Importance of stresses in shaft:

What is  importance of stresses in shaft ?
Sol.: In shaft the following significant stresses occur.

1. A maximum shear stress occurs on cross section of shaft at its outermost surface.

2. The maximum longitudinal shear stress occurs at surface of shaft on longitudinal planes passing through longitudinal axis of shaft.

3. The maximum tensile stress (that is, major principal stress) occurs at the planes 45º to maximum shearing stress planes at the surface of shaft. This stress is equal to maximum shear stress on cross section of shaft.

4. The maximum compressive stress (that is minor principal stress) occurs on the planes at 45º to longitudinal and cross sectional planes at the surface of shaft. This stress is equal to maximum shear stress on cross section.

5. These stresses are significant because they govern the failure of shaft. These stresses develop simultaneously and hence they should be considered simultaneously for design purposes.

6. For most of the engineering materials, fortunately shear strength is smallest as compared to the tensile and compressive stresses and in such cases only maximum shear stress on the cross section of shaft is the important stress for design.

7. For materials for which the tensile and compressive strengths are lower than shear strength, shaft design should be carried for lowest strength.