Composites specimen preparation methods

This expression was used for the P ri) extraction directly from f x), but as this did not remove spurious oscillations, a smoothing procedure was applied, and the method was tested on composite specimens prepared by mixing known quantities of samples of nickel hydroxide, whose crystallite size distributions were previously determined. The Fourier method is in principle an exact... 

The increased use of optical and electron microscopy applied to polymer research has been the result of widespread acceptance of the techniques and extended property requirements of the polymer materials. It is known that the structures present in a polymer reflect the process variables, and further that they greatly influence the physical and mechanical properties. Thus, the properties of polymer materials are influenced by their chemical composition, process history and the resulting morphology. Morphological study involves two aspects prior to the study itself selection of instrumental techniques and development of specimen preparation methods. Structural observations must be correlated with the properties of the material in order to develop an understanding of the material. 

Microscopy techniques can be used to evaluate the size and distribution of particles added to polymer fibers, such as metals that modify the physical, mechanical, or electrical properties. In general, ultrathin sections are examined in either STEM or TEM modes to reveal the particles within the polymer. Energy (EDS) and wavelength dispersive x-ray spectroscopy (WDS) methods are used to map for various elements in order to establish the relation between the particle morphology and chemical composition. A specimen preparation method for x-ray analysis in the SEM is to use a trimmed block face, which remains after cutting thin sections, or to study a thick section. An example of such a study is described below. 

The majority of work done on VGCF reinforced composites has been carbon/carbon (CC) composites [20-26], These composites were made by densifying VGCF preforms using chemical vapor infiltration techniques and/or pitch infiltration techniques. Preforms were typically prepared using furfuryl alcohol as the binder. Composites thus made have either uni-directional (ID) fiber reinforcement or two-directional, orthogonal (0/90) fiber reinforcement (2D). Composite specimens were heated at a temperature near 3000 °C before characterization. Effects of fiber volume fraction, composite density, and densification method on composite thermal conductivity were addressed. The results of these investigations are summarized below. 

Apart from the short beam shear test, which measures the interlaminar shear properties, many different specimen geometry and loading configurations are available in the literature for the translaminar or in-plane strength measurements. These include the losipescu shear test, the 45°]5 tensile test, the [10°] off-axis tensile test, the rail-shear tests, the cross-beam sandwich test and the thin-walled tube torsion test. Since the state of shear stress in the test areas of the specimens is seldom pure or uniform in most of these techniques, the results obtained are likely to be inconsistent. In addition to the above shear tests, the transverse tension test is another simple popular method to assess the bond quality of bulk composites. Some of these methods are more widely used than others due to their simplicity in specimen preparation and data reduction methodology. 

Much of what we know about bonding to composite materials has come through the aerospace industries. The early studies on adhesives, surface preparation, test specimen preparation, and design of bonded composite joints reported for the PABST Program76 gave credibility to the concept of a bonded aircraft and provide reliable methods of transferring loads between composites and metals or other composites. 

The method of adiabatic calorimetry for specific heat measurement has been described by Collings and Smith [ ]. In the previous experiments with alloys, ground and polished surfaces achieved good thermal contact with the heater/thermometer pedestal by means of a thin layer of silicone vacuum grease. For the composites, a different specimen preparation and mounting procedure was used. Each sample was made up of five slabs (about 2.5 cm x 2.5 cm x 0.3 cm) of material cemented together, fibers parallel, with methanol-diluted GE 7031 varnish. To maximize heat transfer, one face of the laminated sample was ground... 

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