Yep, thanks.....but I did ask for that side of it to be left out. FWIW, I know of a vehicle built on a full custom chassis with portals that is fully engineered here in QLD. Not some mate of a mate back yard deal/job either....AND it then had to be registered at DOT. They went over it thoroughly and gave it plates rego and thumbs up. It even had RTA pull up to it once,look over under it and get on their computer....end result was all good and they drove off. Many would bet their lives the above vehicle not possible or legal, but IT IS.
It comes down to many variables. Ie what you are doing, who you are dealing with, who you are and who you know.
Oh and the luck on the day.....
Btt. What are my options to get it to transfer to the bottom inside corner like i have without welding across the flange...
One of the main issues with mounts on LR chassis concerns the thin chassis wall thickness of about 2.4mm.
There are large horizontal loads in the fore and aft direction of the vehicle due to the mass that has to be accelerated/decelerated (vehicle + payload), plus various resistances (wind, slope, obstructions, trailer, etc.). The traction loads are mostly transferred through compressive force in the rear TA's (trailing arms), with a lesser amount from tension in the front RA's (radius arms). Braking loads are mostly transferred through compressive force in the RA's with a much lesser amount through tension in the TA's.
The compressive force in the TA's acts along the long direction of the arm. This force is transferred into the mounts that must distribute/transfer it into a long length of thin chassis material. This length needs to be long enough so that the stress in the welds joining the mount to the thin chassis wall doesn't exceed the value allowed for fatigue of the weld or chassis wall.
It is important to not loose sight of the fact that for equilibrium to be satisfied (as it MUST be), the direction of the force in the TA's is the same as those forces transferred through the material of the mount and into the welds and the chassis.
For fatigue of the welded connections (mounts welded to the chassis), the allowable stress is highly dependent on the details/geometry. The Australian Standard for determining the fatigue strength of welded parts is merely a small sub-set of the British Standard, which is the best resource that I know of. Unfortunately I don't have my copies of either with me.
The worse case is when welds are made in the transverse direction of the force/stress the reduction in the allowable stress (compared to no weld in the parent material) is very great. From memory (I stand to be corrected) the allowable fatigue stress is in the order of 60 MPa in steel that has a yield strength of about 300 MPa and ultimate tensile strength of over 400 MPa. This is a gross simplification – the British standard runs to something like 100 pages.
The designers are allowed to weld across the chassis. Unlike many others making modifications, they can determine that the stresses are within the allowable limits for all possible load cases. Stress is load divided by area, so if the load cannot be reduced the stress can be reduced by increasing the area – this idea is like using a plate under a jack used on sand to reduce the pressure that the sand can withstand.
Regardless of fatigue or not (static load), because all fillet welds involve complex 3 dimensional stress, they have a greater load capacity when the direction of the weld is aligned (not transverse) with the load.
Getting back on topic now. The problem I see with the proposed mount, is that it is based upon the LR design for the body mount outrigger, modified to accept the TA. IMHO this outrigger design doesn't lend itself to adequately transferring the loads from the TA to the chassis. I believe it would be better to base it upon the design for the TA mount, suitably modified for the additional duty as a body mount outrigger.
I have cut-up rangie chassis and seen the various methods used to reinforce the chassis to accommodate concentrated local loads where they place mounts, also where the chassis kicks up/down. Sometimes it is designed for loads applied to the webs (bolts etc.), sometimes it is angles in the corners. I'm not aware of what reinforcement is inside a Defender chassis at the position of the outrigger, and if it is suitable for the additional force from a TA.
In the pic (below) of a TA mount, I have sketched arrows to show how the compressive force in the TA is distributed into the top and bottom flanges of the chassis rail. Note that these particular welds are longitudinal and their length (about 180 mm top flange and 150 mm bottom flange) is far more than that for a body outrigger. Also there is a lip pressed along the long diagonal free edge to stiffen it against buckling. These arrows would reverse direction when the TA's are in tension (braking or reversing direction of travel). There are other forces in the mount, but these are the major ones.
The loads on the body mount outrigger are mainly down at the point where the body weight is supported on the outrigger. On the pic below of a body outrigger I have sketched red arrows to show how the force is distributed to the top flange and web of the chassis rail. The pic doesn't show the bottom of the mount, where the force is directed to the bottom flange of the chassis rail (opposite direction to what occurs at the top flange).
From my sketched arrows you can visualise that with a combined mount there would be forces acting in 2 directions/dimensions. When loads/stresses involve more than 1 direction, we have to use a different failure theory to usual. For ductile materials (like we are concerned with here), and 2 dimensional stress, the failure theory used is called MSS (maximum shear stress theory) – for 3 dimensional stress we use Von-Mises Stress. Both failure theories can be used for 1 dimensional stress, but involve extra effort.
When material is loaded in tension, the principle tensile stress in in the direction of the applied load. As the material is stretched in that direction it gets thinner in the other dimension (it must for its volume to remain constant) – this creates the other principle stress (compressive in this example). Combining these 2 stresses gives shear stress on a plane at 45*.
For external loads loads in 2 dimensions, the induced shear stress is greater and this value is used to determine if the part will be safe.
Although the mount may be sound when subjected to TA, or body loads independently, when the loads act together, but in different directions, the situation becomes more complex and the stresses in the welds will increase.
Normally the failure will occur in the weld or parent metal (mount or chassis) close to the weld. It is not practical to make the welds larger (throat thickness) in this case because we cant easily change the chassis wall thickness. So the option is to make the welds longer in the required direction.
The TA mount in the pic below is on my 110 trayback. When LR built these they stretched the chassis and you can see at the corners of the chassis in front of the mount, how they reinforced the chassis with a pressed C section doubler over both top and bottom flanges. The doublers extend about 50mm beyond where the welds for the chassis extension/splice. The top doubler is about 80 x 20 mm and the bottom about 80 x 40 mm.
This reinforcement method would be very suitable for the location of a mount that was intended to carry both TA and body loads. Extend the 'C' at least 50 mm beyond the extents of the new mount. Saint-Venant's principle is used for good practice and it would dictate about 75 or 80 mm.
It is bad practice to weld at the corners of rolled sections such as C, SHS and RHS because there are residual stresses there from the forming process. It is worse when higher strength material is used. As it is reasonable/prudent to expect residual stresses in the corners of a chassis rail, so it can be considered bad practice to weld there. Toyota go to a great deal more trouble with their 79 series cruiser than LR to keep welds away from the corners of chassis rails.
I am basing my mount on the TA design more so.....or so I thought??? I should have written measurements on it. The top width is the same as TA mount, not the 75mm of the outrigger. The internal gusset is located in the same position as the long diagonal free edge of the TA mount from bush to top corner of chassis rail. But it is full width inside the new mount. I'm am yet to show my added internal piece that is the same as inside the OEM TA mount. Im also thinking to plate the complete bottom of mount with access holes, either dimple died or flanged like the bottom of the OEM RA mount. My mount will also have a couple more gussets in it same as outrigger mount...
I recall my old leaf sprung Austin Gipsey, where the chassis designer went to some detail to provide full perimeter welds in addition to avoid vertical welds when attaching crossmembers and outriggers to the main chassis rails. They simply turned rectangular section outriggers/members 45 degrees. Most of their chassis sections were semi oval with large radius corners. A well engineered vehicle I thought at the time, It was a sad day when it tried to clear my property of the biggest ugliest tree on the place.
Bill.
note the arrows are pointing to a fold. This is a additional plate, 4mm thick that is welded to the mount and chassis. The folds range in size from 10mm up. I was thinking of copying this???
Last edited by uninformed; 9th January 2017 at 07:09 PM.
TA end, showing locations of inturnal gussets. Ignore flap which arrow points to.
mock up of fold for bottom plating:
Top view. Thinking of dimple die holes??? Dotted line is where the internal gusset meets the top corner of chassis rail. It will NOT be welded to chassis, im thinking of a slot in the top of mount to weld to the gusset.
Internal 4mm plate same as LR have inside the TA mount:
Last edited by uninformed; 9th January 2017 at 07:09 PM.
Talk to whoever will be doing the pressing before you start to produce the profiles.
Find out what the minimum flange/lip width they can press with their VEE block. See dimension L3 on the pic below. The flat plate that you start with has to sit across the top of the VEE block and the minimum lip will be L3.
Find out the inside radius that will be pressed with their blade. Bluescope Steel (ex BHP) give the minimum allowable bend radius for the plate thickness. This radius is different if the bend is in the direction of plate rolling or across the rolling direction. You most likely won't know the rolling direction when you get your profiles, so need to know the worst case.
Because you want to press the profiles into 'C' section, with the shortest of the vertical leg lengths of about 180mm (stock body outrigger), if they only have a straight blade, the horizontal flange width will have to be greater than this. See the pic below, where dimension L2 must be greater than L1 so that the toe of leg L2 clears the press blade.
When the thickness is small relative to the width, only the part relatively close to a stiffener is effective for carrying load. Take standard structural section; the to increase the width of a flange outstand from the web (stiffener) they have to increase the flange thickness. Thin wall, cold rolled sections have lips on the flanges to form stiffeners, so the distance from a stiffener (lip or flange) is half of the flange width.
The same principle applies to gussets. Notice on the stock body outrigger the lip (stiffener) that is pressed along the lower, diagonal edge. Without this stiffener the outrigger would be unable to effectively transfer the moment load from the body to the bottom flange of the chassis rail.
I don't understand the need for the dimple die holes. Any weight saving may be less than than the weight of sand, mud and water that they will allow.
I think I know what you are saying regarding the pressing, that is using a V block and ram? I had not actually thought of that. I had just thought, for the main body/mount, that since it is just a "C" section, that it could be done on a press brake??
I will have to do some more research and speak to potential cutter/benders. PSimpson has had some stuff done locally.
"When the thickness is small relative to the width, only the part relatively close to a stiffener is effective for carrying load." Are you saying that loads will only be effectly carried where folds are or where the addition of material has been added to increase the thickness?
Take standard structural section; the to increase the width of a flange outstand from the web (stiffener) they have to increase the flange thickness. Thin wall, cold rolled sections have lips on the flanges to form stiffeners...... I can visualise a standard thin wall steel stud. They are "C" section but on the ends of the flanges have a small fold (say 2-3mm). Is this what you are calling a "lip on the flange to form a stiffener"?
"so the distance from a stiffener (lip or flange) is half of the flange width"
This part Im not undertanding, what are you referring to when you say "distance"? I see the gussets in the OEM body outrigger have flanges folded on them, no lip stiffeners and the flanges are only approx 10-12mm. I see the small section that is folded along the lower diagonal edge of OEM outrigger....but this is only about 75mm long starting at the chassis rail, which leaves a much larger portion flat, not folded???
I have added a pic of the bottom of the OEM front RA and outrigger area. I can see all the little lips, folds etc and have always took them as being there to "stiffen" those areas due to the thin material used. Note the yellow arrows point to the folds to stiffen the open areas/thin material. The red arrows are pointing to a indent, that has been pressed into the plate material, again I figured this is to stiffen a large thin area?
When I say I will plate in the underside of my new mount, I mean the whole thing. I was thinking of either dimple holes or larger, not uniformly round holes and then welding lip/stifferners to them.... I dont have the advantage that LR etc have of huge manufacturing facilities and building dies to press individual parts out....so back to basics. I would also "fix", that is weld somehow, the bottom plate to the internal gussets. I am open to ideas on this, as I figure welding anything adds some sort of stress?
I was also thinking of putting one dimple die hole in the first 2 gussets and maybe one in the large diagonal one...dependant on your advise. At some point im going to have to have a large enough hole to get socket and nut on the end of the TA, whether this be from the bottom or from the other vertical face of mount???
Why dimple dies? they look pretty .... but seriously I have a set (ill dig the sizes out today) I also thought that the more holes the better for the cleaning of mud etc, AND that they would be helping some of which that you have been describing, that is the large sections of thin material, helping by adding the fold in the dimple and stiffening it up.
I had also thought of welding another 3mm plate to the top of the mount, kind of like a large weld washer...because dependant on the design of the mount and its gussets and bottom plating, It may be a bugger to get to the nuts that hold the 2 body mounts. So at 6mm thick I thought I could tap it....plus again, as the top of the mount it now alot bigger than the OEM outrigger, I figured it was more prone to buckling due to the thin material.
maybe Ive looked at to many race trucks
You mention cold rolled steel. I was under the impression that standard plate etc was hot rolled? Should I be specifing Cold rolled??
Sorry im not very good at typing my thoughts out
Last edited by uninformed; 9th January 2017 at 07:09 PM.
John, I have not overlooked or dismissed your comments of the strengthening of the chassis rail itself, as in the pic you posted of your 120. I will come back to that. I would rather stay on point with the mount as we are atm.
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.... but seriously I have a set (ill dig the sizes out today) I also thought that the more holes the better for the cleaning of mud etc, AND that they would be helping some of which that you have been describing, that is the large sections of thin material, helping by adding the fold in the dimple and stiffening it up.
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