In-situ Non-destructive Measurement of Residual Stress on Strengthened Surfaces Based on Laser-induced Ultrasonic Rayleigh Waves

Chen Dan

Fatigue failure of critical aerospace structures mostly originates from structural surfaces. Surface strengthening processes such as shot peening and roller burnishing can introduce compressive residual stress at a certain depth beneath the structural surface to improve fatigue life, wherein the accurate non-destructive measurement of residual stress serves as the key to engineering applications. Traditional X-ray diffraction methods suffer from limitations of shallow detection depth, material specificity and inability for in-situ measurement, while piezoelectric ultrasonic testing relies on coupling agents and exhibits poor environmental adaptability. Accordingly, this paper proposes an in-situ non-destructive measurement method for residual stress on strengthened surfaces based on laser-induced ultrasonic Rayleigh waves. Based on the acoustoelastic effect, the mapping relationship between surface roughness and Rayleigh wave velocity is established to correct wave velocity errors. Taking annealed specimens as the zero-stress reference, the interference caused by grain refinement and plastic deformation is eliminated, realizing two-dimensional distribution imaging of the equivalent average residual stress. Meanwhile, nonlinear narrowband Rayleigh waves are excited via a grating mask. Relying on the linear correlation between the relative nonlinear coefficient and compressive residual stress, the in-situ non-destructive quantitative characterization of the depth distribution of residual stress is achieved. The experimental results show that the nonlinear ultrasonic method possesses higher measurement accuracy than the wave velocity method, with low sensitivity to microstructure and surface roughness and no requirement for acoustoelastic constant calibration. The proposed method enables non-contact, in-situ and high-precision residual stress detection, which provides an effective technical approach for quality evaluation of surface strengthening processes and structural health monitoring of aerospace components.

 

Biography of Chen Dan

Dr. Chen Dan is a Associate Researcher and a Shenzhen Reserve-level High-level Talent. He serves as the Deputy Secretary-General of the Nondestructive Testing Branch of Shenzhen Mechanical Engineering Society and an expert of the working group for formulating industrial standards on nondestructive testing under the Chinese Mechanical Engineering Society. Currently, he works at the Institute of Ultrasonic Technology, Shenzhen Polytechnic University, and holds the position of Director of the Shenzhen Polytechnic-ChengTan Clean Energy Ultrasonic Testing Technology R&D Center. He primary research directions include laser ultrasonic detection, high-frequency ultrasonic microscopic imaging, and ultrasonic nondestructive characterization of material microstructure and properties. He has presided over more than 10 scientific research projects and published over 20 SCI/EI papers in top-tier journals such as Composites Science and Technology, NDT & E International, Optics and Laser Technology, IEEE Transactions on Instrumentation and Measurement, Ultrasonics, and Applied Acoustics.

 

Reinforced Concrete Structure

Li Qiufeng

Concrete structures are widely used in modern architecture due to their durability, load-bearing capacity, and other advantages. However, during the pouring, construction, and service processes, they are susceptible to internal defects caused by material and environmental factors, leading to deterioration of structural performance. Therefore, their internal quality inspection has important engineering value. Ultrasonic testing technology is widely used in this field due to its non-destructive and high sensitivity characteristics. However, due to the large size and complex composition of concrete structures, traditional ultrasonic testing has problems such as low efficiency, poor beam directionality, waveform distortion caused by sound energy attenuation and structural noise, insufficient imaging signal-to-noise ratio and detection accuracy. To this end, a high-resolution combination imaging technology for array ultrasonic testing is proposed, which is based on total focusing method and effectively improves the signal-to-noise ratio of detection signals and enhances the quality of total focusing method for concrete structures through beam directionality correction, detection signal correction, reflection echo focusing enhancement and other processing. The proposed technology can provide technical support for accurate positioning and quantitative detection of internal defects in concrete structures.

 

Biography of Li Qiufeng

He graduated from Nanjing University of Aeronautics and Astronautics in 2008 with a PhD in Engineering. Currently, he is the director of the Metrology and Testing Research Center, professor, and doctoral supervisor at Nanchang Hangkong University. Jiangxi Training Project of a high-level and high-skill leading talents, a talent in Jiangxi Province's "Far Voyage Project", and a national public visiting scholar at Nanyang Technological University in Singapore. Appointed as a member of the Ultrasonic, Acoustic Emission, and Condition Monitoring Professional Committee of the Non-Destructive Testing Branch of the Chinese Society of Mechanical Engineering, and as the Chairman of the Jiangxi Metrology and Testing Society. Selected from the Degree and Graduate Education Expert Database of the Ministry of Education and the National Defense Science and Technology Industry Talent Database of Jiangxi Province, as well as the National Natural Science Foundation of China, the Aviation Science Foundation of China, and the National Defense Science and Technology Bureau project evaluation experts. Editorial Committee member of the journals "Piezoelectric and Acousto optic" and "Failure Analysis and Prevention". Mainly engaged in electrical magnetic acoustic non-destructive testing and evaluation technology, detection signal analysis and processing research, etc. Hosted one "Huiyan Action" project of the Equipment Development Department of the Central Military Commission, more than 20 national natural science foundation projects, published over 100 academic papers, searched over 80 SCI/EI papers, authorized 12 national invention patents, and won three first prizes of provincial and ministerial level science and technology awards.

 

Chang Junjie

  Air-coupled ultrasonic testing is a non-contact non-destructive testing technology that uses air as the coupling medium. It breaks through the limitation of traditional ultrasonic testing that requires coupling agents, avoiding contamination caused by residual coupling agents or damage resulting from contact. It is suitable for detecting special scenarios and sensitive materials. This report first introduces the basic theory of non-contact air-coupled ultrasonic wave testing technology and the key technologies, detection principles and methods needed to achieve air-coupled ultrasonic testing, mainly including body waves and guided waves, same-side detection method, and opposite-side detection method. It also introduces the attempts of air-coupled ultrasonic in acoustic-optic, photoacoustic detection methods and imaging. Finally, it presents the application cases of the development equipment of various detection methods in actual engineering.  

 

Biography of Chang Junjie

 

 

  Through-barrier electromagnetic induction imaging with atomic magnetometers:

a new tool for NDT  

Ferruccio Renzoni

The assessment of corrosion in pipelines remains a critical challenge in the Oil & Gas industry. In particular, corrosion under insulation (CUI) arises from moisture trapped between the insulation layer and the pipe surface, leading to localized damage that can ultimately cause catastrophic failure. Early detection is therefore essential. However, access to the pipeline surface is hindered by insulating layers, which in ageing infrastructure may include hard-to-remove materials such as asbestos.
Existing approaches for CUI monitoring—including infrared thermography, neutron backscattering, radiography, pulsed eddy current testing, and ultrasonic techniques—each suffer from important limitations. As a result, efficient, large-scale inspection of insulated pipelines remains an open problem.
Recent work has demonstrated that electromagnetic induction imaging with atomic magnetometers (EMI-AM) can detect and quantify localized thinning in metallic structures, opening a viable route for CUI inspection. This approach offers several advantages over existing techniques: it is simple, low-cost, and non-ionising, and therefore intrinsically safe. Crucially, its operation at low frequencies enables significant penetration through both insulating and the underlying pipeline structure.
Initial proof-of-concept demonstrations were performed using a laboratory-based system with mechanically translated samples. Moving towards real-world deployment requires instead a portable sensor capable of scanning fixed structures. This has been achieved through the development of a mechanically translatable, unshielded atomic magnetometer, enabling operation in realistic environments and paving the way for field applications.
This talk will review recent progress in EMI-AM for through-barrier imaging and discuss future directions towards practical, deployable NDT solutions.
[1] P. Bevington, R. Gartman, W. Chalupczak, C. Deans, L. Marmugi, and F. Renzoni, Non-Destructive Structural Imaging of Steelwork with Atomic Magnetometers, Appl. Phys. Lett. 113, 063503 (2018).
[2] H. Yao, N. Yin, R. Lee, G. Liu, F. Renzoni, Through-Barrier Sub-mm Electromagnetic Induction Imaging With Atomic Magnetometers, IEEE Trans. Instrum. Meas. 74, 4506708 (2025).
[3] H. Yao and F. Renzoni, High-sensitivity operation of unshielded radio-frequency atomic magnetometers using phase-lock techniques, IEEE Trans. Instrum. Meas. 74, 9535009 (2025).
[4] H. Yao, L. Zhao, T. Ma, and F. Renzoni, Fast electromagnetic induction imaging with unshielded radio-frequency atomic magnetometers in phase-lock mode, IEEE Trans. Instrum. Meas. 74, 8007907 (2025).

 

Biography of Ferruccio Renzoni

• Deputy Head of Department of Physics and Astronomy, University College London
• Member (Sub-panel 9: Physics) in the 2021 Research Excellence Framework (REF).
• Editorial Board Member for Scientific Reports, Nature Publishing Group (August 2015- December 2022).
• Fellow of the Higher Education Academy (FHEA).
• Member of the Institute of Physics.
• Member of the EPSRC Peer Review College (2006-present).
• Guest Editor for a Special Issue of the Journal of Modern Optics (20011).

Research Profile:

Professor Ferruccio Renzoni's research focuses on quantum sensing for non-destructive testing (NDT) and fundamental physics such as Bose-Einstein Condensation (BEC). His primary research areas encompass atomic magnetometry, cold atom physics, and nonlinear dynamics. He is dedicated to advancing quantum sensing technologies based on cold atomic systems and atomic magnetometers. Notably, he was the first to demonstrate electromagnetic induction imaging (EMI) using atomic magnetometers and continues to drive this technology towards practical applications in biomedical imaging, non-destructive testing, and security screening. His work also involves using cold atoms in optical lattices to simulate statistical mechanics phenomena, exploring collective strong coupling regimes in multimode cavity quantum electrodynamics (QED), and conducting in-depth theoretical and experimental investigations into transport and dynamics in nonlinear systems, such as Brownian motors in optical lattices and dissipation-induced symmetry breaking.

He has published over 90 academic papers in journals including Nature Physics and Physical Review Letters, many of which are highly influential with more than 50 citations each.

Professional Service:

He has been a referee for EPSRC, The Royal Society, INTAS, the Leverhulme Trust, the FWF Austrian Science Fund, the Israeli Science Foundation, and the U.S.-Israel Binational Science Foundation.

He has been a committee member or has delivered invited/plenary talks at dozens of major international academic conferences, including the European Physical Society conferences, the International Quantum Electronics Conference, and SPIE conferences on Sensing and Imaging.

 

 

 

Defect Detection Technique Based on Flexible Omnidirectional Interdigital Ultrasonic Sensing
Rao Jing

Ultrasonic interdigital transducers (IDTs) show great promise for non-destructive testing due to their tunable operating frequency and beam-focusing capability. However, conventional ultrasonic IDTs often suffer from limited scanning angles and low spatial coverage efficiency, which restrict their application in real-time, high-precision defect detection. To address these issues, this paper proposes a flexible omnidirectional interdigital ultrasonic transducer (ODIDT) composed of fan-shaped interdigital structures. This design not only enables directional excitation of ultrasonic waves but also excites a single A0 mode guided wave at a center frequency of 380 kHz. Furthermore, a travel-time localization method based on spatial constraints is proposed. By exploiting the directionality of ODIDT transmission and reception, this method effectively suppresses imaging artifacts caused by limited sector sampling and insufficient path information. Experimental results demonstrate that the proposed ODIDT can accurately locate circular hole defects at different positions on a 2‑mm-thick aluminum plate and can identify defects with dimensions approaching the diffraction limit.

 

Biography of Rao Jing

Jing Rao is a professor at Beihang University, a national young talent, and an Alexander von Humboldt Fellow. She received her Ph.D. from Nanyang Technological University, Singapore, and previously worked as an assistant professor at the University of New South Wales, Australia. Her research focuses on non-destructive testing and structural health monitoring. She has led more than 30 research projects funded by the National Natural Science Foundation of China, the Beijing Natural Science Foundation, the National Science and Technology Major Project on Key New Materials R&D and Applications (2030), the Alexander von Humboldt Foundation, the University of New South Wales, and Sinopec, among others. She received the Best Project Award at the Singapore Maritime Technology Congress in 2017, the First Prize in Technological Invention (ranked first) from the China Petroleum and Chemical Automation Application Association in 2025, and the Award at the Far East NDT New Technology Forum in 2025. She currently serves as Associate Editor for Measurement, Ultrasonic Imaging, and the IEEE Open Journal of Signal Processing. She is a member of the Third Committee of the Equipment Structural Health Monitoring and Early Warning Division of the China Instrument and Control Society, a member of the NDT Division of the Chinese Mechanical Engineering Society, a senior member of IEEE and the Chinese Society of Theoretical and Applied Mechanics, and a session chair/TPC member for international conferences such as 2023 IEEE IUS, 2023 IEEE/ASME AIM, and 2021 ACAM.