Inspection of Coatings Using Terahertz Time Domain Spectroscopy System

Coatings and paints are use in almost all branches of modern industry. Mostly as a material for corrosion protection. It is understandable that failure of coating is critical for ability and time of protection. Failure can occur for many reasons – improper selection of coating material for given substrate – lack of compatibility or chemical reactions, – bad adhesion (blistering, flaking, peeling), – strong exterior action as chemical exposure, abrasion, weathering, – poor or inadequate surface preparation or improper application as surface, – contamination, too low surface profile, pinholes, overspray, improper drying, lack of cure, – incompetent design of structure – sharp edges, skip welds. Modern paints, especially lacks for automotive industry are very complex chemical mixtures. They content resins and curing agents (they build up the coat), pigments and solvents. Moreover they content plasticizers, extenders, catalysts, fungicides and so on. This mixture is applied as a very thin layer of 50 - 60 micrometers in thickness. And then all components have to react properly; resin react with curing agent or with oxygen or water from the air. The solvents have to evaporate in proper time, the other non-volatile components must build up the continuous film of constant thickness within curing (or drying) time. As explained, there are many factors that can cause coating failures. There are also many methods of examination of coating failures. They can be roughly divided into methods that allowed on site investigation and methods used in laboratories. One can also divided these methods into simple methods (not demanding complicated equipment) and methods using a sophisticated laboratory equipment. The most simple method is macroscopic examination, followed by microscopic examination. Usually, the next step of failure analysis is chemical analysis of the coating and corrosion products. This can be made by Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM) with energy dispersive x-ray spectroscopy (EDS). Eventually as confirmation for analysis conclusion one can use Accelerated environmental exposure tests; salt spray (fog) tests, humidity tests, and ultraviolet light (QUV) exposure complemented by electrochemical impedance spectroscopy (EIS). As one can see according to complex causes of coating failure it is normal to use very complex methods for investigations of coating failures. These methods mostly dealing with failures that already occurred and can be seen (or their adverse effect). But how can we find defects of coats that cannot be seen because of presence of pigments in multilayer coatings, without damaging the tested structure. One of such method is the terahertz time domain spectroscopy. This paper presents utilized setups, applied image processing algorithms, results of preliminary tests and results of measurements achieved for various kinds of coatings and base material. The coatings containing selected kinds of defects were also prepared and evaluated. The presented results show that the terahertz method can be a good alternative in case of composites’ testing

Inspection of Reinforced Concrete Structures Using Active Infrared Thermography

Reinforced concrete is currently the most widely used construction material. The wide field of applications forces the usage of the advanced techniques for quality control and tests of these structures. Most frequently it is required, that such tests should be possible to perform after the reinforced concrete hardening, during its usage and without damaging the structure. Therefore, various non-destructive testing techniques are here the natural choice. There are several aspects of possible non-destructive evaluation of reinforced concrete structures. One of them is the detection and assessment of the rebars. The authors propose here selected active thermography techniques. In case of the active thermography, an external energy source has to be used to induce the thermal response of the tested specimen. For concrete structures heating source based on the radiation phenomena (like halogen lamps, flash lamps, infrared radiators and similar) may be not effective due to, usually, large size of the examined structures. Therefore, authors propose two different heating techniques: a microwave heating and an induction heating. The microwave heating has volumetric character and its ratio depends not only on thermal properties of the material, but also on electrical properties. In case of metals (rebars made of a steel) microwave heating is not effective, thus the colder spots observed on the specimens’ surface will indicate presence of the rebars. On the contrary, the induction heating, generates the heat by eddy currents only in the metal objects. The hot spots will indicate the rebars’ positions. In this article authors will present selected experimental results, which will allow to evaluate and compare the proposed two techniques of heating suitability of each one to assess the reinforced concrete by using the active thermography will be discussed

Object’s Optical Geometry Measurements Based on EDoF Approach

Machine vision applications are getting more popular in many manufacturing applications. Although vision techniques have many advantages there are still numerous problems related with those methods. One of the drawbacks is that when measuring or performing an inspection task the image resolution must be as high as possible. When inspecting an object of complicated geometry, with a specific lens and camera to achieve a given accuracy, the field of view, or the depth of field might be insufficient for the task. Using cameras placed on manipulators, or on moving stages leads to solving the problem, but it also causes various implementation issues. During the measurement process when the camera or the inspected object is moving, images are acquired and need to be processed separately. If the inspection task is a simple feature extraction might be sufficient. On the other hand if the image processing is more complex it might take time to process each image separately. For example when a feature is located on the border of a image, to measure it or properly assess, two or more images with the feature need to be combined. When it comes to field of view limitations, there are known methods of image stitching, and combining [1,2]. When the depth of field is narrow, for example when using fixed telecentric lenses the problem is more complex. The Extended Depth of Field (EDoF) is an approach known in microscopy imagining. It allows to stitch images taken form a range of distances that are minimum spaced. Acquiring images of the same object with differently placed depth of field reveals elements otherwise hidden (due to shallow depth of field). The methods of extracting information form a set of images taken with different depths of field is known in microscopy and wieldy used [3,4]. On the other hand using EDoF in non-microscopic inspections is not utilized because of the fact of changing the focal distance from the inspected object leads to resizing the object in the frame. The longer the focal length the higher is the compression rate of the imagining. The authors propose a method of using EDoF in macro inspections using bi-telecentric lenses and a specially designed experimental machine setup, allowing accurate focal distance changing. Also a software method is presented allowing EDoF image reconstruction using the continuous wavelet transform (CWT). Exploited method results are additionally compared with measurements performed with Keyence’s LJ-V Series in-line Profilometer for reference matters

Weld Joints Inspection Using Multisource Data and Image Fusion

The problem of inspecting weld joints is very complex, especially in critical parts of machines and vehicles. The welded joint is typically inspected visually, chemically or using radiography imaging. The flaw detection is a task for specialized personnel who analyze all the data on each stage of the inspection process separately. The inspection is prone to human error, and is labor intensive. In the stages of weld joint visual control geometrical measurements are performed, joint alignment, straightness, deformation, as well as the weld\u27s uniformity. Coloration my show the heat impact zone, and melted parts of the base material. Also during this stage the unwanted cracks, pores and other surface defects can be spotted. On the other side during the X-ray inspection other flaws can be discovered. Pores, cracks, lack of penetration and slag inclusions can be observed. The author’s goal was to develop a multisource data system of easier flaw detection, and possibly inspection process automation. The methods consisted of three image sources: X-ray, laser profilometer, and imaging camera. The proposed approach consists combining spatial information in the acquired data from all sources. A novel approach of data mixing is proposed to benefit from all the information. The signal form the profilometer enables geometrical information extraction. Deformation and alignment error assessment. The radiogram provides information about the hidden flaws. The color image gives information about texture and color of the surface as well as helps in combining multiple sources

Examining Ferromagnetic Materials Subjected to a Static Stress Load Using the Magnetic Method

This paper discusses the experimental examination of anisotropic steel-made samples subjected to a static stress load. A nondestructive testing (NDT) measurement system with a transducer, which enables observation of local hysteresis loops and detection of samples’ inhomogeneity, is proposed. Local hysteresis loops are measured on two perpendicular axes, including one parallel to the rolling direction of the samples. The results confirm that the selected features of the local hysteresis loops provide important information about the conditions of ferromagnetic materials. Furthermore, it is shown that the selected parameters of the statistical analysis of the achieved measurements are beneficial for evaluating stress and fatigue changes induced in the material

Nondestructive Examination of Carbon Fiber-Reinforced Composites Using the Eddy Current Method

This paper presents the results of experiments using the eddy current system designated for nondestructive inspection of carbon fiber-reinforced composites. For this purpose, the eddy current testing system with a differential transducer with two pairs of excitation coils oriented perpendicularly and a central pick-up coil was utilized. The transducer measures the magnetic flux difference flowing through the pick-up coil. The transducer of this design has already been successfully utilized to inspect isotropic metal structures. However, the anisotropy of the composites and their lower conductivity compared to metal components made the transducer parameters adjustment essential. Thus, various excitation frequencies were considered and investigated. The system was evaluated using a sample made of orthogonally woven carbon fiber-reinforced composites with two artificial flaws (the notches with a maximum relative depth of 30% and 70%, respectively, thickness of 0.4 mm, and a length of 5 mm). The main goal was to find a configuration suitable for detecting hidden flaws in such materials

Inspection of Coatings Using Terahertz Time Domain Spectroscopy System

Coatings and paints are use in almost all branches of modern industry. Mostly as a material for corrosion protection. It is understandable that failure of coating is critical for ability and time of protection. Failure can occur for many reasons – improper selection of coating material for given substrate – lack of compatibility or chemical reactions, – bad adhesion (blistering, flaking, peeling), – strong exterior action as chemical exposure, abrasion, weathering, – poor or inadequate surface preparation or improper application as surface, – contamination, too low surface profile, pinholes, overspray, improper drying, lack of cure, – incompetent design of structure – sharp edges, skip welds. Modern paints, especially lacks for automotive industry are very complex chemical mixtures. They content resins and curing agents (they build up the coat), pigments and solvents. Moreover they content plasticizers, extenders, catalysts, fungicides and so on. This mixture is applied as a very thin layer of 50 - 60 micrometers in thickness. And then all components have to react properly; resin react with curing agent or with oxygen or water from the air. The solvents have to evaporate in proper time, the other non-volatile components must build up the continuous film of constant thickness within curing (or drying) time. As explained, there are many factors that can cause coating failures. There are also many methods of examination of coating failures. They can be roughly divided into methods that allowed on site investigation and methods used in laboratories. One can also divided these methods into simple methods (not demanding complicated equipment) and methods using a sophisticated laboratory equipment. The most simple method is macroscopic examination, followed by microscopic examination. Usually, the next step of failure analysis is chemical analysis of the coating and corrosion products. This can be made by Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM) with energy dispersive x-ray spectroscopy (EDS). Eventually as confirmation for analysis conclusion one can use Accelerated environmental exposure tests; salt spray (fog) tests, humidity tests, and ultraviolet light (QUV) exposure complemented by electrochemical impedance spectroscopy (EIS). As one can see according to complex causes of coating failure it is normal to use very complex methods for investigations of coating failures. These methods mostly dealing with failures that already occurred and can be seen (or their adverse effect). But how can we find defects of coats that cannot be seen because of presence of pigments in multilayer coatings, without damaging the tested structure. One of such method is the terahertz time domain spectroscopy. This paper presents utilized setups, applied image processing algorithms, results of preliminary tests and results of measurements achieved for various kinds of coatings and base material. The coatings containing selected kinds of defects were also prepared and evaluated. The presented results show that the terahertz method can be a good alternative in case of composites’ testing.</p

Impact of Magnetization on the Evaluation of Reinforced Concrete Structures Using DC Magnetic Methods

The magnetic method is the most promising method that can be used to inspect large areas of reinforced concrete (RC) structures. Magnetization is a crucial process in this method. The paper aims to present the impact of the magnetization method on the results in the detection of reinforced bars (rebars) and the evaluation of concrete cover thickness in reinforced concrete (RC) structures. Three cases (without magnetization, same pole magnetization, and opposite pole magnetization) were considered in the experiments. Results achieved in all the methods are presented and evaluated. Two different sensing elements were used in the measurements: a magneto-optical (MO) sensor and an AMR sensor. The advantages and disadvantages of both mentioned transducers are presented and discussed in the context of a large areas inspection. The new approach involves using various magnetization methods to improve measurement results for complex structures

Evaluation of Reinforced Concrete Structures with Magnetic Method and ACO (Amplitude-Correlation-Offset) Decomposition

The magnetic method is one of the very few nondestructive testing (NDT) techniques that provide the possibility to conduct area tests of reinforced concrete (RC) structures in a fast, cheap, and straightforward way. This paper aims to present a new approach to the simultaneous identification of rebars’ diameter, alloy class, and thickness of the concrete cover tested with this method. Since rebars from different manufacturers may have different electromagnetic properties (standardization only for mechanical properties), preparing an effective and universal database is impossible. In this work, ACO decomposition is proposed, a new attributes extraction method designed to identify object parameters, even if it is impossible to collect a suitable training database (by pattern recognition and analysis of the deviation). Conducted tests prove that the ACO method enables accurate reflection of the waveform shape and limitation of attributes number to three or fewer (avoiding the curse of dimensionality). These properties, combined with the ability to analyze spatial components of magnetic induction (which only magnetic sensors provide), make the complex task of identification of three parameters more straightforward and the separation between the results received for different classes larger. This article presents the measurement results and the whole identification process