Study on Detecting Existence of Flaws in Materials by Observing Radiation Temperature distribution by means of infrared radiometry

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A new thermal radiation technique using an infrared radiometer had been developed to detect internal flaws of materials used, such as inclusion, crack, gap and pinhole. In this study, several incident thermal energies like sun, lamp and hot gas, were injected to the test material with artifical internal flaws. Transient radiation temperature of the surface above the internal flaws were displayd on the CRT by means of the infrared radiometer. The radiation temperature difference between the surface and flaws represents the existance of the internal flaws. Characteristics of various heat injection methods, such as normal and lateral heatings were compared with each others by using test pieces of metal, ceramic, plastic and insulator.Stepwise high-flux heat injection test had been undertaken, using a Halogen lamp with a parabolic stainless mirror coated by gold in case of the normal heating. And the injected heat from lateral side of the test piece flows to the other side of the piece by heat conduction in case of the lateral heating. We visualized the mountainous and valley-like temperature distribution above the internal flaws at the normal heating and discontinuous temperature difference above the flaws at the lateral heating. Test results show that the lateral heating method is more superior than the normal heating in case of detecting the slit flaw and inferior than the normal heating in case of detecting the pin-hole flaw.The detection limit of internal flaws is determined by the surface tempeature variance of the tested material. The transient heat flow arround the internal flaws were numerically analyzed by solving a 2-dimensional heat conduction equation to verify the surface temperature distribution above the flaws.