Composite Materials & Fabrication Processes Flashcards

What is a primary characteristic of composite materials?

Answer: Combine materials for enhanced properties

Composite materials are engineered by combining two or more distinct materials, each retaining its individual properties, to create a new material with superior characteristics. This synergistic combination allows composites to achieve enhanced properties such as high strength-to-weight ratio, stiffness, durability, or corrosion resistance that none of the constituent materials could achieve alone. This makes them highly versatile for various demanding applications.

Which reinforcement is most commonly used in composites?

Answer: Carbon fiber

Carbon fiber is the most commonly used reinforcement in high-performance composites due to its exceptional strength-to-weight ratio and stiffness. When embedded in a polymer matrix, carbon fibers significantly enhance the material's mechanical properties, making it ideal for applications requiring lightweight yet extremely strong components, such as in aerospace, automotive, and sporting goods industries.

What is the function of the matrix in composites?

Answer: Binds fibers and distributes loads

The matrix in composite materials serves as the binder that holds the reinforcement fibers together, protecting them from environmental damage and transferring loads between them. It encapsulates the fibers, ensuring that stresses applied to the composite are efficiently distributed across the high-strength fibers. This critical function allows the composite to act as a unified material, leveraging the strength of its fibrous reinforcement.

Which fabrication process uses hand placement of fibers with resin?

Answer: Hand layup

Hand layup is a traditional and widely used composite fabrication process where layers of reinforcement fabric (like fiberglass or carbon fiber) are manually placed into a mold. Resin is then applied by hand, typically with brushes or rollers, and worked into the fibers to fully impregnate them. This method is versatile for producing a wide range of part sizes and complexities, especially for prototypes or lower volume production.

What is vacuum infusion used for in composite fabrication?

Answer: Drawing resin through fibers with vacuum

Vacuum infusion is a composite fabrication technique where dry reinforcement fibers are laid into a mold, and a vacuum is then applied to draw liquid resin into the mold, impregnating the fibers. The vacuum pressure ensures thorough resin distribution, minimizes air voids, and results in a composite part with a high fiber-to-resin ratio and excellent mechanical properties. This process offers better quality control and reduced resin waste compared to open molding techniques.

What type of defect can occur if curing is incomplete?

Answer: Soft or tacky surfaces

Incomplete curing of a composite material means that the resin has not fully polymerized and cross-linked, leaving it in a partially reacted state. This results in a material that lacks its intended hardness and strength, often manifesting as soft, tacky, or gummy surfaces. Such defects indicate compromised mechanical properties and require further curing or repair.

Which inspection method uses visible light to detect surface defects?

Answer: Visual inspection

Visual inspection is a fundamental non-destructive testing method that involves carefully observing the surface of a composite material under visible light. Technicians look for any visible anomalies such as cracks, scratches, voids, discoloration, fiber misalignment, or signs of delamination. This initial assessment helps identify surface-level defects and often guides the need for more advanced inspection techniques.

What is the purpose of sanding in composite finishing?

Answer: To smooth surfaces

Sanding is a crucial step in composite finishing, primarily performed to smooth the surface of a cured composite part. It removes excess resin, high spots, imperfections, and prepares the surface for subsequent steps like painting, bonding, or clear coating. Proper sanding ensures a uniform, aesthetically pleasing, and functionally sound finish.

What does post-curing accomplish in composite fabrication?

Answer: Increases strength and thermal stability

Post-curing, also known as secondary curing, involves subjecting a composite part to an elevated temperature for a specific duration after its initial cure. This process further cross-links the polymer chains in the resin, leading to a more complete cure. The result is an increase in the material's mechanical properties, such as strength, stiffness, and hardness, as well as improved thermal stability and chemical resistance.