Showing papers on "Metal matrix composite published in 1985"

Effect of Thermal Treatment on the Mechanical and Toughness Properties of Extruded Sic sub w/Aluminum 6061 Metal Matrix Composite.

Abstract: Mechanical, instrumented Charpy V-notch (CVN) energy and plane strain fracture toughness properties of SiC whisker reinforced-6061 aluminium metal matrix composite material from an extruded tube have been determined. The effect of thermal treatment and orientation have been studied. The mechanical strength properties are higher than wrought Al 6061 in the T6 condition. CVN energy values, however, were reduced by an order of magnitude.Klc fracture toughness of the as-received, T6 and degassed + T6 thermal treatments were 50% of the wrought Al 6061 alloy. The effect of orientation showed that the orientation with the least amount of SiC whisker in the crack plane (i.e. greatest mean free path between reinforcements) yields the highest toughness value.

Filamentary structural module for composites

Abstract: This invention includes a continuous in-plane spiral of monofilament/metallic ribbon which forms a preform for metal matrix composite fabrication. The purpose is to provide continuous spiral filament reinforcement around a hole or central core. This spiral monolayer is fabricated by co-winding the filament and a ribbon or wire made from the intended composite material around a mandrel. Monolayers so constructed could then be stacked to form cylindrical or torus-shaped components and consolidated in a direction parallel to the axis of the shape.

Method of welding metal matrix composites

Abstract: A welding method forms a fiber reinforced weld in a fiber metal matrix composite. Novel weld rods or consumable electrodes for introducing the fibers to the molten weld pool are disclosed. Reinforcing fibers are added to a molten weld pool that is initially substantially free of fibers. The fibers strengthen the weld. The concentration of the fiber should be controlled so that the viscosity of the pool remains suitable for welding.

Direct measurements of non-linear stress-strain curves and elastic properties of metal matrix composite sandwich beams with any core material

Abstract: A theory for measuring non-linear stress-strain curves and elastic properties of metal matrix composite (MMC) sandwich beams subjected to pure bending loads is discussed. The beam is made from any core material sandwiched between an upper facing of unreinforced metal and a lower facing of MMC with unidirectional fibre reinforcement or vice versa. The model developed shows that the determination of the position of the neutral axis is critical to the measurements discussed in this paper. The analysis removes the restriction of the effects of the core. With the aid of this model, we show that the position of the neutral axis can be determined directly from surface strain measurements. Measurements of neutral axis position lead directly to the determination of the beam elastic properties and, thus, directly obtained from surface strain measurements. It is shown that the model predicts longitudinal stresses and strains within any layer of the beam. The analysis includes the limiting case of a very weak core material. A consequence of this model is the determination of the MMC facing fibre volume fraction. A detailed error analysis predicts that the longitudinal elastic modulus of an MMC material facing can be obtained with an uncertainty between 4 and 6% if the surface strain measurements and beam dimensions can be obtained with an uncertainty of 1%. The volume fraction can be obtained within 10% uncertainty, although better methods are available for that measurement.

Apparatus and method for rolling a metal matrix composite plate or sheet

Abstract: An apparatus and method for rolling metal matrix composite material is disclosed. The material is confined within an aperture in a frame member during the rolling process. The frame member has deformation properties compatible with that of the metal matrix composite material permitting the frame member to be deformed during the rolling process and allowing the surfaces defining the aperture in the frame member to constrain the material during this process, thus eliminating edge cracking of the material. The frame member may be interposed between a top member and a bottom member both having deformation properties compatible with that of the metal matrix composite material so as to "encapsulate" the material during the rolling process.

Composite metal matrix welding

Abstract: A method for joining individual pieces of material together includes the steps of heating the pieces to be welded together, at least one of which consists of a metal matrix with a relatively low melting point and a reinforcement material distributed therein, the reinforcement having a relatively high melting point. The other piece may be a similar metal matrix composite, or may be a metal or alloy which is to be joined to the first piece. The pieces are heated to a temperature which is above the melting points of the metals and below the melting point of the reinforcement. The pieces so heated are brought into contact with one another and then cooled to a temperature below the melting points of the metals. One technique for practicing the method of the invention is that of capacitor discharge welding.

Comparison of the Various New High Modulus Fibers for Reinforcement of Advanced Composites with Polymers, Metals and Ceramics as Matrix

Abstract: High modulus fibers are used mainly as fibrous reinforcement in resins, metals, or ceramics to provide strength and stiffness. It is instructive to consider what factors led to the development of composites. Structural designs are as likely to be limited by the stiffness as by the strength of the construction material. Hence, engineers have always desired suffer, stronger, less dense and lower cost structural materials. There are a number of materials in the upper center part of the periodic table, such as boron, carbon, silicon carbide and alumina, which all have significantly higher modulus/weight ratios than the common engineering metals. Theoretically, the high modulus would result in high strength if the materials were perfect. Unfortunately, most of the high modulus materials are covalently bonded and are brittle. Small flaws can produce catastrophic failure at drastically reduced stresses. (The flaws may be introduced during manufacture or during service.) Except in some unusual protected environments, primary structural elements can not be made from materials which fail catastrophically. Composite materials offer the potential of using these brittle materials in structures which will not fail catastrophically. The brittle materials are made into fibers to give redundancy and placed into a matrix. The matrix serves to transfer stress into and out of the fibers. The matrix and matrix/fiber interface must also serve to stop cracks which originate in the fibers from propagating through the solid. Hence, a localized impact may break a few fibers, but the crack can be stopped by a ductile matrix or fiber/matrix debond.

Method of fabricating fiber-reinforced metal composites

Abstract: A method of fabricating a fiber-reinforced metal matrix composite including the steps of mounting of a braided fiber tube on a substrate, wrapping a braze foil about the braided fiber tube to form an assembly that is encapsulated by a metal capsule which is creep collapsed onto the assembly at a temperature below the braze foil flowpoint. The encapsulated assembly is subsequently heated to a temperature sufficient to induce flow of the braze foil alloy and later cooled to allow solidification and annealing of the resulting fiber reinforced metal composite.

Designing with Metal Matrix Composites: When, Where and How

Abstract: : This paper presents designs method based upon the concepts of structural indices for the selection of metal matrix composite (MMC) materials as substitutes for conventional materials in cases where direct and indirect weight savings, decreased life cycle costs, thermal deformation, wear resistance, and other parameters are important, and for cases where the available space is severely restricted (high loading stress density), thereby requiring high strength and/or high stiffness materials. General design considerations of technical criteria and of operational and cost criteria are briefly discussed. A brief discussion follows of the relevant MMC material property equations used in this paper. These equations are set in the form of parametric functions of two variables: the ratio of fiber-to-matrix elastic moduli and fiber volume fraction. These functions allow for simple graphing or tabulation of composite properties for a wide range of composite materials. The structural indices are then derived to calculate ratios between MMC and conventional material to compare weight to strength, impact resistance, efficiency of columns and plates, flexural rigidity, structural efficiency indices for plates and shells, and the work of fracture. Keywords: Metal matrix composites; Materials selection/substitutes; Structural properties.

A comparison of measured and calculated thermal stresses in a hybrid metal matrix composite spar cap element

Abstract: A hybrid spar of titanium with an integrally brazed composite, consisting of an aluminum matrix reinforced with boron-carbide-coated fibers, was heated in an oven and the resulting thermal stresses were measured. Uniform heating of the spar in an oven resulted in thermal stresses arising from the effects of dissimilar materials and anisotropy of the metal matrix composite. Thermal stresses were calculated from a finite element structural model using anisotropic material properties deduced from constituent properties and rules of mixtures. Comparisons of calculated thermal stresses with measured thermal stresses on the spar are presented. It was shown that failure to account for anisotropy in the metal matrix composite elements would result in large errors in correlating measured and calculated thermal stresses. It was concluded that very strong material characterization efforts are required to predict accurate thermal stresses in anisotropic composite structures.