JNTU B.Tech IV Year COMPOSITE MATERIALS Previous Question Paper (September - 2022 - R18)

Composites are classified based on their constituent phases and structural arrangement:

1. Based on Matrix Material:

• Polymer Matrix Composites (PMCs): Use a polymer resin (e.g., epoxy, polyester) reinforced with fibers. Example: Carbon fiber reinforced polymer (CFRP).
• Metal Matrix Composites (MMCs): Use a metal matrix (e.g., aluminum, titanium) to improve strength and wear resistance. Example: Silicon carbide reinforced aluminum.
• Ceramic Matrix Composites (CMCs): Use ceramic matrices for high-temperature applications. Example: Carbon-fiber reinforced silicon carbide.

2. Based on Reinforcement Structure:

• Particulate Composites: Contain particles of various shapes and sizes. Example: Concrete (aggregate in cement).
• Fiber-Reinforced Composites: Use continuous or discontinuous fibers. Example: Glass fiber reinforced plastic (GFRP).
• Structural Composites: Composed of both homogeneous and composite materials. Example: Laminates and sandwich panels (e.g., honeycomb core panels).

In fiber-reinforced composites, the matrix and the dispersed phase (fibers) perform distinct mechanical roles:

• Matrix Phase: The matrix is typically a ductile, lower-modulus material. Its primary functions are to bind the fibers together, protect them from environmental damage, and transfer applied loads to the fibers via shear stress. It provides toughness and keeps the fibers in the desired orientation.
• Dispersed Phase (Fibers): The fibers are high-strength, high-stiffness, and often brittle materials. They are the primary load-bearing components of the composite. They provide the necessary tensile strength and stiffness to the structure.

The mechanical synergy relies on the interface: the matrix must be sufficiently compliant to allow for load transfer without premature fracture, while the fibers must possess high aspect ratios to effectively carry the stress distributed by the matrix.