Meaning
Boundary in multi-axial stress space that defines the limit of purely elastic behavior and the onset of permanent plastic deformation represents the failure criterion for a polymer under combined loading. Constructing a yield stress surface is necessary for predicting how plastic components will perform when subjected to complex, multi-directional forces. This surface is highly dependent on the temperature and strain rate of the material.
Stress State
Multi-axial tests apply combinations of tensile, compressive, and shear forces to the polymer specimen to map the yield points. These test points are plotted in stress space to define the boundary of the elastic region, showing that polymers typically yield at lower stress levels under tension than under compression.
Deformation Mode
Plastic flow begins once the state of stress reaches the boundary surface of the material. This deformation behavior depends on the shear bands and crazing mechanisms that occur at the microstructural level of the polymer.
Structural Design
Simulating complex load cases with finite element analysis requires a defined yield criterion to evaluate the safety margins of molded components. If the stress state under operating loads extends beyond the boundary, the part will undergo permanent deformation, so engineers use this modeling method to optimize wall thickness and rib placements for long-term load bearing.
