Ceramics, Polymers, Composites, and Electronic Materials
Ceramics
Ionic and covalent bonding gives high stiffness, high melting point, low toughness, and strength that is statistically distributed. Expect Weibull statistics: a high Weibull modulus means a narrow flaw population and a reliable part, whereas a low modulus means scatter. Ceramics are strong in compression and weak in tension; thermal-shock resistance rises with high thermal conductivity and low expansion (figure of merit ~ strengthk/(Ealpha)).
Polymers
Know glass transition temperature Tg versus melting, crystallinity (which raises modulus, strength, and opacity), viscoelasticity (Maxwell and Kelvin–Voigt models, stress relaxation, creep), and the thermoplastic/thermoset split - thermosets crosslink irreversibly. Molecular weight, chain branching, and plasticizers all shift properties.
Composites
Rule of mixtures gives the upper bound (isostrain, fibers parallel to load); the inverse rule gives the lower bound (isostress). Critical fiber length, fiber volume fraction, and interfacial bonding control real behavior, and properties are strongly anisotropic.
Electronic materials
Concepts include band gap and the conductor/semiconductor/insulator split, doping (n- and p-type), dielectric constant and loss, piezoelectricity, and magnetic soft versus hard behavior.
Traps
Using the rule of mixtures as if it were a safe design value; confusing Tg with melting; assuming a polymer's room-temperature stiffness is time-independent; treating ceramics with a metal-like safety factor.
Worked example
A composite with 60 vol% glass fiber (E = 72 GPa) in epoxy (E = 3 GPa) loaded along the fibers gives E = 0.672 + 0.43 = 44.8 GPa; loaded across the fibers it drops to about 6.4 GPa. Anisotropy is roughly a factor of seven here.