Simultaneous shearographic and thermographic NDT of aerospace materials

A Survey of Scrutinizing Delaminated Composites via Various Categories of Sensing Apparatus

“…The basic concept of phase shifting interferometry is inserting a device (e.g., a PZT transducer) into the optical path to incorporate known phase shifts. As depicted in Figure 5, the techniques may classified into camera-based interferometry [65][66][67][68][69][70][71] and detector-based interferometry , out of which the former is limited in temporal domain resolution, whereas the latter limited in spatial domain resolution [11]. In second classification, when coupling a broadband light into the fiber, local FBG sensors using Bragg gratings as sensing elements placed within an optical fiber reflect back a narrowband signal whose peak wavelength (Bragg wavelength) depends on the grating's period and effective refractive index.…”

“…With regard to the shearography application to delamination inspection in CFRP laminates, perturbed speckle patterns revealed delamination shape and size while assessing the delamination depth through embedding both resonant frequencies derived from shearography and theoretical ones as a function of delamination depth (within the idealized delaminated area) into an optimization process [70]. In testing composite structures via shearography synchronized with thermography, delamination was dramatically localized through shearography based fringe patterns, particularly when incorporated with phase shifted technique using filtering and color routines [71]. Delamination of a lower depth shows more fringes compared with deeper ones, the fringes number, thus can be an indicator of delamination depth.…”

Benchmarking shearographic NDT for composites

“…The objective of this paper is a call for the standardisation of digital shearography based on the involvement of interested parties calling for the start of the process, perhaps as is suggested here, by the technical committee TC 135 of the ISO. (a laser) is used to illuminate the object and produce the required speckled image, Gryzagoridis et al (7) .…”

“…A number of fringes (N), that appear superimposed on the image of the surface of the object under test, are lines of constant gradients of out-of-plane surface displacements, along the direction of the shear or lateral shift created by tilting one of the mirrors of the modified Michelson interferometer. The out-ofplane displacement gradients can be quantified as shown (7) by the following expression: where λ is the wavelength of the laser, N is the number of fringes observed, and S is the lateral shear imposed. Clearly, the sensitivity of the instrument depends on the amount of tilt of the mirror and hence the magnitude of shift S. The process of identification of defects or flaws from the fringe anomalies is quite effortless and is possible even to the untrained eye.…”

Detection of Simulated Defect Using IR Temperature Sensors and One Point Heating

“…An IR thermographic device is a possible solution for the application, because it has widely been applied to various defect detections, such as the inspection of composite materials [1-3], aerospace materials [4], laminated wood [5], and thermal barrier coating [6]. The device was also used in the inspection of artificial defects in polystyrene and a plaster [7].…”