Downloaded from https://www.everyspec.com 4.! AMCP 706101 Neutrons are absorbed differently by dif- A chemical that has a frosty appearanca ferent materials (nuclei), Thow differetnces and a known melting temperature. is applied sometimes can be exploited for better flaw to the nlement and heat applied, A poor discrimination. Most heavy materials do not bond causes a change in appearance. The absurb neutrons well, so that thick sections method can be used on other materials, can be Investigated with shorter expo,;ure times.
Neutrons can he us~ed to examine The temrerature profile of a surface can materials (such as many plastics) which con- be sensed by a coating of a phosphor sus- taki hydrogen, A dlsadvantage iA that pended in a liquid, TIhe reaction of the neutrons are difficult to record on film, and phosphor to ultsviolet light changes as a a special process is required for detection, function of' temperature Alpha and beta particles are both used for Tempilstiks' are crayons made of a thickness neusuring.
By using a wide range material that melts at a calibrated temper- of energies, thicknssa mnasurernntts using ature, A specimeln Is marked with the appio- beta sources can be made from IS uin, of priate TempilstikS before heat is applied. 'z aluminum to 0.050 in. of steal. Alpha The mark molts at its calibrated temperature. particles have been usod to measure 1% thick. Other similar Ttmpil products, such as nes changes in thin foils and pper (Ref. 2). Templlaq® anid temperatu;e sensitive pl. lots, art available commercially, ;, Radiography is probably the most widely lal used NDE method. Equipment for these Temperature-sensitive paints (Thermo- tests is readily available.
The topic is color, Ref, 3) which change color as a thoroughly described in Ref. 3, function or temperature also can be used. Some of theme paints change color as often 6-4 THERMAL METHODS as four times Ft four different temperature level#, The changes are permnrent und pro- The flow of heat through nj niaterial is vide a good permanent record, The•se paints altered by discontinuities in tho material, can be used on almost any surface over a 'rhoes discontinuities produce variations in range of i04A to 2912*F and are accurate temperature at the surface of' the item. The within *9 deg F. The point must dry for 30 location and size of an anomaly can be de- min before time and must.
be removed after termined by the temperature profile 4at the use. The sirfacoe to which it is applied surface. Thermal methods are useful for must be thoroughly clean before applica- evaluating bonds between two materials, tion, The heat can be applied artificially o.' muy Infraied photugraphy and photomicro, be generated by the operation of the item. graphy can be ased to record temperature For example, engine cylinders can be aid- proffil of surfaces. A newer and more formly heated by being filled with hot oil, sophisticated method Is infrared scanning, An operating microcircuit produces heat Here, the surlace of the specimen is scanned internally.
Many methods of detecting and by an optical-mechanical system which recording the surface temperature gradients focuses small portions of the surface onto are available, Table 8-4 outlines the char- a IR detector (Ref. 4). This technique can acteristics of these techniquos, be used to determine the temperature pro. 114f.l of microcircuits. Temperature differ. The "frost" tost can be used for testing the ences as low as 0.5 deg C can be resolved, bond quality of clad nuclour fuel elements, and components supaiated by as little as 84I