If the size of a standard specimen for fatigue testing machine is increased the endurance limit for the material will

This question was previously asked in

UPPSC AE Mechanical 2019 Official Paper I (Held on 13 Dec 2020)

Option 3 : Decreases

__ Explanation__:

The endurance limit of the specimen is given by

**S _{e} = K_{a} K_{b} K_{c} K_{d} S_{e}**'

where K_{a} = Surface finish factor, K_{b }= Size factor, K_{c} = Reliability factor, K_{d} = Modifying factor to account for stress concentration, S_{e} = Endurance limit stress of a particular mechanical component subjected to reversed bending stress (N/mm^{2}), S_{e}' = Endurance limit the stress of a rotating beam specimen subjected to reversed bending stress (N/mm^{2})

- When the surface finish is poor, there are scratches and geometric irregularities on the surface. These surface scratches serve as stress raisers and result in stress concentration. The endurance limit is reduced due to the introduction of stress concentration on these scratches.
**When the machine part is larger**greater is the probability that a flaw exists somewhere in the component, the chances of fatigue failure originating at these flaws are more.**The endurance limit, therefore, reduces**with the increasing size of the component.- The greater the likelihood that a part will survive, the more is the reliability factor. The reliability factor K
_{c}depends upon the reliability that is used in the design of the component.

∴ **The endurance limit is reduced due to stress concentration**.