Meaning
Multi-axial fatigue limit evaluation uses a combination of the local shear stress amplitude and the instantaneous hydrostatic stress to predict the onset of failure. Engineers apply the dang van criterion to components subjected to complex loading histories where the principal stress axes change direction over time.
Hydrostatic Sensitivity
Pressure components of the stress state influence the fatigue resistance of a material by opening or closing microscopic defects. The dang van criterion accounts for this by adding a fraction of the hydrostatic stress to the shear amplitude. High compressive hydrostatic stress increases the allowable shear range while tensile stress reduces it.
Elastic Shakedown
Microscopic grains within the metal must reach a stable state of elastic deformation for the component to survive an infinite number of cycles. If the local loading exceeds the dang van criterion then plastic work accumulates at the grain level. This accumulation eventually leads to the formation of a macroscopic crack even if the bulk material appears to remain in the elastic regime.
Precise assessment of these local stresses allows for the design of durable automotive components that must endure billions of cycles without failure.
Validation Method
Laboratory testing on notched specimens provides the data required to calibrate the material constants for the model. Researchers compare the predicted fatigue limit against experimental results obtained from rotating bending and torsion tests. This validation ensures that the dang van criterion accurately reflects the behavior of specific alloy grades used in automotive drivetrains.
