Figuring Unibody Max Load

The test that you would like to do is a simple torque test - of the whole car! It's called resistance to twisting.

You would have to solidly attach the front axles to solid fixtures, which are attached to the bed of the test table. The rear axles would also be attached to fixtures, but they would be attached to a beam which is attached to the bed with a rocker point, somewhat like a playground teeter-totter.

The tester would attach weights to the end of the beam holding the rear axle, and continue to do so until the beam began to deflect a certain amount.

After you did the welding, you could have it tested again, to see the numbers, to see the actual resistance to twisting which you have created.

Now, after the fact, you can get an estimate by using the following formula:

(Linear feet of welding wire applied / linear feet of welded surface) times

one of the following factors:

a.) 1.78722 for welds made with stainless steel, as the additional rigidity would continue to contribute to the overall integrity of the body structure over time;

or

b.) 1.48643 for welds made with carbon steel rods, as they will add only the equivalent of (mass x fusion) / the molecular disintegration of the original metal up until the time of welding; (Note: these welds will deteriorate over time at a rate of 2.4356% per month x hours of use per month squared.)

or

c.) .23475 (which means the integrity of the structure is approximately one-quarter of the original structure) if your welding was done at a temperature of 1835 degrees or higher, since that would temper the steel already present - which takes the necessary flexibility out of it. This means that the car could be incredibly stiff - right now - and crack apart violently in the future.

Tom

P.S. All of the above formulas apply only to welds meeting ASE standard 08-795 for automotive frame applications, which require that the welds have a ripple pattern regularity of 3/64ths of an inch per 3/8ths inch bead; or 4/48ths of an inch ripple pattern for welds of a 5/8ths inch bead; etc. See tech sheet PFT-759.97.53106 for the entire table.

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