shigley example 7-4
DESCRIPTION
solution manualTRANSCRIPT
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Machine Design: Shafts
Example 7-2
Oct 19th 2015
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1. Perform free body diagram analysis to get reaction forces at the bearings.
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2. Torque in the shaft between the gears
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3. Shear Moment Diagrams
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4. Total Moments
A G I J K B
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5. Real Work Begins!
A G I J K B
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Which dimensions?D4, D5, D6, D7
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Locate critical areas and start with them
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• Mm=Ta=o; Tm, Ma->
• Select Material: Sut, Se’->Se
• Assume a safe kb to find Se
• Use table 7-1 for the critical area selected:
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At ‘I’
• r/d = 0.1
• Kt = 1.7; Kts = 1.5
• Kf=Kt, Kfs=Kts
• Material: Sut-> Se
• Use DE Goodman criterion of eq. 7-8 for ‘d’
• Select a standard size below the value of ‘d’ found = dreal
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Why a standard size below the value of ‘d’ found:
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Next: Use dreal as ‘d’
• Find -> D (D/d=1.2 (Any value between 1.5-1.02) Fig A-15-7) ‘D’ (D4) & ‘d’ (D5) (Selected D/d)
• Find ‘r’ (d*0.1) -> now you have r/d, and D\d Kt,kts
• Kt (A-15-9), q(6-20)-> Kf,
• Kts(Table A-15-8), q(6-21)-> Kfs,
• find Kb using ‘d’ Se
• Goodman Criterion for ‘n’
• N yielding
• If n>1.5, the selected d is fine for that critical area (‘I’ in this case).
• Now check ‘n’ at other critical locations using that ‘d’.– If all the value of n for all the critical locations is greater than 1.5,
select that diameter ‘d’
– Else change the material with one having greater strength or increase the diameter and perform calculations again.
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• von Mises stresses for rotating round, solid shafts
• Goodman Criterion for ‘n’
• Or directly using:
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• N yielding
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Quick summary For ‘I’ :
• r/d = 0.1
• Kt = 1.7; Kts = 1.5
• Kf=Kt, Kfs=Kts
• Use DE Goodman criterion of eq. 7-8 for ‘d’
• Select a standard size below the value of ‘d’ found
• -> D (D/d=1.2 (Any value between 1.5-1.02) Fig A-15-7) ‘D’ (D4) & ‘d’ (D5) (Selected D/d)
• Find ‘r’ (d*0.1) -> now you have r/d, and D\d Kt,kts
• Kt (A-15-9), q(6-20)-> Kf, Kts(Table A-15-8), q(6-21)-> Kfs,
• find Kb using ‘d’ Se
• Goodman Criterion for ‘n’ and n yielding
• Check n at other locations using newly found and select a value of d with n>1.5 at all critical locations.
• In this way find all the required diameters.
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Kt
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q (Kt) bending
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Kts
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q (Kts) torsion
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