Reading Assignment
- 8.5Composite Materials (review)
- 14.5 Fabrication of Composite Materials
Recommended
- Modern Marvels – Carbon (video)
- NASA 360 – Composite Materials (video)
- Vacuum Bagging Techniques (pdf)
- How to Mold Fiberglass Parts (video series)
- Basics of Composite Mold Making (video series)
Outline
Introduction to Composites
Composites Manufacturing
Most processes are slow and require considerable amounts of hand labor.
Fabrication of particulate composites
- Consist of discrete particles dispersed in a ductile, fracture resistant polymer or metal matrix
- Processed by introducing particles into a liquid melt or slurry
- Powder metallurgy methods
Fabrication of Laminar Composites
- Include coatings, protective surfaces, claddings, bimetallics, and laminates
- Processes are designed to form a high-quality bond between distinct layers
- If metals are used, composites can be produced by hot or cold roll bonding
- U.S. coins use this process
- Explosive bonding bonds layers of metal
- Pressure wave induces bonding
- Adhesive bonding
- Gluing
- Pressing of unpolymerized resins
- Sandwich structures
- Corrugated cardboard
- Honeycomb structure
Fabrication of Fiber-Reinforced Composites
- Matrix and fiber reinforcement provide a system that has a combination of properties
- Fibers can be oriented in a way that optimizes properties
- The fibers can be continuous or discontinuous
- Discontinuous fibers can be combined in a matrix to provide a random or preferred orientation
- Continuous fibers can be aligned in a unidirectional fashion in rods or tapes, woven into fabric layers, wound around a mandrel, or woven into three dimensional shapes
Production of Reinforcing Fibers
- Many are produce through conventional drawing and extrusion processes
- Materials that are too brittle, such as Boron, carbon, and silicon carbide, are produces by deformation processes
- Individual filaments are often bundled
- Yarn- twisted assemblies of filaments
- Tows- untwisted assemblies of fibers
- Rovings- untwisted assemblies of filaments or fibers
Processes Designed to Combine Fibers and a Matrix
- Casting-type processes
- Capillary action
- Vacuum infiltration
- Pressure casting
- Centrifugal casting
- Prepegs- sheets of unidirectional fibers or woven fabric that have been infiltrated with matrix material
- Mats- sheets of nonwoven randomly oriented fibers in a matrix
- Mats can be stacked later into a continuous solid matrix
- Individual filaments can be coated and then assembled
- Drawing through a molten bath
- Plasma spraying
- Vapor deposition
- Electrodeposition
- Can be wound around a mandrel with a specified spacing and then used to produce tapes
- Sheet-molding compounds are composed of chopped fibers and partially cured thermoset resins
- Bulk-molding compounds are fiber-reinforced, thermoset, molding materials with short fibers distributed randomly
Fabrication of Final Shapes from Fiber-Reinforced Fibers
- Pultrusion- continuous process that is used to produce long lengths of relatively simple shapes with uniform cross section
- Fishing poles, golf club shafts, and ski poles
- Filament Winding
- Resin coated or resin-impregnated filaments, bundles, or tapes made from fibers of glass, graphite, and boron
- Produces cylinders, spheres, cones and other containers
- Resin coated or resin-impregnated filaments, bundles, or tapes made from fibers of glass, graphite, and boron
Lamination and Lamination-Type Processes
- Pre-pegs, mats, or tapes are stacked to produce a desired thickness
- Cured under pressure and heat
- High strength laminate with a smooth, attractive appearance
- Laminated materials can be produced as sheets, tubes, or rods
- Final operation in lamination is curing
- Typically involves elevated temperatures and/or applied pressure
- Manufacturing processes that require zero to moderate pressures and low curing temperatures can be used to produce simple curves and contours
- Boat bodies, automobile panels, aerospace panels, safety helmets, etc.
Lamination Processes
- Vacuum bag molding process
- Entire assembly is placed in a nonadhering, flexible bag and the air is evacuated
- Pressure bag molding
- A flexible membrane is positioned over the female mold cavity and is pressurized to force the individual plies together
- Parts may be cured in an autoclave
- Compression molding
- Resin-transfer molding
- Hand lay-up (open mold processing)
- Successive layers of pliable resin-coated cloth are placed in an open mold and draped over a form
- Slow and labor intensive process
- Low tooling costs
- Large parts can be made as a single unit
- Additional Processes
- Spray molding
- Chopped fibers, fillers, and catalyzed resins are mixed and sprayed onto a mold
- Spray molding
- Sheet stamping
- Thermoplastic sheets are reinforced with nonwoven fibers and press formed
- Injection molding
- Chopped or continuous fibers are placed in a mold and then a resin is injected
- Braiding, three dimensional knitting, and three-dimensional weaving
Fabrication of Fiber-Reinforced Metal-Matrix Composites
- Continuous-fiber metal-matrix composites can be produced by filament winding, extrusion and pultrusion
- Fiber-reinforced sheets can be made by electroplating, plasma spray deposition coating, or vapor deposition of metal onto a fabric or mesh
- Casting processes
- Products that use discontinuous fibers can be produced by powder metallurgy or spray-forming
- Concerns with metal-matrix composites
- Possibility of reactions between the reinforcements and the matrix during processing at the high melting temperatures
- Graphite-reinforced aluminum is twice as stiff as steel and 1/3rd to 1/4th the weight
- Aluminum reinforced with silicon carbide has increased strength as well as hardness, fatigue strength, and elastic modulus
- Often fail due to flaws in the matrix
- Fibers or mats may be passed through a slurry mixture that contains the matrix material and then dried, assembled and fired
- Chemical vapor deposition
- Chemical vapor infiltration
- Hot-pressing
Secondary Processing and Finishing of Fiber-Reinforced Composites
- Most composites can be processed further with conventional equipment
- Sawed, drilled, routed, tapped, threaded, etc.
- Composites are not uniform materials, so care should be taken
- Sharp tools, high speeds, and low feeds are generally required
- Many of the reinforcing fibers are abrasive and quickly dull the cutting tools