Yield Function, Von Mises Yield Surface and Hardening Rule — Lesson 2

This lesson covers the concept of yield surfaces in the context of three-dimensional thermo-mechanical problems. It delves into the functional form of yield surfaces, the assumptions required to derive certain functional forms, and how these forms can be represented in terms of principal stresses. The lesson also discusses isotropic materials, the concept of hydrostatic stress, and the representation of stress invariants. It further explains the concept of plastic deformation and how it can be represented in terms of deviatoric stress components. The lesson also touches upon the concepts of isotropic pressure-independent materials, the Bauschinger effect, and the representation of yield surfaces in terms of stress invariants. For instance, if we consider a material undergoing a uniaxial tensile test, the yield point would be the same for both tensile and compressive loads, indicating no Bauschinger effect.

Video Highlights

01:40 - Functional form of ill surface for isotropic material
06:46 - How the functional form can be simplified by assuming that plastic deformation is independent of the hydrostatic stress component and by considering the isotropic properties of the material
13:25 - How the functional form can be further simplified by assuming no Bauschinger effect and by considering the isotropic properties of the material
20:22 - Functional form represented in terms of the principal stress components
33:42 - Functional form can be used to represent the strain hardening effect in elastoplastic analysis
38:17 - How the functional form can be used to represent the isotropic hardening and kinematic hardening effects in elastoplastic analysis

Key Takeaways

- Yield surfaces can be theoretically assumed and then derived based on certain assumptions.
- For isotropic materials, yield surfaces can be represented in terms of principal stresses.
- Plastic deformation is independent of hydrostatic stress and can be represented in terms of deviatoric stress components.
- The Bauschinger effect refers to the phenomenon where the yield point for tensile and compressive loads is the same.
- Yield surfaces can be represented in terms of stress invariants, which are functions of the principal stress values.