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.
1000, 1100 and 1150°C isothermal sections of the Ti-Al-Nb system were studied using x-ray diffraction, scanning electron microscopy and electron probe microanalysis. A small island-like region of single b 0 is present at 1000, but absent at 1100 and 1150°C. c 1 is not a stable phase at 1000 and 1150°C. Three three-phase fields (a 2 ? b 0 ? r, b 0 ? r ? c and a 2 ? b 0 ? c) are identified in the 1000°C isothermal section (30-60 at.% Ti content). The 1100°C isothermal section is firstly studied completely. It includes six three-phase and thirteen two-phase fields. Two three-phase fields b ? a 2 ? c and b ? r ? c are identified in the isothermal section (30-60 at.% Ti content) at 1150°C. These data are helpful to the fabrication of the TiAl and Ti 2 AlNb intermetallics. Keywords intermetallics Á microstructure Á phase diagram Á TiAl alloy Dedicate to the celebration of Prof. Zhanpeng Jin's 80th birthday. This invited article is part of a special issue of the Journal of Phase Equilibria and Diffusion in honor of Prof. Zhanpeng Jin's 80th birthday. The special issue was organized by Prof. Ji-Cheng (JC) Zhao,
Lock-in thermography is a technique which is increasingly being used for the evaluation of relatively thin materials such as composite materials in aircraft structures. In such cases, the models available in the literature cannot accurately predict the difference in phase values between defective and nondefective regions. This is because the models do not consider the convection conditions and the fact that the thickness of the sample is finite. This article proposes two models (a single-layer model and a multilayer model) to rectify this situation. The single-layer model was used to analyze the thermal wave behavior in homogeneous media and the multilayer model was used to analyze the thermal wave behavior in inhomogeneous media. Based on the theoretical and experimental results, the influence of the combined heat transfer coefficient was discussed. The results predicted by the models were consistent with that obtained experimentally.
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