Why diamond shaped repair plates?

[etpm]

I have seen it mentioned here that diamond shaped plates should be used to repair cracked plates on tractors and I have seen diamond shaped plates welded onto structures. In fact, my backhoe was repaired with diamond shaped plates that were welded to the larger arm on my Case 580CK backhoe. These plates were welded in place to repair obvious damage to the backhoe. In fact, I have always wondered if the backhoe rolled down a hill or came off of a trailer while going down a freeway at 70MPH because of the damage to the loader arms and the backhoe arms. However, the only repairs that really seemed professional were the diamond shaped plates. These plates were obviously repairs. They were not part of the original structure.
Thanks,
Eric

 

[MAX-24-Dean]

My grandfathers blacksmithing and weld shop used to repair a lot of truck and trailer frames. The diamond shape was used to help reduce stress fractures that may have been caused by the heat when welded.

 

[MTGreen]

My understanding is you need to have weld beads in multiple axes for max strength for repairing a plate/flat surface. A diamond shape provides this and also generally keeps all weld beads at different angles than your part edges. Which further improves strength

 

[34Willys]

Also used for wood instrument repairing cracks. Best shape for distributing stress to an already stressed component.
I'm not an engineer, but I have repaired guitars with these.

Cleatus - Crack Repair System - Music City Bridge

Cleatus is a guitar repair system that allows you to perfectly install our CNC cleats end to end over a crack using a viewing film so you can see through the wood.

musiccitybridge.com

Patrick

 

[4570Man]

You don’t want to use a basic rectangle plate for repairs. It focuses the stress more and makes a future crack more likely. A circular or oval plate is the best.

 

[mrmikey]

As 4570Man said.
Think of it this way, if you had two pieces of 2 x 2 pine couple of feet long and grabbed each one in a vice from the end. One one scribe a line across it just up from the vice and then try to break both, which one will break first?

 

[DarkBlack]

generally keeps all weld beads at different angles than your part edges.

^ This

 

[etpm]

Thanks everyone for the quick replies. Of course, once I read the replies they made a ton of sense about distributing the stresses.
Eric