Looking to improve fatigue life of steel shaft with 1.75" diameter in fully reversed, cantilevered, bending. Current material is 1018 CF. Would using 4130 alloy for the shaft be a good solution for extending fatigue life or is this too brittle for fatigue bending?
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Material options to replace 1018 steel shaft in bending?
- Thread starter dlrn78
- Start date
Dlrn78:
Generally, you will do as much or more to improve fatigue life by paying particular attention to surface finish and its orientation, lowering the stress range by reducing bending moment/stress and shear stresses; although there is some correlation btwn. fatigue life and Fy and Fu. Also, pay particular attention to any stress raisers such key ways, press fits, changes in shaft shape (dia.), and size and shape of transition fillets, etc. to name a few. A sketch with loads and dimensions would help get you better answers, and if there is welding involved, on any shaft, it’s a whole new design problem.
Generally, you will do as much or more to improve fatigue life by paying particular attention to surface finish and its orientation, lowering the stress range by reducing bending moment/stress and shear stresses; although there is some correlation btwn. fatigue life and Fy and Fu. Also, pay particular attention to any stress raisers such key ways, press fits, changes in shaft shape (dia.), and size and shape of transition fillets, etc. to name a few. A sketch with loads and dimensions would help get you better answers, and if there is welding involved, on any shaft, it’s a whole new design problem.
As metengr says, not enough information.
Where is the fatigue initiating? If there is a section change or stress raiser, then reducing the stress concentration will give you the best improvement. If the cracks are initiating on a constant diameter surface, then improving surface finish and improving UTS and YS will both help. Without knowing the application, it is hard to tell which way to go.
rp
Where is the fatigue initiating? If there is a section change or stress raiser, then reducing the stress concentration will give you the best improvement. If the cracks are initiating on a constant diameter surface, then improving surface finish and improving UTS and YS will both help. Without knowing the application, it is hard to tell which way to go.
rp
dlrn78,
For full reverse bending fatigue, 4130 in any condition would do better than 1018. As others noted, your first step would be to remove/reduce stress concentrations, optimize the part shape to equalize stress distribution, and pay attention to surface finish requirements. Putting the stressed surfaces in pre-compression by shot peening or some similar mechanical process will greatly improve fatigue life.
Good luck.
Terry
For full reverse bending fatigue, 4130 in any condition would do better than 1018. As others noted, your first step would be to remove/reduce stress concentrations, optimize the part shape to equalize stress distribution, and pay attention to surface finish requirements. Putting the stressed surfaces in pre-compression by shot peening or some similar mechanical process will greatly improve fatigue life.
Good luck.
Terry
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