Step 1: Identify given parameters and relationships.
The given parameters are:
• Inner diameter of bronze sleeve (and outer diameter of steel shaft), di=ds=80mm=0.08m.
• Torque carried by bronze sleeve Tb=2Ts.
• Shear modulus of steel Gs=2.5Gb.
• Maximum allowable shear stress in steel τs,max=60MPa=60×106Pa.
• Maximum allowable shear stress in bronze τb,max=40MPa=40×106Pa.
• Rotation speed N=200r/min.
Step 2: Calculate the outside diameter of the sleeve (do).
For a compound shaft, the angle of twist per unit length (θ) is the same for both components:
GsJsTs=GbJbTb
Substitute the given relationships Tb=2Ts and Gs=2.5Gb:
2.5GbJsTs=GbJb2Ts
2.5Js1=Jb2
Jb=5Js
The polar moment of inertia for a solid shaft is J=32πd4. For a hollow shaft, J=32π(do4−di4).
For the steel shaft (solid): Js=32πds4.
For the bronze sleeve (hollow): Jb=32π(do4−di4).
Substitute these into Jb=5Js:
32π(do4−di4)=532πds4
do4−di4=5ds4
Since di=ds:
do4−ds4=5ds4
do4=6ds4
do=(6)1/4ds
Substitute ds=80mm:
do=(6)1/4×80mm≈1.56508×80mm
do≈125.206mm
The outside diameter of the sleeve is 125.21mm.
Step 3: Determine the limiting shear stress and calculate individual torques.
The shear stress in a shaft is given by τ=JTr. For the maximum stress, r is the outermost radius.
For the steel shaft: τs=JsTs(ds/2)=32πds4Ts(ds/2)=πds316Ts.
For the bronze sleeve: τb=JbTb(do/2)=32π(do4−di4)Tb(do/2)=π(do4−di4)16Tbdo.
From Step 2, we know Tb=2Ts, do=(6)1/4ds, and do4−di4=5ds4.
Let's find the ratio of the stresses:
τsτb=πds316Tsπ(do4−di4)16Tbdo=Ts(do4−di4)Tbdods3
Substitute the relationships:
τsτb=Ts(5ds4)(2Ts)((6)1/4ds)ds3=52(6)1/4
τsτb≈52×1.56508≈0.626032
So, τb≈0.626032τs.
Now, check which material limits the torque:
• If τs=τs,max=60MPa, then τb=0.626032×60MPa≈37.56MPa. This is less than τb,max=40MPa, so it is acceptable.
• If τb=τb,max=40MPa, then τs=0.62603240MPa≈63.89MPa. This is greater than τs,max=60MPa, so it is not acceptable.
Therefore, the maximum torque is limited by the steel shaft reaching its maximum allowable shear stress, τs=60MPa.
Calculate the torque carried by the steel shaft (Ts):
Ts=16πds3τs=16π(0.08m)3(60×106Pa)
Ts=16π×0.000512m3×60×106Pa=1920πN⋅m
Ts≈6031.858N⋅m
Calculate the torque carried by the bronze sleeve (Tb):
Tb=2Ts=2×1920πN⋅m=3840πN⋅m
Tb≈12063.716N⋅m
Step 4: Calculate the total torque that may be transmitted (Ttotal).
The total torque is the sum of the torques carried by each component:
Ttotal=Ts+Tb=1920πN⋅m+3840πN⋅m=5760πN⋅m
Ttotal≈18095.574N⋅m
The torque that may be transmitted is 18.10kN\cdotm.
Step 5: Calculate the power transmitted.
First, convert the rotation speed from r/min to rad/s:
N=200r/min=60200r/s=310r/s
The angular velocity ω is:
ω=2πN=2π×310rad/s=320πrad/s
ω≈20.94395rad/s
The power transmitted P is given by P=Ttotalω:
P=(5760πN⋅m)×(320πrad/s)
P=35760×20π2W=1920×20π2W=38400π2W
P≈38400×(3.14159)2W≈379800.36W
P≈379.80kW
The power transmitted is 379.80kW.
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