# Static B.C & first moment of area of connecting rod

• GYan
GYan
Hello everyone,

I am doing a project in FEM, and we first have to assess the mechanical behavior of a connecting rode in which there is a hole in the center part of height b. The connecting rode has a trapezoidal shape (when seem from the top view), so the cross section is gradually decreasing from the big articulation, with an angle of 5°. The connecting rod is subjected to a distributed force P (oriented to a degree alpha) on its small articulation. I have two questions, hoppening someone will answer to them:

1° How can I write the static boundary conditions on the inner surface of the small articulation: T_j = n_i sigma_ij ?
2° How do I compute the first moment of area of the cross-section of the center part (with the hole, so two discontinuous rectangles), knowing that the height changes along the longitudinal axis?

I don't know how to join files in here, but if you tell me, I can provide some to understand the background.

Thank you !

[Mentor Note: Thread moved from the technical forums to the schoolwork forums]

Last edited by a moderator:
Welcome to PF.

Use the "Attach files" link below the Edit window to upload PDF and JPEG files. Also, is this project for schoolwork?

berkeman said:
Welcome to PF.

Use the "Attach files" link below the Edit window to upload PDF and JPEG files. Also, is this project for schoolwork?

Yes, it's for a schoolwork, but I don't want the answer, I just want someone to explain me how to go through, because I tested a lot of things and all don't make sense.

Last edited by a moderator:
WWGD
GYan said:
Hello everyone,

I am doing a project in FEM, and we first have to assess the mechanical behavior of a connecting rode in which there is a hole in the center part of height b. The connecting rode has a trapezoidal shape (when seem from the top view), so the cross section is gradually decreasing from the big articulation, with an angle of 5°. The connecting rod is subjected to a distributed force P (oriented to a degree alpha) on its small articulation. I have two questions, hoppening someone will answer to them:

1° How can I write the static boundary conditions on the inner surface of the small articulation: T_j = n_i sigma_ij ?
2° How do I compute the first moment of area of the cross-section of the center part (with the hole, so two discontinuous rectangles), knowing that the height changes along the longitudinal axis?

I don't know how to join files in here, but if you tell me, I can provide some to understand the background.

Thank you !

[Mentor Note: Thread moved from the technical forums to the schoolwork forums]
Here is the project statement:

#### Attachments

• ProjetMain29(1) (2).pdf
292.8 KB · Views: 2
I'm not sure what software you are using. You can, in ANSYS, for instance apply a pressure on the surface with a resulting total force equal to P. A minor detail, but you likely would not want to include to area opposite the force in your pressure application (so there is no pulling).

This appears to be a FEM problem, so not sure why you need to compute anything analytically. Just run the simulation. In general, areas with higher stress need more supporting material, areas with lower stress can have reduced material.

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