SBIR-STTR Award

A novel nondestructive inspection (NDI) technique is proposed for detecting surface flaws beneath a thin coating. The basic technique relies on the ability of laser holography to detect very small surface displacements due to thermal expansion effects caused by a propagating thermal pulse. The technique is closely related to the method of infrared imaging which employs an infrared video camera to detect temperature changes due to an expanding heat pulse. The technique being proposed will have greater resolution than infrared imaging due to the very high sensitivity of the holographic detection mechanism which will allow for the detection fine surface cracks. A further advantage of the Laser Holography Thermal Pulse Propagation (LHTPP) technique is that it can be used for all material systems including ferromagnetic, non ferromagnetic, insulators and conductors. In addition LHTPP readily lends itself to computer automation. Currently existing image analysis codes can be directly applied to the storage, enhancement and analysis of the holographic data. This will allow for the development of convenient field units for on site testing as well stationary laboratory setups.

Phase I investigations using laser holography coupled with thermal pulse propagation (LHTPP) as a method of nondestructive inspection have been successfully completed. In Phase II a prototype LHTPP instrument is planned for delivery to the Navy. The proposed instrument would upgrade the current experimental setup to a fully functional tool for nondestructive inspection of subsurface cracks in metals and composite materials. Features and attributes are as follows: - Compact portable instrument for safe lab and field use. - Fully automated with online computer for storage and analysis of holographic inspection images. - Insensitive to residual stresses and magnetic history of metal samples. - Gives visual indication of subsurface flaws without use of potentially hazardous X-rays. - Adaptable to scanning over a wide range of profiles and contours. A further advantage of the (LHTPP) technique is that it can be applied to composite structures and all material systems including ferromagnetic, non-ferromagnetic, insulators and conductors. In addition LHTPP readily lends itself to computer automation. The computerized data archiving capability will facilitate recall of previously stored and characterized holographic data. The continuous development of an ongoing data base will allow for a more accurate, conventient and reliable instrument.