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In materials science and engineering, the von Mises yield criterion is also formulated in terms of the von Mises stress or equivalent tensile stress, . This is a scalar value of stress that can be computed from the Cauchy stress tensor .
Hence, both the normal to the yield surface and the plastic strain tensor are perpendicular to the stress tensor and must have the same direction. For a work hardening material, the yield surface can expand with increasing stress. We assume Drucker's second stability postulate which states that for an infinitesimal stress cycle this plastic ...
Maximum distortion energy theory (von Mises yield criterion) also referred to as octahedral shear stress theory. [4] – This theory proposes that the total strain energy can be separated into two components: the volumetric (hydrostatic) strain energy and the shape (distortion or shear) strain energy. It is proposed that yield occurs when the ...
If the stress exceeds a critical value, as was mentioned above, the material will undergo plastic, or irreversible, deformation. This critical stress can be tensile or compressive. The Tresca and the von Mises criteria are commonly used to determine whether a material has yielded. However, these criteria have proved inadequate for a large range ...
Figure 3 shows the von Mises yield surface in the three-dimensional space of principal stresses. It is a circular cylinder of infinite length with its axis inclined at equal angles to the three principal stresses. Figure 4 shows the von Mises yield surface in two-dimensional space compared with Tresca–Guest criterion.
The yield function is often expressed as an equation consisting of some invariant of stress and a model for the yield stress (or plastic flow stress). An example is von Mises or plasticity. In those situations the plastic strain rate is calculated in the same manner as in rate-independent plasticity.
In continuum mechanics, stress triaxiality is the relative degree of hydrostatic stress in a given stress state. [1] It is often used as a triaxiality factor, T.F, which is the ratio of the hydrostatic stress, σ m {\displaystyle \sigma _{m}} , to the Von Mises equivalent stress , σ e q {\displaystyle \sigma _{eq}} .
The applied stress to overcome the resistance of a perfect lattice to shear is the theoretical yield strength, τ max. The stress displacement curve of a plane of atoms varies sinusoidally as stress peaks when an atom is forced over the atom below and then falls as the atom slides into the next lattice point. [18]