23.6 : 平面応力下での延性材料の降伏基準

Structural elements and machine parts made from ductile materials are designed to resist yielding under an expected load.

The yield point is identified through a tensile test on a similar material under uniaxial stress. However, predicting failure is not straightforward when the stress state changes to the plane stress, resulting in biaxial stress.

This condition is different from uniaxial stress and requires the establishment of a failure criterion to compare the effects of these two stress states.

The Maximum Shearing Stress Criterion, based on shearing stresses causing yield in ductile materials, proposes that a component is safe if its maximum shearing stress is smaller than that in the yielding of a tensile test specimen.

Graphically represented by Tresca's hexagon, it helps predict material failure under different stress conditions.

The Maximum Distortion Energy Criterion, also known as the Von Mises criterion, determines the safety of a structure based on distortion energy per unit volume.

The component is safe if the distortion energy is less than that, which causes yielding in a tensile test specimen.