D. A. Nesteruk

Thermal (infrared) tomography: Terminology, principal procedures, and application to nondestructive testing of composite materials

The methods of infrared (thermal) tomography are reviewed. Approaches to the dynamic thermal tomography of composite materials are described, which are based on the analysis of changes in the surface temperature with time. Most experimental illustrations refer to thermal testing of fiber reinforced plastic as the typical material used in the air- and spacecraft industry.

Application of principal component analysis in dynamic thermal testing data processing

The principles and features of the application of statistical principal component analysis (PCA) in active thermal testing are considered. A comparison between PCA and Fourier analysis in finding defects in composite materials, detecting corrosion in aluminum, and determining moisture content in construction materials is performed. It is concluded that, generally, images of principal components increase the signal-to-noise ratio and are close in performance to phase diagrams; nevertheless, the results of this method are poorly predictable and require further analysis.

Detecting water in aviation honeycomb structures: the quantitative approach

Infrared thermographic inspection of water in aviation honeycomb panels is a wellknown technique. The hidden water can be detected due to its high thermal capacity that makes temperatures changes slow. A transient thermal regime can be realized by using external heaters or natural heating by the ambient. The paper describes some quantitative aspects of the water detection problem. The presented simulation results have been obtained by analyzing a one-dimensional model of a multi-layer plate where the ice-to-water phase transformation takes place. Some experimental results of inspecting Russian airplanes are also presented.

Accuracy issues in modeling thermal NDT problems

Two models which can be regarded as extreme simulation cases in thermal nondestructive testing are studied numerically with accent being made on the accuracy issue. Four computer programs (ThermoCalc-2D, ThermoCalc-6L, ThermoModel and Comsol Multiphysics) are compared in calculating both absolute temperatures and thermal NDT parameters, such as differential temperature signal and running contrast.

Infrared thermographic inspection of water ingress in composite honeycomb panels

Quantitative aspects of infrared thermographic detection of water in aviation honeycomb panels are discussed in the framework of both 1D analytical and 3D numerical models. A criterion for the transition from 3D to 1D test geometry is introduced, and the influence of the honeycomb cell structure on the modeling results is demonstrated. Optimal test conditions are formulated both theoretically and experimentally in two practical cases where the force of gravity causes the water to be against the facesheet at the bottom of the cells or where a water gap separates the water from the top facesheet.

Evaluating water content in aviation honeycomb panels by transient IR thermography

The paper contains new results obtained in detecting and evaluating water hidden in honeycomb panels of aircraft under exploitation. The accent is made on evaluating water content by using the ice-to-water phase transformation and visible size of temperature patterns in water sites.

An apparatus for the active thermal testing of corrosion in steel cylindrical containers and test results

An apparatus that works on the thermal-testing principle involving infrared thermal imagers of different types and optical and convective heating devices is described. The main purpose of the apparatus is to detect hidden corrosion in 1- to 2-mm-thick steel containers that are intended for temporary storage of radioactive wastes.

Active thermal inspection of composite materials with the use of neural networks

The results of the processing of experimental data on the inspection of a carbon-fiber composite with the use of two neural networks that provide both the qualitative detection of latent flaws and the elements of flaw metering are considered.

Evaluating the thermal resistance of building structures by using infrared thermagraphy under transient conditions

Algorithms for determining the thermal resistance under the conditions of a time-dependent thermal regime, namely, a moving average, a black box, and nonlinear fitting, are studied on the basis of analysis of theoretical and experimental data.

An Automated Practical Flaw-Identification Algorithm for Active Thermal Testing Procedures

Results of analyzing the infrared thermograms of flawed carbon-, glass-fiber reinforced composites steel, and aluminum samples obtained in active thermal-testing procedures are described. The reproducibility of the results of testing conducted by thermography operators using manual and automated image-processing procedures has been evaluated. The advantage of an automated thermogram-analysis algorithm that halves the spread in informative parameters over manual data processing has been demonstrated.