Abstract
Material defects in fiber-reinforced polymers such as delaminations can rapidly degrade the material properties or can lead to the failure of a component. Pulse thermography (PT) has proven to be a valuable tool to identify and quantify such defects in opaque materials. However, quantification of delaminations within semitransparent materials is extremely challenging. We present an approach to quantify delaminations within materials being semitransparent within the wavelength ranges of the optical excitation sources as well as of the infrared (IR) camera. PT experimental data of a glass fiber-reinforced polymer with a real delamination within the material were reconstructed by one-dimensional (1D) mathematical models. These models describe the heat diffusion within the material and consider semitransparency to the excitation source as well to the IR camera, thermal losses at the samples surfaces and a thermal contact resistance between the two layers describing the delamination. By fitting the models to the PT data, we were able to determine the depth of the delamination very accurately. Additionally, we analyzed synthetic PT data from a 2D simulation with our 1D-models to show how the thermal contact resistance is influenced by lateral heat flow within the material.
Highlights
Fiber-reinforced polymers (FRP) are used in many industries like aerospace, automotive, energy, or sports equipment due to their excellent mechanical properties and low weight
The 1D-models are fitted to the Pulsed thermography (PT) data to quantify the delamination within the material
We determine the thickness of the sample and the area of delamination using the 1-layer model
Summary
Fiber-reinforced polymers (FRP) are used in many industries like aerospace, automotive, energy, or sports equipment due to their excellent mechanical properties and low weight. Defects within FRP such as delaminations, impact damage or moisture can rapidly degrade those material properties. Many FRPs like glass-FRP (GFRP) are semitransparent to optical excitation sources in PT experiments, such as lasers or flash lamps. They can be semitransparent to the wavelength range of the infrared (IR) camera. For the PT experiment, usually the samples are coated to absorb the radiation of the excitation source at the surface of the material. In this case, the absorption within the material does not have to be taken into account. Coatings are often undesired because they are very difficult to be removed completely afterwards
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