weave pattern for fiber reinforced composites

[wetwilly17]

I am specifically interested in carbon fiber re-inforced composites. Generally I see relatively finely woven patterns. However, in some materials i have seen a larger weave, more resembling a checkerboard, where there is less weaving of the fibers per length. I understand the finer weaving is probably more costly to manufacturer and would require more fiber. However i was wondering if someone could explain, in detail the effect that the finer weave has on the mechanical properties of the composite. Thanks in advance.

 

[Compositepro]

With carbon fiber the "finess" of the weave is determined by the tow size (tow is the untwisted fiber bundle). Carbon usually comes in 1K, 3K, 6K, 12K, and some larger tows. The numbers indicate how many thousands of filaments are in the fiber bundle. Larger than 12K tow is rarely used for weaving. 3K and 6K are most common. Smaller tows cost more per pound than larger tows.

Larger tows are less expensive to produce and weave but cannot be used for making thin fabrics except with very special equipment to make "spread tow fabrics".

Crossplied unidirectional tape gives the highest mechanical properties, but has drawbacks. It's drape or ability to conform to compound contours is not good. Also, fibers can be peeled out for long lengths at damaged areas.

Fabric is far more conformable because the fiber is already wavy (buckled), and it will easily deform in shear (scissor). Finer weaves are more expensive but will have higher properties. Loads are carried by the fiber bundles but have to be transfered between bundles. Larger bundles carry larger loads per bundle but have proportionately less surface area to transfer to other bundles. So shear stresses between resin and fiber bundles increases. This is the weakest property of carbon composites.

So it is a cost versus performance compromise.

Spread tow fabrics have some of the same problems as unitape and do not have all the advantages of standard weaves. So, again it is a compromise.

 

[wetwilly17]

"Larger bundles carry larger loads per bundle but have proportionately less surface area to transfer to other bundles. So shear stresses between resin and fiber bundles increases."

are you saying that larger bundles ('checkerboard' as i called it) will delaminate easier compared to smaller bundles, all else equal?

the reason i am asking is because i play hockey. usually my blades fale by delamination. the most durable, hi performance blade i have found uses large bundles. i have found that it doesn't delaminate as easy as other hi performance blades with smaller bundles. my instinct tells me that a finer weave, smaller bundles would not delaminate as easy but that has not been the case. i guess it is the matrix or manufacturing process that causes the blade with larger bundles to resist delamination better?

also, a very popular stick has just switched to a blade with larger bundles. this may be because it is cheaper to manufacture, but generally hockey sticks move in the direction of stronger, higher-performing and more expensive rather than the opposite direction.

 

[wetwilly17]

in the previous post, i included an example of a blade with large bundles. here is an example of one using smaller bundles.

 

[Compositepro]

There are so many differences in design and construction between completing blades that it would be impossible to attribute your observations to any one factor. In sporting goods the carbon fabric pattern is often silk screen printed even though carbon fabric is used. The printing cosmetics is more uniform than real carbon. That is not to say that the pictures you attached are not true fabic patterns, I just can't tell for sure.

 

[RPstress]

There is a Scandinavian company (I think Swedish but can't remember the name) which has found a way to weave quite wide tape, about an inch across from memory. This has the appearance of the first stick. This has some advantages, with fewer fiber kinks than the usual stuff plus it looks good. However, it doesn't give any interlaminar advantages that I'm aware of.

They may just have moved to a more expensive resin which is a good bit tougher than the usual. Just possibly they've stitched or Z-pinned it. That could potentially be hard to spot from the outside. It might well show up when you next break a blade.

Also, as 'Pro says, just because you can see something on the surface doesn't mean that that's what's inside it...

 

[PanelGuy]

I agree with this, sorry man but I have done "Carbon" sporting goods with Glass fiber and Carbon dust filled Epoxy to tint it black.

However, most of the blades are using carbon and a blend for strength. The different tow sizes and weave patterns also allow the lamintes to stretch and shift before failure. Actually the large weave acts like a spring shock. Not much but the effect is there.

The bigger issue is the adhesive and substrate design. Depnding on the core material that can be the weak point the forces the delam. An adhesive here needs flexiblizers etc. I think the one thing overlooked by players is the ability to make the blade flex a little differently, once you learn the way to control it, you can get better power and durability out of a more flexible blade.

There are so many factors in the laminate that could cause the delamination that weave size probably does not affect it. Although, the larger weave may be using a glass blend which would absorb impact better than the carbon. Your better bet is to look for blades with a higher glass content, but with Carbon reinforcement dow the length of the blade for stiffness. Good luck seeing it through the packaging and labels.

Welcome to being a discriminating composite consumer.

From the Engineers view...C'Mon guys, why use Carbon? Pro players changes blades more than they change socks. They need the stiffness and durability, but Carbon is so brittle you are better off to use it sparingly as a stiffener and spend the money on a good core...like a foam filled honeycomb or mid weight PE.

Happy Holidays!