Principles of Materials Science & Engineering – Master Study Notes

Importance & Educational Goals of Engineering Materials

• Engineering Materials underpin both fundamental research and practical applications; mastering them is essential for societal advancement.
• Main instructional objectives (course “Engineering Materials”):
  • Familiarise students with material properties for informed selection/ application.
  • Build understanding of how composition & structure dictate properties.
  • Supply property data so designs can avoid repetitive testing.
  • Reveal manufacturing/testing routes that ensure integrity & quality.
• Recommended core textbooks (Smith, Van Vlack, Callister, Budinski, Askeland, Thai translations) for cross-reference.

What Is A Material? – Definitions & Grand Taxonomy

• Material = any matter (inorganic or organic) formed from chemical substances, surrounding us in every artefact.
• Engineering material = any material intentionally deployed in engineering work.
• Canonical 5 categories (each with unique structure & property envelope):
  1. Metallic materials
  2. Polymeric materials (plastics)
  3. Ceramic materials
  4. Composite materials
  5. Electronic materials

1 Metallic

• Inorganic; may be single element or alloy (≥2 metallic elements, with minor non-metals possible).
• Typical traits: good electrical/thermal conductivity, high strength, toughness, ductility.
• Sub-classes:
  • Ferrous (iron-based) – e.g.
    • steels, cast-iron.
  • Non-ferrous – Al, Cu, Zn, Sn, Ni, Mg, etc.

2 Polymeric (Plastics)

• Mostly organic (C, H, N, O, Cl, F, S). Large chain/network molecules, amorphous or semi-crystalline.
• Light density, wide range of stiffness, insulation, variable $T_m$ .
• Two commercial families:
  • Thermoplastics – remeltable (e.g. $\text{PE}$, $\text{PVC}$).
  • Thermosets – once set cannot remelt (e.g. Bakelite).

3 Ceramic

• Inorganic compounds of metals+non-metals bonded ionically/covalently.
• Hard, high-T strength, brittle, good thermal/electrical insulation.
• Include advanced (space-shuttle tiles, thermocouple sheaths, engine parts).

4 Composite

• Broadly: physical mixture of ≥2 constituents (distinguishable optically, microscopically or even at atomic scale) that do not dissolve fully, giving superior combined performance.
• Engineering sense: 2+ materials blended to out-perform parents – e.g. concrete, plywood, GRP, fibre-reinforced polymers.

5 Electronic

• Crucial to high-tech age; pure silicon exemplar → chips, MEMS, semiconductors.

Property Sets for Material Selection (Fig 1.1)

• Four master categories:
  1. Chemical (corrosion, composition). Lab tests; destructive or non-destructive.
  2. Physical (colour, density, $T_m$, magnetism, optical, electrical, acoustic …). No chemical change during test.
  3. Mechanical (elastic–inelastic response, hardness, strength, toughness, fatigue, creep …).
  4. Dimensional (shape, size availability, surface texture, tolerances).
• Matrix in Fig 1.1 summarises which sub-property matters for metals, plastics, ceramics, composites.

Mechanical & Dimensional Details

• Typical application/property matrix provided (Table 1.1). E.g. Cu wire – conductivity; Si $\text{Barium titanate}$ – piezoelectric; GRP – lightweight strength.
• Strength comparison plot (Fig 1.2) spans materials.
• ASTM grain-size number $N = 2^{n-1}$ (#grains per $\text{in}^2$ at ×100). Example conversions included.

Crystal Structure & Bravais Lattices

• 7 lattice systems ➔ 14 Bravais unit cells (simple, BCC, FCC, base-centred).
• Lattice parameters + atomic radii examples:
  • BCC metals (Fe $a=0.287\,\text{nm}$, $R=0.124\,\text{nm}$ …).
  • FCC metals (Al $a=0.405\,\text{nm}$…).
  • HCP list with $c/a$ ratios (Zn 1.856 …).

Solidification & Grain Structures

• Nucleation density controls grain size: rapid cooling ⇒ many nuclei ⇒ fine equiaxed grains; slow ⇒ coarse columnar.
• Grain refiners (Ti, B, Zr) added to Al alloys.
• Single-crystal growth (Czochralski) critical for semiconductors.

Imperfections in Crystals

• Point: vacancies, self-interstitials, Schottky & Frenkel in ionic solids.
• Line: edge & screw dislocations ($b$ Burgers vector).
• Surface: grain boundaries (2–5 atomic radii thick, impurity segregation).
• Bulk: voids, cracks, inclusions.

Solid Solutions

• Substitutional vs interstitial; Hume–Rothery rules (size <15 %, same crystal, similar electronegativity, valence).
• Example: C in $\gamma\text{-Fe}$ interstitial up to $2.08\%$ at $1148^{\circ}\text{C}$.

Electrical Conduction in Metals

• Ohm’s law $i=V/R$ ; resistivity $\rho = RA/l$ ; conductivity $\sigma=1/\rho$.
• Drift velocity $v<em>d = \mu E$ ; current density $J=nev</em>d$.
• $\rho<em>{total}=\rho</em>T+\rho<em>r$ ; $\rho</em>T$ ↑ with T (Fig 4.5), $\rho_r$ from defects/solute (Fig 4.7, 4.8).

Mechanical Testing of Metals

• Engineering stress $\sigma=F/A<em>0$ ; strain $\varepsilon=(l-l</em>0)/l_0$.
• Hooke $\sigma=E\varepsilon$ ; typical $E$ values table (Al 10.5 Msi, Steel 29 Msi …).
• 0.2 % offset yield (Fig 5.9). Ultimate tensile strength, %elongation, %RA formulas.
• Hardness tests: Rockwell (depth $t$), Brinell, etc.
• Impact (Charpy/Izod) – transition curves (Fig 5.13), carbon content effect (Fig 5.14).

Polymers

Definitions & Classes

• Polymer = many repeating units (monomers). Plastics vs elastomers.
• Thermoplastic vs thermoset differences.

Chain-Growth Polymerisation (PE Example)

• Initiation (peroxide → free radical) ➀
• Propagation $R!!−CH<em>2−CH</em>2^{\bullet}+CH<em>2=CH</em>2\rightarrow…$ ➁
• Termination (radical combination or inhibitor) ➂.
• Degree of polymerisation (DP) for commercial PE $3500–25000$.

Polymer Structures & Properties

• LDPE (branched), HDPE (linear), LLDPE (linear-low-density) – {$\rho$, crystallinity, strength} table.
• PVC: amorphous; Cl pendant raises polarity → stiff/brittle; property tailored with plasticiser (phthalate), stabiliser, lubricant, filler.
• PP: isotactic PP $T_m\,165–177^{\circ}\text{C}$ , light $\rho\,0.90$.
• PS, ABS, PMMA, fluoroplastics (PTFE $T<em>m 327^{\circ}\text{C}$). Tables list density, $\sigma</em>t$, impact, $T_{use}$.

Processing Methods

• Injection moulding, extrusion, compression & transfer moulding, blow moulding, thermoforming, calendaring, casting, reaction-injection moulding.

Thermosets & Elastomers

• Phenolics, epoxies, polyesters: network cross-linking, high heat stability.
• Rubber: natural cis-1,4-polyisoprene; vulcanisation $\text{C=C}+S\rightarrow\text{crosslinks}$ (Fig 6.5, 6.6). Synthetic rubbers SBR, NBR, neoprene; property table.

Ceramics

Traditional vs Engineering Ceramics

• Traditional: clay–silica–feldspar → brick, tile, porcelain; Table 8.3 compositions.
• Engineering: high-purity $\text{Al}<em>2\text{O}</em>3$, SiC, $\text{Si}<em>3\text{N}</em>4$, ZrO₂.

Fabrication

• Powder prep (mix, binder). Forming: dry-press, isostatic, hot-press; slip casting; extrusion.
• Firing: drying, sintering (densification, Fig 8.1, 8.2), vitrification.

Electrical / Electronic Ceramics

• Dielectric constant $k$, breakdown strength; low-loss steatite, fosterite, alumina (Table 8.4).
• Piezoelectrics (BaTiO₃) convert mech ↔ electric.
• Glass basics – amorphous SiO₂ networks, compositions Table 8.5 (soda-lime, borosilicate, fused silica, glass-ceramics).

Composites

Definition Recap

• Multi-phase material with matrix + reinforcement, properties superior to constituents.

Fibre-Reinforced Plastics

• E-glass ($E\approx72\,\text{GPa}$) cheapest; S-glass (>650\,\text{ksi}) high strength; carbon & aramid (Table 9.1).
• PAN → carbon fibre process: stabilisation (200 °C), carbonisation (1000–1500 °C), graphitisation (>1800 °C) (Fig 9.1).
• GRP (glass-polyester) : strength scales with fibre volume (up to 80 %).

Concrete

• Composite of Portland cement (C₃S, C₂S, C₃A, C₄AF) + aggregates + water + entrained air.
• Water/cement ratio critical; $\text{compressive strength}\downarrow$ as $w/c\uparrow$ beyond 0.4.
• ASTM cement types I–V (Table 9.2) for different heat, sulfate conditions.
• Reinforced concrete: steel tendons carry tension; prestress (pre- & post-tension) introduces beneficial compressive stress.

Asphalt & Wood as Composites

• Asphalt: bituminous matrix + mineral aggregate; natural vs petroleum-refined sources; used in pavements, waterproofing.
• Wood: natural composite of cellulose fibres in lignin matrix; structural zones (heartwood, sapwood, cambium) ; engineered wood – plywood, laminated veneer, fibre/particle boards.

Key Equations (Selection)

• ASTM grain: $N=2^{n-1}$.
• Resistivity: $\rho = RA/l$ , $\sigma=1/\rho$.
• Drift: $v<em>d=\mu E$ ; $J=nev</em>d$.
• Hooke: $\sigma=E\varepsilon$.
• Modulus from stress–strain diagram; 0.2 % offset method.
• Concrete mix absolute-volume balance $V<em>{cement}+V</em>{water}+V<em>{agg\,(fine)}+V</em>{agg\,(coarse)}+V_{air}=1$.

Ethical & Practical Considerations

• Material selection balances cost, availability, environmental impact (e.g., concrete footprint; forest conservation for wood; recyclability of thermoplastics; energy cost of alumina firing).
• Safety: dielectric breakdown limits, toughness transition (ductile–brittle) critical for pressure vessels; reinforcing corrosion affects concrete longevity.

Real-World Linkages & Trends

• Aerospace pushes carbon-fibre composites & high-temperature ceramics.
• Microelectronics reliant on single-crystal Si and alumina substrates.
• Sustainable engineering driving recycled plastics, low-cement concrete, engineered wood.