shaft design mu
TRANSCRIPT
ShaftDesigner is developed for SKF Solution
Factory - Marine Services
Ken YoussefiMAE dept., SJSU 5
It has been recognized that a metal subjected
to a repetitive or fluctuating stress will fail at
a stress much lower than that required to
cause failure on a single application of load.
Failures occurring under conditions of
dynamic loading are called fatigue failures.
Fatigue failure is characterized by three stages
Crack Initiation
Crack Propagation
Final Fracture
Crack initiation site
Fracture zone
Propagation zone, striation
Motor
Load
Typical testing apparatus, pure bending
Ken YoussefiMAE dept., SJSU
7
a =max min
2
Alternating stress
Mean stress
m=max min
2
+
Ken YoussefiMAE dept., SJSU 8
Finite
life
Infinite life
N < 103 N > 103
S′e
= endurance limit of the specimenSe
′Fatigue design equation
nfSe
1=
Sut
′a ′m+ Infinite life
Finding the DIAMETER of the shaft.
Using Fatigue approach.(not static)
We need to know- Maximum Bending
Moment, Maximum Torque-
If Directly Given than no need to find.
Design for Critical Section.
PSG 7.6- Formulas for fatigue
PSG 1.42,Formula for endurance limit
PSG 7.8, Kf,Ks
PSG 1.9, Carbon Steel
PSG 7.20, R20 Series
Medium carbon steel-
C40,C45 etc
Low notch sensitivity
Respond to heat treatment
Easy to Machine
Low cost.
High strength
PSG 1.9, C45
σut = 670 N/mm2 σyt = 340 N/mm2
PSG 7.6
a =max min
2
Alternating stress
Mean stress
m=max min
2
+
????????
PSG 7.6
Ksf- Surface Finish Factor
Assuming Polished ground Surface(always
assume if not given) PSG 7.17
For σut=670 N/mm2 Ksf=0.91
Kr- Relibility Factor= 0.997 for 90% relibility,
Conservative approach, VB Bhandari
PSG 7.17
Ks- Reduction Factor- 0.75 Assuming Maximum
reduction(For corrosion)… VB Bhandari
Kf: Stress concentration factor
Annealed Profile Keyway for bending, Kf= 1.6…… PSG 7.8
Sled runner- End of shaft, Flat key
Profile- Middle of shaft, Tapered key
PSG 7.8
PSG 7.8
Questions?