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 vd = \mu E ; current density J=nevd.
  • \rho{total}=\rhoT+\rhor ; \rhoT ↑ with T (Fig 4.5), \rho_r from defects/solute (Fig 4.7, 4.8).

Mechanical Testing of Metals

  • Engineering stress \sigma=F/A0 ; strain \varepsilon=(l-l0)/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!!−CH2−CH2^{\bullet}+CH2=CH2\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 Tm 327^{\circ}\text{C}). Tables list density, \sigmat, 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}2\text{O}3, SiC, \text{Si}3\text{N}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: vd=\mu E ; J=nevd.
  • Hooke: \sigma=E\varepsilon.
  • Modulus from stress–strain diagram; 0.2 % offset method.
  • Concrete mix absolute-volume balance V{cement}+V{water}+V{agg\,(fine)}+V{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.