Chapter 16: Composites

Composites exploit the principle of combined action, where strategic integration of metals, ceramics, and polymers produces superior strength, stiffness, toughness, and thermal resistance. Particle-reinforced composites encompass large-particle systems like concrete and cermets, where the matrix transfers stress to rigid particles, and dispersion-strengthened materials such as sintered aluminum powder and thoriated nickel, in which fine particles obstruct dislocation movement and enhance high-temperature performance. Fiber-reinforced composites represent the most technologically significant category, designed for exceptional specific strength and modulus through careful control of fiber length, critical length threshold, and orientation. Continuous aligned fibers maximize anisotropic reinforcement, while discontinuous and randomly oriented fibers provide reduced but more isotropic properties. The chapter classifies reinforcements into whiskers (SiC, Al₂O₃), conventional fibers (glass, carbon, aramid), and wires (steel, tungsten), and details how matrix phases bind fibers, distribute load, protect surfaces, and arrest crack propagation. Polymer-matrix composites using glass, carbon, or aramid fibers in epoxy and polyester resins dominate aerospace and automotive applications. Metal-matrix and ceramic-matrix composites extend operational envelopes to higher temperatures through aluminum, titanium, or superalloy matrices reinforced with SiC and Al₂O₃, while ceramic-matrix systems improve fracture toughness via crack deflection and transformation toughening mechanisms. Carbon-carbon composites retain strength beyond 2000°C despite oxidation vulnerability. Processing techniques including pultrusion, prepreg production, and filament winding enable diverse structural configurations. Laminar composites and sandwich structures with honeycomb or foam cores provide tailored rigidity and weight optimization. The Boeing 787 case study illustrates how composites constitute 50% of structural weight while reducing costs and maintenance. Nanocomposites introduce carbon nanotubes, graphene, and nanoclays into polymer, metal, and ceramic matrices, delivering enhanced mechanical properties, electrical conductivity, barrier performance, flame resistance, and biomedical functionality across packaging, aerospace, and electronics applications.