Infrared thermography of masonry structures

The attention of the present paper was devoted to nondestructive evaluation of masonry structures with a Focal Plane Array infrared camera. Tests were carried out in laboratory on specimens, which simulated one- and two-layer structures, with defects of different geometry and nature and located at different depths. The defects detection was analysed through a cause/effect relationship between the characteristics of defects and hosting material and the observed defect thermal signature, or contrast, on the hosting material.     

Real-time quantification of Staphylococcusaureus in liquid medium using infrared thermography

We previously showed that infrared thermography (IRT) could be used to quantify viable Escherichiacoli, a representative gram-negative bacterium, in liquid growth media. Here, we evaluated the ability of IRT to enumerate a viable representative gram-positive organism, Staphylococcusaureus. We found that the energy content (EC) of the media was strongly positively correlated (r = 0.999) to measured viable counts of S.aureus ranging from 85 colony-forming units (CFU)/ml to ∼4 × 10⁸ CFU/ml. The EC of S.aureus was ∼2-fold higher than that of E.coli at comparable cell concentrations suggesting that IRT may be used to distinguish genera.     

Quantitative modeling and mapping of blistering zone of the Magoksa Temple stone pagoda (13th century,Republic of Korea) by graduated heating thermography

Blistering occurring at the stone’s subsurface layer is easily overlooked compared to different deterioration types, so conservation treatments are not applied often. Therefore, non-destructive detection and mapping of blistering zones with the infrared thermography are very important for preservation of the original forms of stone monuments. In this study, the critical temperature and transitional zone of the blistering zone were established by drawing the temperature distribution curve and the mapping for blistering zone was completed by monochrome process and extraction of vector lines. Analysis of the blistering deterioration degree of the Magoksa Temple stone pagoda with the quantitative modeling yielded a total area and average rate of blistering zones of approximately 2.6 m² and 7.4%, respectively. Thus, there is a high probability of scaling on the stone pagoda (area of approximately 2.6 m²) if conservation treatment is not applied to the blistering zones as early as possible. Therefore, the blistering zones require joining and filling, and state changes of the blistering zones should be continuously monitored after completion of the intensive conservation treatments. Modeling will improve the reliability of deterioration maps by mapping for blistering zone; most deterioration maps to date have overlooked blistering zones.     

红外热成像技术在高分子科学研究中的应用

红外热成像技术是一种非接触、非破坏性的测试材料表面温度的方法,具有既能生成优质图像,又能够精确测温的特点。该技术已被广泛用于全球工业行业的过程状态检测,如电力、建筑、医疗、军事等领域,但在高分子科学的研究领域应用还较少。本文介绍了红外热成像技术的基本原理,综述了红外热成像技术在高分子科学研究中的应用状况,包括研究材料在拉伸、冲击、疲劳过程的热效应特征,研究纤维成形过程的纺丝动力学及高分子聚合过程的反应动力学。     

Filler effects on the thermomechanical response of stretched rubbers

This paper deals with the calorimetric analysis of deformation processes in filled styrene-butadiene rubbers. More especially, the study focuses on the effects of the addition of carbon black fillers on the calorimetric response of “demullinized” SBR. Temperature variations are measured by infrared thermography during cyclic uniaxial tensile tests at ambient temperature. Heat sources¹ produced or absorbed by the material due to deformation processes are deduced from temperature fields by using the heat diffusion equation. First, the results show that no mechanical (intrinsic) dissipation is detected for weakly filled SBR, meaning that the heat produced and absorbed over one mechanical cycle is the same whatever the stretch ratio reached. Second, the mechanical dissipation in highly filled SBR is significant. The quantitative analysis carried out highlights the fact that it increases quasi-linearly with the stretch ratio. Finally, a simplified framework is proposed to discuss the identification of the heat sources, in particular the mechanical dissipation.     

Wavelet subspace decomposition of thermal infrared images for defect detection in artworks

Health of ancient artworks must be routinely monitored for their adequate preservation. Faults in these artworks may develop over time and must be identified as precisely as possible. The classical acoustic testing techniques, being invasive, risk causing permanent damage during periodic inspections. Infrared thermometry offers a promising solution to map faults in artworks. It involves heating the artwork and recording its thermal response using infrared camera. A novel strategy based on pseudo-random binary excitation principle is used in this work to suppress the risks associated with prolonged heating. The objective of this work is to develop an automatic scheme for detecting faults in the captured images. An efficient scheme based on wavelet based subspace decomposition is developed which favors identification of, the otherwise invisible, weaker faults. Two major problems addressed in this work are the selection of the optimal wavelet basis and the subspace level selection. A novel criterion based on regional mutual information is proposed for the latter. The approach is successfully tested on a laboratory based sample as well as real artworks. A new contrast enhancement metric is developed to demonstrate the quantitative efficiency of the algorithm. The algorithm is successfully deployed for both laboratory based and real artworks.     

Cooling-down of thermal thick probes after flash excitation – A measure for the real energy density?

Though flash lamps are one of the most applied heat sources in the field of Thermographic Testing (TT) using active thermography, only little is known about the actually achieved energy input into test objects. In this paper, an easy to realize sensor concept is proposed and experimentally evaluated. The concept is based on the measurement of the surface temperature of a thermal thick probe after flash excitation. After considering the sensor concept with FEM simulations the experimental investigation of four materials (two polymer and two building materials) is described. It will be shown that a suited coating is essential for the realization of the sensor concept. The experimental results prove the suitability of black rigid PVC as the most promising material. Using a coated PVC sample the energy density of short laser pulses, similar to flashes of flash lamps, could be determined exactly with an estimated relative uncertainty of only a few percent.     

Real-time quantification of viable bacteria in liquid medium using infrared thermography

Quantifying viable bacteria in liquids is important in environmental, food processing, manufacturing, and medical applications. Since vegetative bacteria generate heat as a result of biochemical reactions associated with cellular functions, thermal sensing techniques, including infrared thermography (IRT), have been used to detect viable cells in biologic samples. We developed a novel method that extends the dynamic range and improves the sensitivity of bacterial quantification by IRT. The approach uses IRT video, thermodynamics laws, and heat transfer mechanisms to directly measure, in real-time, the amount of energy lost as heat from the surface of a liquid sample containing bacteria when the specimen cools to a lower temperature over 2 min. We show that the Energy Content (EC) of liquid media containing as few as 120 colony-forming units (CFU) of Escherichia coli per ml was significantly higher than that of sterile media (P < 0.0001), and that EC and viable counts were strongly positively correlated (r = 0.986) over a range of 120 to approximately 5 × 10⁸ CFU/ml. Our IRT approach is a unique non-contact method that provides real-time bacterial enumeration over a wide dynamic range without the need for sample concentration, modification, or destruction. The approach could be adapted to quantify other living cells in a liquid milieu and has the potential for automation and high throughput.     

Breakpoint detection of heating wire in wind blade moulds using infrared thermography

In order to manufacture the fibre glass wind blades, one kind of mould embedded with heating wire is used not only for making numerous ‘copies’ of the original sample, and also heating the mould to a certain temperature for curing. The heating wire is embedded in fibre glass as a sandwich structure, and it may break after a long time usage at high temperatures. In this study, a high voltage discharging (HVD) circuit is used to trigger HVD at the breakpoint, which generates heat and therefore causes temperature increase at the corresponding front surface, one infrared camera is used to monitor the temperature evolution. It successfully and quickly detects breakpoints in spar moulds.     

Quantitative study of the temperature dependence of normal LWIR apparent emissivity

In a previous work, a method of measurement of apparent emissivity in situ was implemented. This approach has the decisive advantage of being suitable for any commercial infrared systems. It was tested successfully to characterize the normal LWIR apparent emissivity of an aluminium nitride plate in the temperature range [40–550 °C]. Apparent emissivity exhibits a tight temperature dependence. By using the classical model of apparent emissivity and taking into account the spectral emissivity of aluminium nitride ceramic and the spectral response of the IR sensor, we modelled our apparent emissivity measurement with 5% of accuracy and with dispersion better than 1% within the overall temperature range. The effect on the apparent emissivity of both the detection window and the temperature dependence of the spectral emissivity are highlighted.