Design of a shaft subject to torsion/bending/fatigue

In summary, the individual is seeking help with a design task and has already created a Free body diagram (FBD) and calculated the unknown torque force. They have also drawn shear force, bending moment, and torque diagrams. However, they are now unsure of how to proceed and need guidance on how to use the relevant equivalent bending moment and torque diagrams to calculate a suitable diameter for the shaft. They also have questions about determining the Mmax value and which T force to use.
  • #1
danz001
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I have attached the design task I have been given and I am unsure as to what to do next! I will explain that which I have done so far and if anyone can point me in the appropriate direction that would be greatly appreciated!
1. I have created a Free body diagram (FBD), and drawn in the unknown two reaction forces at bearings and the torques where known.
2. For the unknown torque force 'F' I have assumed there is no net torque for the system, and stating my positive Z direction and using T=(f2-f1)xr, have deduced that F=1.1KN
3.I have then gone back to my FBD and drawn in the newly calculated force, and by considering moments throught the first bearing support A and deduced the reaction force at B is 5.877KN. Using the sum of Y forces = 0, I could then calculate for at A=6.023KN.
4. I then drew my shear force diagram, followed by my bending moment and torque diagrams!

Now I am stuck!
I am lead to believe that I must use the relevant equivalent bending moment and torque diagrams, and tau, sigma and twist rate values calulate a suitable diameter for the shaft.
Where:
Me= 0.5[ Mmax +[Mmax^2+T^2]^0.5 ]
Te=[Mmax^2+T^2]^0.5
Is my Mmax value simply deduced from my highest value on my BM diagram, and what T force do use?
I'm not sure if these questions are rather elementary, apologies if that is the case!
Many thanks
Dan
 
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FAQ: Design of a shaft subject to torsion/bending/fatigue

1. What is the purpose of designing a shaft subject to torsion/bending/fatigue?

The purpose of designing a shaft subject to torsion/bending/fatigue is to ensure that the shaft can withstand the various loads and stresses it will experience during its intended use. This includes torsional forces, bending moments, and fatigue cycles, which can all cause failure if the shaft is not properly designed.

2. How is the diameter of a shaft determined for torsion/bending/fatigue design?

The diameter of a shaft is determined by considering the maximum torque and bending moment it will experience, as well as the material properties and safety factor. These factors are used to calculate the required shaft diameter using equations from engineering design standards or software programs.

3. What materials are commonly used for shafts subject to torsion/bending/fatigue?

Some common materials used for shafts subject to torsion/bending/fatigue include steel, aluminum, and titanium. The specific material chosen will depend on the application and required strength and stiffness of the shaft. Other factors such as cost and availability may also play a role in material selection.

4. How does fatigue affect the design of a shaft?

Fatigue is a major consideration in the design of a shaft subject to torsion/bending/fatigue. Fatigue failure occurs when a material is subjected to repeated cycles of stress, even if the stress is below the material's ultimate strength. To prevent fatigue failure, the shaft must be designed with a sufficient safety factor and appropriate materials and geometry to withstand the expected number of cycles.

5. Are there any design guidelines or standards for shafts subject to torsion/bending/fatigue?

Yes, there are several design guidelines and standards available for designing shafts subject to torsion/bending/fatigue. These include industry-specific standards and codes, as well as general engineering design handbooks and software programs. It is important to follow these guidelines to ensure a safe and reliable design for the shaft.

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