max stress not on the surface 3

[beginnerfeaeng]

Hello all, I am a beginner FEA analyst and would really appreciate your thoughts to some of the problems I am having with my analysis. I have a model where the max von-Mises stress is not on the surface node but inside node of the surface element. I have attached a picture. I am not quite understanding what does it mean and was wondering if anyone could help. Thank you so much in advance.

 

[missil3]

Looks like you are using solid elements not shell (surface) elements. Solid elements are 3d elements and the area at which v-m stresses are max is inside the solid and not on the surface of the solid.

 

[beginnerfeaeng]

Thank you so much for your reply missil3. I don't think I understood the problem very well when I posted it. Max stress is not quite on the surface element. I have attached a stress plot with really fine mesh.
In terms of the force, I just doesn't understand it. The boundary I have is "frictionless support" on the bold whole to represent the bolt body area, and zero displacement (Z=0) on the area where the bolt head makes contact, the force is pulling it up (in Z). Now I am thinking if I have my boundary correct.
Thank you in advance for your reply.

 

[inline6]

It is hard to see what this is? is the pciture a section plot? is this a contact problem? bad mesh can make things appear that are not real. I advise you to do a deformation plot highly exaggerated to see if you can understand what is happening.

 

[YoungTurk]

My first guess is that you are seeing an artifact of bad mesh; though it is hard to be sure from the picture. Stress contours in the image appear to wrap around areas where the element size ratios are extreme. This could, however, just be an artifact of the location of the section cut if that is what it is.

Another thought is that there is not a guarantee that the maximum VonMises stress will be on the surface. Most load cases lead to that solution, but given the zero stress normal to the surface there may be specific situations in which the vonmises stress has a maximum value at an internal location.