechanical properties, is extremely difficult because most interfaces with which we are concerned are buried inside the material. Furthermore, the microscopic and often nanoscopic nature of interfaces in most useful advanced fiber composites requires the characterization and measurement techniques to be of ultrahigh magnification and resolution for sensible and accurate solutions. In addition, experiments have to be carried out in a well-controlled environment using sophisticated testing conditions (e.g. in a high vacuum chamber). There are many difficulties often encountered in the physico-chemical analyses of surfaces. 

The fiber fragmentation test is at present one of the most popular methods to evaluate the interface properties of fiber-matrix composites. Although the loading geometry employed in the test method closely resembles composite components that have been subjected to uniaxial tension, the mechanics required to determine the interface properties are the least understood. 

Main Parts of a Solid-Propellant Engine. The case is a thin, high-tensile-strength metal or fiber-composite envelope in which the propellant is directly cast and bonded. The mechanical requirements for this part are that it offer sufficient resistance to service pressure and loading conditions during flight, such as vibrations and acceleration, and have optimum weight. 

Braids Is used to give high strength three-dimensional (3-D) reinforcement, incorporating more than one type of fiber, if required. Conventional woven fabrics are limited to providing reinforcement at orthogonal orientations, but many reinforced plastics structures are loaded in non-orthogonal fashion. Woven fabrics are, therefore, not necessarily mechanically efficient. 

Flexibility in terms of variations in material combinations in structural components is also severely limited by use of semifinished products. Large volumes of the same material combination are produced to ensure economical production of the semifinished products. There is thus no application-specific modification or stabilization of the material and the glass fiber content cannot be adapted specifically to the mechanical requirements of the structural components. These are the reasons why semifinished products are available in a limited number of material variants only. 

The structure and orientation of the reinforcing fibers in the matrix system are essential for the mechanical properties of the work-piece. The choice of a particular architecture is dependent on multiple factors like drapeabiUty of the fabric, geometry/shape of the workpiece, mechanical requirements, and manufacturing process. Compraients made of unidirectional layers (laminates) are showing the best mechanical properties since the fibers are completely stretched (no undulation). Usually the single layers of a laminate are showing different fiber orientations. This causes anisotropic material behavior in the planar direction. The structure of a multiaxial layered laminate is shown in Fig. 2. 

It is important to note that isostress and isostrain loading conditions represent theoretical limits for the design of a composite material reinforced by continuous fibers. In practice, most of the time, mechanical performances fall between these limits. On the other hand, in the isostrain loading situation, a lower volume fraction of fibers is required to obtain a similar stiffness of the composite. 

With regards to the mechanical properties of substituted polyacetylenes, aromatic polymers like poly(diphenylacetylene) derivatives are generally hard and brittle, whereas aliphatic polymers with long alkyl chains like poly(2-octyne) are soft and ductile.Considerations of mechanical properties are especially important when polymer membranes or fibers are required for the specific application. 

An even more advanced method of field termination utilizes no-epoxy, no-poKsh connectors. An optical fiber stub is cured into place in the fiber ferrule and polished at the factory. The field fiber is matched up to the fiber stub and a mechanical or fusion splice is made as appropriate inside the connector body. These connectors are typically very quick to install and require few consumables. Although single- and dual-fiber no-epoxy, no-polish connectors are the most common types used, twelve-fiber mechanical splice connectors are also available for use on ribbons. 

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