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Number of integration points

[ Edited ]

I apologize if this topic has already been covered .. but I can not find in the reference the number of integration points for cquad4 element.

I can guess that their 4 pieces, but I'm confused what is considered a "centroid stress"? I know about extrapolation stress at Gauss points to nodes. 


Whether the "centroid stress" is integration in natural coordinates at the point (0, 0) or, perhaps, we have one point of the Gaussian in the center? In general I will be very grateful for your tips!

Also, I'm interested in how I can see the results of the stresses at the integration points?


Re: Number of integration points

[ Edited ]

Four integration points would be standard for a quadrilateral element in the element natural coordinate system; unless a reduced integration scheme was selected, which I don't think Nastran exposes for shell elements.


I don't think you can recover stresses at the integration points for shell elements, Nastran automatically outputs the stresses either at the centroid or at the corner nodes AND centroid depending on your case control specification for STRESS(Corner) = ALL   I've only seen options to recover stresses at the integration points for some solid elements and this is usually controlled in the PSOLID bulk data entry or via a PARAM entry.


The centroidal stress would then just be an interpolation for point (0,0) given the element shape functions and the stresses calculated at each integration point.  There wouldn't be a "5th" integration point at the element center.


Once again I'm no Nastran programmer so maybe someone more familiar could also respond or correct anything I may have misstated.









Re: Number of integration points

[ Edited ]

Thanks for your replay!

"unless a reduced integration scheme was selected, which I don't think Nastran exposes for shell elements."
why you think so? Zienkiewicz sad that "for a liner quadrilateral element a single point integration is adequat"..


I know that 2x2 Gause points beter but i want to understand Nastran stress output.


Corner results output is the "analyze option" for CQUAD4 element, but centroid stress calculate always..and therefore i am doubted, because for solid, how you said, i can see stress in Gauss points) And i cant understand why its not possible for CQUAD4..


But despite my doubts, I still tend to the fact that the points of the gauss in the element are not one..