Dipper snapped

[John T]

Looks like those notches were caused by the thumb mounting bolt ? If so, the 'patch plate' could have been longer ,past the notches.

yeah I wasn't sure which side that was....

 

[McMXi]

Steel is strong in tension… not so much in compression.

 

[selftot]

Looks like those notches were caused by the thumb mounting bolt ? If so, the 'patch plate' could have been longer ,past the notches.

Yes - I removed some material there thinking a notch would help prevent any sliding of the thumb. But the thumb bolts have compressed the metal ridges there as well.

 

[Russell King]

Steel is strong in tension… not so much in compression.

That is an incorrect statement. Steel is as strong in all directions under tension or compression.

Shear strength is different than tensile strength.

Steel members can buckle under compression if they are too long and “thin”. That same shape can hold more in tension than compression.

Is that what you are trying to state?

 

[Henro]

That is an incorrect statement. Steel is as strong in all directions under tension or compression.

Shear strength is different than tensile strength.

Steel members can buckle under compression if they are too long and “thin”. That same shape can hold more in tension than compression.

Is that what you are trying to state?

I think GeoHorn may confused steel with concrete...

 

[McMXi]

I think GeoHorn may confused steel with concrete...

Then he's doubly confused since concrete is strong in compression but not in tension.

In general steel is an isotropic material.

 

[JohnDB]

Steel in static applications: roughly as strong in tension or compression.
Dynamic applications - whole different story, wide range of factors at play. Shape, temperature, alloy, production process, load frequency and load variation...

 

[GeoHorn]

Lot’s of (incorrect) conjecture about what I meant.

Concrete is great under compression….lousy in tension. Steel will withstand tension better then compression.…. (within certain boundaries as regards shape and duty-cycle, as Russell points out.)
The excavator arm is a hollow, sq-sided tube. It would be strengthened if reinforcing plates were added where tension is experienced… Not so much where compression occurs.

My intent was to suggest that the reinforcing/repair plates along the side of the arm are good…but that addt’l plates on the other surfaces would add strength to that weakened area.