Patches
A patch is a ply that covers only part of the laminate (on the spar: the rails and root pads, declared on regions on top of the full-web plies; AddPly can also keep a linked patch a declared distance from its parent). Every patch edge is a ply drop, a source of out-of-plane stress, so guidelines keep patches covered (Irisarri et al. 2014).
Predict · at 0:51 in the video
A patch on the outside surface, or one covered by a continuous ply: which peels more easily?
The exposed one. Its edge has nothing holding it down. So published design guidelines say it plainly: don't drop the covering plies on the outer surfaces.
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, plus hosted drape studies and linear FEA with maximum-stress screening, within their stated limits. The lessons teach the theory behind those on our own simulations, so you can judge the results. AddPly needs an Addcomposites sign-in.
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.
