Max stress and max strain
Max stress compares each ply stress (along, across, shear) with its strength and the first to reach 100% names the mode; max strain does the same with strains (strength ÷ modulus). They agree on the axes and almost agree off-axis (120 vs 123 MPa at 45°), but under combined stress they part: with 2,000 MPa along the fibres, max strain allows 99 MPa across, max stress 60, because of Poisson.
Predict · at 1:03 in the video
Do max stress and max strain predict the same failure?
On the axes, yes, by construction. Pulled at forty-five degrees, almost: 120 against 123 megapascals. But combine loads, and they part.
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.
