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Shearography is an optical measurement technique based on the interference between two laterally displaced images of the region of interest. Due to its quasi-equal-path configuration, shearography is robust enough for applications outside the laboratory. In fact, shearography has been successfully used for nondestructive testing in composite materials mainly in the aerospace, boating and, more recently, in the oil and gas industries. There are several demands in the oil and gas industry for nondestructive testing on subsea metallic elements coated with composite materials to prevent or mitigate the effects of corrosion. The present work deals with the underwater shearography for nondestructive testing in metal parts coated with composite materials. The paper begins with considerations about the propagation of light in underwater environments and a discussion on the elements that disturb the measurements with shearography such as changes in wavelength, absorption, dispersion, distortions caused by refraction in the air-glass-water interfaces among others. The different loading possibilities to reveal defects in the tested elements are analyzed: by pressure loading, thermal loading by radiation and thermal loading by induction. Exploratory experiments carried out inside water tanks involving the three loading techniques are presented and discussed. The results are compared and the combinations that led to the best results are emphasized. Finally, future works that involve a fully immersed system for underwater shearogaphy are briefly announced.

A new shearography configuration was developed to simultaneously acquire images of a specimen in three different shearing directions, the proposed configuration is capable of performing measurements of shearography with multiple shearing directions using just one single interferogram. The device uses a three aperture mask and a single imaging lens to produce interference speckles with carrier fringes in three different directions. A set of three wedge prisms are used in combination with the three apertures to produce simultaneous shearing interferograms for three different orientations. A single high-resolution image of the specimen is captured for each loading level and the phase maps are computed by FTM (Fourier Transform Method). Additionally, as the device has no movable parts and just a single shot image is acquired, it is very compact, robust and can be successfully used outside the optical bench. The paper presents the optical setup and a practical application for the new technique.

This work presents the development of a special shearography system with radial sensitivity and explores its applicability for detecting adhesion flaws on internal surfaces of flanged joints of composite material pipes. The inspection is performed from the inner surface of the tube where the flange is adhered. The system uses two conical mirrors to achieve radial sensitivity. A primary 45° conical mirror is responsible for promoting the inspection of the internal tubular surface on its 360° A special Michelson interferometer is formed replacing one of the plane mirrors by a conical mirror. The image reflected by this conical mirror is shifted away from the image center in a radial way and a radial shear is produced on the images. The concept was developed and a prototype built and tested. First, two tubular steel specimens internally coated with composite material and having known artificial defects were analyzed to test the ability of the system to detect the flaws. After the principle validation, two flanged joints were then analyzed: (a) a reference one, without any artificial defects and (b) a test one with known artificial defects, simulating adhesion failures with different dimensions and locations. In all cases, thermal loading was applied through a hot air blower on the outer surface of the joint. The system presented very good results on all inspected specimens, being able to detect adhesion flaws present in the flanged joints. The experimental results obtained in this work are promising and open a new front for inspections of inner surfaces of pipes with shearography.

The most common optical configuration used to produce the lateral shifted images, in a Shearography system, is the Modified Michelson interferometer, because of its simple configuration. Tests carried out in recent years have shown that the modified interferometer of Michelson is a device that presents good results in a laboratory environment, but still presents difficulties in the field. These difficulties were the main motivation for the development of a more robust system, able to operate in unstable environments. This paper presents a new shearography configuration based on Diffractive Optical Element (DOE). Different from the diffractive common-path setups found in literature, in the proposed configuration, the DOE is positioned between the image sensor and the objective lens and mounted on a flexible holder, which has an important function to promote the system's robustness. Another advantage of the proposed system is in respect to phase shifting, since it is insensitive to wavelength variations. The lateral movement of the DOE produces a phase shifting in the shearography system. Since the pitch of the diffractive grating used is about 60 times greater than the wavelength of a green laser, the DOE configuration becomes much more robust to external influences compared to the Michelson Interferometer configuration. This work also presents an evaluation of the proposed shearography system designed, and some comparative results regarding a classical shearography system.

Shearography is an interferometric technique capable of measuring the gradient of the displacement field. Shearography has also been used to determine out-of-plane displacement fields. In the latter case, conventional integration procedures are not the ideal method for determining the displacement field, as they are more susceptible to error propagation. In this work, two integration techniques are presented, the deconvolution technique and a new procedure called analytical integration, both are capable of determining the complete out-of-plane displacement. For the deconvolution technique, an appropriate kernel is proposed to process the sum of two shearography images with orthogonal shear directions. The analytical integration technique makes use of a weighted combination of two shearography images with different shear directions. The proposed techniques were applied to simulated and experimental shearography images obtained in a controlled experiment using a circular aluminum sample. Both techniques showed results with errors lower than 6% compared to the reference displacements.

Speckle shear interferometry, or shearography, has been more and more frequently used in the aerospace and oil and gas industry for in-field nondestructive inspections of flaws in composite materials. Nowadays new applications have emerged demanding the ability to operate in harsher environments, requiring more robust systems to meet this type of application. A recent modified shearography device allows multiple and simultaneous measurements with different shearing directions on a single grabbed image. This work proposes a robust integration algorithm by error minimization to obtain full-field displacement measurement. Simulated images are used to validate the effectiveness of the integration algorithm. Further, experiments are performed on a clamped circular plate with uniform loading. The proposed algorithm leads to a more accurate estimate of defect size measurement in composite materials.

Pipelines usually transport hydrocarbons in the oil and gas industry. Small amounts of salt water may be present, which can cause corrosion from the inside to outside. Severe corrosion may produce through holes in the pipe wall. External protective layers of fiber reinforced plastics has been applied to postpone the need to stop production to perform a definitive repair, but do not stop the internal corrosion. It is very important to monitor the dimensions of through holes hidden by the protective layers of composite materials, which cannot exceed critical size and compromise pipe safety. Classical methods, such as ultrasound, do not give very reliable answers when composite materials and steel are combined. There is a great demand for a reliable and practical in field non-destructive inspection method. This work brings a hybrid and reliable solution, which combines a new configuration of a portable one-shot shearography system with finite element methods, resulting in a portable and easy to apply solution. The paper describes the principle of the portable one-shot shearography system that is able of simultaneously measuring in three shearing directions[1]. Considerations and modeling of finite element to determine the response of the composite material to the variation of the internal pressure of the duct are discussed. The report details how the experimental data and numerical model results are combined through an iterative process to determine the diameter of the hidden hole. Instead of integrating the experimental results of shearography, the authors differentiate the results of finite element in the same directions as the one-shot shearography system does simultaneously. The minimum of the square error results in an estimation of the hidden hole diameter. Experiments were performed with 150 mm diameter tubes with 20 to 50 mm diameter holes hidden by 6 to 24 mm thick glass fiber reinforced plastic protective layers. Smaller thickness and bigger diameters led to better results. Mean deviations of the order of 10% were found for the whole set of tests. Although the authors consider it is possible to improve the results, deviations of the order of up to 10% are very acceptable results and represent a significant improvement over the classic methods used today. The robustness of the optical system, the ease of use of the algorithm and the level of uncertainty already achieved make the authors believe that the techniques developed here achieve the requirements and will be very useful for the oil and gas industry demands.

Compounds based on smart materials are functional structures that can be used as thermochromic sensors for temperature monitoring in equipment such as pipelines, motors, and heat exchangers. We developed thermochromic coatings based on 1,3,3-trimethylindolino-β-naphthopyrylospiran acrylic polyurethane with and without 2-(2H-benzotriazol-2-yl)-4,6-ditertpentylphenol photostabilizer additives and antioxidant butylated hydroxytoluene and applied them on stainless-steel plates by the spray lay-up method. The samples were analyzed using a weathering chamber with UVA and UVB radiation to monitor their degradation process, revealing complete degradation of the coating without antioxidant and photostabilizer, leading to loss of its thermochromic characteristic.

This paper presents a numerical-experimental procedure to characterize through-holes with arbitrary shapes present on metallic substrates under composite material sleeves using pulsed laser shearography and dynamic excitation combined to the finite element method. The so-called fitting process consists of matching experimental and numerical results in order to determine the shape and dimensions of the holes under the composite repair, or even quantify defects between layers of the composite laminate. The results show that the technique is capable of characterizing, in the worst case, the geometry of a hole with 83% accuracy and its respective area with a maximum error of approximately 20%. The advantageous results achieved in this research show that the fitting process can be very useful for real applications in the oil and petroleum industry.

Shearography is a quite robust optical measurement technique frequently used for in-field testing. Defect inspections with shearography on fiber-reinforced plastics parts, widely used in aircrafts, ships, chemical and oil and gas industries, are often performed outside of the lab. However, environmental disturbances can make this task difficult or even impossible. Mechanical vibrations, air and thermal instabilities are among the most disturbing agents in harsh environments that can destroy the interference signal or, at least, dramatically reduce the interference signal quality, what raises the measurement uncertainty to unacceptable levels. For a successful testing, it is crucial to neutralize the influence of those agents. Compactness, high stiffness, robust mechanical design and an effective clamping system are very important design considerations to minimize the influence of those agents. However, the most effective solution is using a single-shot measurement technique; namely, acquiring a single image instead of a series of images. The exposure time is kept short enough to “freeze” any relative motion between the parts or drift of the measurement signal. This paper presents, describes and explores two configurations of multiple aperture single-shot shearography used by the authors for testing fiber-reinforced plastics used in the oil and gas industry outside the lab. The first one is a two-aperture setup variation based in an already existing configuration that produces carrier fringes on the speckle pattern and allows fringe processing in the 2D Fourier plane. The second one is a new three-aperture configuration that allows acquiring three fringe patterns simultaneously form three different shearing directions for each given loading state. A set of three wedges are used in combination with the three apertures to produce simultaneous shearing interferograms in three different orientations. One single shot image is acquired using a single high-resolution camera before a loading is applied to the specimen and another single shot image for each different loading levels. Since the resulting fringe patterns have carrier fringes in different orientations they are easily separated in the Fourier plane. Once the device has no movable parts and a single shot image is acquired, it is very compact, robust and can be successfully used outside of the optical bench. The paper presents applications of both devices. They have a great potential to expand the use of shearography for testing in harsh environments.

High subjectivity, lack of attention and fatigue are factors inherent to human analysis in inspection activities such as shearography, a non-destructive optical method. In order to minimize the probability of human error, a study was conducted in which a binary classification from 256 shearography test samples obtained from pipes repaired with glass fiber patches was performed. The dataset was split into major and minor defects and used to train two convolutional neural networks architectures, - a specific artificial neural network well known for its application on image classification. Architecture A achieved a maximum accuracy of 73% on major defect detection, while architecture B, slightly more complex, led to better results. Posterior studies on architecture B led to the conclusion that a combination of double layer filters and dropout layers are the best setup for this type of classification problem. It is possible that other architectures might lead to better results, but no grid search was performed to confirm this assumption. An accuracy of 79% was achieved with Architecture B, therefore is reasonable to say that convolutional neural networks are able to learn from parameters which are difficult to correctly process, such as the fringe patterns obtained from shearography test samples.

Mechanical vibrations, air and thermal instabilities are among the most disturbing agents that make difficult or impossible a successful speckle interferometry measurement in harsh environments. Usually, they destroy the interference signal or, at least, dramatically reduce the interference signal quality, what raises the measurement uncertainty to unacceptable levels. Understanding the effects of disturbing agents on speckle interferometry is a first step towards finding strategies to perform effective measurements in harsh environments. There are three main strategies to successfully measure under unfavorable conditions: isolation, robustness and both. By isolation, we mean ways to avoid the action of the disturbing agents on the speckle interferometer and on the measurand. By robustness, we mean using a robust mechanical design, a robust optical technique, a robust data reduction algorithm and/or a robust configuration that is not much disturbed by mechanical, thermal or air instabilities. Compactness, high stiffness, robust mechanical design and an effective clamping system are very important considerations to minimize the influence of mechanical vibrations. One-shot measurement and averaging are also robust strategies to minimize the negative effects of mechanical vibrations as well as air and thermal instabilities. Protective enclosures are useful solutions for reducing air instabilities effects, but sometimes ineffective for achieving thermal stability outside the lab. Robust optical techniques are perhaps the most effective way to reduce the effects of thermal dilatation. The paper describes these concepts and discusses four speckle interferometry systems developed and successfully used by the authors in harsh environments: An achromatic speckle interferometer, using a diffractive optical element, was developed and has been applied to in-situ measure of residual stresses in pipelines. The second and third systems are compact and attachable shearography systems for in-field testing of the adhesion of joints of composite material pipes. Finally, the fourth system is a configuration of a shearography system using two apertures to produce carrier fringes for the measurement from a single image for each loading stage.

Metallic pipes installed at top side offshore platforms may show corrosion damage. The corrosive process can be external or internal. One of the forms for mitigation consists in installation of composite repair to recompose the structural integrity of the corroded pipe segment. These kinds of repairs are normalized and considered temporary. After the designed time the repairs must be removed. To bypass the inconvenience of repair removing and production losses associated with the replacement of the corroded area, several projects are running to develop methods to ensure the integrity of the repair and the maintenance of the integrity of the piping. This article presents the development of a shearography system for integrity assessment of composite repairs. This system was developed in conjunction with UFSC. Several laboratory tests performed at real piping systems were done to develop: optomechanical and electronic systems, software and procedure to data acquisition. After laboratory tests, several field tests were performed at offshore and onshore situations to defined the final methodology to be used at real situations. Among the tests performed during development can be cited a campaign held in the PRCI. The technology was field proved at Campos Basin platform and shows that shearography inspection could help Integrity Management groups to keep the installation running in a safety conditions. Auxiliary systems derivatives were tested in similar situations in the inspection of structural composite repairs on hulls of FPSO. It was concluded that shearographic inspection is suitable to assessing the integrity of composite repairs on offshore piping. The next step will be hired this type of service in a regular basis.

Pipelines are subject to a variety of defects such as wall thickness loss, grooves, dents and holes. To restore the pipe integrity, polymeric composite repairs can be used. The inspection of repaired pipes is of fundamental importance, not only to verify the initial integrity, but also to monitor their state over time. Shearography is a laser optical strain measurement technique which compares a strain image in unstressed and stressed conditions to reveal the presence of defects and provides useful information about the interface between the repair and substrate, identifying delamination, interfacial disbond and holes. In this work, two pipes repaired with composites from two different providers were submitted to shearography inspection in order to analyze the repair system integrity. The inspections were performed to verify the presence or absence of detachments between the composite repair and subtracts and/or between the layers of the repair itself. After the procedure, the repairs were removed to compare and confirm the inspection results. Repair A presented some difficulty to be removed, what is in accordance with shearography results that exhibited the presence of only some superficial defects. The pipe surface aspect after composite removal was good, without any type of corrosion. On the other hand, the shearography inspection of repair B indicated lack of adhesion between the steel pipe and the composite repair. The repair removal was very easy, corroborating the inspection results. Also, it was observed that the pipe surface presented metal oxides. Through these inspections it could be noted an excellent correlation between shearography inspection results and the degree of difficulty to remove the repairs. The results from an inspection in an offshore platform are also presented. This inspection showed that shearography is an efficient method to inspect steel pipes repaired with composite materials in field.

The increasing industry demand for specialized materials promotes a breakthrough in material engineering. In this context, composite materials have gained recognition and have been increasingly employed in the most diverse segments of the industry. When applied to equipment with structural requirements, it is fundamentally important to periodically inspect these materials to ensure their integrity and safety. Often inspections are performed in the field, under unstable conditions generated by operational and environmental factors. Shearography is a valuable method of nondestructive testing (NDT) for industrial applications. This optical technique is less sensitive to environmental disturbances when compared to other interferometric techniques. This paper presents a new shearography configuration based on Diffractive Optical Elements (DOE). In the proposed configuration, a diffraction grating is positioned between the camera sensor and the imaging lens. Therefore, a more compact and robust system is obtained. Another advantage of the proposed system is related to phase shifting, which is generated by the lateral movement of the diffraction grating. Thus, phase shifting is relative to the diffraction grating period and not the laser wavelength as in traditional interferometers. This feature makes the system insensitive to variations in laser wavelengths. Since the period of the diffraction grating used is about 60 times greater than the laser wavelength applied, the shearography system using diffraction grating becomes much more robust for external influences compared to other configurations based on the Michelson interferometer. This paper also presents the evaluation of the proposed shearography system as well as prospective steps.

This work presents the development of a special shearography system with radial sensitivity and explores its applicability for detecting adhesion flaws on internal surfaces of joints of composite material pipes. The system uses two conical mirrors to achieve radial sensitivity. A primary 45° conical mirror is responsible for promoting the inspection of the internal surface all way around 360°. A special Michelson-like interferometer is formed replacing one of the plane mirrors by a conical mirror. The image reflected by this conical mirror is shifted away from the image center in a radial way and a radial shear is produced on the images. The concept was developed and tested. Two tubular steel specimens internally coated with composite materials and having known artificial defects were analyzed to test the ability of the system to detect the flaws. The system presented very good results on all inspected specimens. The experimental results obtained in this work are promising and open a new front for inspections of inner surfaces of composite pipes with shearography.

This article presents an alternative approach for retrieving phase information from a sequence of images with unknown phase shifts. A sequence of five or more discrete interferograms with unknown and different phase shifts are used to determine the parameters of N-dimensional Lissajous figures. A set of N-dimensional discrete points are used to calculate the relative phase shifts. Once zthe phase shifts are determined, the phase values for each image pixel are determined from a generalized phase calculation equation for irregular phase shifts. The article presents the physical and mathematical basis of the developed approach and discusses some results obtained from simulated data and real data from controlled experiments.

Speckle shear interferometry, or shearography, has been more and more frequently used in the industry for in-field nondestructive inspections of flaws in composite materials used in the aerospace and oil and gas industry. Nowadays new applications has emerged demanding the ability to operate in harsher environments. Bringing interferometric systems to harsh environments is not an easy task since they are very sensitive to many harsh environmental factors. Due to the quasi-equal-path property, shearography is an intrinsically robust interferometric technique that has been successfully used in the field, but there are still limits to overcome. Mechanical vibrations are probably the most challenging factor to cope in the field measurements. This work presents a potentially robust shear interferometer configuration. It uses a Wollaston prism as the shearing element rather than a traditional Michelson interferometer and polarizers to achieve the phase shift. The use of the Wollaston prism makes the optical setup more compact and robust, given that a rotating polarizer is the only movable part of the interferometer.

RESUMO Os materiais ditos inteligentes sao materiais funcionais projetados para servir a propositos especificos de uma forma controlada, como para atuacao em ambientes especiais ou de dificil acesso ou mesmo para que apresente uma resposta a um dado evento. Entre os materiais funcionais, em especifico, a classe dos compostos termocromicos permite o desenvolvimento de aplicacoes para o monitoramento visual da temperatura. Neste trabalho foi utilizado 1,3,3-Trimetilidolino-beta-naftoespiropiran (comercialmente denominada de Spyropiran T0423) para o desenvolvimento de um sensor aplicado ao monitoramento de temperatura em diversos tipos de processos. O Spyropiran foi aplicado em um substrato contendo um verniz poliuretânico e as mudancas de temperaturas foram monitoradas observando as alteracoes de cor para caracterizacao deste sensor. Ensaios para determinacao das condicoes de aplicacao, como a analise de ciclo de resistencia termica e aderencia ao aco inox, tambem foram realizados.

Phase retrieval is a basic step for most interferometric techniques. Both spatial and temporal approaches are frequently used. Temporal methods require a sequence of images with very well know phase shifting increments to produce accurate results. Sometimes environmental disturbances can add random phase values that can result in a sequence of images with virtually unknown phase shift increments. This paper presents and evaluates an approach to retrieve phase values from a sequence of five or more phase shifted images by unknown quantities. The phase shifting increments are determined from Lissajous ellipsis. This paper introduces the use of N-dimensional Lissajous figures to determine phase shifting increments. The use of additional dimensions makes the phase shifting increment determination more robust and less dependent of the pixel choices. The mathematical background is detailed and discussed. The paper presents and evaluates simulations and real world examples using fringe projection and speckle interferometry.

This paper presents a new approach to improve the quality of shearographic phase maps acquired in a harsh environment. During in-field nondestructive inspections, the presence of higher disturbances, mainly vibrations, can introduce unknown phase deviations in the sequence of shearographic images. This paper presents a different approach that combines the N-dimensional Lissajous algorithm [Int. J. Optomechatron.8, 340 (2014)1559-961210.1080/15599612.2014.942933] and the concept of phase of differences [Proc. SPIE6345, 634510 (2006)PSISDG0277-786X10.1117/12.693149] to improve the quality of phase maps. The concept is compared with two other methods. Results, advantages, and difficulties of each method are also presented and discussed by using real fringe maps.