How can I reduce ply maximum shear stress using tailoring

[Kristina Sornikova]

Hello, I ask this question for composite expert.

I have 8 ply all zero angle fiberglass cloth layup, complex box part. Open top, rest is a box enclosure with some areas with contours radius areas.

I seeing high ply "max shear stress" in my FEM. Assume that area is at the top lip, where it is open.

Load is a pressure load on one face from the inside out.

What can I do to reduce the max shear stress? I tried to make some plies 45 degree, but this increased max ply 1 and 8 shear stresses. If you need any more information please reply, I provide in my reply.

Thanks,
Kristina.

 

[RPstress]

A sketch or at least a view of the FE model with the loading and restraints will help considerably. Usually shear is helped by 45 deg plies but the fibers must be in the directions of high stress. An open-sided box will not be much good at carrying torsion. Sketch of loading and restraints needed please.

 

[Kristina Sornikova]

Hi, RPstress wish I could, but cannot.

Imagine a cooler box no lid.

Put on floor, have a strap tie down it from left bottom floor to above it to right bottom floor, another strap tie down it from left back to front of it to right back.

Back wall supports box which simply sits on floor, not other restraints.

And forward load is on inside front face. I hope this helps clarity.

 

[SWComposites]

What can I do to reduce the max shear stress? > make the part thicker (i.e, add plies)

 

[Kristina Sornikova]

Thank you SWComposites, fiberglass 7781 has very low in plane shear allowable strain/stress.. I add ply before, helped a little bit. But I curious if %45 plies helps. I finding it does not help, made worse than all zero plies. I thought more %45 should help?

 

[RPstress]

We don't know how detailed your model is. Are the high stresses predicted in the curved part of the corners or in some corners that are modelled more simply? A crude hand sketch would allow sensible answers. P.S.: is the FE model simple and linear static? Are the high stresses definitely inplane? If so then adding (not just changing plies' orientations) plies at 45 deg local to the high shears should reduce the problem.

 

[SWComposites]

Yes, without knowing a lot more details its hard to make any useful recommendations. For start, need to know the stress state st the critical location. And is it a stress peak or relatively uniform stress field?

 

[Kristina Sornikova]

Thank you all, simply sdded lot more 0/90 plies.. it reduced the shear stresses a lot...