Evaluation of defects in composite plates under convective environments using lock-in thermography

Abstract

Lock-in thermography is a technique which is increasingly being used for the evaluation of subsurface defects in composite materials such as carbon-fibre-reinforced polymers (CFRPs) in aircraft structures. Most CFRP structures have a finite thickness and non-destructive inspection is performed in a natural ambient environment. In this paper, a photothermal model is developed in order to investigate the behaviour of thermal waves in homogeneous plates and layered plates with finite thicknesses under convective conditions. The model is then utilized to predict the phase differences produced by multi-layer subsurface defects and optimum inspection parameters. The theoretical results are compared with the experimental results. The detectivity of lock-in thermography for CFRP is also presented in this paper.

Infrared exploration of the architectural heritage: from passive infrared thermography to <em>hybrid</em> infrared thermography (HIRT) approach

“…7c,d, respectively. The definition of the absolute phase contrast is: [5] where, φ defective is the phase for a defective area, and φ defect-free is the phase value for a defined sound area (47). It is well known that Eq.…”

Carbon fiber composite inspection and defect characterization using active infrared thermography: numerical simulations and experimental results

“…According to [25], blind frequency ( f b ) is the frequency at which the phase contrast is enough for a defect to be visible, i.e., at frequencies higher than f b , it is not possible to detect it. The thermal diffusion length (μ), described by [26], can be used to fit experimental data and estimate the depth (z) as proposed by [27]:…”

Nondestructive Evaluation (NDE) of Advanced Fiber Reinforced Polymer Composites

“…In further development of thermographic inspection approaches for composites, a recent report by Bai and Wong (2001) discusses the use of lock-in thermography. Lock-in thermography utilizes an infrared camera to detect the surface temperature of a thermal wave propagating into the material and then produces a thermal image, which displays the local variation of the thermal wave in phase or amplitude.…”