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# buckling

I have some problems to simulate an object by compresing it and produce buckling.

How do I simulated bucking on columns in NX 8.5?

Thanks.

6 REPLIES

## Re: buckling

Dha,

NX 8.5 supports linear buckling pre/post processing for NX Nastran. In a SIM file you create a new solution that is SOL 105 Linear Buckling. This will produce a solution with 2 subcases. The first subcase is a linear statics subcase that contains all loads defined for the problem. The second subcase is an eigenvalue subcase. It will calculate the buckling modes and load factors of each buckling mode relative to the applied loads in the first subcase.

Regards,

Mark

Mark Lamping

Simulation Product Management

Product Engineering Software

Siemens Industry Sector

Siemens Product Lifecycle Management Software Inc.

mark.lamping@siemens.com

www.siemens.com/plm

## Re: buckling

Thanks Mark

I have one more question. I don´t understand very good the interpretation of the eigenvalue, I guess is the same as the load factor. If I want to meassure the real displacement and the stress results of buckling, how do I find this values? What is the meaning of the eigenvalue and the load factor you meant?

Thanks!

## Re: buckling

Dha,

The load factor is equivalent to the eigenvalue. The first eigenvalue is representative of the critical load. Eigenvectors are normalized. They are physically meaningless from a magnitude point of view, but they are meaningful with respect to their shape. The NX Nastran Users Guide has a section devoted to linear buckling. I suggest that you review it for more information on this topic. Below is a snip of the introduction to that users guide discussion.

Regards,

Mark

In linear static analysis, a structure is normally considered to be in a state of stable equilibrium. As the applied load is removed, the structure is assumed to return to its original position. However, under certain combinations of loadings, the structure may become unstable. When this loading is reached, the structure continues to deflect without an increase in the magnitude of the loading. In this case, the structure has actually buckled or has become unstable; hence, the term “instability” is often used interchangeably with the term “buckling.”

Only linear buckling or elastic stability is considered in the discussion which follows; in other words, assume there is no yielding of the structure and the direction of the forces do not change (i.e., follower force effects are ignored). Other assumptions of elastic stability are discussed in “Linear Buckling Assumptions and Limitations.” For a description of follower forces, see the chapter “Follower Stiffness” in this User's Guide.

This chapter is organized into the following sections:

Finite element approach

Eigenvalue extraction method

Assumptions and limitations of linear buckling analysis

Examples

Mark Lamping

Simulation Product Management

Product Engineering Software

Siemens Industry Sector

Siemens Product Lifecycle Management Software Inc.

mark.lamping@siemens.com

www.siemens.com/plm

Solution
Solution
Accepted by Ganesh_S (Community Manager)
‎08-26-2015 04:32 AM

## Re: buckling

Dha,

A linear buckling analysis (SOL 105) will only give you the buckling load factor (yes, this is the eigenvalue) and an idea of the location where buckling ocurrs (based on the shape/eigenvector).

To calculate real quantities (displacements/stresses/etc.), you need to do a nonlinear analysis. A typical nonlinear analysis will fail to converge after the onset of buckling so you can use it to see the stresses/displacements up to the point where the structure buckles. For a post buckling analysis, you need to use some type of arc length/displacement control stepping methods. These are available in SOL 106 and SOL 601. Look for NLPCI in the SOL 106 (Basic Nonlinear) user's guide and the LDC method in the SOL 601 (Advanced Nonlinear) user's guide.

Regards,

Jim

## Re: buckling

Thanks Jim

Daniel Hoyos
Escuela de ingenieria, university

## Re: buckling

Thanks Mark,

Daniel Hoyos
Escuela de ingenieria, university