Von Mises Stress: Yield Stress & Elasticity

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Discussion Overview

The discussion revolves around the relationship between von Mises stress, yield stress, and material behavior, particularly focusing on whether a material can be assured to behave elastically when the von Mises stress is below the yield stress. The scope includes theoretical considerations and practical applications in materials science and engineering.

Discussion Character

  • Technical explanation, Conceptual clarification, Debate/contested

Main Points Raised

  • One participant suggests that if the von Mises stress is below the yield stress, it can be assured that the material is behaving elastically.
  • Another participant agrees but emphasizes the importance of expressing the relationship mathematically.
  • A different viewpoint indicates that the assurance of elastic behavior may only hold for a single or low number of cycles, highlighting the need to consider fatigue strength under cyclic loads.
  • It is noted that the applicability of the von Mises yield criterion depends on the material type, with some participants arguing it is suitable for ductile materials like steel, while others point out its limitations for materials like concrete and ceramics, which may require different yield criteria.
  • Specific alternative yield criteria are mentioned, such as the Drucker–Prager criterion for concrete and ceramics, and the Mohr-Coulomb criterion for soil.

Areas of Agreement / Disagreement

Participants express differing views on the conditions under which the von Mises stress can be used to assure elastic behavior, indicating that multiple competing views remain regarding the applicability of the von Mises yield criterion across different materials.

Contextual Notes

Limitations include the dependence on material types and the conditions of loading, such as cyclic versus static loads, which may affect the validity of the assumptions made regarding elastic behavior.

mattyboson12
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If the von mises stress well is below the yield stress, am I right to assure the material is behaving elastically?
 
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Yes, if you express it correctly mathematically.
 
mattyboson12 said:
If the von mises stress well is below the yield stress, am I right to assure the material is behaving elastically?

Possibly, but only for a single or low number of cycles. If you're dealing with cyclic or repeatedly-applied loads, you'll need to account for the material's fatigue strength.

https://en.wikipedia.org/wiki/Fatigue_(material)
 
Thank you
 
It depends on material. Von-mises yield criterion is good for steel and similar ductile and homogenous materials. For concrete, ceramics etc it is not accurate because of the different behaviour under tension and compression, where other yield criteria can be used like the Drucker–Prager one. For soil the Mohr-Coulomb criterion is often used.
 
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