{"id":380577,"date":"2024-08-27T08:40:30","date_gmt":"2024-08-27T08:40:30","guid":{"rendered":"https:\/\/innovationspace.ansys.com\/forum\/forums\/topic\/forcemoment-reactions-at-contact-weldline-evalution-nominal-stress-concept\/"},"modified":"2024-09-10T08:59:56","modified_gmt":"2024-09-10T08:59:56","slug":"forcemoment-reactions-at-contact-weldline-evalution-nominal-stress-concept","status":"publish","type":"topic","link":"https:\/\/innovationspace.ansys.com\/forum\/forums\/topic\/forcemoment-reactions-at-contact-weldline-evalution-nominal-stress-concept\/","title":{"rendered":"Force\/Moment Reactions at Contact (Weld Seam Evaluation: nominal stress concept)"},"content":{"rendered":"

<p><p><p class=”MsoNormal”><span lang=”EN-US” style=”mso-ansi-language: EN-US;”>Dear Ansys Community,<\/span><\/p><p class=”MsoNormal”><span lang=”EN-US” style=”mso-ansi-language: EN-US;”>I’m extracting force and moment reactions at bonded contacts for a weld seam evaluation by <span style=”text-decoration: underline;”>nominal stress concept<\/span>. So, I only extract reactions via FEM and do the stress calculation analytically by hand. I set up a simple example I can entirely solve analytically, to verify my results. I’m not entirely happy with the moment reactions. I try explaining everything as brief as possible.<\/span><\/p><p class=”MsoNormal”><span lang=”EN-US” style=”mso-ansi-language: EN-US;”>In fig. 1 you see my test case, a simple cantilever beam <\/span><\/p><p class=”MsoNormal”><span lang=”EN-US” style=”mso-ansi-language: EN-US;”><\/span><\/p><p class=”MsoNormal”><span lang=”EN-US” style=”mso-ansi-language: EN-US;”>Figure 1<\/span><\/p><p class=”MsoNormal”><span lang=”EN-US” style=”mso-ansi-language: EN-US;”>I analyzed two cases I and II. In the following I focus on case I (both cases lead to the same “problem”). The weld seams are assumed to be located directly at the end of the beam (of course that’s not correct, the fillet weld is placed on the outer side of the beam, but let’s keep it simple). The resulting stress distribution is obvious (see fig. 2). I’m calculating sig_y,max analytically <span style=”text-decoration: underline;”>and<\/span> based on reaction forces\/moments. The result should be more a less identically. The analytic calculation is shown in fig. 2.<\/span><\/p><p class=”MsoNormal”><span style=”mso-no-proof: yes;”><br><!–[endif]–><\/span><\/p><p class=”MsoNormal”><span lang=”EN-US” style=”mso-ansi-language: EN-US;”>Figure 2<\/span><\/p><p class=”MsoNormal”><span lang=”EN-US” style=”mso-ansi-language: EN-US;”>When extracting the reaction moment (RM_x) for the entire contact (therefore I defined ONE SINGLE contact – contact faces: top\/bottom\/left\/right | target face: total face of the back plate) Ansys gives us 350Nm. Same result as derived analytically (see fig. 1 bottom right). All good so far!<\/span><\/p><p class=”MsoNormal”><span lang=”EN-US” style=”mso-ansi-language: EN-US;”>Now I want to calculate sig_y,max (on the upper edge of the top surface, see fig. 3) just by extracting reaction forces\/moments of the top surfaces (therefore I split the single contact into 4 contacts, where top, bottom, left, right are glued to the back plate respectively). For the contact “top-surface to backplate” (only this contact will be investigated in the following) I get the reaction force RF_y=7265,4N and reaction moment RM_x=333,4Nmm. Only these are relevant for sig_y acting on the top surface.<\/span><\/p><p class=”MsoNormal”><span lang=”EN-US” style=”mso-ansi-language: EN-US;”><\/p><p><\/p><p><\/span><\/p><p class=”MsoNormal”><span lang=”EN-US” style=”mso-ansi-language: EN-US;”>Figure 3<\/span><\/p><p class=”MsoNormal”><span lang=”EN-US” style=”mso-ansi-language: EN-US;”>The resulting stresses of RF_y and RM_x are calculated in figure 3. For this simple case, the actual sig_y,max can be derived based only on RF_y. RF_y devided by the area of the top surface gives us the mean stress sig_y,mean. Since we have a linear stress distribution and we know the cross section we can easily derive sig_y,max based on sig_y,mean:<\/span><\/p><p class=”MsoNormal”><span lang=”EN-US” style=”mso-ansi-language: EN-US;”>sig_y,max = sig_y,mean * (20mm\/19mm) = 95,58 MPa <\/span><\/p><p class=”MsoNormal”><span lang=”EN-US” style=”mso-ansi-language: EN-US;”>Compare this to the analytical solution sig_y,max,analyt. (95,41) given in fig. 2. This fits quite good (error < 1%). That’s why, the reaction force RF_y is trustworthy to me!<\/span><\/p><p class=”MsoNormal”><span lang=”EN-US” style=”mso-ansi-language: EN-US;”>And now we arrive at my problem.<\/strong> Summing up sig_y,mean and sig_y given in fig. 3, should also lead to a correct sig_y,max. However, summing up sig_y,mean (=90,8MPa) and sig_y (=12,5MPa) leads 103,3 MPa. Compared to sig_y,max,analyt., that’s an error of more than 7%. Of course, not super bad, BUT imho too big to be fully OK with it. Does anybody have some helpful ideas? MANY THANKS IN ADVANCE!<\/span><\/p><p class=”MsoNormal”><span lang=”EN-US” style=”mso-ansi-language: EN-US;”>Finally, a few more details to the simulation Model:<\/span><\/p><\/p><\/p><\/p>\n