Abstract: An autogenously welded structure is provided that includes a first face sheet, a plurality of individual stiffener elements, and a second face sheet. The stiffener elements each have a first edge disposed against the first face sheet and an opposed second edge. Each stiffener element has a central portion extending between the opposed edges. The central portion is disposed at an angle to the first face sheet. The stiffener elements include at least some stiffener elements that are disposed at an angle to at least some of the other stiffener elements. The second face sheet is disposed against the second edges of the stiffener elements and the first and second face sheets are autogenously welded to the edges of the stiffener elements.

Abstract: An autogenously welded structure is provided that includes a first face sheet, a plurality of individual stiffener elements, and a second face sheet. The stiffener elements each have a first edge disposed against the first face sheet and an opposed second edge. Each stiffener element has a central portion extending between the opposed edges. The central portion is disposed at an angle to the first face sheet. The stiffener elements include at least some stiffener elements that are disposed at an angle to at least some of the other stiffener elements. The second face sheet is disposed against the second edges of the stiffener elements and the first and second face sheets are autogenously welded to the edges of the stiffener elements.

Abstract: A process for improving the strength of laser-machined articles formed of a silicon-based ceramic material such as silicon nitride, in which the laser-machined surface is immersed in an etching solution of hydrofluoric acid and nitric acid for a duration sufficient to remove substantially all of a silicon film residue on the surface but insufficient to allow the solution to unduly attack the grain boundaries of the underlying silicon nitride substrate. This effectively removes the silicon film as a source of cracks that otherwise could propagate downwardly into the silicon nitride substrate and significantly reduce its strength.

Abstract: Laser scanning apparatus and a related method for scanning a workpiece in a raster scan pattern, to remove a series of thin, overlapping layers in the workpiece and thereby provide a stepwise approximation to a contoured, three-dimensional shape. In one embodiment, the beam follows a raster scan pattern with scans that are parallel to the removed layer's boundary. The wall bounding the layer is made to be substantially perpendicular to the plane of the removed layer, regardless of the wall's orientation, by tilting the beam about an axis normal to a specified reference plane and by elliptically polarizing the beam to a selected degree. A substantially constant proportion of the beam's average intensity is thereby absorbed at each point along the boundary wall, regardless of the wall's orientation relative to the reference plane. In another embodiment, the beam scans repeatedly along an axis parallel to a specified reference plane.

Abstract: Optical proximity apparatus, and a related method, for monitoring the proximity and angular orientation of a surface and for maintaining that surface in a desired relative position. The apparatus directs two coplanar beams of modulated light onto the surface such that they converge toward a central axis and reach the axis at the point where it intersects the surface's desired position. Two photodetectors receive light scattered from the surface along two detection axes, in the plane of the two modulated beams and on opposite sides of, and equidistant from, the central axis. The relative intensities of the two separate modulated beams received by the two photodetectors can be determined and suitably analyzed to determine the surface's actual proximity and angular orientation relative to its desired position.

Abstract: A polycrystalline article is densified to provide either a nonporous body or a body with controlled interconnected porosity. A mixture of fine powders of the polycrystalline material and a sintering aid is compacted and outgassed under reduced pressure. The outgassed compact is then subjected to a permeation anneal step in which it is heated in a closed chamber to a temperature sufficient to form a liquid of the sintering aid, but under pressure conditions which inhibit evaporation of the sintering aid. The sintering aid can then be leached out to provide a densified article having interconnected porosity. Alternatively, the sintering aid can be leached out at elevated temperature, further densifying the compact to form a substantially nonporous body. Alternatively, the sintering aid can be removed by subjecting the densified article to an evaporation anneal step in which the article is heated to evaporate the sintering aid, further densifying the compact to form a substantially nonporous article.

Abstract: A polycrystalline article is densified to provide either a nonporous body or a body with controlled interconnected porosity. A mixture of fine powders of the polycrystalline material and a sintering aid is compacted and outgassed under reduced pressure. The outgassed compact is then subjected to a permeation anneal step in which it is heated in a closed chamber to a temperature sufficient to form a liquid of the sintering aid, but under pressure conditions which inhibit evaporation of the sintering aid. The sintering aid can then be leached out to provide a densified article having interconnected porosity. Alternatively, the sintering aid can be leached out at elevated temperature, further densifying the compact to form a substantially nonporous body. Alternatively, the sintering aid can be removed by subjecting the densified article to an evaporation anneal step in which the article is heated to evaporate the sintering aid, further densifying the compact to form a substantially nonporous article.