Non-destructive inspection (NDI) of additive manufactured (AM) metal alloys

Additive manufactured (AM) metal alloys has enabled the fabrication of lightweight and high complexity components for the aerospace and automotive industry. Similar to traditional processing methods (e.g. casting, welding), porosity is a common concern in AM metal alloys.

X-Ray Computed Tomography (CT) scanning is the “ultimate” tool for porosity measurement in metal alloys. However, the equipment is costly, bulky and the data requires large storage size and long processing time. Therefore, there is a need to develop alternative non-destructive testing (NDT) techniques that are reliable yet less costly and impose lesser demand on post-measurement processing.

In this work, we reported the use of infrared thermography (IRT) and ultrasonic testing (UT) for porosity measurement of AM metal alloys. The samples-under-test are AM metal specimens with different degree of porosity. Consequently, we obtained the correlation between the IRT and UT results with respect to the degree of porosity. We believe that our method will be beneficial to researchers or engineers working on the NDI of AM metal alloys.

Numerical and experimental investigation of eddy current thermography technique on metallic samples

Current and future industry requirements demand advances in NDT. Fast and efficient methods and techniques for defect detection and characterization would be one of the main focus thus improving inspection results. Eddy current thermography is an emerging advanced NDT technique which combines the well-established eddy current testing with thermography inspection. It uses induced eddy current to heat the sample being inspected and defect detection is based on the changes of the induced eddy current flows revealed by thermal visualization over a relatively large area captured by an infrared camera. This work presents the results from 3D FEM simulation and experimental investigation of eddy current thermography on defects in metallic samples. The underlying phenomena of eddy current thermography testing are explored through the simulation which provides the explanation and reasoning of results. Experimental validation and investigation offers an insight to its potential for industrial application. The work demonstrates the effectiveness of eddy current thermography in providing comprehensive and reliable defect assessment.


Due to the recent concern in the Building Fire Safety area in Brazil, especially in the most southern State of the country, Rio Grande do Sul, which was beaten by a commotion wave since the Kiss night club fire in 2013 (killing 242 people), new legislations and standards have been developed. The academic and technical areas are joining efforts to improve the fire safety of buildings and researches have been developed to provide information for legislations and standards. In this context, it is important to understand the fire resistance of non-structural brick masonries, since they are commonly used for wall sealing in reinforced concrete structures, especially in fire escape routes, where a high fire resistance is required. An important concern for brick masonry is to determine the fire resistance time of the walls during a fire situation in order to control the time to evacuate the building. Since standard tests to determine the fire resistance of brick masonry are expensive and time consuming, this paper presents an alternative solution to determine the quality of structural masonry during a fire simulation using thermography analysis and reduced scale elements. The technique comprises in exposing reduced scale brick masonry walls (800 mm high x 800 mm wide with different brick dimensions) to a temperature controlled oven to simulate a fire situation. The output results are in terms of time to propagate the heat through the thickness of the wall considering the various brick configurations, the propagation of cracks, the heat distribution along the wall surface and the fire resistance time. The experimental results demonstrate that the thermography technique is capable of providing precise and complete information on the fire resistance of non-structural brick masonry, even if a reduced scale wall is used.

Leakage detection in hydraulic and pneumatic systems through infrared thermography and CO2 as tracer gas

Every aircraft is plenty of fluid systems, both hydraulic and pneumatic. These systems are necessary for tasks such as fuel distribution and storage, mechanical actuators and carrying air to cabin interior between others. Manufacturing and assembly of these systems require the performance of leak testing for quality assurance. Traditionally, leakage detection testing is performed through system pressure decay monitoring once the system is filled with an inert gas or working fluid. If a pressure decrease is detected, leakages must be located usually by the application of soapy liquid in each junction point of system, which is a time-consuming task.
In this work, new advances in leakage detection are presented by active infrared thermography and using carbon dioxide (CO2) as tracer gas. The application of post-processing algorithms, developed within this work, allows the automatic detection of the leakages, as well as a qualitative approach for its sizing. These algorithms have been tested on different scenarios that simulate aircraft systems in an industrial environment.

Super-resolution thermagraphic imaging using blind structured illumination

In non-destructive imaging of opaque or turbid samples, the spatial information about subsurface structures, such as defects, can be extracted from measured surface data, such as acoustic pressure for ultrasonic imaging or temperature for thermographic imaging. The information about the defects is transferred from the samples interior to its surface by acoustic waves or heat diffusion, respectively. Recently, we showed that the entropy production of these propagation processes limits the transferred information. This poses a principle resolution limit, similar to the Abbe limit in optics. The reason for the entropy production, which reduces the available information about the subsurface structures in the measured surface data, are the thermodynamic fluctuations. They are extremely small for macroscopic samples, but are highly amplified in the ill-posed problem of image reconstruction. For macroscopic samples, the resolution limit depends only on the amplitude of these fluctuations.

Diffusive processes show a high entropy production with increasing diffusion length. Therefore, the resolution limit for thermographic imaging is found to be proportional to the subsurface depth and is described by a depth-dependent thermal point-spread-function (PSF). Like in optics or acoustics, the blurring of imaged structures for thermographic imaging is modelled by convolution with this thermal PSF. Structures smaller than the width of the PSF cannot be resolved in conventional thermographic imaging. Circumventing such a principle resolution limit is called super-resolution. We discuss how blind (unknown) structured illumination combined with non-linear reconstruction algorithms using sparsity of the imaged structures allows thermographic imaging without high degradation of spatial resolution for deeper lying structures.

In turbid media, a coherent light from an infrared excitation laser produces unknown speckle-patterns inside the sample. This blind structured illumination was used for pulsed photothermal radiometry in an epoxy sample to demonstrate a resolution better than the principle limit given by the thermal PSF.

Vibrothermography using vibration modes

The present work deals with the temperature monitoring of a viscoelastic planar structure submitted to flexural vibrations. In such materials heat sources are generated when submitted to mechanical stresses. This phenomenon has been studied and used for NDT purposes with low frequency ultrasonic compressional and flexural waves (typically from tens to hundreds kHz). Here, the excitation is provided in the audible frequency range so that the first flexural modes of the structure are excited. The center of the plate is clamped to a shaker that provides a mechanical sinusoidal excitation at a frequency corresponding to a chosen vibration mode. The heat source pattern appear to be depending on the vibration pattern of the structure, it is to say, on the mode shape. The underlying phenomenon is studied both experimentally and numerically with an anisotropic plastic plate. Extra effort has been made to measure both the mechanical and the thermic properties of the sample in order to simulate the complete behavior of the structure. Experimental and numerical results are in good agreement. This excitation technic offers perspectives for the localization of defects in large structures.

Combining acoustic emission with passive thermography to characterize damage progression in cross-ply CFRP laminates during quasi-static tensile loading

Understanding the gradual failure process of carbon fiber reinforced plastics (CFRP) is the key for exploiting their full potential for lightweight applications. Acoustic emission (AE) can support this process through the detection and evaluation of transient acoustic signals released from loaded CFRP specimen in the moment of damage initiation and progression. This way, not only the presence of damage, but also its location, severity and type can be determined by analyzing arrival times as well as energy and frequency contents of the acquired acoustic signals.
In order to differentiate between different types of damage, one has to identify their acoustic signature. This is usually done by correlating extracted AE parameters from acquired signals during a mechanical test with the resulting damage pattern of the specimen that is visualized offline in a time consuming process by imaging methods such as X-ray tomography or microscopy.
In this study, passive thermography is utilized to identify occurring damage inline on the basis of their released heat patterns to support the AE analysis in the identification of acoustic fingerprints and the characterization of damage progression.
Mechanical tests are performed on cross-ply CFRP coupon specimen subjected to quasi-static tensile loading in the 0° and 90° fiber direction while an IR camera and two wide band AE sensors are utilized to monitor the specimen during the test. Heat patterns are extracted from the series of IR data through advanced image processing techniques and correlated with the generated AE signals in order to identify damage modes such as fiber breakage or matrix fracture. An unsupervised pattern recognition approach is then utilized to find similar AE signals and characterize the gradual failure process in the specimen. The outcome is validated with the resulting damage pattern that is visualized offline via X-ray tomography after the mechanical test.

Conducting a analysis of the technical condition of steam pipelines, determining the geometric parameters of defects and calculating the remaining life using the IR Thermography

Pipeline transport is used for transportation of various media, both gas and liquid, including high-temperature water vapor. Steam lines operate under extreme conditions with a vapor temperature of up to 450 ° C, a pressure of up to 7 MPa and a steam speed of up to 30 m / s, while condensate is formed due to heat loss through the pipe walls. The presence of these factors leads to the formation of walls corrosion and erosion, their thinning and subsequent destruction. Thus, it becomes necessary to perform an express analysis of the technical condition of the steam pipelines without removing them from service using non-destructive testing methods.
Non-destructive testing of steam pipelines has a number of features that do not allow the use of contact methods (ultrasonic, x-ray, magnetic) during their operation. These features include the high temperature of the steam and, as a consequence, the high temperature of the pipe wall. Thus it is expedient to apply remote control methods. The presence of a temperature gradient on the surface of the pipe allows us to apply the IR Thermography, which is remote, fast-acting and highly informative method.
The application of the subsequent mathematical processing of the received information in the form of radiometric tables allows to determine the geometric parameters of the defects (area, depth, thermophysical characteristics), and also to calculate the remaining life of the investigated steam pipelines.
A new approach is proposed for determining the geometric parameters of the defects and calculating the residual life of steam pipelines with a diameter greater than 400 mm with calculation of the defect area and the subsequent solution of the one-dimensional heat conduction problem by the sweep method. This approach allows us to accelerate the procedure for calculating the geometric parameters of defects by solving only a one-dimensional problem.

Positioning of Indications in Composite Materials by Infrared Thermography

Infrared Thermography (IRT) methods have experienced a strong growth during the last decade, extending their application fields to multiple industrial sectors as aerospace, energy, naval, automotive, etc. Reason is the fact that IRT is a fast and portable inspection procedure, where a short calibration time is required, enabling a significant reduction of the lead time. Internal defects are detected and their external dimensions and location on the component surface determined. The weak point of this technique is the lack of accurate data about defect position in component thickness: traditional IRT techniques only provide qualitative information about depth, being possible to distinguish if defects are close to front or rear surface, according to the time where they are identified in the infrared sequence.
In this work, advanced post-processing methods, based on Thermographic Signal Reconstruction (TSR) technique, have been applied for analysing infrared sequences. This procedure merges the information from the whole sequence in only one thermal image where quantitative data about defects depth are included.

Feasible of Optical Infrared Thermography Test for Heat Shrinkable Tapes Inspection Used in Oil and Gas Pipeline

Pipeline is the main pathway for oil long-distance transmission. PE heat-shrinkable tape sticking to the pipe is usually used in the field coating of welded joints in China, in the process of its manufacturing and maintenance.Failure of field coating of welded joints because of bonding problem can lead to corrosion, which important common damage of pipeline.Rapid detection technology for heat-shrinkable tape bonding quality is the foundation of pipeline quality control. Nonetheless, finding a effective inspection technology for heat-shrinkable tape bonding quality is a challenging task. In this study, we work on the utilization of optical infrared thermography test for heat-shrinkable tape bonding quality evaluation. A uniform heating infrared lamp is used for the surface heating, thermal detector records the change of the surface temperature. This technology provides a rapid bonding quality testing and assessment technology. The successes and limitations of this technique will be discussed in this article.