Will my PA66 (Nylon) beam plastic deform?

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Discussion Overview

The discussion revolves around the potential plastic deformation of a PA66 (Nylon) beam when subjected to a vertical force. Participants explore the relationship between applied force, stress, and strain, particularly in the context of material properties and structural analysis methods.

Discussion Character

  • Technical explanation
  • Debate/contested
  • Mathematical reasoning

Main Points Raised

  • The original poster reports successfully displacing a Nylon beam by 1mm with a force of 30N, noting that the Von Mises stress exceeds the yield strength while the strain remains below the yield strain of 5%.
  • Some participants inquire whether classical analysis methods have been employed to evaluate the problem.
  • One participant emphasizes the importance of understanding bending moment tensile stress at the base of the cantilevered section and suggests resolving the force vector accordingly.
  • Another participant warns about potential issues in finite element analysis (FEA) modeling and stresses the need to grasp basic principles of force vectors and stress analysis.
  • There is a suggestion to incorporate fillet radii in high-stress areas to potentially reduce stress concentrations and improve the analysis.

Areas of Agreement / Disagreement

Participants express differing views on the evaluation methods and the implications of stress and strain on the material's behavior, indicating that the discussion remains unresolved regarding the likelihood of plastic deformation.

Contextual Notes

Limitations include the original poster's inability to perform evaluations beyond straight beams and the reliance on FEA, which may introduce inaccuracies without a solid understanding of fundamental stress analysis principles.

dsire4u
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Hello,
I have this model that required to be pressed vertically 1mm.
I successfully displaced 1mm vertically with 30N of force.
Unluckily, Von mises stress goes way beyond the yield strength.
However, the strain is below the yield strain of 5%.
I do not understand how ductile/flexible material like Nylon will plastic deform with 30N of force applied.
Can someone explain to me if my model will plastic deform or not?
Please help,
Thank you
Included the x_b file of the part model.
model.PNG
Displacement.PNG
stress.PNG
Strain.PNG
 

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Have you done any evaluation of your problem using the classical analysis methods?
 
JBA said:
Have you done any evaluation of your problem using the classical analysis methods?

I was not able to. I can only do evaluation of the straight beams...
 
your primary concern is the bending moment tensile stress at the base of the angle cantilevered section. For a start , resolve your force vector and treat the problem as a cantilever beam connected to the base.

FEA is subject to a number of issues in its modelling, so it is important that you understand the basic principle elements of the force vectors and stress analysis that apply to the problem you are analyzing in order to evaluate the accuracy or its solutions.
 
Two words.

Fillet radius.
 
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I am with Chris. Add fillet radii wherever possible but particularly around the high stress areas and re-analyse it. I would go for a radius of 25% of the wall section to start with.
 

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