Glossary and acronyms
Welded components for machines. Elastic behaviour

Main constraint; Main stress

Value of the normal stress (positive or negative) observable along a direction in which shear is zero. In a 3D elastic medium, three principal stresses exist (σ₁, σ₂, σ₃), and their conventional designation is: σ₁ > σ₂ > σ₃.

Ligne isostatique; Isostatic line

A line such that the tangent at any point is directed along one of the principal constraints. In 2D, isostatic lines form a network of orthogonal curves.

Ligne isocline; Isoclinal line

A line such that the principal stress at any point makes a constant angle with a given direction. In photoelasticimetry, isoclinic lines are used to obtain isostatic lines.

Ligne iso-${\sigma }_{}$