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A novel rapid prototyping technology incorporating a curved layer building style was developed. The new process, based on laminated object manufacturing (LOM), was designed for efficient fabrication of curved layer structures made from ceramics and fiber reinforced composites. A new LOM machine was created, referred to as curved layer LOM. This new machine uses ceramic tapes and fiber prepregs as feedstocks and fabricates curved structures on a curved‐layer by curved‐layer basis. The output of the process is a three‐dimensional “green” ceramic that is capable of being processed to a seamless, fully dense ceramic using traditional techniques. A detailed description is made of the necessary software and hardware for this new process. Also reviewed is the development of ceramic preforms and accompanying process technology for net shape ceramic fabrication. Monolithic ceramic (SiC) and ceramic matrix composite (SiC/SiC) articles were fabricated using both the flat layer and curved layer LOM processes. For making curved layer objects, the curved process afforded the advantages of eliminated stair step effect, increased build speed, reduced waste, reduced need for decubing, and maintenance of continuous fibers in the direction of curvature.

The piezoresistive response of epoxy/vapor-grown carbon nanofiber composites prepared by four different dispersion methods achieving different dispersion levels has been investigated. The composite response was measured as a function of carbon nanofiber loading for the different dispersion methods. Strain sensing by variation of the electrical resistance was tested through four-point bending experiments, and the dependence of the gauge factor as a function of the deformation and velocity of deformation was calculated as well as the stability of the electrical response. The composites demonstrated an appropriate response for being used as a piezoresistive sensor. Specific findings were that the intrinsic piezoresistive response was only effective around the percolation threshold and that good cluster dispersion was more appropriate for a good piezoresistive response than a uniform dispersion of individual nanofibers. The application limits of these materials for sensor applications are also addressed.

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Three commercially available, silver filled, snap cure isotropically electrically conductive adhesives for surface mount applications were selected for study. Fundamental material characterizations were conducted on these materials, including thermal analysis [differential scanning calorimetry (DSC), thermo-gravitational analysis (TGA), and thermo-mechanical analysis (TMA)], rheological, and dynamic mechanical analyses. Microstructural investigations [scanning electron microscopy (SEM), transverse electromagnetic (TEM), Auger)] were performed to identify the silver flake size, distribution, and contact morphology. These analyses were related to the cure process and electrical conduction mechanisms of isotropically conductive adhesives (ICA's).The resistivity of these materials was monitored during cure and related to the cure kinetics of the epoxy matrix. The resistivity decreased dramatically (>k 1 cm to m 1 cm) around a specific temperature with ramp cure and over a narrow time range (<10 s) with isothermal cure. Successive heating (25-150 C) and cooling cycles yielded different degrees of consecutive resistivity decreases for these materials which were cured according the manufacturer's recommended schedules. Microstructure development during cure was studied with a hot stage in an environmental scanning electron microscope (ESEM) to relate morphological changes with the observed changes in resistance. No significant structural changes and silver flake movements were noticed during cure. The conduction development was accompanied by breakage and decomposition of the tarnish, organic thin layers which cover the silver flake surface, and by the enlargement of the contact area between silver flakes by thermal stress and shrinkage during the epoxy cure. The temperature coefficients of resistance (TCR) were measured for these materials; the TCR is closely related to a conduction mechanism dominated by constraint resistance between the flakes or by the silver flake metallic conduction.The resistivity and interfacial resistance of these materials with bare copper and gold plated pads (with five selected cure schedules) were measured through 85 C/85% RH exposure up to 900 h. The bulk resistivity decreased in the first 100 h of exposure and did not change with humidity; however, the interfacial resistance increased with the copper pads for some materials. This is caused by the oxidation of the copper pads due to moisture attack.

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The influence of the dispersion of vapor-grown carbon nanofibers (VGCNF) on the electrical properties of VGCNF/Epoxy composites has been studied. A homogenous dispersion of the VGCNF does not imply better electrical properties. In fact, it is demonstrated that the most simple of the tested dispersion methods results in higher conductivity, since the presence of well-distributed nanofiber clusters appears to be a key factor for increasing composite conductivity.PACS: 72.80.Tm; 73.63.Fg; 81.05.Qk