Strain Gauge Rosette

A single gauge cannot see shear, which is why rosettes have three. The rosette type matters more than anything else here — reducing 0/60/120 readings with the 0/45/90 formula gives an answer that is wrong but entirely plausible, and nothing downstream will flag it.

Readings are microstrain (µε = 1×10⁻⁶). Stresses assume plane stress, which holds at a free surface — the only place a gauge can be bonded — and an isotropic, linear-elastic material. Composites need the orthotropic reduction instead. The defaults are a pure uniaxial 200 MPa state on steel, which reduces to exactly 200 / 0 MPa.