MIL-HDBK-793, MILITARY HANDBOOK: NONDESTRUCTIVE ACTIVE TESTING TECHNIQUES FOR STRUCTURAL COMPOSITES (06 NOV 1989)., Nondestructive testing is the testing of materials or structures without causing failure of the item being tested. There are three acronyms that are in general usage: nondestructive testing (NDT), nondestructive evaluation (NDE), and nondestructive inspection (NDI) (or nondestructive investigation (NDI). These terms are used by various authors to describe the same basic types of testing.