SHEET 03 — THE HARDENING BRANCH

Materials

What hardens, what doesn't, and what the coupon says.

• 11Yield Is Not Failure6 min readThe first permanent millimetre. Yield is where a material stops returning to its original shape — and the reading this publication is named after. Why crossing it is not the same as breaking, why it is nevertheless the line that governs design, and what a structure that has yielded is afterwards.
• 12The Coupon Tells the Truth6 min readA machined test bar, pulled apart, honestly reports about ten thousand tonnes of steel. How a coupon is cut, what the test measures, and the statistics that let one small specimen speak for a heat.
• 13Ductile and Brittle Are Behaviours, Not Materials5 min readThe same steel can do both depending on temperature, rate and geometry. What shifts a material from one behaviour to the other, and why the transition temperature is one of the most consequential numbers in the field.
• 14Strain Hardening3 min readWhy a metal that has been deformed becomes harder to deform further, what that does to the shape of the curve, and how the effect is used deliberately in manufacturing.
• 15The Sum of Small Days7 min readNo single cycle is dangerous. Fatigue is the arithmetic of millions of harmless loads, and it is the mechanism behind a large share of in-service failures. How damage accumulates, and why the fatigue limit is a more slippery idea than it looks.