Mr. Nan Tao Profile

Nan Tao

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Publications (5)

Proceedings Article | 15 August 2023 Poster + Paper

Comparative performance of high and medium resolution cameras for defect detection in carbon-fiber reinforced composites by digital shearography

Kazi Monowar Abedin, Nan Tao, Andrei Anisimov, Roger Groves

Proceedings Volume 12618, 126181X (2023) https://doi.org/10.1117/12.2669718

KEYWORDS: Shearography, Composites, Digital cameras, Defect detection, Nondestructive evaluation, Spatial resolution, Shearing interferometers, Deformation

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Proceedings Article | 9 August 2023 Presentation + Paper

Application of shearography with thermal loading for the structural inspection of Rembrandt’s Night Watch

Nan Tao, Andrei Anisimov, Esther van Duijn, Lisette Vos, Ilse Steeman, Katrien Keune, Petria Noble, Roger Groves

Proceedings Volume 12620, 126200A (2023) https://doi.org/10.1117/12.2673263

KEYWORDS: Inspection, Shearography, Cameras, Equipment, Deformation, 3D image processing, Cultural heritage, Optical metrology

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Proceedings Article | 8 July 2021 Presentation + Paper

Application of shearography and the percussion method for the structural inspection of wall paintings: a case study of St. Christopher in Maria Church, Nisse

Valentina Gatto, Andrei Anisimov, Wouter Lettinga, Nan Tao, Merel Lantman, Bernice Crijns, Roger Groves

Proceedings Volume 11784, 117840K (2021) https://doi.org/10.1117/12.2591911

KEYWORDS: Shearography, Inspection, Infrared cameras, Thermography, Temperature metrology, Lamps, Interferometry, Halogens, Defect detection, Data fusion

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Structural delamination in mural paintings is a complex phenomenon and is considered among the most frequent types of damage. In conservation practice, the most common technique to identify structural detachments in wall paintings is the percussion method, otherwise known as the ‘tap and listen’ approach. Full-field optical techniques based on interferometry, such as shearography, can potentially provide a more scientifically substantiated evaluation of the condition of heterogeneous structures of wall paintings. The empirical nature of the percussion method was observed during the condition assessment of two medieval wall paintings in Maria Church, Nisse, Netherlands. Consequently, the need to obtain more knowledge regarding the structural condition of these wall paintings was established. Furthermore, to allow the formulation of specific treatment needs for structural delamination in wall paintings, accurate defect mapping is needed. The application of shearography coupled with thermography was believed to provide an holistic representation of the structural condition of the wall painting depicting St. Christopher in Maria Church. A comparison of the practical execution and the interpretation of data between shearography and the percussion method was conducted to deliver a description of both techniques. Initial comparison of the two methods confirmed what was already hypothesised: I) the percussion method can provide an approximate indication of delaminated areas. Results, which are considered both non-qualitative and non-quantitative, are dependent on the experience of the conservator; II) shearography can produce qualitative and quantitative results regarding the presence of delamination in complex structures of wall paintings. Analysis of the shearography data together with the percussion method may result in a reliable way to map the defects for future conservation activities. The next steps include optimisation of the thermal excitation for shearography to maximise the defect detection and adapt the shearography output for onsite interpretation by conservators and professionals in the cultural heritage.

Proceedings Article | 20 June 2021 Presentation + Paper

Spatially modulated thermal excitations for shearography non-destructive inspection of thick composites

Nan Tao, Andrei Anisimov, Roger Groves

Proceedings Volume 11782, 117820V (2021) https://doi.org/10.1117/12.2592293

KEYWORDS: Shearography, Modulation, Composites, Inspection, Nondestructive evaluation, Defect detection, Ocean optics, Wind energy, Signal to noise ratio, Signal detection

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Proceedings Article | 27 July 2019 Presentation

Multimodal nondestructive inspection of impact damages in composite laminates: a case study to assess the damage volume (Conference Presentation)

Andrei Anisimov, Mariya Serikova, Nan Tao, Chirag Anand, Fardin Esrail, Christos Kassapoglou, Roger Groves

Proceedings Volume 11059, 110590W (2019) https://doi.org/10.1117/12.2525808

KEYWORDS: Inspection, Composites, Nondestructive evaluation, Ultrasonics, Data modeling, Numerical modeling, Phased arrays, Shearography, Algorithm development, Data analysis

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The objective of this case study is to characterise and to numerically assess the volume of impact damages in composite laminates with multiple non-destructive testing techniques. Reliable and robust assessments of the damage volume will be used as input and validation data for the existing and developing numerical models of composite materials. In everyday work, researchers in the area of composite materials mostly use 2D assessment of the damaged area acquired with conventional inspection methods as ultrasonic c-scan. This practice is supported by the relative simplicity of the data analysis carried in 2D. It is proposed to assess the damage volume in 3D which may serve as a more reliable criterion to improve coupling with the numerical modelling. In this paper micro X-ray computed tomography (CT) was used as the reference technique for the damage volume assessment and comparison with an industrial ultrasonic c-scan. In addition, for this case study, ultrasonic phased array technique with the full matrix capture algorithms was used for the inspection together with shearography (speckle pattern shearing interferometry). A comparison of all techniques referenced to the CT data formed the guidance for their applicability. In addition, an attempt to fuse the multiple assessments was made to support the comparison of 2D and 3D inspection techniques. For the experimental part, carbon fiber reinforced polymer (CFRP) specimens of three layups were manufactured and damaged with 4 different impact energies in the range of 18-45 J. The layups were orthotropic, quasi-isotropic and a novel one adapted for the impact events. In total 12 specimens were inspected with multiple non-destructive testing techniques to numerically assess the volume of the impact damages. 3 additional specimens were used to assess the repeatability of the damage in the specimens with the same layup and impact energy. 3D CT reconstructions were made by a rotation of specimens using a cone-beam system with the voxel side size of 50 μm. A developed automatic segmentation algorithm was used for the damage volume estimation in all specimens. The phased array inspection was made with a full-matrix capture technique with the frequencies of 2.25 and 5 MHz. An available 3D shape shearography setup was used to characterise the damages both with the in- and out-of-plane surface strains with a thermal loading of the specimen. Future developments include the comparison of the inspection results together with the numerical modelling predictions and with residual strength after the impact.

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