Composite wishbones

[riff_raff]

marcush,

"BUT: the same is even more true for carbon fibre,isn´t it?And this does not stop F1 making CF wishbones.."

No, the reversing load cycle fatigue limitations of aluminum are not the same for carbon epoxy composites. While it is true that composite structures don't do as well in compression as they do in tension (can't push on a string, right?), they also do not have a defined fatigue life like conventional metal structures. Metal structures fail in fatigue due to fractures that propagate through the section, and these fractures usually originate from the outer surfaces of the metal structure where the stresses are highest. Surface fractures in a composite structure do not propagate through the section in the same manner because the composite structure is a series of discrete fiber layers within a resin matrix. So a fracture in one layer will only propagate as far as the next resin bond line, and will be halted.

The trick to making a composite structure good in compression is to make sure that your fiber alignment is kept as straight as possible under compressive loads. The limit to compressive strength of composites is usually related to how well it can handle buckling within the individual fibers.

Good luck.
Terry

[marcush.]

marcush,

"BUT: the same is even more true for carbon fibre,isn´t it?And this does not stop F1 making CF wishbones.."

No, the reversing load cycle fatigue limitations of aluminum are not the same for carbon epoxy composites. While it is true that composite structures don't do as well in compression as they do in tension (can't push on a string, right?), they also do not have a defined fatigue life like conventional metal structures. Metal structures fail in fatigue due to fractures that propagate through the section, and these fractures usually originate from the outer surfaces of the metal structure where the stresses are highest. Surface fractures in a composite structure do not propagate through the section in the same manner because the composite structure is a series of discrete fiber layers within a resin matrix. So a fracture in one layer will only propagate as far as the next resin bond line, and will be halted.

The trick to making a composite structure good in compression is to make sure that your fiber alignment is kept as straight as possible under compressive loads. The limit to compressive strength of composites is usually related to how well it can handle buckling within the individual fibers.

Good luck.
Terry

terry ,sorry for not being clear here,i fully agree with your statement ,but my thoughts were more directed towards some foreign objects hitting the carbon wishbone at speed ...as these loads /impacts will just shatter the carbon fibre to
pieces in the same moment whereas any non cast piece of metal will bend ,buckle or whatever but not transform to dust.
I´m not aware if wishbones do actually have build in some dyneema stringers build in to at least keep them from completely disintegrating.

[conni]

2 ways of doing CF wishbones open and closed toyota used the closed method with rohacell in the middle but sufferd a high scrap rate others use the open method make them in 2 halves then machine down the sacraficial plies then 1 piece of film bond to join em, cost? A LOT about 320hrs per pair

conni

[marcush.]

2 ways of doing CF wishbones open and closed toyota used the closed method with rohacell in the middle but sufferd a high scrap rate others use the open method make them in 2 halves then machine down the sacraficial plies then 1 piece of film bond to join em, cost? A LOT about 320hrs per pair

conni

ah .then there was some film bonding in wing section in F1 ....as proposed a few weeks ago .Not that I had any doubts that the idea was feasible and sound but I was
totally knocked out by the statements only rohacell core crushing was the way to do it.
No it isn´t -plus you have not much control in the process -

I wonder who will do that sort of work in F1 when you only got 180 headcount per team when a car set of wishbones for two cars will bind two person for no less than
8 months..not even think about partslifing or crash damage......I guess at FI they will surely franticly search for a new brain for Mr.Sutil ...

[conni]

all F1 wings ive made in the last few years have all been crushed rohacell

conni

[polarboy]

lot more hollow wings out there than compressed Rohacell,LOTS of diffrent ways to do wishbones,an if your doing hollow your a lot better doing 2/3or4 ply staggered joining strip rather than just film glue