Why ±45 is everywhere
Shear is carried by fibres at ±45°: a [±45]s laminate is about 5 times stiffer in shear than a [0/90]s one (35.6 against 6.9 GPa), because shear is tension along one diagonal and compression along the other.
Predict · at 0:44 in the video
Now turn the plies to plus and minus forty-five, same material, same thickness. How much stiffer in shear? Twice? Five times? Ten?
About five times: 36 gigapascals against 7. At forty-five degrees, the fibres lie along the diagonals, so they carry the shear as tension and compression, which is what fibres do best.
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.
