USA As Represented by Secretary of the Navy

Richard K Everett

Alan Shane Edelstein

John Harry Perepezko

Pehr E Pehrsson

Benji Maruyama

Paul M Natishan

Peter Matic

William F Henshaw

Andrew B Geltmacher

Virginia G DeGiorgi

Arthur M Morrish

Jonathan M Peritt

Patricia P Trzaskoma

A material test specimen design is taught for the determination of critical strain and stress states for multiaxial fracture. The objective of the specimen is to increase the amount of data obtained per specimen while retaining simplicity in testing procedure by using standard tension testing machines to generate the primary deformation of the specimen. The specimen, in conjunction with analytical or computational simulation, uses nonuniform deformation fields produced by secondary and tertiary strain concentrations to generate and track these multiaxial strain states to fracture. Typically, the primary deformation is uniaxial tension of a panel, the secondary strain concentration is a circular hole in the panel and the tertiary strain concentrations are areas of reduced thickness within the deformation field of the circular hole. Multiaxial strain ratios from &minus;0.50 to &minus;0.10 and control over fracture initiation sites may be generated by a test specimen design of the type taught by this invention.

Test specimen design incorporating multiple fracture sites and multiple strain state material fractures

A debonding layer is formed on fibers such as silicon carbide fibers by forming a thin film of a metal such as nickel or iron on the silicon carbide fibers and then annealing at a temperature of about 350-550&deg; C. to form a debond layer of a metal silicide and carbon. These fibers having the debond coating can be added to composite forming materials and the mixture treated to form a consolidated composite. A one heating-step method to form a consolidated composite involves inserting the silicon carbide fibers with just the initial metal film coating into the composite forming materials and then heating the mixture to form the debond coating in situ on the fibers and to form the consolidated composite. Preferred heating techniques include high temperature annealing, hot-pressing, or hot isostatic pressing (HIP).

In situ-formed debond layer for fibers

A debonding layer is formed on fibers such as silicon carbide fibers by fing a thin film of a metal such as nickel or iron on the silicon carbide fibers and then annealing at a temperature of about 350-550.degree. C. to form a debond layer of a metal silicide and carbon. These fibers having the debond coating can be added to composite forming materials and the mixture treated to form a consolidated composite. A one heating-step method to form a consolidated composite involves inserting the silicon carbide fibers with just the initial metal film coating into the composite forming materials and then heating the mixture to form the debond coating in situ on the fibers and to form the consolidated composite. Preferred heating techniques include high temperature annealing, hot-pressing, or hot isostatic pressing (HIP).

Filamentous substrates are coated with diamond by a chemical vapor deposition process. The substrate may then be etched away to form a diamond filament, such as a diamond tube or a diamond fiber. In a preferred embodiment, the substrate is copper-coated graphite. The copper initially passivates the graphite, permitting diamond nucleation thereon. As deposition continues, the copper-coated graphite is etched away by the active hydrogen used in the deposition process. As a result a substrate-less diamond fiber is formed. Diamond-coated and diamond filaments are useful as reinforcement materials for composites, is filtration media in chemical and purification processes, in biomedical applications as probes and medicinal dispensers, and in such esoteric areas as chaff media for jamming RF frequencies.

Process for making diamond and diamond-coated filaments

A porous material of desired porosity and pore size is made by mixing a piculate material and fungible beads that are thermally decomposable until the desired distribution is attained; compacting the mixed material and beads to form a green body that has sufficient strength to be handled where the beads are undecomposed; and compacting and heating the green body to fuse the material particles and to decompose the beads to gas.

Method for forming porous metals

Graphite or carbon particles with a graphitic skin are intercalated with a compound including an oxidized form of a metal and then reduced in a hydrogen atmosphere. This process reduces the driving force for the galvanic reaction between the particles and active metals in aqueous environments. The particles may be present as a reinforcement for a metal matrix (e.g., graphite/aluminum metal matrix composites) or as a reinforcement for a non-metallic material (e.g., graphite/polyimide, graphite/polyester or graphite/cyanate composites). In the latter case, the composite is adjacent to a metal in a structure. By way of example, the graphite or carbon particle may be a fiber, the metal subject to attack may be aluminum or magnesium, and the intercalation compound may be NiCl.sub.2.

Modified carbon for improved corrosion resistance

A fiber spreader is provided which reduces fiber damage that occurs during preading. The fiber spreader includes a thin electrically grounded support sheet for supporting a layer of fibers on one surface thereof. The fibers supported on the support sheet are guided by a plurality of guide rollers past at least one corona discharge region at which the fibers are spread substantially uniformly. A motor driven spool advances the support sheet past the corona discharge region. The fibers are attached to the support sheet by an electrostatic attraction. The guide rollers are positioned so as to provide at least one region in which the sheet and the fibers are physically separated to allow for the uniform spreading of the fibers. After the fibers are spread, the fibers and the support sheet are united again and collected on a motor-driven spool.

Electrostatic fiber spreader including a corona discharge device

An improved metal, alloy, or intermetallic matrix composite containing carbon reinforcing fibers is formed. The carbon reinforcing fibers are protected from interaction with the matrix material by an inner and an outer barrier layer. The outer layer is any one of the group of stable, non-reactive ceramic materials used to protect fibers, and the inner layer is a ductile, low density, oxygen desorbing rare earth metal. The carbon fibers are particularly useful in forming composites with a titanium aluminide matrix.

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Alexandria, VA, United States of America

Richard K Everett