Pääjännitykset

Pääjännitykset, or principal stresses, are the normal stresses that exist on a plane where the shear stress is zero. These are the maximum and minimum normal stresses at a point in a material under load. Imagine a small cube of material. When forces are applied to it, the internal stresses will be complex. However, at any given point within that material, you can always find three mutually perpendicular planes where the stress acting on them is purely normal, meaning there is no shearing component. These normal stresses are the principal stresses.

The largest of these is called the major principal stress, and the smallest is called the minor principal stress. The third principal stress is intermediate in value. These stresses are crucial in engineering for predicting material failure. When the stresses within a material exceed its yield strength or ultimate tensile strength, it will deform permanently or fracture. By calculating the principal stresses, engineers can assess whether the material is likely to fail under the applied loads. The directions of these principal stresses are known as the principal directions. Understanding principal stresses is fundamental to the field of solid mechanics and the design of structures and components.