Fiber composites specimen preparation

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. 

Paper specimens were obtained from Mead Paper, Printing and Writing Paper Division (Chillicothe, Ohio 45601). Samples were identified as being free from other materials, i.e., no preservatives, slimicides, defoamers, etc. Internally-sized samples were sized by conventional alum/rosin sizing surface-sized materials were prepared by an application of starch at the size press and all the other samples were unsized. Whatman filter paper was extracted with a 68/32 mixture of chloroform/acetone to remove any organic binder from the fiber surface. The fiber composition of the Whatman filter paper was identified by optical microscopy as cotton. The sample identified as "No Sizing" was... 

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... 

Unidirectional composites using ramie fibers and SPC resin were prepared by Nam and Netravali [23, 90]. Composites with unidirectional lay up of fibers was possible because of the small dimensions of the specimens prepared. The fibers used in this case were between 600 and 1700 mm long. The average diameter of the ramie fibers was measured to be 123 pm. The average tensile stress and modulus were found to be 627 MPa and 31.8 GPa, respectively. 

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. 

It is necessary to recognize here that in this stutty the comp< ite specimens were prepared from fibers which were coated by polymers formed under one set of electropolymerizations conditiors, and that these conditions were not optimized with respect to composite pro rties. The results are thus taken oidy to indicate the potential of electropolymerization for interphase modification in graphite fiber composites and the need to standardize electropolymerization conditions and monomer system to control polymer film properties and, through them, composite properties. 

---