KAM or Ashcroft CV's & Shafts ?

[will4x4]

Oh yes, i am looking on my iphone so my screen is a bit small... well its close lol but you can see which is stronger.. ill print them off and look later when i have time.

[gazelle]

Both Ian (Ashcrofts) and Nige (KAM).......

Ooops sorry Dave.

[Bush65]

Static strength of these components is a product of material properties to withstand particular stress levels and the amount of material resisting the load to minimise the stress (stress is load per unit area).

Static strength is what is being measured by a single load cycle, applied at a slow rate such as in a testing machine that loads the shaft, etc. up to its failure point. it is useful for comparisons when used with appropriate judgement, but is not real life.

Fatigue strength is more complicated and not well understood because repetitive load cycles can cause failure at load values well below the static strength. Areas of components can cause stress concentrations that lead to crack formation. As cracks progress the section carrying the load is effectively reduced and ultimate failure can occur at a very low load. This type of failure is far more common for what we are discussing here. Good design to reduce stress concentrations and good manufacture (including heat treatment) to avoid flaws (often microscopic) where cracks can start is important for improving fatigue strength.

Impact strength (also called resilience) is also complicated and not well understood. It is the ability for the components to dissipate/absorb the energy from suddenly applied (impact or shock) loads by converting it into strain energy in the components. In a suspension system, this is what the springs do - imagine the how long it would take to destroy you vehicle if you mounted the axles solidly without springs to absorb the impacts. Another example is the use of a snatch strap for vehicle recoveries vs a chain - on can absorb suddenly applied loads better than the other. Good design, of the half shafts in particularly, but also the cv's to a lesser extent can improve the impact strength. Material choice and heat treatment also has a great influence on impact strength. There are specific material testing standards for ascertaining material properties for impact (e.g. Charpy).

Now stock cv joints are designed for long wear life while subjected to the normal expected loads. The design only allow the balls to contact the hub and bell over very small area. The stresses at the impact points is known as Hertzian stress, and are are function of the curvature of the surface in contact. So stock c's use large diameter balls (to reduce Hertzian contact stress) and very hard material so as not to wear to rapidly due to the high contact stresses.

The hard material used in stock c's is good for wear but poor for shock loads and can suffer brittle fracture. The large diameter balls necessitates a reduction in the cross section of the hub and bell, hence reduces their strength.

After market cv's address the strength issues by using materials that are better for static and impact strength, but sacrifice some wear life. They often use smaller balls so the material can be added to other components, but sacrifice some wear life through higher Hertzian stresses. They often make other design changes to reduce stress concentrations, particularly when the wheel is at or near full lock and the balls are close to the edges of the hub and bell. So these factors, design, materials, manufacture can lead to one being superior to another.

A good half shaft designed to maximise the resilience can reduce the impact loads imposed on cv's, R&P, etc.

[mickeyw]

Well that was quite an in depth view of things, had to read it twice for it all to sink in.

Anyway, the static tests that have been done at least give a comparison against the standard product, in the same conditions.

Are you suggesting that the percentage difference in static strengths are not proportional to the fatigue or impact strength increases?

[zim]

Morning,

So it looks like i should run Ashcroft on the N/S and Kam on the O/S

Gordon

[jad]

also just to check, they are both 24 spline at the diff so is it possible to say use ashcroft shafts etc with a KAM diff?

cheers

Jad

[Hybrid_From_Hell]

Yes

or any other 24 spline Shaft

Nige

[Bush65]

...

Are you suggesting that the percentage difference in static strengths are not proportional to the fatigue or impact strength increases?

There is no rule of thumb or other easy way to relate static strength to either fatigue or impact strength.

Components can be designed to achieve best fatigue strength and resilience (ability to absorb impact loads). Also 2 different materials and heat treatments can have same tensile strength but different properties that affect impact loads.

Fatigue strength is very dependent on reducing stress concentrations at changes in section and flaws (particularly at the surface) where crack might start. None of those have much affect on static strength - in other words the static strength of one design can be the same as another and even use the same material, but have regions with terrible stress concentrations and surfaces that promote crack initiation.

During a static load the very high stresses that occur at regions of stress concentration, simply result in local yielding (which only affects a very small portion of material) and a re-distribution of the stress and load in the material. The behaviour is much different during cyclic/repetitive loading and load reversals over the life of the components and it gets very complicated to predict component life.

Design for better resilience is about maximising the volume of material at the same stress level relative to ultimate stress. Take 2 half shafts for example, one waisted and one not:

At the spline section of the shaft the effective cross sectional area is reduced and this limits the torque that will produce failure at that section - it is not possible to apply a higher torque than what that section can withstand. If the shaft is not waisted, most of the volume of material in the shaft will be at a lower stress level than at the spline section. If the shaft is waisted so the stress is maximum at all parts of the shaft at the same time when the maximum torque can still be withstood.

Now when torque lower than required to cause failure is applied to both half shafts the waisted shaft will twist more than the one that is not waisted - this is strain (stress is load divided by area (L/A), strain is elongation per unit length (e/l), modulus of elasticity is stress divided by strain).

Energy is force/load times distance. A fundamental law of physics is that energy can not be created or destroyed, it can only change form.

For our half shafts the kinetic energy from shock loads (for example a heavy spinning wheel in the air suddenly grabs traction) is is mostly absorbed by converting it to strain energy in the material of the half shaft - this is torque times twist. The waisted shaft is able to absorb more impact energy at the torque capacity of the spline section. A long side half shaft will absorb more impact energy than a short shaft because strain occurs in a greater volume of material.

If you look at the charts that Dave Ashcroft produced when he broke various half shafts in their test rig, you can compare the energy applied to each of the shafts by comparing the area bounded by the curve of torque vs angle and the horizontal axis of the graph. Clearly the area under the red curve is much greater than the others - see pic below.

My comments in this my other post are not aimed at any manufacturer, but pointing out that static strength is not the only property to be concerned with and is different to how these parts fail in the real world of a 4WD.

My personal preference is for absorbing shock over having a notch/fuse that breaks before the other stuff. But that is just my bent, and I can appreciate the advantage of the fuse for those who regularly break stuff and can't overcome the weaknesses.

[zim]

Well....i'm unsure as to which is stronger but i've gone for the Kam stuff. Got rear shafts, front shafts and cv's.

What i can comment on is the excellant service i got They managed to have the patience with me over the phone as i was measuring up my rear axle to find out what length shafts i needed etc - cheers steve.

Goods were ordered the Tuesday and delivered at 9am Wednesday morning Very well packed i must add.

So now i'm skint but hopefully won't break anything this weekend at slindon.

Cheers

Gordon

[will4x4]

good stuff

[missingsid]

Hi all,

I have some KAM shafts but still have not used them.

The question I have is this.

Something will break, don't care what you put in there will always be a weak link. What you do with different parts is move the weakness to a different place ( Diff > halfshaft > CV > stubshaft).

The thing is which suits you best? Break something cheap, something easy to change?

KAM's idea is to break something cheap and easy to fix. However what people want is to not break anything at all hence the dislike of the fuse-able link for racing, why make something weaker than it can be? Maybe what is needed is a set of different strength links for different uses so the customer can decide?

HfH/Steve is this a possible choice in the KAM product range?

Isn't a clutch system for this available but bulky?

Marc.

[Hybrid_From_Hell]

Hi all,

I have some KAM shafts but still have not used them.

The question I have is this.

Something will break, don't care what you put in there will always be a weak link.

What you do with different parts is move the weakness to a different place ( Diff > halfshaft > CV > stubshaft).

The thing is which suits you best? Break something cheap, something easy to change?

KAM's idea is to break something cheap and easy to fix. However what people want is to

not break anything at all hence the dislike of the fuse-able link for racing, why make

something weaker than it can be? Maybe what is needed is a set of different strength

links for different uses so the customer can decide?

HfH/Steve is this a possible choice in the KAM product range?

Isn't a clutch system for this available but bulky?

Marc.

Steve I agree, nothing is unbreakable inc my Propshafts now it seems (

Moving the weak point is 100% valid IMHO, but, oddly enough we already do a

selection of "Tuned fuses", so that we can ensure that whatever shafts, Diffs,

CVs etc you are running (and seriously here we are talking of quality components - ie

std Genuine, Maxidrive, ashcroft, quaffie etc and NOT tuning a Stub to suit a Britpart

CV etc) but for Zim as he had the strongest shafts, CVs and diff already he had

the "Highest" Setting for the fuse.

For our older Heavy duty shafts, we drop the breakpoint lower, as the shafts are

not as strong as the new AS Shafts, however, in the main people either buy at the

pont of sale NEW shafts from us with the CV kit OR most likley have already done

so, etc, we would then comment if the "Fuses" would need to be the lower break point then.

For what its worth, if the customers says when buying our CV kit with fuses that they

have ashcroft maxidrive or qulaffie units we suplly the highest strnegth versions.

Hope this helps

Nigs

[Off Road Toad]

If i may add to HFH's comment - the stub shafts we supply (in minimum undercut) are still quite alot stronger than a standard equivilent LR part.

Some people don't like our system, thats fine - i understand why, but it works for me, we didnt break a single stub shaft doing either the Trophy Cevenol or the Transilvania trophy.

We did break some other stuff though

Steve

[Maverik]

If i may add to HFH's comment - the stub shafts we supply (in minimum undercut) are still quite alot stronger than a standard equivilent LR part.

Some people don't like our system, thats fine - i understand why, but it works for me, we didnt break a single stub shaft doing either the Trophy Cevenol or the Transilvania trophy.

We did break some other stuff though

Steve

Holy monkeys, so when are you launching your new "heavy duty" prop shaft flanges then... ...

[Daan]

With regards to the fusable stubaxle and fatigue strangth: It would be much better to waist the stub shaft over the full length between the splines, rather than just the groove. This would give it much more flexibility in the shaft and would represent much less shockloads on the whole front drivetrain, while still being the weakest point.

Daan

[iomlt]

fit GKN shafts and CV's they work well for me (10 spline)

[Hybrid_From_Hell]

fit GKN shafts and CV's they work well for me (10 spline)

Yes these are / were VVVVVVV Good (if not a tad spendy)

but I didn't think these were still made ?

If so how much and who do / does them ??

Nige

[iomlt]

http://www.devon4x4.com/index.php?option=com_virtuemart&page=shop.browse&category_id=299&Itemid=14

they have the shafts. i got my cv's of Gwyn lewis.

[Hybrid_From_Hell]

£400 for a pair of 10 spline HD Shafts

"Kin Oooo n Ouch"

Nige

[iomlt]

cheaper in the long run if you have 10 spline already with funny ratio diffs. at least gkn give us the option of uprated 10 spline stuff.. unlike many other manufactures

[Bowie69]

Crown diffs do them too

And they aren't *that* much more than 24 spine versions from Ashcroft.