Strategy of the Course Structural Materials

Overall Goals

1. Provide a general overview of structural materials.
2. Teach general principles that underlie the subject.
3. Teach the vocabulary of the subject.
4. Teach what is most likely to be retained after the end of the course.
5. Enable the student to elaborate later on this base.

General Strategy

1. Employ an application that provides a conceptual framework familiar to the student (i.e., the bicycle).
2. Start with something that the student has learned about already (i.e., corrosion).
3. Introduce topics in the order needed to tell a coherent story and only to the extent necessary for that part of the story.
4. Be as quantitative as necessary to make the story coherent, but don't get bogged down in detail; let that go for advanced courses.
5. In the first part of the course, use metals and alloys to illustrate phenomena and principles, because metal science is the oldest and most highly developed of all the materials sciences.

Execution of the Strategy

Chapter 1 Corrosion and Corrosion Protection

• Reviews high-school-level electrochemistry.
• Adds galvanizing and passivation.
• Introduces solid solutions (substitutional and interstitial) and cubic crystal unit cells.
• Shows applications to bicycle wheel and spokes.

Chapter 2 Mechanical Behavior

• Introduces stress and strain (engineering and true), normal and shear.
• Separates small-scale from large-scale deformation.
• Introduces early stress-strain curve to teach elastic behavior and yielding; provide atomistic picture.
• Uses total stress-strain curve and wire drawing to teach uniaxial and biaxial large-scale plastic flow; include necking criterion and rupture.

Chapter 3 Microstructure and Crystal Structure

• Describes and illustrates how to do metallogrphy, including grain boundary structure.
• Uses cubic crystals to teach about close-packed structures and Miller and direction indices; uses games to let the student learn the latter independently.

Chapter 4 Slip, Dislocations, and Strain Hardening

• Uses FCC crystals to introduce slip on close-packed planes in cp directions.
• Uses animations to teach edge, screw, and mixed dislocations and dislocation loop expansion.
• Shows imaging of dislocations in the TEM and explains diffraction contrast.
• Teaches the stress fields and strain energy of dislocations in the simplest possible way.
• Teaches the mechanism of strain hardening using the Taylor model, again as simply as possible, and shows why a Taylor-type stress-strain curve is parabolic.

Chapter 5 Annealing of Cold-Worked Metals

• Starts with review of basic thermodynamic principles, energy, enthalpy, entropy, Gibbs free energy, criterion for equilibrium.
• Explains recrystallization as the primary mechanism of softening; uses it to explain the substitution-(nucleation-and-growth) transformation-type of kinetics.
• Uses recovery to explain decay-type-transformation kinetics and to introduce the idea of equilibrium defects (vacancies) and self diffusion.
• Uses grain growth to introduce the role of interfacial energy in solid-state reactions
• Shows the relationship between grain size and strain hardening.
• Uses carbon steel to teach the mechanism and driving force of the coarsening of a second phase and particle-inhibited grain growth during annealing.

Chapter 6 Carbon Steel: Plastic Deformation and Fatigue Resistance

• Uses BCC iron to introduce a number of topics: the difference between interstitial and substitutional diffusion, segregation of solutes to dislocations, asymmetrical distortion around interstitials and pinning of screw dislocations in BCC crystals, metal fatigue and the fatigue limit, the temperature dependence of yielding and the ductile-brittle transition in BCC metals.

Chapter 7 Phase Diagrams

• Uses the need for lowering of the freezing point in soldering and brazing and in road salt to motivate interest in phase diagrams.
• Uses a model eutectic diagram to teach the rules, especially about the composition of each phase and the relative amount of each phase in a two-phase region.
• Uses the Pb-Sn system to connect microstructures with the phase diagram, emphasizing non-equilibrium effects and the reasons for morphologies like dendrites and lamellar eutectics.
• Defines the chemical potential from considering the stability of a two-phase alloy, and uses it to derive the phase rule and show its applications.

Chapter 8 Phase Transformations in Carbon Steel

• Uses a eutectoid steel to explain the need for kinetic diagrams to understand solid-state phase transformations, where the driving forces and diffusion rates are much smaller than in the liquid-to-solid eutectic freezing.
• Uses a hypoeutectoid steel to show how the cooling rate can affect microstructures in a eutectoid decomposition.
• Introduces the martensite transformation.

Chapter 9 Friction and Wear; Hard Materials

• Friction, wear, and lubrication are motivated by the chain and bearings of a bicycle, and the role of hard materials is demonstrated.
• This leads to a consideration of hardening and tempering of steel.
• Surface hardening of steel by carburization is used to explain diffusion equations and solutions applied to this problem.
• The brittleness of hard surface layers is used to introduce elementary fracture mechanics.
• Silicon nitride for bearings is used as the end point for the discussion of ceramics as hard materials.

Chapter 10 Precipitation Hardening

• Using aluminum alloys for the examples, the thermodynamics and kinetics of precipitation from solid solution are presented.
• The influence of the shape of the solvus line of the phase diagram, the importance of homogeneous nucleation and of metastable precursor precipitates, the factors that control the interfacial energy, and the stages of precipitation are covered.

Chapter 11 The Bicycle Frame

• The bicycle frame is used to demonstrate the importance of considering the geometrical design of a structure together with the selection of the materials; this uses the interplay between the tube geometry and the strength, stiffness, and density of the tube materials.
• The effects of different methods of joining: brazing, welding, and adhesive bonding, on the properties of joints in steels, aluminum alloys, and titanium alloys are shown.
• Cast lugs are used to discuss problems of castings, and welding defects are also discussed.

Chapter 12 Polymeric Materials

• Tires are used to motivate the discussion of polymers, which starts with extensive consideration of polyethylene.
• The main topics are addition polymerization, crystallization, the glass transition, effects of molecular architecture, and viscoelastic behavior. Polyethylene is contrasted with polystyrene.
• The effects of cross-linking are introduced and elaborated upon with conjugated dienes; the elastomeric behavior of rubber is shown to be an entropic effect.

Chapter 13 Composite Materials; Rigid Matrix

• The elementary mechanics of fiber strengthening are discussed in terms of continuous and discontinuous fibers and the effect of the direction of loading on the elastic modulus of a composite.
• Both organic and inorganic fibers are described, as are network polymers for composite matrices and for adhesives produced by condensation polymerization.
• CFRP bicycle frames are used as the case study for extended discussion, including the failure of such composites.

Chapter 14 Complex Multi-scale Composites: Tires

• Tires are used to teach more on polymer science and engineering, including emulsion polymerization and anionic and cationic polymerization.
• The role of carbon black is shown to be analogous to that of precipitates in a precipitation-hardening alloy.
• The blending, mixing, and molding of tires, as well as the process of delayed-action accelerated vulcanization are discussed.

Chapter 15 Flexible Connective Tissue

• The leg, and particularly the knee joint, are used to describe the microstructure, properties, and mechanical behavior of articular cartilage, the meniscus, tendon, and ligament.
• The types of injury and the healing processes in these tissues are also discussed.

Chapter 16 Rigid Connective Tissue: Bone

• The microstructure, properties, and mechanical behavior of compact and spongy bone are discussed.
• The development of long bones, remodeling, and the effect of aging on the structure and properties are discussed.
• The processes of cracking and healing are considered in some detail.

Chapter 17 Skeletal Muscle

• The microstructure of skeletal muscle is considered down to the molecular level, emphasizing the microstructure of sarcomeres.
• The cross-bridge cycle for muscle contraction is described, as are the energetics involved.
• The transmission of nerve impulses and the chemistry involved are discussed.
• The effects of training on fast-twitch and slow-twitch fibers are demonstrated, as are various types of injury and healing.