Thread: Off road equipment.

Ben I went to a lot of trouble to source my tubing and a competent fabricator - and I'm sure you are aware that there are a myriad of factors to consider when designing tubing that is not regulated to set sizes or thicknesses, not just the yield strength (or even the ultimate tensile strength, as aluminium and steel alloys have very different behaviours when approaching the plastic limits). I also know that you know I'd be aware ...........

I believe my stand-off bars to be the strongest you can fit to a D3/4 without compromising ground clearance. I don't believe I could accomplish the same in steel without delving into some very exotic alloys. As it is, the aluminium alloy I use is costly enough, and welding it is an art.

There are some benefits to using steel, but for my particular design the ally was a better choice.

Cheers,

Gordon

I think you will find that you would never be able to use 6mm thick steel sliders due to weight considerations. Gordon uses 6mm alloy for the aluminium sliders according to the GOE website.

Since the yield strength of the aluminium and steel are similar (only slightly lower for alloy) 6mm aluminium will have twice the bending capacity of 2 to 3mm steel bars of the same pipe diameter so they will certainly not deform plastically more easily than the steel bars. Aluminium bars are more flexible in the elastic range, however, due to the lower elastic modulus and this should allow them to absorb energy better without yielding and hence permanently deforming.

The argument that steel is stronger than the alloy bars is only valid if the thickness and pipe diameters are the same, which I don't think is the case. Gordon can perhaps elaborate on the sizes better than I can.

Originally Posted by gghaggis

Ben I went to a lot of trouble to source my tubing and a competent fabricator - and I'm sure you are aware that there are a myriad of factors to consider when designing tubing that is not regulated to set sizes or thicknesses, not just the yield strength (or even the ultimate tensile strength, as aluminium and steel alloys have very different behaviours when approaching the plastic limits). I also know that you know I'd be aware ...........

I believe my stand-off bars to be the strongest you can fit to a D3/4 without compromising ground clearance. I don't believe I could accomplish the same in steel without delving into some very exotic alloys. As it is, the aluminium alloy I use is costly enough, and welding it is an art.

There are some benefits to using steel, but for my particular design the ally was a better choice.

Cheers,

Gordon

Gordon,... no need to be defensive. I am sure your product is very good quality and entirely fit for purpose. I was simply correcting your posts about the properties of steel - and I thought that AULRO was about free and open discussions?

I note that you still haven't stated which aluminium alloy you use???

I also know that you know I'd be aware ...........

I thought your qualifications are in IT/modelling/neural networks, not engineering???

Originally Posted by BobD

I think you will find that you would never be able to use 6mm thick steel sliders due to weight considerations. Gordon uses 6mm alloy for the aluminium sliders according to the GOE website.

Since the yield strength of the aluminium and steel are similar (only slightly lower for alloy) 6mm aluminium will have twice the bending capacity of 2 to 3mm steel bars of the same pipe diameter so they will certainly not deform plastically more easily than the steel bars. Aluminium bars are more flexible in the elastic range, however, due to the lower elastic modulus and this should allow them to absorb energy better without yielding and hence permanently deforming.

The argument that steel is stronger than the alloy bars is only valid if the thickness and pipe diameters are the same, which I don't think is the case. Gordon can perhaps elaborate on the sizes better than I can.

240 MPa is about as good as it gets for alloy. After welding, the HAZ will be significantly lower than 240 MPa. To get the same weight as 6 mm alloy, you would have to go down to ~ 2.5 mm steel. I know from experience that 250 MPa 2.5 mm steel will bend in hard offroading. However 3 or 4 mm thick 250 MPa steel is fine IME. That would certainly be heavier than 6 mm Al though.

Alloy is hard to bend back into shape, when I bent these and had to bend them back so we could open the door, I broke them at the weld, where they had been re-welded a couple times before from looking at them, once by us when we first got them (as Gordon said they are second hand)

So I have gone to steel because they are a lot easier to repair, price isn't issue as they are being replaced through insurance, with steel I can repair them myself, I can't weld alloy and alloy can't be bashed or bent back into shape.

Baz.

Originally Posted by isuzurover

Gordon,... no need to be defensive. I am sure your product is very good quality and entirely fit for purpose. I was simply correcting your posts about the properties of steel - and I thought that AULRO was about free and open discussions?

I note that you still haven't stated which aluminium alloy you use???

I thought your qualifications are in IT/modelling/neural networks, not engineering???

Hmm - didn't mean to come over as defensive. Yes, I think the sliders we make are fit for purpose. And my point (perhaps poorly made) was that steel bar in this application would bend more easily. Not that alloy per se is less subject to bending. Due to the difference in density, one can achieve greater structural rigidity with the alloy I'm using (which I believe is around 300 MPa yield strength) than with steel. As an aside, one can source aluminium alloy with a YS around 600 MPa, so I don't know where you're getting the 240 MPa limit from? What specific alloy I use and where I get it from is something my supplier can comment on if he wishes.

My undergrad degree was in Engineering (albeit electronic). So I'm no Materials Engineer, but as I model mechanical deformation in mineral assemblages (amongst other things), I have a passing familiarity with the equations of stress-strain and how to use them. And I have no qualification in IT (although I have often performed as a software engineer, which is perhaps what's confusing you).

The stand-off bars are primarily designed to protect against lateral impact. That is why they extrude beyond the curve of the side panels. Otherwise they'd be shorter, like some of the other steel ones; however, I believe side panel damage is more likely (and more costly), so that's what they're designed to protect against. Like all genuine stand-off bars and side-steps, they are not supposed to withstand the weight of the car coming down onto an obstruction without some bending. Mine bend less than most, but at some point they will all bend - there are too many moments of freedom at the unsupported edge of the bar. Obviously drivers/spotters need to be aware of this and plan a path appropriately. Sometimes however, accidental damage will occur and in that instance steel repair is probably easier to arrange than that for alloy. In the newer design of these bars, I've made a greater allowance for bending of the bar prior to it fouling the door, so a much greater vertical impact on the tubing can be tolerated.

So my view is that the alloy sliders (as opposed to steel) are lighter, stronger but harder to repair.

Cheers,

Gordon

Prospeed in the UK have these new sliders:
Launch of new Rock and Tree Slider for Discovery

Interesting to see the holes cut in for High Lift jacks, I'd be dead scared to use these for their intended purpose with the possibility of the jack tipping and ending up in you door!

Video of testing:
Discovery Rock and Tree Slider Testing - YouTube

Could not find any word of construction materials though.

Originally Posted by ~Rich~

Prospeed in the UK have these new sliders:
Launch of new Rock and Tree Slider for Discovery

Very nicely engineered product. It does impact on the clearance under the sills though.

Cheers,

Gordon

Originally Posted by gghaggis

Very nicely engineered product. It does impact on the clearance under the sills though.

Cheers,

Gordon

Gordon,

Since the chassis and air tank is below the sills do you find that the sliders actually do much sliding or are they mostly protecting from side impact? My chassis has been gouged a couple times on hard gravel / rock but nowhere near the sills.