ENGINEERING COMMISSION #7973: stress, strain, temper — the foundry story ending at Corning and Gorilla Glass per the predecessors law (#7971 optics lineage).
Strong, Stiff, Tough — Three Different Things
Glass is strong and brittle. Rubber is tough and weak. Steel is stiff. Students use the three words as synonyms and engineers never do: strength is the load it takes, stiffness is how far it bends, toughness is how much it absorbs before it breaks.
Why Things Break
Not because the material was overloaded on average, but because a crack found a place to start. Griffith showed that a flaw concentrates stress at its tip — which is why a scratched glass rod snaps where the scratch is.
The Stress-Strain Curve
Pull a specimen and plot force against stretch. The line is straight, then it bends, then the material never comes back. That bend — the yield point — is where a paperclip stops being a spring and starts being a shape.
Fatigue
A load far too small to break something, applied a million times, breaks it. The Comet airliners came apart at the window corners for this reason. Fatigue is the failure mode that punishes designers who only test once.
Composites
Take something strong in tension and something strong in compression and glue them together: straw and mud, steel and concrete, carbon and epoxy. Nature got there first — bone and wood are both composites.
The Drawer of Samples
Twelve materials, one bench, one set of tests. Bend each, scratch each, weigh each, ring each. Record the results in the same columns for all twelve. The table a student builds here is the beginning of materials science.
A bench of broken things arranged as evidence: the cup-and-cone fracture, the shattered rod, the delaminating laminate.