In the diameter or size of the components is more the surface area will have greater number of surface defect. Hence endurance strength of component reduced with increase in size

Explanation:
When the size of a standard specimen for a fatigue testing machine is increased, the endurance limit for the material decreases.

What is the endurance limit?
The endurance limit, also known as the fatigue strength, is the maximum stress level at which a material can endure an infinite number of stress cycles without failing. It is an important parameter in fatigue testing as it determines the fatigue life of a material.

Effect of specimen size on endurance limit:
When the size of a standard specimen used in fatigue testing is increased, several factors come into play which influence the endurance limit of the material.

1. Stress concentration: The larger the specimen size, the greater the possibility of stress concentration at notches, cracks, or other irregularities. Stress concentration can lead to the initiation and propagation of cracks, reducing the endurance limit of the material.

2. Residual stresses: Larger specimens may have higher levels of residual stresses due to manufacturing processes such as forging or casting. Residual stresses act as additional loads on the material, reducing its endurance limit.

3. Microstructural effects: The microstructure of a material can vary depending on its size. Larger specimens may have different microstructural characteristics compared to smaller specimens. These differences can affect the material's fatigue properties, including its endurance limit.

4. Statistical variations: The endurance limit is influenced by statistical variations in the material's properties. Larger specimens can exhibit different statistical distributions of defects and flaws, leading to a lower endurance limit compared to smaller specimens.

Conclusion:
In summary, when the size of a standard specimen for a fatigue testing machine is increased, the endurance limit for the material decreases. This is primarily due to the increased potential for stress concentration, higher levels of residual stresses, microstructural effects, and statistical variations in larger specimens.

In the diameter or size of the components is more the surface area will have greater number of surface defect. Hence endurance strength of component reduced with increase in size.