Non-destructive testing of wood defected samples by ESPI

Deterioration of wood artwork is often connected to mechanical material degradation that starts on microscopic scales. Insight into decay mechanisms can be obtained by monitoring surface microscopic deformation and displacement fields. This paper presents the application of Electronic Speckle Pattern Interferometry (ESPI) to detect invisible on the surface intrinsic defects of a wood samples. The different artificial defects were created under the pine wood surface to simulate "defected" samples. The fiber-optic ESPI set-up based on a He-Ne CW laser has been developed and used for the studying the possibility determination of locations, sizes and shapes of wood defects. For this end two digital holograms of the test object, corresponding to vibrating states of the non-heated and heated states of object, are captured at two video frames of the CCD camera, transferred in a frame-grabber and then processed in a PC. The resulted the fringe pattern has the information about the defects. Obtained fringe patterns of all defects are presented. The purpose of work was determining the sensitivity of ESPI method in application to different sizes and forms of defects.