Hello,

For a laminated rectangular plate (Unstiffened) with uniaxial compression (Nx) Hyperizer uses the general orthotropic equation to calculate the Nxcr. But in a case where a moment about z axis is applied on the edges then Nx would be non uniformaly distributed along the edges in order to obtain the proper resultant moment. Hypersizer assumes this as uniformly distributed along the edges and uses the classical buckling equation in calculating Nxcr. My question is: 1.) Isn't this approach too conservative?

For the first case you describe, assume that half the plate is in compression and half is in tension. (see the attached image at the bottom of this post - you must be signed it to see it)

HyperSizer does two things.

First, it averages just the compressive stress, therefore the tensile stress is ignored completely. Also, the load applied is not the maximum compressive stress, but the average.

Second, it takes into account the fact that the buckling length should be adjusted such that only the compressive part of the panel should be included in the buckling length. So if half of the panel is in compression and half in tension, then the buckling length should be modified to approximately one-half the entered buckling length. To see this effect, generate a stress report with sample calculations for panel buckling, and look at the panel buckling sample calculation. The adjusted buckling lengths should be presented.

These two operations should give reasonable buckling results that will match a buckling analysis that takes the actual load gradient into account and not be over-conservative.

2.) In the case of biaxial loading with Nx being positive and Ny being negative I understand that Nxcr is calculated taking into account the +ve Nx. But is the stress ratio Rx calculated based on the compressive stress in the Y direction i.e; Rx= Nxcr/Ny

Thanks

HyperSizer doesn't really calculate the critical Nxcr directly, rather given the Nx and Ny load, it calculates the eigenvalue for buckling. From the eigenvalue, you can get the critical Nx and Ny by multiplying Nx_cr = Eigv * Nx_applied; Ny_cr = Eigv * Ny_applied.

Example,

Nx_applied = +300

Ny_applied = -1000

Eigv = 1.3

Nx_critical = Eigv * Nx_applied = +300 * 1.3 = +390

Ny_critical = Eigv * Ny_applied = -1000 * 1.3 = -1300

So the critical buckling load is:

Nx = +390

Ny = -1300

Note: The margin of safety reported on the Failure tab is:

MS = Eigv - 1

Please let me know if you need further clarification.