Hi,
I made some carbon fibre and mechanically tested for tensile and flexural. Now I am trying to use the Tsai-wu and hashin criteria “for anisotropic composites” to check its failure criteria. I have a problem with understanding what sigma 11 and sigma 22 are? are these just the upper yield points from the strain strain graphs?? and also sigma 31 and sigma 33, are these the shear stresses??
Is there a formula to workout the axial shear strength??
Thx
Sid
Its been a while but…Yes, assuming you tested a uni sigma 11 is the 0 degree (fiber direction) ultimate stress and sigma 22 is the ultimate stress in the 90 (transverse) direction. Sigma 33 for a uni is the same as sigma 22. Simga 12 is inplane shear which is the same as sigma 13 for a uni. Sigma 23 is through thickness shear stress.
For Tsai wu you need both tension and compression numbers to calculate the coefficients.
I prefer max sress or strain as they are simpler.
What are you designing?
sorry about the late reply. I am testing a carbon fibre composite to see its failure criteria. Whether it fails at delamination or total failure according to the theories. When the tensile and flexural testing do you know how i could work out the shear stresses??
Thx for the help btw
Yeah you can work it out pretty easily. As it’s all in-plane UDs you only need to calculate the [A] matrix to determine your laminate’s elastic constants. There’s no bending/ non-symmetry so you don’t need to bother with the [b] & [D] matrices. You’ll need to work out both poisson’s ratios first though.
To do this, you’ll need to read up about classical laminate theory first. Try mechanics of composite materials & structures by Mukhopadhyay.
Let me know how you get on. In this case it’s not particularly difficult, but is quite time consuming.
Andy
Sid
I have some of the preliminary calculations in a thread stickied in this forum. I never got around to completing it but its a start in the right direction.
Can you post up your material properties and your laminate stack and I’ll put up a full work through of how to get your laminate properties?