A transmission shaft that is under bending loads should be designed based on which theory?

• A. Maximum normal stress theory
• B. Maximum shear stress theory
• C. Maximum normal stress and maximum shear stress theories
• D. Fatigue strength

Answer: (C)

When designing a transmission shaft that is subjected to bending loads, it is essential to account for both maximum normal stress and maximum shear stress theories. This dual consideration is crucial because bending loads primarily induce normal stresses, but they can also create shear stresses due to the shaft’s cross-section and the distribution of forces acting upon it.

The maximum normal stress theory focuses on the failure of materials under tensile and compressive forces. In bending situations, the outer fibers of the shaft experience the highest tensile or compressive stresses. Evaluating these stresses ensures that the material will not yield or fail under the expected load.

On the other hand, the maximum shear stress theory addresses the potential for torsional or transverse forces that can lead to shear failure. In real-world applications, even if a shaft is primarily subjected to bending, shear forces may arise from the change in the direction of the load and could lead to fatigue or fracture, particularly at points of stress concentration.

Considering both theories allows for a more comprehensive assessment of the shaft’s performance under bending loads. This approach helps ensure that the design will withstand both normal and shear stresses, leading to a safer and more reliable shaft for transmission purposes. By integrating the aspects of both theories, engineers can optimize the design to prevent failure from