The tensile-strength test is basically damaging; at the time of the process of gathering research, the sample is obliterated. While this is not an issue when a good store of the sample is at hand, nondestructive techniques are preferred for materials that are expensive or arduous to create or that have been shaped into finished or semicompleted products.

Liquids

One tried and true nondestructive procedure, utilized to find surface markings and flaws in samples, takes a penetrating liquid, either visibly dyed or fluorescent. After being rubbed on the surface of the metal and set to fill into any perceptible breaks, the liquid is cleared, leaving easily visible imperfections and flaws. A similar test, used for nonmetals, takes an electrically charged liquid painted on the sample surface. After superfluous liquid is rubbed off, a dry powder of opposite charge is sprayed on the surface of the nonmetal and draws to the breaks. Neither of these techniques, however, can find internal weaknesses.

Radiation

Internal, like external flaws, can be detected through the use of X-ray or gamma-ray technologies in which the radiation scans the object and impresses on an ideal photographic film. Under some circumstances, it can be possible to target the X rays onto a particular part within the piece, allowing a 3rd dimensional perspective of the flaw markings as well as its site.

Sound

Ultrasonic inspection of sections takes transmission of sound waves above human hearing range through the test material. In the reflection technique, a sound wave is transmitted from one area of the subject, reflected off the far end, then returned into a receiver that is located at the original area. By impinging on a weakness or crack in the test sample, the sound wave is reflected and its signal altered. The actual delay is a measure of the flaw's location; a map of the subject can be made to show the area and shape of the flaws. By the through-transmission process, the transmitter and receiver are located at opposite parts of the material; delays in the transmission of the sound waves are studied to isolate and measure cracks. Sometimes a water medium is used through the use of which transmitter, sample, and receiver should be immersed.

Magnetism

As the magnetic characteristics of a material are heavily influenced by its overall shape, magnetic techniques can be employed to demonstrate the area and relative dimensions of flaws and marks. For magnetic testing, an object is employed that contains a big length of wire through which flows a steady alternating current (primary coil). Nested inside this first wire is a shorter coil (the secondary coil), to which is linked an electrical measuring device. The steady current in the first coil causes further current to move in the secondary coil by the process of induction. If an iron sample is slotted in the secondary coil, sudden changes in the secondary current can signal marks in the piece. This method only finds changes within areas in the length of a piece and cannot find longer or continued flaws very easily. A parallel method, making use of eddy currents induced with a primary coil, also may be utilized to locate errors and cracks. A steady current is induced within the test item. Cracks that lie within the transmission of the current change resistance of the test sample; this alteration may be measured by suitable tools.

Infrared

Infrared methods have also been used to find material continuity in involved construction situations. While testing the strength of adhesive joints in the sandwich core and facing sheets of a standard sandwich structure object such as plywood, for example, heat is applied in the face of the sandwich skin item. Where bond lines are found to be continuous, the core samples provide a heat depression within the surface object, and the localised temperatures of the surface then appear steadily on those bond lines. In the case that the bond line can be not enough, missing, or in error, however, local temperature can not fall. Infrared photography of the surface can then indicate the location and shape of the defective adhesive. Another kind of method utilizes thermal coatings that change colour on reaching a specific heat.

Conclusively, nondestructive processes also are now being sought to allow a entire understanding of the mechanical elements of a test material. Ultrasonics and thermal techniques appear most valuable in this area.