Agreed with all above, was just curious since I haven't seen any failures myself
Having grown up on a farm and regularly seeing farm trucks heavily overloaded and not being used for their intended purpose, I have seen a number of frames crack. Most are related to the hydraulic dump boxes and attachments to the frames that then propagated to the rest of the frame. So, I saw the frame get repaired, then break again at a later date.
I was fascinated by how the cracks would form and where they went, so it made me aware of how the forces were pushed through the frame, even though I didn't understand them at the time.
I had heard all the parts about "the steel will crack next to a good weld" and all those things. I now know that the steel next to the weld is the HAZ and has a different molecular structure to the weld itself as well as the surrounding base metal. The molecular structure can be readjusted with heat control and pre-heating / post-heating to control heating and cooling when proper repairs are done.
Most repairs are NOT done in proper circumstances or procedures, because most people don't know what those should be. I've been dealing with welding for 35+ years professionally and there is still a ton that I don't know. I am NOT a CWI, but I do a lot of weld inspection for our company. We rarely have critical power-plant or oil rig type weld requirements, but they all fall within the AWS window of requirements.
My brother is was a shop superintendent for a trucking company for 13 years and had moved on to be a truck and diesel instructor for another 25. He has sent me pics of frame damages and repairs over the years and all of these repairs had to be done by certified welders following proper procedures so the trucks could be re-certified by the DOT of that state in order to be put back on the road. Some states have no regulations.
Most of the current truck frames are specialized materials and have stickers on them that say "Do Not Weld" on them. I would suspect that the 80 series (and newer) LC's also have frames made of materials other than A-36 carbon steel, based on how rigid they are and the flex they can take before failure.
All of the repairs I had seen were the Z-cut at a 45° with football-shaped fish plates.
I still find this all very interesting and I get the pleasure of dealing with failed welds from job sites and analyzing what the root cause could have been and how we can prevent them in the future.
I thought this was one of the better snippets of questions about truck frame welding.
AWS Truck Frame Welding Q's
