The development of various new high-strength alloys and the broadening range of their applications, particularly in aerospace and in cryogenics, has brought about increased emphasis on the study of fracture characteristics. As a result, the technology of testing for fracture toughness and crack propagation has grown rapidly in recent years. So, too, has understanding of how to apply this testing technology to design problems such as selection of materials, heat treatment, welding procedures, structural shape and size, and effects of environment.