The 10% rule
Design guidelines ask for a minimum share of plies in each of 0, ±45 and 90 (10% in one widely used list, 8% in another) so a laminate tuned for one load still copes with the loads nobody planned for: adding just 10% of 90° plies to a 20-ply 0/±45 stack raises its across-stiffness from 21.5 to 34.2 GPa.
Predict · at 0:40 in the video
The ten percent rule says: at least ten percent of the plies at each of zero, plus and minus forty-five, and ninety. Is that physics, or practice?
Practice. It's a design guideline, not a law of mechanics. And the number varies.
This course is our own. These books go deeper.
- Basic Mechanics of Laminated Composite Plates, A. T. Nettles, NASA Reference Publication 1351, 1994
- Mechanics of Composite Materials, R. M. Jones, Taylor & Francis, 2nd ed., 1999
- Engineering Mechanics of Composite Materials, I. M. Daniel & O. Ishai, Oxford University Press, 2nd ed., 2006
- Design and Analysis of Composite Structures, C. Kassapoglou, Wiley, 2nd ed., 2013
- Composite Materials Handbook (CMH-17), Volume 3, Rev. G, CMH-17, SAE International, 2012
The course designs in AddPly, our browser app for laminate design: regions, ply stacks with live stacking-rule checks, thickness, mass and the ply book. It does not do strength, failure or draping; where a lesson covers those, the simulation is our own.
Simulations in this lesson are our own. Ply data come from the datasheet or textbook named on screen; where a number rests on an assumption, the video says so.
