Warp versus Fill strength
Warp versus Fill strength
(OP)
Can anybody tell me why, on a fabric with exactly the same fibers/tows etc on the warp and fill the warp is stronger?
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Warp versus Fill strength
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RE: Warp versus Fill strength
Also, even if the vendor claims the tows per inch are the same in both directions, in reality they are not.
RE: Warp versus Fill strength
The higher degree of waviness in the fill direction would explain why the stiffness might be lower. However, to fail a tow would require the bundle to straighten out after the matrix pockets around the bundles have failed rendering the waviness obsolete. Thoughts?
RE: Warp versus Fill strength
SW
RE: Warp versus Fill strength
RE: Warp versus Fill strength
Wrong - they are used all the time in all sorts of structure, with all types of loads.
SW
RE: Warp versus Fill strength
jjprototype, are you facing some design issues because the strengths are significantly different?
RE: Warp versus Fill strength
RE: Warp versus Fill strength
RE: Warp versus Fill strength
Great point about being careful how harness satins are stacked. If you stack a group of harness satins all the same "direction" (meaning, say warp side down every time), you have to worry about "nesting" issues when fiber tows from surrounding plies fill in matrix pockets during cure. This can accentuate fiber waviness and can affect strengths. I've seen strength values affected in the 10-20% range when nesting is an issue but am curious if more manufacturing oriented individuals have better ideas of how much strength values are affected since I only have limited places to draw numbers from...
-CM
RE: Warp versus Fill strength
RE: Warp versus Fill strength
Layer nesting refers to the interaction between neighboring fabric layers of a textile composite laminate. Idealized layer nesting configurations were investigated in five-harness satin weave carbon/epoxy laminates under static compression loading. A methodology was developed to fabricate three idealized nesting cases: stacked, split-span, and diagonal. All three idealized nesting cases produced reductions in compressive strength and ultimate strain when compared to the conventional randomly-nested laminates. The diagonal nesting geometry produced the largest strength reductions. Finite element results showed consistent strength reduction trends for the idealized nesting cases; however, the magnitudes of compressive strengths were overpredicted. These results suggest that regions of idealized nesting in conventional woven composites, particularly diagonal nesting, may be sites of failure initiation. Additionally, differences in compressive strength associated with idealized nesting configurations may explain the considerable scatter observed in compressive strength for these materials.
Can you explain more about how nesting helps balance internal stresses?
-CM
RE: Warp versus Fill strength
Internal stresses are caused by the vastly different properties between resin and fibers in different directions. Unbalanced weaves, like satin weaves, have most fibers in each face running in orthogonal directions. If one cures a single ply of such fabric it will warp into a potato chip due to unbalanced internal stresses. If two plies are cured together with warp-face to warp face, then the laminate will stay flat. Balanced lay-up can be made by flipping alternate layers or, more commonly by making one half of laminate stack mirror the other half.