FAQ
Why do my results differ from the Excel spreadsheet?
Ensure you are using the same load convention (CLT vs NASTRAN). The moment sign convention differs between the two, which affects ply-level bending strains. Also verify that the ply order matches — the tool stacks plies from top (ply 1) to bottom, consistent with the Composite_Laminates.xlsm workbook.
What does a non-zero [B] matrix mean?
A non-zero [B] matrix indicates a non-symmetric laminate with bending-extension coupling. In-plane loads will produce curvatures and bending moments will produce mid-plane strains. This is usually undesirable in practice — use the Symmetric button to mirror your ply stack.
Which failure criterion should I use?
It depends on your application and regulatory requirements:
- Max Strain / Max Stress — Simple and widely used; good for initial sizing and conservative checks.
- Tsai-Wu — Most commonly used interaction criterion in aerospace; accounts for strength differences in tension and compression.
- Hashin / Puck / LaRC03 — Mode-separated criteria that distinguish between fiber and matrix failure; preferred when understanding the failure mechanism matters.
When in doubt, run multiple criteria and compare. The Failure Summary Panel lets you toggle criteria on/off to see how they affect the critical margin.
How are stress allowables derived from strain allowables?
Stress allowables are converted from strain using the appropriate directional modulus:
Strain allowables are in microstrain (με), moduli in Msi, resulting stresses in ksi.
Can I save my laminate configuration?
Currently, laminate configurations are session-local and reset when you reload the page. A persistent save/load feature is planned for a future release.