In connection with the discussion of technological tests in Ch. 7, it was stated that the tensile test specimen after some degree of stretching tends to become unstable, due to the onset of necking. With further stretching, there is neck growth in the specimen, and finally a fracture is formed in the neck, so that the specimen breaks into two pieces.

When compression testing was discussed, it was stated that for ductile metals, larger strains can in general be obtained in this test than in tensile testing, because neck formation is avoided in compression. But also in the compression test there are limitations on how much the specimen can be deformed. This is because various cracking phenomena may occur, especially when low-ductility materials are tested.

In metal forming, it is a common problem that the material of the workpiece breaks down during forming, in a manner like that for materials subjected to technological tests. In this chapter, different phenomena that cause material failure during metal forming operations will be discussed, with special emphasis on failure due to necking, tensile stress cracking, and shear cracking.

Formability and Workability

Formability and workability are terms that refer to the property of a material with regard to its ability to be shaped in metal forming without breakdown during the forming operation.