Yielding Stage in Mild Steel Specimen

The yielding stage is an important phase in the mechanical testing of materials, especially metals like mild steel. During this stage, the material undergoes plastic deformation, and its behavior changes significantly. Let's discuss the possible scenarios during the yielding stage in a mild steel specimen.

Constant Strain (Option A)

If the strain remains constant during the yielding stage, it would imply that the material is not undergoing any further deformation. However, in the yielding stage, the material is expected to undergo plastic deformation, which means there is a change in shape and size. Hence, this option can be eliminated.

Decreasing Strain (Option B)

If the strain starts decreasing during the yielding stage, it would indicate that the material is recovering from the deformation and returning to its original shape. However, in the yielding stage, the material is expected to undergo plastic deformation, which means there is a permanent change in shape. Therefore, this option can also be eliminated.

Increasing Strain without an Increase in Load (Option C)

During the yielding stage, the material experiences plastic deformation, which means it continues to strain even without any increase in load. This behavior is a characteristic of ductile materials like mild steel. As the material is subjected to increasing stress or load, it undergoes plastic deformation and continues to strain even when the load remains constant. This phenomenon is known as strain hardening or work hardening.

During strain hardening, the material rearranges its crystal structure, causing dislocations and impeding the movement of atoms. This resistance to further deformation leads to an increase in strain without an increase in load.

This behavior is illustrated by the stress-strain curve of mild steel, where the curve exhibits a gradual increase in strain even when the stress or load remains constant. This is the characteristic feature of the yielding stage in mild steel, and it is well-known for its ductility and ability to undergo plastic deformation.

None of the Above (Option D)

Since we have already explained that Option C is the correct answer, Option D can be eliminated.

In conclusion, during the yielding stage in a mild steel specimen, the strain increases without any increase in load. This behavior is a result of strain hardening, which is a characteristic feature of ductile materials like mild steel.