Browsing by Author "Chen, Zhenmao"
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Item Open Access A cyclic self-enhancement technique for complex defect profile reconstruction based on thermographic evaluation(Springer, 2025-05) Liu, Haochen; Wang, Shuozhi; Zhao, Yifan; Deng, Kailun; Chen, ZhenmaoAlthough machine Learning has demonstrated exceptional applicability in thermographic inspection, precise defect reconstruction is still challenging, especially for complex defect profiles with limited defect sample diversity. Thus, this paper proposes a self-enhancement defect reconstruction technique based on cycle-consistent generative adversarial network (Cycle-GAN) that accurately characterises complex defect profiles and generates reliable artificial thermal images for dataset augmentation, enhancing defect characterisation. By using a synthetic dataset from simulation and experiments, the network overcomes the limited samples problem by learning the diversity of complex defects from finite element modelling and obtaining the thermography uncertainty patterns from practical experiments. Then, an iterative strategy with a self-enhancement capability optimises the characterisation accuracy and data generation performance. The designed loss function structure with cycle consistency and identity loss constrains the GAN’s transfer variation to guarantee augmented data quality and defect reconstruction accuracy simultaneously, while the self-enhancement results significantly improve accuracy in thermal images and defect profile reconstruction. The experimental results demonstrate the feasibility of the proposed method by attaining high accuracy with optimal loss norm for defect profile reconstruction with a Recall score over 0.92. The scalability investigation of different materials and defect types is also discussed, highlighting its capability for diverse thermography quantification and automated inspection scenarios.Item Open Access An efficient electromagnetic and thermal modelling of eddy current pulsed thermography for quantitative evaluation of blade fatigue cracks in heavy-duty gas turbines(Elsevier, 2020-03-19) Tong, Zongfei; Xie, Shejuan; Liu, Haochen; Zhang, Weixu; Pei, Cuixiang; Li, Yong; Chen, Zhenmao; Uchimoto, Tetsuya; Takagi, ToshiyukiThe blade surface fatigue cracks often occur during service of Heavy-Duty Gas Turbines (HDGT) in high temperature, high rotational velocity and high frequency vibration environment. These fatigue cracks seriously threaten the safe operation of heavy-duty gas turbines, which would cause significant hazard or economic loss. The quantitative evaluation of blade surface fatigue cracks is extremely significant to HDGT. Eddy current pulsed thermography (ECPT) is an emerging non-destructive testing technology and show great potential for fatigue crack evaluation. This paper proposes a novel electromagnetic and thermal modelling of ECPT to achieve fast and effective quantitative evaluation for surface fatigue cracks. First, the proposed numerical method calculates electromagnetic field using the reduced magnetic vector potential method in the frequency domain based on frequency series method. The thermal source is transformed to an equivalent and simple form according to the energy equivalent method. Second, the temperature signals of ECPT are calculated through the time-domain iteration strategy with a relatively large time step. Then the ECPT experimental setup is established and the developed simulator is validated numerically and experimentally. The developed simulator is five times faster than the previous one and can be applied to eddy current thermography (ECT) with any kind of excitation waveforms. Finally, the depth of surface fatigue crack is quantitatively evaluated by means of the developed simulator, which is not only a promising simulation progress for ECPT, but also can be an effective tool embedded HDGT though-life maintenanceItem Open Access A fiber-guided motorized rotation laser scanning thermography technique for impact damage crack inspection in composites(IEEE, 2023-04-11) Liu, Haochen; Tinsley, Lawrence; Deng, Kailun; Wang, Yizhong; Starr, Andrew; Chen, Zhenmao; Zhao, YifanLaser Thermography manifests superior sensitivity and compatibility to detect cracks and small subsurface defects. However, the existing related systems have limitations on either inspection efficiency or unknown directional cracks due to the utilization of stationary heat sources. This article reports a Fiber-guided Motorised Rotation Laser-line Scanning Thermography (FMRLST) system aiming to rapidly inspect cracks of impact damage with unknown direction in composite laminates. An optical head with fibre delivery integrated with a rotation motor is designed and developed to generate novel scanning heating in a circumferential rotation manner. A FEM model is first proposed to simulate the principle of FMRLST testing and produce thermograms for the development of post-processing methods. A damage enhancement method based on Curvelet Transform is developed to enhance the visualization of thermal features of cracks, and purify the resulting image by suppressing the laser-line heating pattern and cancelling noise. The validation on three composite specimens with different levels of impact damage suggests the developed FMRLST system can extract unknown impact surface cracks efficiently. The remarkable sensitivity and flexibility of FMRLST to arbitrary cracks, along with the miniaturized probe-like inspection unit, present its potential in on-site thermographic inspection, and its design is promising to push the LST towards.Item Open Access Inspection of delamination defect in first wall panel of Tokamak device by using laser infrared thermography technique(IEEE, 2018-04-16) Liu, Haochen; Pei, Cuixiang; Qiu, Jinxing; Chen, ZhenmaoFirst wall panels (FWPs), which adjoin the inner wall of the blanket modules in the vacuum vessel (VV) of a Tokamak device, are in structures of multilayer bounded together with a solid welding technique in order to perform its heat exchange, VV protection, and neutron breeding functions. The quality of the welding joint between layers is the key factor for FWP integrity. In order to conduct online inspection of the delamination defect in the FWPs, a nondestructive testing (NDT) method capable to detect delamination defect without accessing into the VV is required. In this paper, the feasibility of the laser infrared thermography (LIRT) testing NDT method was investigated experimentally for this purpose. To clarify its detectability under practical VV environment, inspections of several inspection modes were conducted based on the practical structure of FWP and VV of the EAST Tokamak device, i.e., modes of different distances and angles of FWPs toward the LIRT transducers. In practice, an LIRT testing system was established and several double-layered plate specimens with different artificial delamination defects were inspected under the selected testing conditions. Through thermography signal reconstruction, an image processing algorithm was proposed and adopted to enhance the defect detectability. From the results of different inspection modes, it was found that the angle factor may worsen the inspection precision and reduce the detectability for delamination defects in case of big defect depth-to-width ratio, even though the LIRT method is still applicable for inspection of relative large defects in FWP. Finally, the detectability in different inspection modes was clarified, which proved the feasibility of LIRT for FWP online inspection.Item Open Access Inversion technique for quantitative infrared thermography evaluation of delamination defects in multilayered structures(IEEE, 2019-10-31) Liu, Haochen; Pei, Cuixiang; Xie, Shejuan; Li, Yong; Zhao, Yifan; Chen, ZhenmaoInverse analysis is a promising tool for quantitative evaluation offering informative model-based prediction and providing accurate reconstruction results without pre-inspections for characterization criteria. For traditional defect inverse reconstruction, a large number of parameters are required to reconstruct a complex defect, and the corresponding forward modelling simulation is very time-consuming. Such issues result in ill-posed and complex inverse reconstruction results, which further reduces its practical applicability. In this paper, we propose and experimentally validate an inversion technique for the reconstruction of complexly-shaped delamination defects in a multilayered metallic structure using signals derived from infrared thermography (IRT) testing. First, we employ a novel defect parameterization strategy based on Fourier series fitting to represent the profile of a complicated delamination defect with relatively few coefficients. Secondly, the multi-medium element modelling method is applied to enhance a FEM fast forward simulator, in order to solve the mismatching mesh issue for mesh updating during inversion. Thirdly, a deterministic inverse algorithm based on a penalty conjugate gradient algorithm is employed to realize a robust and efficient inverse analysis. By reconstructing delamination profiles with both numerically-simulated IRT signals and those obtained through laser IRT experiments, the validity, efficiency and robustness of the proposed inversion method are demonstrated for delamination defects in a double-layered plate. Based on this strategy, not only is the feasibility of the proposed method in Infrared thermography NDT validated, but the practical applicability of inversion reconstruction analysis is significantly improved.Item Open Access Laser array spots thermography for detection of cracks in curved structures(IOS, 2020-12-10) Jinxinga, Qiu; Pei, Cuixiang; Yang, Yang; Liu, Haochen; Chen, ZhenmaoThe laser array spot thermography (LAST) is a fully non-contact and non-destructive method for the inspection of surface cracks with high efficiency. In this study, the detection capability of this method for the inspection of surface cracks in structures with curved surfaces is experimentally studied. The influence of the inspection angle on the crack imaging results is also investigated. The experiment results show that cracks in surface of the pipes with different dimeters can be detected and imaged by LAST.Item Open Access Progress on the ultrasonic testing and laser thermography techniques for NDT of tokamak plasma-facing components(Elsevier, 2019-06-24) Pei, Cuixiang; Liu, Haochen; Qiu, Jinxing; Liu, Tianhao; Chen, ZhenmaoDuring manufacturing and operation, different kinds of defects, e.g., delamination or surface cracks, may be generated in the plasma-facing components (PFCs) of a Tokamak device. To ensure the safety of the PFCs, various kinds of nondestructive testing (NDT) techniques are needed for different defect and failure mode. This paper gives a review of the recently developed ultrasonic testing (UT) and laser thermography methods for inspection of the delamination and surface cracks in PFCs. For monoblock W/Cu PFCs of divertor, the bonding quality at both W-Cu and Cu-CuCrZr interfaces was qualified by using UT with a focus probe during manufacturing. A noncontact, coupling-free and flexible ultrasonic scanning testing system with use of an electromagnetic acoustic transducer and a robotic inspection manipulator was introduced then for the in-vessel inspection of delamination defect in first wall (FW). A laser infrared thermography testing method is highlighted for the on-line inspection of delamination defect in FW through the vacuum vessel window of the Tokamak reactor. Finally, a new laser spot thermography method using laser spot array source was described for the online inspection of the surface cracks in FW.Item Open Access Quantitative evaluation of surface crack depth with laser spot thermography(Elsevier, 2019-02-28) Qiu, Jinxing; Pei, Cuixiang; Liu, Haochen; Chen, ZhenmaoIn this study, a numerical method based on finite element method (FEM) is developed to simulate the heat flow generated by laser spot source and investigate the relationship between crack size and temperature distribution. The feasibility of the simulation method is validated by experiments both in time and spatial domains. The simulation and experiment results also show that the crack depth can be described by two characteristic parameters. Furthermore, a quantitative retrieval method based on neural network is developed for the crack depth evaluation by using the parameters. By using the proposed method, crack depth can be determined only by analyzing measured surface temperature values.Item Open Access Remote measurement and shape reconstruction of surface-breaking fatigue cracks by laser-line thermography(Elsevier, 2020-09-15) Qiu, Jinxing; Pei, Cuixiang; Yang, Yang; Wang, Rongbang; Liu, Haochen; Chen, ZhenmaoIn this paper, a method for remote measurement and shape reconstruction of fatigue cracks by using laser-line thermography (LLT) technique is developed. A new feature parameter derived from the LLT signals is proposed to evaluate the length and estimate the general inner profile of a surface-breaking fatigue crack. An inversion analysis scheme based on conjugate gradient optimization algorithm is then applied to reconstruct the detailed inner profile and dimension of the crack. The reconstruction results with both numerically simulated LLT signals and experimental signals proved the feasibility of proposed inversion scheme and remote LLT method. Based on methods of this paper, not only the size of cracks can be quantitatively evaluated, but the inner profile is also reconstructed for cracks in different shapes from the LLT signals