What is the name of the imaginary line near the center of the metal during bending?

The neutral axis is the correct answer because it represents the imaginary line in the material where there is no stress or strain during the bending process. When a material bends, one side is compressed while the other side is stretched. The neutral axis is located between these two areas, thus it experiences neither tension nor compression. This is a crucial concept in mechanics of materials, especially in structural applications, as understanding the behavior of materials under bending loads allows engineers and mechanics to design components that can withstand these stresses without failing.

The other terms, such as center axis, bend line, and reference axis, don’t accurately define the location in the material where bending stresses balance out. Each of these alternatives may refer to different concepts in geometry or structural analysis, but they do not specifically identify the point of zero stress that the neutral axis does.