Pretest Prediction Composite Isogrid
Composite, Grid-Stiffened Panel Design for Post Buckling
Using HyperSizer®
HyperSizer optimized stiffening pattern of this all composite fairing. Flight certified.
Read the article at http://www.afrl.af.mil/successstories/2004/emerging_tec/04-vs-11.pdf
| Due to weight and cost goals, a grid-stiffened panel concept is being used for redesign of a structural component on the Minotaur OSP space launch vehicle. By designing the structural panels to carry operational loads past the point of initial buckling (local post-buckling), the resulting grid stiffened panel concept is lighter and 30% less costly to manufacture than other design candidates such as the existing honeycomb sandwich panel concept flown today. During June 2001 in Seattle, Boeing performed a structural certification experiment of a composite, grid stiffened, cylindrical panel loaded in axial compression. Pretest predictions were made for linear elastic (bifurcation) buckling, and non-linear post buckling. The tools used for pretest analysis were HyperSizer®, and the FEM based tools MSC/NASTRAN™ and STAGS™. Local buckling of the facesheet triangular shaped skin pocket occurred at a load of around 230 (lb/in). The test panel was able to sustain considerable additional loading, with post buckling failure occurring at 1320 (lb/in). The HyperSizer post buckling pretest prediction was 1300 (lb/in), the STAGS pretest prediction was 1250 (lb/in), and the MSC/NASTRAN pretest prediction ranged from 1425 to 2000 (lb/in). HyperSizer’s implementation of local post buckling based on an effective width approach is presented. |
Orbital's Minotaur OSP
space launch vehicle with the
existing honeycomb fairing
Grid-stiffened test panel
HyperSizer graphic display of an
optimum grid stiffened pattern,
rib spacing, thickness & height
|
SUMMARY OF PRETEST ANALYSIS PREDICTIONS COMPARED TO EXPERIMENTAL TEST RESULTS
SUMMARY TABLE: PRETEST FAILURE ANALYSES
|
Method
|
-Nx
(lb/in)
|
| Linear elastic buckling (local pocket buckling) |
|
| • Test Data |
235 |
• HyperSizer FBD linear 1 (including a
0.9 knockdown factor) |
265 |
• NASTRAN eigenvalue (including a 0.8
knockdown factor) |
345 |
• NASTRAN geometric non-linear
analysis |
340 |
• STAGS, eigenvalue (including a 0.8
knockdown factor) |
310 |
| • STAGS, non-linear analysis |
310 |
Non-linear/post buckling 2
(panel buckling and/or crippling) |
|
| • Test Data |
1320 |
• HyperSizer FBD nonlinear 3
(including a 0.8 knockdown factor) |
1300 |
• NASTRAN 4, geometric non-linear,
practical post buckling load limit using
HyperSizer for material strength and
crippling 5 |
1425 |
• NASTRAN 4, geometric non-linear,
theoretical limit based on solution non
convergence, and falling load
carrying capability |
2000 |
| • STAGS 4, 6 |
1250 |
| |
|
Refer to the downloadable published paper: "Composite, Grid-Stiffened Panel Design for Post Buckling Using Hypersizer".
ADDITIONAL TEST VALIDATION
On 23 April 2002, Boeing tested another Cylindrical Grid-Stiffened panel. This panel had a different layup, cross sectional dimensions, and thickness from the first test described above. The test failure load and pretest analysis predictions are included in the following table.
SUMMARY TABLE: PRETEST FAILURE ANALYSES
| Method |
-Nx
(lb/in) |
|
|
| • rib joint disbond, test failure load |
27.2k |
| • post buckling, test failure load |
33k |
| • post buckling, HyperSizer pretest analysis |
31.5k |
| • post buckling, NASTRAN FEA analysis |
31k |
|
|
|
