STUDY GUIDE · GKU 3
Material properties and processing study guide (Mechanical Engineering)
A machine part is only as good as the material it is made from and the process that shaped it, and this unit covers both. The first half explains properties from the inside out: how bonding and crystal structure set stiffness, density and conductivity; how defects, grain size and cold work set strength; how the tensile test and hardness tests measure it; how phase diagrams, diffusion and heat treatment change a steel from soft to hard; how parts fail by fracture, fatigue, creep and corrosion; and how to choose a material for a job with performance indices. The second half follows the material through the factory: casting, bulk and sheet forming, polymer moulding and powder metallurgy, welding and fastening, and machining, with the forces, power, time and cost each process needs and the process parameters that decide the quality of the part.
Structured by the official ETEC subject standard for this topic: every listed topic and learning outcome, with formulas, figures and worked examples. The full sections are available to members in the app.
SKU 3.1 · Material properties and selection
Material classes, bonding and physical properties
Why metals, ceramics, polymers and composites behave so differently, traced back to the bond between atoms, and the electrical and thermal properties that follow from it.
Crystal structures and crystallography
How atoms stack in metals (BCC, FCC, HCP), how to count atoms, packing and density from the unit cell, and how X-ray diffraction measures the lattice.
Imperfections, dislocations and strengthening
Point, line, planar and volume defects; why dislocations make metals ductile; and the four ways to make a metal stronger, including Hall–Petch grain refinement and cold work.
Stress–strain diagrams and mechanical testing
Reading a tensile test as a materials engineer: engineering and true values, strain hardening and necking, resilience and toughness, plus hardness and impact tests.
Ferrous metals: steels and cast irons
The families of iron-based alloys, how carbon and alloying elements change them, how to read a steel designation, and where each family is used.
Engineered materials: polymers, ceramics, glasses and composites
What makes polymers soft and ceramics brittle, how non-crystalline solids differ, and how the rule of mixtures predicts the stiffness of a fibre composite.
Equilibrium phase diagrams and the lever rule
How to read a binary phase diagram: which phases are present, what each contains, how much of each there is, and how the microstructure forms on cooling.
The iron–carbon diagram and steel microstructures
The phases of iron and steel, the eutectoid reaction that makes pearlite, and how the lever rule predicts the microstructure and strength of any plain-carbon steel.
Diffusion and reaction rates
How atoms move through a solid, why the rate rises so steeply with temperature, and how to size a carburising treatment from Fick's laws.
Phase transformations and heat treatment of steel
How fast austenite transforms and into what (TTT diagrams, Avrami kinetics, martensite), and the role of each heat treatment: annealing, normalising, hardening, tempering, case hardening and age hardening.
Classification and selection of materials
A systematic way to choose a material: translate the design, screen out what fails a constraint, rank the rest with a performance index, and read the answer off an Ashby chart.
Fracture and fatigue
Why parts break below their tensile strength: cracks and fracture toughness, the ductile-to-brittle transition, and failure under repeated loading.
Creep, thermal failure and corrosion
Failure that takes time or temperature: creep under steady load, thermal stress and thermal shock, and the electrochemistry of corrosion with the ways to prevent it.
SKU 3.2 · Manufacturing processes
Manufacturing processes: classification and selection
The families of manufacturing processes, the material properties that decide which ones are possible, and how batch size and tooling cost decide which one is cheapest.
Casting and moulding
How a sand mould is built, how fast metal fills it, how long it takes to freeze (Chvorinov's rule), how to size a riser, and which casting process suits which part.
Bulk forming: rolling, forging, extrusion and drawing
How solid metal is squeezed into shape, hot or cold, and how to estimate the force and power each process needs from the flow curve.
Sheet-metal processes
Shearing, blanking and piercing, bending and deep drawing: the forces they need and the die dimensions, allowances and limits that a designer must respect.
Forming of plastics and powder metallurgy
The main processes for thermoplastics, thermosets and composites, and the press-and-sinter route for metal powders, with the clamp force, density and shrinkage calculations each needs.
Joining: welding, brazing and mechanical fasteners
How fusion, resistance and solid-state welding put heat into a joint, how brazing and soldering differ from welding, and how a riveted or bolted joint is checked against its three ways of failing.
Material removal: chip formation, cutting forces, power and tool life
What happens at the cutting edge: the chip ratio and shear angle, the forces measured on the tool and what they mean on the shear plane and rake face, the power a cut needs, and how cutting speed sets tool life.
Machine tools, machining time, surface finish and measurement
Turning, drilling and milling on their machine tools; how cutting speed, feed and depth set the spindle speed, the removal rate, the machining time and the surface roughness; and the instruments that check the result.
Basics of CNC machining and part programming
What a CNC machine is, how its axes are named, the structure of a G-code program and its most common words, and how the programmed spindle speed and feed rate come from the cutting data.
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