composite laminates/stress prediction at different angles
composite laminates/stress prediction at different angles
(OP)
Hello,
We are producing composite materials which consist of plies stack on each other at different angles (like 0°/90°, 45°/45°, 15°/75°,30°/60°).
For the 0°/90° case, we have the same tensile strength in X and Y (principle) directions.
I want to estimate the maximum stress that a laminate(for instance 15°/75°) can withstand from the 0°/90° test. i found some document (actually it is from MIT's open courses).
There it is written:
sigma1=sigmaX.cos2teta+sigmaYson2teta+2taoXYsintetacosteta
another formula for sigma 2 and a formula for new tao12.
Here teta is the angle from the x acis to the 1 (fiber) axis.
Can I use this formula to estimate my maximum stress for different ply angles?
We are producing composite materials which consist of plies stack on each other at different angles (like 0°/90°, 45°/45°, 15°/75°,30°/60°).
For the 0°/90° case, we have the same tensile strength in X and Y (principle) directions.
I want to estimate the maximum stress that a laminate(for instance 15°/75°) can withstand from the 0°/90° test. i found some document (actually it is from MIT's open courses).
There it is written:
sigma1=sigmaX.cos2teta+sigmaYson2teta+2taoXYsintetacosteta
another formula for sigma 2 and a formula for new tao12.
Here teta is the angle from the x acis to the 1 (fiber) axis.
Can I use this formula to estimate my maximum stress for different ply angles?
Best Regards,
Sartor





RE: composite laminates/stress prediction at different angles
If you have woven plies then the 0 (or 90) degree strengths are the basic 0 degree ply strength and you can use the formulas ok. Even if the plies are unidirectional this should still work, but the 0/90 layup strength is not the basic ply strength.
NB: I assume that your 15/75 and 30/60 stacks are actually 15/-75 and 30/-60. Also your stacks either need to be symmetric about the centerline or a symmetric weave, probably twill or plain. (It's good practice to make the laminate symmetric in any case.)
RE: composite laminates/stress prediction at different angles
Hinton, M. J., Kaddour, A. S. and Soden, P. D., "A Comparison of the Predictive Capabilities of Current Failure Theories for Composite Laminates, Judged Against Experimental Evidence", Composite Science and Technology, Vol. 62, 2002, pp. 1725 – 1797
Then dive into the referenced papers.
Or, just run tests on your various laminates.
RE: composite laminates/stress prediction at different angles
RE: composite laminates/stress prediction at different angles
In either of those cases, you will need to look at very different approaches than the simplified academic theories.
And as SWComposites has mentioned, the basic formulas can not always be translated into a confident prediction of strength due to the complex nature of composites. This is why industry often relies on semi-empirical approaches, which add the necessary confidence via testing.
Brian
www.espcomposites.com