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# Weld post processing using Fsum/PRNLD command on coupled nodes (cpintf)

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## Weld post processing using Fsum/PRNLD command on coupled nodes (cpintf)

(OP)
Hi,

I am trying to find the weld stresses (weld shear and weld tension) using the forces output in 3 -directions (Fx, Fy and Fz) using FSUM/PRNLD command in Ansys post-processing.

The mesh (SHELL281, 8 noded quadratic elements) is uniform in size (=10mm) across the model and the weld is simulated using "CPINTF" command in Ansys. So, two set of nodes of the model where there is a weld are connected through couplings (one by one in a loop).

During postprocessing, I am selecting one node set from a weld (couplings between two set of nodes) and after each node selection, I write the forces Fx, Fy and Fz in a text file. I know the spacing between nodes so for each node I get Fx, Fy and Fz and I calculate the resultant force causing shear (two directions) and I do a SRSS of forces Fx, Fy and Fz (square root of sum of squares) - which gives shear force per unit element length (distance between two nodes) using the former and unit force (SRSS) per unit element length using the latter.

I then pick a size of weld and calculate throat, then dividing this shear force per unit length of element by the throat which gives me the shear stress and same for the unit stress (SRSS of Fx Fy and Fz per unit element length per throat). Then compare these values with allowable as min.[0.4Sy (base material),0.3Su] (outlined in AWS D1.1 table 2.3)

Problem is that I have a mid-side node and it connects two elements whereas the corner nodes connects 4 elements. And when I calculate the weld stress using a full penetration weld (size equals to plate thickness) the weld fails. There is high force on one of the midside nodes. I do not understand why it happens and what can I do to avoid this high force. If I exclude that node, then I need a less size of weld (15mm plate thk will require 8mm groove weld) and all is hunky-dory.

Shall I mesh with linear elements and see the forces so that I only have corner nodes to get the Fx, Fy and Fz for these nodes?

FYI, the coupling or cpintf command generates coupling between midside nodes also (in WB) which I can see in Ansys Classic if I save the db and rst file in WB and then open the same in Ansys Classic.

Shiraz
Sr. Engineer

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