Reply To: Geometric stiffness matrix for solid elements

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Hello, thank you for your reply. Initially, I also followed the formula (3-60) from the ANSYS help documentation, as you mentioned, to calculate the geometric stiffness matrix. This theoretical expression produces a geometric stiffness matrix with zero elements, which can be verified using Mathematica. When extracting the geometric stiffness matrix in ANSYS APDL, I first performed a static analysis, then a buckling eigenvalue analysis, and used the following command to output the .out file, in which the geometric stiffness matrix is included. I calculated the 8-node hexahedral element (cube, full integration, single element) and the 20-node hexahedral element (cube, full integration, single element), and their extracted results are as follows. Finally, I validated the results using MATLAB and found that the eigenvalues calculated from the extracted geometric stiffness matrix and the material stiffness matrix matched the results output by ANSYS APDL. This implies that the formula used by ANSYS APDL to calculate the geometric stiffness matrix for solid elements is different from what is documented in the ANSYS help manual or existing literature. That’s why I am reaching out to you for assistance. Thank you for your time and response!