gigapascal

The gigapascal is the unit of stiffness. Every materials datasheet lists Young's modulus in GPa: steel about 200, aluminium 70, glass 70, concrete around 30, bone roughly 15, and diamond near 1100, the stiffest bulk material known. Keeping moduli in GPa and strengths in MPa holds the two properties three orders of magnitude apart on the page, which mirrors the physics: a steel that is 200 GPa stiff yields at about 0.35 GPa, so metals stretch elastically by only a fraction of a percent before yielding. A metal yield strength quoted in GPa is usually a unit slip, though high-performance fibres genuinely get there: Kevlar breaks near 3.6 GPa and carbon fibre between 3 and 7.

The other home of the gigapascal is high-pressure science. A diamond anvil cell squeezes a sample between the tips of two gem-cut diamonds and reaches pressures of several hundred GPa, beyond the roughly 360 GPa at the centre of the Earth, in a device that fits in the palm of a hand. Natural diamond itself forms in the mantle at only 5 or 6 GPa, so the cell recreates and then far exceeds the conditions that made its own anvils.

One ratio worth exploiting: stress in MPa divided by modulus in GPa gives strain in parts per thousand directly, which turns any quick elastic-stretch estimate into mental arithmetic.