Stanovení hloubky defektu s nízkým poměrem hodnot velikost/hloubka a nízkou tepelnou odrazivostí pomocí flash pulzní IR termografie

Studie se zabývá kvantitativním stanovením hloubky defektů pomocí flahs pulzní termografie. Nová metoda vyhodnocení navržená v této práci zohledňuje 3D difuzi tepla, konečnou velikost defektů a koeficient tepelné reflexe mezi materiálem a defekty. Metoda je založena na kombinaci známých analytických modelů a procedury nelineárního fittingu (NLF). Algoritmus je ověřen numericky a experimentálně na vzorcích z PLA plastu vyrobených pomocí 3D tisku. Přesnost metody a její efektivcita byla hodnocena porovnáním s referenční metodou založenou rekonstrukci termografického signálu.This study is focused on the quantitative estimation of defect depth by applying pulsed thermal nondestructive testing. The majority of known defect characterization techniques are based on 1D heat conduction solutions, thus being inappropriate for evaluating defects with low aspect ratios. A novel method for estimating defect depth is proposed by taking into account the phenomenon of 3D heat diffusion, finite lateral size of defects and the thermal reflection coefficient at the boundary between a host material and defects. The method is based on the combination of a known analytical model and a non-linear fitting (NLF) procedure. The algorithm was verified both numerically and experimentally on 3D-printed polylactic acid plastic samples. The accuracy of depth prediction using the proposed method was compared with the reference characterization technique based on thermographic signal reconstruction to demonstrate the efficiency of the proposed NLF metho

Detecting Delaminations in Semitransparent Glass Fiber Composite by Using Pulsed Infrared Thermography

Thanks to its good strength/mass ratio, a glass fibre reinforced plastic (GFRP) composite is a common material widely used in aviation, power production, automotive and other industries. In its turn, active infrared (IR) nondestructive testing (NDT) is a common inspection technique for detecting and characterizing structural defects in GFRP. Materials to be tested are typically subjected to optical heating which is supposed to occur on the material surface. However, GFRP composite is semitransparent for optical radiation of both visual and IR spectral bands. Correspondingly, the inspection process represents a certain combination of both optical and thermal phenomena. Therefore, the known characterization algorithms based on pure heat diffusion cannot be applied to semi-transparent materials. In this study, the phenomenon of GFRP semi-transparency has been investigated numerically and experimentally in application to thermal NDT. Both Xenon flash tubes and a laser have been used for thermal stimulation of opaque and semi-transparent test objects. It has been shown that the penetration of optical heating radiation into composite reduces detectability of shallower defects, and the signal-to-noise ratio can be enhanced by applying the technique of thermographic signal reconstruction (TSR). In the inspection of the semi-transparent GFRP composite, the most efficient has been the laser heating followed by the TSR data processing. The perspectives of defect characterization of semi-transparent materials by using laser heating are discussed. A neural network has been used as a candidate tool for evaluating defect depth in composite materials, but its training should be performed in identical with testing conditions

Infrared thermographic testing of hyperconductive flat heat pipes

Active infrared thermography has been applied for the evaluation of the internal structure and operation quality of hyperconductive flat mini heat pipes used in satellite electronics. The distribution of effective transverse thermal diffusivity in heat pipes has been obtained by means of the Parker technique to exhibit areas with low content of fluid in the porous structure. The lateral components of thermal diffusivity were determined by placing a slit mask between a flash heater and a heat pipe. Peculiarities of heat pipe operation in a working regime have been experimentally studied by placing a local heat source on the pipe surface and following the surface temperature dynamics

Infrared thermographic analysis of thermal property variations in composites subjected to impact damage, thermal cycling and moisture saturation

The new results on the relationships between impact damage energy and thermal property variations in carbon and glass fiber reinforced plastics have been obtained on “dry” composite samples, as well as on the samples subjected to thermal cycling and moisture saturation. The estimates of impact damage detection limit are presented, and the impact energy ranges where variations of effusivity and diffusivity linearly depend on energy are obtained. The experiments on the samples subjected to long-term moisture saturation and thermal cycling revealed no significant influence of these impacts on thermal property. It is concluded that thermal nondestructive testing may serve as a reliable tool for estimating severity of impact damage in aircraft composite structures

Influence of severe plastic deformation by extrusion on microstructure, deformation and thermal behavior under tension of magnesium alloy Mg-2.9Y-1.3Nd

The microstructural investigation, mechanical properties, and accumulation and dissipation of energies of the magnesium alloy Mg-2.9Y-1.3Nd in the recrystallized state and after severe plastic deformation (SPD) by extrusion are presented. The use of SPD provides the formation of a bimodal structure consisting of grains with an average size 15 µm and of ultrafine-grained grains with sizes less than 1 µm and volume fractions up to 50%, as well as of the fine particles of the second Mg24Y5 phases. It is established that grain refinement during extrusion is accompanied by an increase of the yield strength, increase of the tensile strength by 1.5 times, and increase of the plasticity by 1.8 times, all of which are due to substructural hardening, redistribution of the phase composition, and texture formation. Using infrared thermography, it was revealed that before the destruction of Mg-2.9Y-1.3Nd in the recrystallized state, there is a sharp jump of temperature by 10 ◦C, and the strain hardening coefficient becomes negative and amounts to (−6) GPa. SPD leads to a redistribution of thermal energy over the sample during deformation, does not cause a sharp increase in temperature, and reduces the strain hardening coefficient by 2.5 times

Influence of Zr-1 wt.% Nb alloy structure state on its deformation and thermal behavior under quasi-static tension

The influence of the average size of the structure elements on the deformation and thermal behavior of the Zr-1 wt.% Nb (Zr1-Nb) alloy under quasi-static tension was investigated using the digital image correlation and infrared thermography methods. It is shown that with increasing average size of the structural elements in the range 0.2–2.0 mm the physico-mechanical properties, such as yield strength, microhardness, maximal true strain, and maximal temperature increment during deformation decrease, while longitudinal and transverse strain increase. According to the obtained results, correlations between the mentioned deformation characteristics and the average size of the structural element d–1/2 can be described by linear functions