Balance and shear coupling
An off-axis ply without an opposite-angle partner makes the laminate shear when it is pulled: NASA RP-1351's own [0/+45]s example has A16 = 47,055 lb/in and shears about half a unit for every unit of stretch; add the −45 partners and the coupling vanishes. AddPly checks balance live.
Predict · at 0:36 in the video
NASA's laminate primer works through a stack of zero, plus forty-five, plus forty-five, zero. No minus forty-five at all. Pull it along zero. Does it only stretch?
No, it shears too. Laminate theory has a coupling term for exactly this. For this stack, NASA's primer gives it as 47,055 pounds per inch.
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.
