Homebuilt coilover system
03-23-2011, 02:54 PM
#111
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Thread Starter
Join Date: Jun 2005
Location: So. California
Posts: 2,258
Here's a write up by a friend who did the same mods on the lower arm.
http://budgetrestomod.weebly.com/roller-lcas.html
My setup is slightly different because I added 1/4" plate around the sleeve on the bottom side of the arm as well. I wasn't comfortable with just welding to the stock arm 1/8" thick material.
http://budgetrestomod.weebly.com/roller-lcas.html
My setup is slightly different because I added 1/4" plate around the sleeve on the bottom side of the arm as well. I wasn't comfortable with just welding to the stock arm 1/8" thick material.
03-23-2011, 03:16 PM
#113
Join Date: Apr 2009
Location: New Jersey
Posts: 26
If you use that heim, for added strength weld on another piece of steel above the heim to your lower shock mount. That way when you pass a bolt through the exiting clevis mount & then the heim, there will be a second piece of steel above the heim for the bolt to pass through. This adds strength to the mount and makes it less prone to bending. I have a great example pic of double sheer but I can't seem to attach anything from my hard drive....
03-23-2011, 03:31 PM
#114
Join Date: Apr 2009
Location: New Jersey
Posts: 26
Look at the image in post #47
http://www.jalopyjournal.com/forum/s....php?p=5809334
That's double sheer.
http://www.jalopyjournal.com/forum/s....php?p=5809334
That's double sheer.
03-24-2011, 11:16 AM
#115
Join Date: Nov 2005
Posts: 48
Double sheer is mostly beneficial for bolt strength. Bolt shear strength typically doubles when in double shear compared to single shear (I'm a structural engineer). For example a high strength 5/8" bolt has a shear strength of 11000 pounds in single shear, whereas that same bolt has 22100 pounds of shear strength in double shear.
03-24-2011, 01:01 PM
#116
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Join Date: Feb 2007
Location: state of confusion
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I beg to differ a bit . . .
Statically applied shear loading is one thing.
But local moments and stresses develop in and around single shear connections even from purely axial rod loading, as a consequence of the load path no longer being straight. And because it isn't straight, stress concentration effects also exist which may or may not leave the local stresses within the material endurance limit. If, in fact, the material has an endurance limit (not all do).
Since most automotive suspension fasteners (and the things that they fasten together) are subject to reversed cyclic loading you get to consider fatigue (at roughly an inverse 5th power relationship to local stress once your stresses rise above the material endurance limit).
Most times, it's just easier to avoid single shear. When it's not possible to do so, you overbuild.
You might want to indicate whether that 11,000 lbs is with or without threads in the shear plane, as IIRC that makes a difference too.
Norm
Statically applied shear loading is one thing.
But local moments and stresses develop in and around single shear connections even from purely axial rod loading, as a consequence of the load path no longer being straight. And because it isn't straight, stress concentration effects also exist which may or may not leave the local stresses within the material endurance limit. If, in fact, the material has an endurance limit (not all do).
Since most automotive suspension fasteners (and the things that they fasten together) are subject to reversed cyclic loading you get to consider fatigue (at roughly an inverse 5th power relationship to local stress once your stresses rise above the material endurance limit).
Most times, it's just easier to avoid single shear. When it's not possible to do so, you overbuild.
You might want to indicate whether that 11,000 lbs is with or without threads in the shear plane, as IIRC that makes a difference too.
Norm
Last edited by Norm Peterson; 03-24-2011 at 01:03 PM.
03-24-2011, 01:07 PM
#117
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Thread Starter
Join Date: Jun 2005
Location: So. California
Posts: 2,258
I beg to differ a bit . . .
Statically applied shear loading is one thing.
But local moments and stresses develop in and around single shear connections even from purely axial rod loading, as a consequence of the load path no longer being straight. And because it isn't straight, stress concentration effects also exist which may or may not leave the local stresses within the material endurance limit. If, in fact, the material has an endurance limit (not all do).
Since most automotive suspension fasteners (and the things that they fasten together) are subject to reversed cyclic loading you get to consider fatigue (at roughly an inverse 5th power relationship to local stress once your stresses rise above the material endurance limit).
Most times, it's just easier to avoid single shear. When it's not possible to do so, you overbuild.
You might want to indicate whether that 11,000 lbs is with or without threads in the shear plane, as IIRC that makes a difference too.
Norm
Statically applied shear loading is one thing.
But local moments and stresses develop in and around single shear connections even from purely axial rod loading, as a consequence of the load path no longer being straight. And because it isn't straight, stress concentration effects also exist which may or may not leave the local stresses within the material endurance limit. If, in fact, the material has an endurance limit (not all do).
Since most automotive suspension fasteners (and the things that they fasten together) are subject to reversed cyclic loading you get to consider fatigue (at roughly an inverse 5th power relationship to local stress once your stresses rise above the material endurance limit).
Most times, it's just easier to avoid single shear. When it's not possible to do so, you overbuild.
You might want to indicate whether that 11,000 lbs is with or without threads in the shear plane, as IIRC that makes a difference too.
Norm
03-24-2011, 02:05 PM
#118
Join Date: Nov 2005
Posts: 48
That is with threads included and my intent was to keep it simple without adding extra fluff to confuse people. With threads excluded you get a few extra thousand (kips) pounds of shear strength. Double shear also helps with bolt bearing strength on the plates, as the pressure from the bolt is applied over both plates (assuming the single shear plate is smaller than the combined top/bottom plate thicknesses in double shear). I agree with you that when moments are introduced at the connection then other criteria must be considered, such as fatigue, bending strength, prying action, among many others. Unfortunately I don't do much in suspension component design, otherwise I would be able to help more in determining if that clevis is sufficient. I have not clue what forces/moments act at the strut rod-to-LCA connection, but if you have a better idea Norm I'm all ears.
03-24-2011, 02:13 PM
#119
Join Date: Nov 2005
Posts: 48
Basically, if you have a post sticking up from the ground that is leaning and you apply a load down the center of the post, that post will still want to bend at the ground (or tip over). While the load may be at the center of the end of the post, extending that same line down to the ground is no longer at the center of the post.
To put it into perspective of your strut rod, the rod is not perfectly level to the ground (most likely). When you hit a pot hole, the same bending will want to occur at that connection point to the LCA since the direction of the force will not occur directly down the centerline of the rod at each end. Correct me if I'm wrong Norm, its been a long week at work for me!
To put it into perspective of your strut rod, the rod is not perfectly level to the ground (most likely). When you hit a pot hole, the same bending will want to occur at that connection point to the LCA since the direction of the force will not occur directly down the centerline of the rod at each end. Correct me if I'm wrong Norm, its been a long week at work for me!
03-24-2011, 04:05 PM
#120
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Join Date: Feb 2007
Location: state of confusion
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The local effects don't particularly depend on the inclination of the strut rod from the horizontal, although that may affect the magnitude of the axial load itself. You get bending equal to force "F" times the offset distance between their lines of action.
Let me try a sketch.
The black lines are as you assemble the joint and it is under no load.
The red lines are how it wants to be under a nominally axial load (the axial load really wants to be in a straight line with itself, or zero "offset").
What you end up with is something in between the black and the red outlines.
The devil is in the details, so the moments and the deformed shapes are only indicated (crudely). If you've got a thick piece bolted to a thin piece, the thin piece will bend far more than the thick piece will.
If the joint were to open up, the pin (bolt) can also come in for a bending stress term.
This is probably why the OE strut rods have two bolts each, in order to minimize the local effects of those single shear connections.
Norm
Let me try a sketch.
The black lines are as you assemble the joint and it is under no load.
The red lines are how it wants to be under a nominally axial load (the axial load really wants to be in a straight line with itself, or zero "offset").
What you end up with is something in between the black and the red outlines.
The devil is in the details, so the moments and the deformed shapes are only indicated (crudely). If you've got a thick piece bolted to a thin piece, the thin piece will bend far more than the thick piece will.
If the joint were to open up, the pin (bolt) can also come in for a bending stress term.
This is probably why the OE strut rods have two bolts each, in order to minimize the local effects of those single shear connections.
Norm
Last edited by Norm Peterson; 03-24-2011 at 04:07 PM.