During a dye penetrant inspection, what process allows the penetrant to enter a crack?

In the context of dye penetrant inspection, capillary action is the fundamental process that enables the penetrant to enter into cracks or voids in the surface of a material. This phenomenon occurs because the surface tension of the liquid penetrant causes it to be drawn into narrow spaces, such as cracks. When a liquid comes into contact with a solid surface, the adhesive forces between the liquid and solid can exceed the cohesive forces within the liquid, causing it to "climb" into the cracks.

This property is particularly useful in non-destructive testing because it allows for the detection of very small imperfections that may not be visible to the naked eye. The other options involve processes that do not effectively describe how dye penetrants operate within the context of inspecting for cracks in materials.