Internal Defects
Cracks caused by an internal defect in a (dogbone) type testing rod. (Smith, William)
Cracks caused by an internal defect in a (dogbone) type testing rod. (Smith, William)
Internal defects are a lot like notches in the respect that they create a stress concentration in the materail they inhabit. There are several causes for internal defects: large grain boundaries, large conentrations of point defects in the area and defects that occurred during processing. The bad news about cracks due to internal defects is that they start in the middle and cannot be detected until it has reached the surface. By then it is usually to late to do anything about it. The good news is that a material will usually fail from a crack generated externally long before it fails from a crack generated internally.