Composites Essay

8768 WordsApr 26, 201236 Pages
Chapter 16 – Composites A composite is a multiphase material that exhibits a significant proportion of the properties of both constituent phases such that a better combination of properties is realized (principle of combined action) - Composites maintain an interface between components to provide tailored properties not obtainable by one of the original components acting alone - The primary needs for all the advanced composites are: light weight, higher operating temperatures, greater stiffness, higher reliability and affordability Introduction – Definition Two phase composite: Matrix is the continuous phase and surrounds the other phase Reinforcement is the dispersed phase, which normally bears the majority of stress Classification of composites - Particle reinforced: large, dispersion strengthened - Fibre reinforced: continuous, discontinuous (short) - Structural: laminates, sandwich panel Large-particle The particulate phase is harder and stiffer than the matrix material The particles are of macroscopic scale, and restrain the movement of matrix, which transfer the applied load to the particles The improvement of mechanical behaviour depends on the interface bonding Examples: - Cermets (WC or TiC reinforced cobalt or nickel) - Concrete(aggregate-gravel and sand-reinforced cement) - SiC or Al2O3 particle reinforced Al matrix. Dispersion-strengthened The particles are very small, 0.01 to 0.1 mm in diameter The strengthening mechanisms occur on atomic or molecular scale The matrix bears the major portion of the load The particles hinder the motion of dislocations and thus the plastic deformation: e.g. precipitation hardening in 2014 Al-Cu alloys | Elastic Behavior-Longitudinal Loading When load is applied along the longitudinal direction Fc = Fm + Ff σc Ac= σm Am + σf Af σc= σm Am/Ac + σf Af/Ac= σm Vm + σf Vf εc = εm= εf (for an

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