Fatigue failure of BS 970 : 817M40T
Fatigue failure of BS 970 : 817M40T
(OP)
Does anyone have any data on allowable stress for 817M40T ?
I have an application which requires a 6" Circular Pitch spur pinion to be overhung from it's last supporting bearing to engage with a large Ring Gear (approx 28 ft pitch diameter). The pinion and it's shaft are machined from a single shape specific forging 1732 mm long. The pinion has a face width of 500 mm. The shaft is supported vertically (pinion at the bottom) on two spherical roller bearings nominally 400 mm bore and on 600 mm centres. I have experienced failure of the shaft between the two bearings from fatigue, propagating from an undercut used to locate a split collar which supports the weight of the shaft & pinion on the inner race of the lower bearing. Fatigue is from stress reversal due to separating forces of Pinion and Ring Gear.
I have an application which requires a 6" Circular Pitch spur pinion to be overhung from it's last supporting bearing to engage with a large Ring Gear (approx 28 ft pitch diameter). The pinion and it's shaft are machined from a single shape specific forging 1732 mm long. The pinion has a face width of 500 mm. The shaft is supported vertically (pinion at the bottom) on two spherical roller bearings nominally 400 mm bore and on 600 mm centres. I have experienced failure of the shaft between the two bearings from fatigue, propagating from an undercut used to locate a split collar which supports the weight of the shaft & pinion on the inner race of the lower bearing. Fatigue is from stress reversal due to separating forces of Pinion and Ring Gear.





RE: Fatigue failure of BS 970 : 817M40T
http://www.welding-advisers.com/
RE: Fatigue failure of BS 970 : 817M40T
RE: Fatigue failure of BS 970 : 817M40T
If AISI 4340 is nearly identical to your material as mentioned then ESDU definitely include data for this material in data item 'ENDURANCE OF HIGH STRENGTH STEELS (IN BENDING)'.
This might be a bit too expensive for a 'one off', although the other references might be of some use.
RE: Fatigue failure of BS 970 : 817M40T
Such data may probably be available from your steel supplier.
If you can determine from past failures that they are not Low Cycle Fatigue driven, that is if it takes quite some time from crack initiation to failure, it may be advantageous to schedule non destructive testing to catch the initial crack before it is too late. Advance alert would allow to plan for spare part purchase and substitution at convenient time.
Suitable local NDT could be Flurorescent Magnetic Particles Inspection or Ultrasonic inspection, possibly without dismantling the part from the assembly if accessible.
http://www.welding-advisers.com/