What caused this to fail
What caused this to fail
(OP)
Would anyone want to list their best guess as to why this shaft failed?
Shear, tension or compression? Was it a cyclic load or an abrupt failure?
What can you tell from just this picture?
Thanks
Shear, tension or compression? Was it a cyclic load or an abrupt failure?
What can you tell from just this picture?
Thanks





RE: What caused this to fail
RE: What caused this to fail
GUESS: Based on the different colors I would guess first that it is too much overhung load on the shaft. This causes excessive bending loads at the flange. Cyclic loading during rotation kill fatigue life. Probably a stress riser of some sort initiated a small crack which propagated, then catastophic torsional shear failure across the remaining diameter of the shaft.
It's just a guess based on my experience of the most common failure mode of shafts. Need bigger picture.
TygerDawg
Blue Technik LLC
Advanced Robotics & Automation Engineering
www.bluetechnik.com
RE: What caused this to fail
Can you take a close-up of the fracture surface?
RE: What caused this to fail
Thanks
RE: What caused this to fail
RE: What caused this to fail
This shaft is the working end of a punch ram where the tooling is connected. Under "normal" conditions, the shaft would only see axial compression loading.
RE: What caused this to fail
RE: What caused this to fail
That is a weird one. It has the appearance of a rotary bending fatigue failure--does the part rotate? The off center nature of the center, final separation is one clue; the eccentric shaped propagation of the outer periphery is another clue that suggests rotary bending fatigue as the fracture mode. There is insufficient definition in the photo to identify an origin, other than to say that it was in the thread root. Multiple fatigue origins are common with these types of failures.
The apparent step at the 6 o'clock postion suggests the fatigue started in more than one thread.
RE: What caused this to fail
RE: What caused this to fail
The appearance and size of the final fracture area (off center) suggests high stress concentration in this location of the shaft.
RE: What caused this to fail
http://www.tribology-abc.com/default.htm
RE: What caused this to fail
http://www.fatiguecalculator.com/
http://www.roymech.co.uk/
RE: What caused this to fail
Here is another picture that I made. You can see the beach marks on each side (pear shaped pattern around the center). The spacing of the beach marks indicate that it didn't withstand the loading but a few times before it failed completely.
It was intersting to see what everyones thoughts were about the failure.
Thanks.
RE: What caused this to fail
RE: What caused this to fail
RE: What caused this to fail
200ksi bolts tend to be very brittle. if you need 130 ksi (presumably with all your safety factors included, why not 160-180 ksi ?
you say that the part failed in "compression fatigue" ... ?? maybe, since the bolt was under strength to failed in simple tension, what sort of preload do you apply (a lot I'm guessing) ? maybe this caused the bolt to yield during installation, then the operating loads caused the bolt to fail in tension fatigue ??
RE: What caused this to fail
This part is made from tool steel, heat treated and then drawn down to 50 to 55 Rc.
RE: What caused this to fail
not quite sure about the build-up ... is the thread used to guide/control the position of various pieces of the tool ? otherwise, if the thread is used to join two pieces together isn't there going to be a torque (and so a preload?)
RE: What caused this to fail
This may be of intrest. Do a search on Punch Head Failure
RE: What caused this to fail
RE: What caused this to fail
One of the better pictures of the business end.
http:
From the info. and photos karthur sent I think the failure mechanism is the same as in die heads.
RE: What caused this to fail
There is a narrow stripe worn in the green flange face. It appears to only go part way 'round the threaded hole, like there was a small flange on the punch tool. By small I mean a little larger than the thread major diameter.
RE: What caused this to fail
http://www.epi-eng.com/RW-ShaftFatigue.htm
RE: What caused this to fail