Rockslider FEA/Stress analysis

Hey guys, just some pretty pictures. Work is a engineering consultancy firm, which means I go through periods of being flat out when we win work, to periods of dead quiet when we lose some bids in a row.

In the quiet times I played around with designing some rocksliders for the Patrol (not building them as I found a place that make good ones at a good price - I don't know how to weld anyway).

Compared the difference between RHS and CHS for the main/inner slider, used a bunch of different thicknesses/grade and impact locations.

Seeing rockslider design guides on forums, I noticed so many of them talk about loads 'midspan' and stating RHS was better because of it's geometry to resist bending, but they never had any mention about bearing load effects and impacts at the forward or rear end of the slider, such as driving a wheel over a rock and dropping onto said rock once the wheel is past, which causes most of the load to only go through one mount. I believed this would be the worst case and set out to see what it took to design to this impact.

From memory it took an OD88.9 CHS about 6mm thick for no damage, of course that means the chassis is now at risk and you lose clearance and add weight, ended up settling on OD60.3 with 2.9mm thickness as a balance. A 75x50x4 RHS was at a similar level to the CHS, but again less clearance, more weight, because the load is not pure bending, the bearing and twisting effects were causing the corners of lower thickness RHS to be overloaded compared to the 2.9mm thick CHS which spread the load more evenly around its shape.

Here are a few pictures showing the results. Was done a while ago, looking back at it now, I realise the RHS should actually be a higher grade than the CHS, the results would still be the same values, but the RHS scale should go up to 450, not 350 MPa. Would mean a 75x50x3 would be similar to the OD60.3x2.9 CHS. Although it would still be less clearance and more weight.

One of the items that needed a fair bit of attention was the forward mount itself, initialy started off just as an L bracket, but required bracing, turned out very similar to what ARB do, guess there is a reason their stuff is expensive, it's properly engineered using FEA, which takes considerable time.

That's insane mate!!!! Suitably impressed!!!

Love to see the finished product.

Cheers. Scrapped the plans to actually try build them as I have never welded before, and found some custom fabricators that already build very similar designs (theirs would be accurate anyway as they have done it before).

Might eventually build a set for something to do when I have funds and my own shed, parents is fairly full as it is. But that's still a while off.

My other half is about to start making rock sliders for Amelia & Frank - will make sure he checks this thread out!! (he's a boilermaker)

Been doing a bit more research lately, most places use DN40 (outside 48.3mm) for the tube, again for clearance, weight and so the slider isn't too stiff to risk the chassis. Probably the better way to go. Slider will crush on any decent hits, but better that than the chassis.

hey they look good im in the middle of looking at what is around at the moment
be good to see finished product.

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Originally Posted by Outrage

Been doing a bit more research lately, most places use DN40 (outside 48.3mm) for the tube, again for clearance, weight and so the slider isn't too stiff to risk the chassis. Probably the better way to go. Slider will crush on any decent hits, but better that than the chassis.

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That's what I've always used for sliders. Doesn't crush or damage the chassis either.

Great to see it designed like this, What I've never see yet is a "ROCK SLIDER" in the true sense.
Most just have tube pipe, be it seamless whatever on a 45 degree angle, A mob years ago
called Davond actually made a rock slider about circa 1995. Rock slider as in "sill protector"
and isn't that what everyone is trying to achieve, minimum damage in rocky terrain. Never seen an
aftermarket one yet either. Oh well might have to fab one up, saw some great steel years back that they make
cattle yards/gates from about 100mm x 45mm bur round in a rectangle shape. Then again maybe no market for
them. Love that machine/programme BTW

What do you mean by a real rock slider John? Seen you say that a few times but never explained it.

Trying to use Motorculture

Basically as it sounds it more a sill saver, Winch challenge and Tuff truck use them as those steps would never be used as a "step".
fits the same as those angled pipe steps but you would remove the step part, leaving a pipe along your sill which you slide on. Don't think many would use that Driving style
and maybe better suited to Competition than weekend stuff. If your Patrol is not too high and you can get in ok without steps it may be worth looking at.
As an example check any 100s with OE side steps not that we care but I've never seen a straight one on any 100 that's been off road. Some use the slider as a water tank.
See if you can Google a Troopy called "BOGGER" from WA that had an awesome set of sliders/water tank.

That sounds to me like normal rock sliders that are very broadly commercially available.

Trying to use Motorculture

Nah never seen one yet . Mildweld might do one if asked I suppose

Quote:

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Originally Posted by threedogs

Basically as it sounds it more a sill saver, Winch challenge and Tuff truck use them as those steps would never be used as a "step".
fits the same as those angled pipe steps but you would remove the step part, leaving a pipe along your sill which you slide on. Don't think many would use that Driving style
and maybe better suited to Competition than weekend stuff. If your Patrol is not too high and you can get in ok without steps it may be worth looking at.
As an example check any 100s with OE side steps not that we care but I've never seen a straight one on any 100 that's been off road. Some use the slider as a water tank.
See if you can Google a Troopy called "BOGGER" from WA that had an awesome set of sliders/water tank.

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Arent all "rock sliders" Sill savers?? I know thats why i bought mine, didnt want to smash my sills.
My sliders are fairly similar to those in the original post, a steam pipe frame with a steel plate alone the bottom to allow it to actually 'slide'. I havent abused mine yet as they are only 3 weeks old, but my old house mate has the same ones and he has abused them and they 'slide' quite well, and dont smash your sills.