ANS:A - duralumin sheets.

Stretcher strains typically occur in low carbon steel sheets during sheet metal forming processes. Here's an explanation:

1. Sheet Metal Forming: Sheet metal forming processes involve shaping metal sheets into desired shapes and configurations using various mechanical or hydraulic forces. These processes include bending, stretching, deep drawing, and forming.
2. Stretcher Strains: Stretcher strains are localized elongations or deformations that occur in the metal sheet during stretching operations. These strains are characterized by narrow bands or lines of localized deformation that may appear on the surface of the metal.
3. Low Carbon Steel Sheets: Low carbon steel sheets are commonly used in sheet metal forming due to their good formability, ductility, and relatively low cost. During stretching operations, such as deep drawing or forming, the metal undergoes localized stretching, resulting in the formation of stretcher strains.

While other materials like duralumin sheets, austenitic stainless steel sheets, and Ni-base alloy sheets are also used in sheet metal forming, they may exhibit different behaviors during stretching operations. For example, duralumin sheets are aluminum-based alloys with good strength-to-weight ratios but may not exhibit stretcher strains to the same extent as low carbon steel sheets during forming processes. Therefore, stretcher strains are typically associated with low carbon steel sheets in sheet metal forming processes.