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.
Time-resolved emission and scattering imaging are employed to analyze the ablation mechanisms of silver thin films induced by femtosecond laser irradiation of Gaussian intensity profile under different laser fluences and gas background pressures. At fluences near the ablation threshold, nanoparticles (NPs) of 40 nm-100 nm in size are ejected in the vertical direction from the target sample. The average ejection speed of these NPs increases with the laser fluence and also as the background gas pressure drops from ambient atmospheric to $10 À5 Torr. At higher fluences, a plume is formed at the center of the laser beam and NPs are released in oblique trajectories from the peripheral area of the laser-irradiated spot.
Single-crystal Si was ablated by pulsed 532 nm laser radiation, and the volume of removed material and the time-resolved current of ejected ions were measured. These data were used to determine the ion fraction of ejected material. The ion fractions provide direct evidence that the break point is due to the laser-plasma interaction. This is confirmed by the speed distributions of the positive ions and from the integrated intensities of the low-speed ion component.
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