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This systematic review investigates the state of the art of smart fasteners and smart washers. The collected documents were systematically classified, focusing on fasteners and washers equipped with embedded sensors capable of detecting flaws, corrosion, cracks, or monitoring features like structural response, applied load, and preload. The review emphasizes sensor technologies rather than devices made from smart materials. A total of 148 documents were found through electronic databases, of which 32 were thoroughly analyzed and categorized into 5 categories depending on the sensing capabilities, actuating capabilities, ability to transmit data, and their combinations. The analysis showed that most devices incorporate piezoelectric materials as sensing or actuation elements, primarily aimed at detecting fastener loosening or monitoring preload and load in fastened joints. Despite progress, several challenges limit industrial adoption, including sensor integration affecting bolt integrity, durability and calibration issues, and high costs. Few studies address scalability or measurement performance, highlighting the need for reliable, low-cost, and industrially scalable solutions.
- smart fastener
- smart washer
- smart joints
- structural health monitoring
Bolts, nuts, cap screws and rivets are used for joining parts into a structural assembly; their characteristics must be chosen to ensure integrity under service conditions that may induce loosening, such as vibration and fluctuating loads [1]. Since its introduction, bolted joints have been extensively adopted in both civil and mechanical engineering applications to create non-permanent joints, thanks to their high strength and ease of use. Given that such joints are often subjected to complex, multi-axial loading, their design requires careful consideration. Particularly when considering that the connection is influenced by cyclic loading and various working conditions [2][3][4][5][6].
Since accidents may occur because of loosened bolted joints, periodic manual and visual inspection is adopted for structures such as bridges, skyscrapers, power plants, and aerospace applications. However, manual and visual inspection is time-consuming and subject to human actions [7][8]. Several techniques can be used to inspect bolted joints, such as visual inspection for surface condition monitoring, Non-Destructive Inspection (NDI) for corrosion detection, or acoustic emission to detect material loss gaps that could cause structural integrity loss. Still, these techniques do not provide continuous monitoring of the joint. In this contest, Structural Health Monitoring (SHM) plays a fundamental role, as SHM is the process of continuously assessing the integrity and performance of structures through embedded or attached sensors and data interpretation methods that convert measurements into meaningful information on the structure status [9]. Recent work by Zhaoet al. [10] demonstrated the effectiveness of machine learning models for assessing structural information based on measurement data. Moreover, as highlighted in the in [11], advances in smart sensing technologies have significantly expanded the applicability of SHM, enabling real-time detection of corrosion, fatigue, and cracks in complex structures. The use of smart monitoring systems that do not need human involvement brings several advantages: they are effective, reliable, cost-effective, repeatable, accurate, and, often, they do not require heavy structural changes. Beyond force monitoring, innovative sensors are integrated into bolted joints to support structural health monitoring and facilitate predictive maintenance strategies for timely fault identification [4][12][13][14]. Within this framework, smart fasteners and washers represent a specific class of localized SHM nodes, capable of capturing load, strain, or damage information directly at the joint level. The sensing element can be either the bolt or the washer. Both of them are considered in this systematic review.
To the best of our knowledge to date, there are no studies focused on the systematic review summarizing the available technologies for smart fasteners and washers, both for structures and production systems.
The paper is structured as follows: the search strategy, eligibility criteria, and data analysis procedures are described in Section 2. Section 3 presents the results of the systematic review on sensing techniques applied to bolts and washers. Section 4 summarizes the results and critically analyzes the different techniques. Paper conclusions are drawn in Section 5.
This entry is adapted from the peer-reviewed paper 10.3390/encyclopedia5040196
References
- Smith, J.D.; Pothier, S.G. Load Sensing System Including RFID Tagged Fasteners. U.S. Patent US 11/460,819, 19 August 2006.
- Huo, L.; Chen, D.; Liang, Y.; Li, H.; Feng, X.; Song, G. Impedance based bolt pre-load monitoring using piezoceramic smart washer. Smart Mater. Struct. 2017, 26, 057004.
- Zhu, S.; Huang, S.S. Intelligenter Befestiger. Europe Patent EP2803871A1, 2 November 2016.
- Groche, P.; Brenneis, M. Manufacturing and use of novel sensoric fasteners for monitoring forming processes. Measurement 2014, 53, 136–144.
- Yin, H.; Wang, T.; Yang, D.; Liu, S.; Shao, J.; Li, Y. A Smart Washer for Bolt Looseness Monitoring Based on Piezoelectric Active Sensing Method. Appl. Sci. 2016, 11, 320.
- Eslami, B.; Ganye, R.; Bunai, C.; Thamire, C. Smart Fasteners and Their Application in Flanged Joints Available to Purchase. In Proceedings of the ASME International Mechanical Engineering Congress and Exposition, Houston, TX, USA, 9–15 November 2012.
- Tanaka, T.; Okugawa, M. Adopting supervisor for bolt loosening detection by using smart washer. In Proceedings of the ASME 2008 Conference on Smart Materials, Adaptive Structures and Intelligent Systems, Ellicott City, MD, USA, 28–30 October 2008.
- Akdeniz; Kollgaard, J.; Malkin, M. Active Washers for Monitoring Bolted Joints. U.S. Patent US7698949, 20 April 2010.
- Chen, H.-P.; Ni, Y.-Q. Introduction to Structural Health Monitoring. In Structural Health Monitoring of Large Civil Engineering Structures; John Wiley & Sons: Hoboken, NJ, USA, 2018.
- Zhao, H.-W.; Zhang, X.; Ding, Y.; Guo, T.; Li, A.; Soh, C.-K. Probabilistic mixture model driven interpretable modeling, clustering, and predicting for physical system data. Eng. Appl. Artif. Intell. 2025, 160, 112069.
- Liu, Z. Smart Sensors for Structural Health Monitoring and Nondestructive Evaluation. Sensors 2024, 24, 603.
- Wang, G. Strain-Gsuged Washer for Measuring Bolt Preload. U.S. Patent US9719900B1, 1 August 2017.
- Schoess, J.N.; Havey, G.D. Smart Fastener. U.S. Patent US5549803A, 27 August 1996.
- Aske, J.; Wilson, J.; Smith, R.; Berden, M. Intelligent Fasteners. U.S. Patent 11,074,490, 27 July 2021.
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