Broken bolt.

[1930fordpickup]

I wonder how this happened. Snapped right off below the head. I found this out back at my step mothers house and cleaned it up some at work. I got as close as I could for the picture. 

[1930fordpickup]

No one is biting on this one. So I will show the real size. This is  1/4-20 ×2.00 inches long sitting on the bolt head. Yes that is the head of a 2 inch Socket head cap screw. 

[1930fordpickup]

[slusher]

 Did it have a crack were air and water gets in the bolt…

[Ace-Garageguy]

Big honkin' bolt.

Looks to me like classic metal fatigue that probably started at a flaw at the junction of the bolt head and the shank.

Google's AI actually gets this right:   

Fatigue is a process of progressive material damage caused by repeated cyclical stresses, even at stress levels well below the material's yield strength. When a bolt experiences repeated loads, a crack can initiate at a point of weakness, such as a flaw at the head-shank junction. The crack then propagates incrementally with each load cycle until the remaining cross-sectional area of the bolt can no longer support the applied load, leading to fracture. 

In essence, the combination of stress concentration at the head-shank junction and the potential presence of flaws makes this area a likely starting point for fatigue cracks that can eventually lead to bolt failure. 

 

A similar failure that illustrates crack propagation:

Edited July 1 by Ace-Garageguy

[1930fordpickup]

4 hours ago, slusher said:

 Did it have a crack were air and water gets in the bolt…

I dont think there was a crack to start this with water. 

I believe what Bill posted was what happened. The only thing different (before I turned the back smooth) was that it looked like it snapped all at once. There was no noticeable smooth area that picture above called Fatigue propagation. 

 This came from a plant called Doeler Jarvis in Toledo. They poured white metal castings. They did a lot of stamping also. My Step moms first husband worked there. 

[johnyrotten]

That probably came from one of the stamping presses. Or a die. We've got a 10ft, 60 ton brake at work that will pop heads off bolts if you push it to bend something it doesn't want to. My boss found that out hard way. Impressive if that let go all at one time, with the size of those machines I'm not surprised. 

[Muncie]

I'll go with Bill with an extra dose of over or under torque, might also add failure to check torque as part of regular maintenance.

That's a big bolt.