Jawaharlal Nehru Technological University Hyderabad B.Tech IV Year NANOCOMPOSITES Previous Question Paper (July - 2021 - R16)

Nanocomposites exhibit enhanced properties compared to conventional composites due to the high surface-to-volume ratio of the nanofillers and the interfacial interactions at the nanoscale. Key properties include:

• Mechanical Strength: Significant improvement in tensile strength, stiffness, and hardness even at low filler concentrations.
• Thermal Stability: Enhanced heat resistance and flame retardancy due to the barrier effect of dispersed nanoparticles.
• Barrier Properties: Reduced gas and moisture permeability caused by the tortuous path created by high-aspect-ratio fillers like nanoclays.
• Electrical and Optical Properties: Tunable conductivity and transparency, enabling applications in sensors and optoelectronics.

Applications include automotive components for weight reduction, aerospace structural materials, high-performance packaging films, conductive adhesives, and biomedical scaffolds for tissue engineering.

The stress-strain curve for nanomaterials often deviates from bulk materials, typically showing higher yield strength and a modified elastic modulus. The curve starts with a linear elastic region, followed by a non-linear plastic deformation region, and concludes with fracture.

Key conclusions from the stress-strain behavior include:

• Hall-Petch Strengthening: As grain size decreases to the nanoscale, the yield strength increases significantly because grain boundaries act as barriers to dislocation motion.
• Ductility-Strength Trade-off: Nanomaterials often exhibit high strength but may show reduced elongation before failure due to limited dislocation storage capacity.
• Strain Rate Sensitivity: Nanomaterials often demonstrate higher sensitivity to strain rates compared to bulk materials, influencing their deformation mechanisms.
• Interface Dominance: The high volume fraction of grain boundaries or phase interfaces in nanocomposites dictates the stress transfer efficiency, directly impacting the slope of the elastic region.