What term describes the part of the material that experiences no stress when bending metal?

The correct term that describes the part of the material that experiences no stress when bending metal is the neutral line. When a beam or metal piece is subjected to bending, it will undergo a change in shape, causing different areas of the material to experience varying degrees of tension and compression. The neutral line, located at the center of the material's cross-section during this bending process, is the boundary where the stress is essentially zero. On one side of the neutral line, the material experiences compression, while on the other, it experiences tension.

Understanding the neutral line is crucial in material mechanics and structural design, as it aids engineers and designers in predicting how materials will behave under load and helps in developing structures that can safely withstand a variety of forces. The other terms, such as shear point, stress line, and elastic limit, refer to different aspects of material behavior under stress and are not applicable in describing the region with zero stress in bending scenarios.