Design-to Deformation derivation

[garyjh]

How are the Design-to Deformation strains ex, ey & exy generated for unstiffened plate/sandwich panel family components?

Whilst selecting only the unstiffened plate concept, I have tried to generate them myself to understand more by using the following calc (Load/Thickness)/Modulus for each Design-to Load Nx, Ny & Nxy and i can only get the exy to match. The ex is close but not a match and the ey is not close and the opposite sign. Is the calculation I am carrying out to simple?

Also the Design-to deformation strain are not the ones in the report used to generate the margins of safety. Why is this? How are the strains in the report derived?

An example showing how the Design-to Loads Nx, Ny & Nxy are converted to Design-to deformation strains and then converted to the strains used to generate margins of safety would be of great benefit.

Thanks.

[Phil]

Hi Gary,

Is this a composite analysis?

First, the Design-To Deformation strains and their relation to the forces are simply derived using the ABD matrix of the laminate.  So, the relationship will be:

{Nx, Ny, Nxy}T = [A] {ex, ey, exy}T

(this is assuming the laminate is symmetric... if not, then there are contributions from the B matrix)

You can find the ABD matrix on the Computed Properties tab.

For the strains used to calculate margins of safety, there are a couple possibilities.  First, what ply is shown in the report?  Is it a 0, 45, or 90 ply?  The strains used to calculate margins are in ply coordinates, therefore for anything other than a 0 ply, I would expect the strains to be different for the ply than from the laminate.

Second, is there any bending of your laminate?  When HyperSizer calculates the strains, it uses the Kirchoff Hypotheses to calculate the strain both due to membrane and bending loads.

Finally, if you are using laminate based analysis, then HyperSizer calculates strain in each of the principal directions (-45/0/45/90) and then calculates the margins of safety in each direction.  It may be this that you are seeing in the report.

Please let me know if any of these situations are what you are encountering.

Phil

[garyjh]

Phil,

it is a composite ply based failure analysis on an unstiffened panel with bending applied as well as in plane loads.

Initially I used a balanced symmetric laminate and created an effective laminate and this, as you know from another post, caused me confusion with regards to the allowables generated from the effective laminate and their subsequent use.

I have carried out some hand calcs, with & without bending, and get the Designed-to Deformation strains to match Hypersizer (when there is no bending applied). The bending does make a difference.

Also when using a laminate rather than an effective laminate the stress report composite ply based failure MOS calculations are more easily followed to determine the applied loads and allowables used. However, what is a bit more difficult to follow is when a 45° or 90° ply is the critical ply. More data on the applied strains for each ply orientation in a laminate would be beneficial.