Factory Defect or Bear and Tear?

[Wildergarten]

I was welding up the frame reinforcements today when what do you know just as I was finishing up I noticed these cracks under the arch over the rear axle only on the driver's side. The interesting thing is that these cracks don't carry to the spring hangars nor to the two brackets meant to support the factory overload springs, I am almost certain for a heavy camper.

When I bought it, both rear springs had been replaced, as had the front hangars. The frame was a tad sway backed, but otherwise straight and parallel with tight rivets, not nearly as damaged as my old '69 truck. So I'm asking if anybody has seen these before, what these cracks might portend, and what I might do about them if anything.

Given that this is meant to be a 4X4 dump truck, dragging logs, carrying gravel and dirt etc., it's not like I can afford a wimpy frame, which is obviously why I just replicated the factory stiffeners along the straight parts of the frame. I can grind them out, weld it up, and then anneal it to relieve the weld stresses, but I don't have a clue as to what that would do because I don't know that much about the parent material. Thoughts?

[PwrWgnDrvr]

Looks to me more like surface spalling when the radius was rolled. Is it really a crack that goes all the way through? Do you see it on the inside surface?
Seems like a simple grind and weld fix. If it ever fails, at least you won't be far from home.
Oh, have never seen that on a frame before and I've cut up dozens.

[Wildergarten]

Looks to me more like surface spalling when the radius was rolled. Is it really a crack that goes all the way through? Do you see it on the inside surface?

No.

Seems like a simple grind and weld fix. If it ever fails, at least you won't be far from home.
Oh, have never seen that on a frame before and I've cut up dozens.

That helps.

I think I may have a reinforcement plan. I have spare frames from which I can cut a doubler like a curved piece of angle and heat form it to fit. Cut a scalloped top edge to keep the fillet welds in the web from forming a line and possibly add a few fillet holes under them for oversized plug welds. Welding fillets at the edge of the flange is a no-brainer. Prime, seal with Sikaflex, and paint. The good news is that I can cut a pair out now and just keep them until I make a decision. I suspect I can even add them after the truck is done.

I'll cut out a pair from the '69 tomorrow and post a photo.

[Wildergarten]

OK so... definitely it is a factory defect. The inside radius of the bend where it was rolled is sharper where the surface breaks are worse. There are similar surface breaks along other parts of the driver's side of the frame, especially at the front shackle. I don't know how it made it to the riveting process. Yet these are not cracks per se, but breaks in a surface 'lamination.' They don't go deep but they do represent a loss of strength. The research papers I could find indicate that this type of surface failure occurs when the direction in which the sheet is rolled in the mill is the same as the axis of the fold. Here is one such description on the importance of grain direction when folding: https://es3.co.nz/2019/07/04/the-import ... n-folding/

The good news is that it held up for 50 years. The bad news is that it is defective and not as strong as I may need when hauling dirt. Don't know what I'm going to do. I've got a lot of time into this one.

[PwrWgnDrvr]

Well, the defect is at the top of the web, so the vertical strength of the frame should pretty much be optimal. The flange resists twisting off of vertical and lateral force damage, so it would seem a simple weld along that fold line would solve the problem and have minimal effect on the vertical strength of the web. We already know that welding all along the bottom of the frame does not weaken it, (which you just did) so what's there to worry about?
I've seen plenty of metal exhibit that same effect when heating and bending heavy stuff, especially if the bend is too sharp. Not surprising to see that, but surprising that it wasn't rejected.

[Wildergarten]

Well, the defect is at the top of the web,

No, the frame is currently upside down. The cracks are on the bottom. The loads are funny in that arch. Most of it is between the two ends from the leaf spring pulling inward on spring compression and pushing outward on relaxation. The other loads are bending moments from the frame outside the spring. When I dump a load, the bulk of the weight will be on that tail section making a fulcrum out of that back spring shackle. That puts the cracked section in compression. Because the shackle brackets are on the outside of the frame, it will pull that bottom flange outward against the web. The surface having the cracks would then be in tension. You are also forgetting the impact of the rubber bump stop, which tries to lift the flange, again stretching the metal at the cracks. Not good.

I cut one of the two "doublers" out this morning (photo). With the bed elevated as it is now, it is behaving exactly as described. The only serious complication I see is the foreward bracket taking the load from the overload spring.

so the vertical strength of the frame should pretty much be optimal.

Not so. The web is there to transfer buckling forces to the flange, which is wider there than elsewhere on the span. Without the flanges, the web would buckle in or out under load.

The flange resists twisting off of vertical and lateral force damage, so it would seem a simple weld along that fold line would solve the problem and have minimal effect on the vertical strength of the web.

Unless the weld shrinkage creates a stress concentration that propagates as a crack.

We already know that welding all along the bottom of the frame does not weaken it, (which you just did) so what's there to worry about?

It doesn't weaken it because it is connected to additional shear and moment support in the stiffener. If one just put welds along the bottom of the frame with no additional structure, it would be weaker.

I've seen plenty of metal exhibit that same effect when heating and bending heavy stuff, especially if the bend is too sharp. Not surprising to see that, but surprising that it wasn't rejected.

Me too.

4:30PM, Both doublers are out, rivets pulled, wire wheeled, and are ready to forge a new relationship with the other frame.

[Wildergarten]

Decision made. This frame went through a set of springs with these defects without indication of further damage. I have produced means to repair it after the truck is built and running should the need arise. Although welding the doublers in is easier with the frame upside down as it is now, it's not such a big deal that I plan to change the plan.

Moving forward with completing the bumper.