Schmid's law

In materials science, Schmid's law (also Schmid factor[lower-alpha 1]) describes the slip plane and the slip direction of a stressed material, which can resolve the most shear stress.

Schmid's Law states that the critically resolved shear stress (τ) is equal to the stress applied to the material (σ) multiplied by the cosine of the angle with the vector normal to the glide plane (φ) and the cosine of the angle with the glide direction (λ). Which can be expressed as:[2]

${\displaystyle \tau =m\sigma }$

where m is known as the Schmid factor

${\displaystyle m=\cos(\phi )\cos(\lambda )}$

Both factors τ and σ are measured in stress units, which is calculated the same way as pressure (force divided by area). φ and λ are angles.

The factor is named after Erich Schmid who coauthored a book with Walter Boas introducing the concept in 1935.[3]