megapascal

The megapascal is the unit strength is written in. Concrete is specified from about 20 to 50 MPa, ordinary structural steels yield between 235 and 460, reinforcing bar at 500, and aluminium alloys anywhere from 100 to 500 depending on temper. Hydraulic machinery runs its oil at 20 to 35 MPa, injection moulding packs plastic at similar pressures, and a waterjet cutter operates near 400 MPa, roughly four times the water pressure at the bottom of the Mariana Trench.

Concrete grades carry a quirk worth decoding. A European class written C25/30 is not a range: it is the same concrete tested two ways, a characteristic strength of 25 MPa on a cylinder and 30 MPa on a cube. The shorter, wider cube is confined by friction against the testing machine's platens and reads about 20 percent stronger than the more slender cylinder, so the shape of the specimen is worth a fifth of the answer. Both numbers describe one material, and each design code states which of the two its equations expect.

The identity that makes metric stress arithmetic pleasant is that one megapascal is exactly one newton per square millimetre. Section dimensions in millimetres and forces in newtons therefore produce stresses in MPa with no conversion constant anywhere, which is the quiet reason metric design checks run so cleanly from drawing dimensions to stress.