A Model for Chemical Vapor Infiltration of Fibrous Substrates

Abstract

A model is presented for CVI of a fibrous preform under isothermal and thermal gradient conditions. Transport and geometric properties during densification are calculated from a novel structural model, allowing prediction of deposition profiles and experimentally observed trends without the use of empiricism.

Characterization of a hybrid laser-assisted mechanical micromachining (LAMM) process for a difficult-to-machine material

“…The mean cutting force data does not exhibit a consistent trend with increase in laser power. On the other hand, the mean thrust force data shows a decrease with increase in laser power although the difference between the 5 W and 10 W cases does not appear to be sign fican nd with the laser located 100 μm s seen in the cutting force data at 10 mm sitivity of the thrust force to changes in m marks burnt during the laser spot alignment process [20].…”

“…Since the depth of cut is of the order of a few microns, a small deflection of the machine and/or thermal expansion of the tool can change the depth of cut. Previous studies [19][20] have shown that the thermal expansion of the tool can be as high as 2.2 μm. The reduced thrust force due to laser heating causes a smaller deflection of the machine stage and results in a higher effective depth of cut than that obtained without laser heating.…”

“…A logical solution to this limitation is to employ a hybrid process that combines the beneficial aspects of laser heating and 3-D mechanical micro-cutting. Initial investigations by Singh and Melkote [19][20] have demonstrated laser softening in AISI 1018 and hardened H-13 steels. Recently, Jeon and Pfefferkorn [21] have also studied the effect of laser preheating on micro-end milling of metals (Al 6061-T6 and 1018 steel).…”

“…1) developed by Singh and Melkote [19][20] consists of a 2-35 W continuous wave Ytterbium doped fiber laser (wavelength 1064 nm) integrated with a mechanical micro grooving machine. The laser beam is focused in front of a miniature cutting tool to soften the workpiece material just ahead of the cutting tool thereby lowering the forces required to cut the material.…”

Carbide, Nitride and Boride Materials Synthesis and Processing

“…Several CVI modeling efforts have described non-isothermal processes (Starr, 1988(Starr, , 1992Chou, 1989, 1990;Melkote and Jensen, 1990;Starr et al, 1993). In these systems, there are additional complexities associated with heat transfer and forced convection as infiltration proceeds and the structure of the material changes.…”