Laminate properties (0/90) and (0/+45/-45/90)

[jblakes]

Evening all,

im hoping somebody can help or point me in the right direction.
We have tested these two laminates, one tensile and other three point bend test. The (0/90) has a higher uts, elastic modules, and flexure strength.
(0/+45/-45/90) has a higher flexural modulus. Both roughly same toughness.

I can seem to find anything that clearly explains why this is. To me the (+45/-45) one should have have higher uts as its got two more plies to add strength, but then read somewhere about it fails as more angles means it fails through midplane.

Can somebody explain this and give a resource to read?

Kind regards
Andy

 

[Chestermiller]

Have you carried out analyses to determine the stresses within the individual plies, and the inter laminar shear stresses?

 

[jblakes]

No, we have just performed a tensile and 3point bend test on a
(0/90/0/90/0/90/0/90) 8layers
(0/45/-45/90/90/-45/45/0) 8layers,

the question i need to answer is how the stacking sequence effects the properties. I've tried reading laminate theory but just don't seem to understand. Am i right in thinking the first one is a symmetric cross ply and the second one is a quasi-isotropic laminate?

 

[Chestermiller]

No, we have just performed a tensile and 3point bend test on a
(0/90/0/90/0/90/0/90) 8layers
(0/45/-45/90/90/-45/45/0) 8layers,

the question i need to answer is how the stacking sequence effects the properties. I've tried reading laminate theory but just don't seem to understand. Am i right in thinking the first one is a symmetric cross ply and the second one is a quasi-isotropic laminate?

The second is what I would call a symmetrically stacked laminate. The first isn't, but it can probably be treated as such if the loading is along the principal directions of the reinforcement. Before you start trying to deal with something like this, you need to develop some understanding of laminate theory. That way you can determine the stresses within each layer. See book by Byron Pipes.