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Draft:Self-sensing composites

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  • Comment: Draft shows serious signs of LLM generation. CostalCal (talk) 05:56, 6 August 2026 (UTC)

Self-sensing E-glass composites are glass-fibre-reinforced polymer composites in which selected E-glass filaments or bundles function both as structural reinforcement and as optical sensing elements. Changes in transmitted light can indicate deformation, fibre fracture or changes during manufacture. The approach is used in structural health monitoring (SHM) to reduce reliance on separate surface-mounted or embedded sensors and to increase the volume of material being monitored.[1]

Self-sensing behaviour has been demonstrated in carbon-fibre-reinforced polymers through changes in electrical resistance, in nanocomposites containing conductive fillers, in cementitious composites, and in glass-fibre composites in which the reinforcing fibres act as optical waveguides.[2][3] Signals from self-sensing materials may be combined with conventional non-destructive testing, acoustic emission, fibre-optic sensors or data-driven diagnostics.[1]

Definition and scope

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A conventional smart structure usually contains a host material and a distinct sensing element. In a self-sensing composite, the material that carries mechanical load also participates in transduction. For example, carbon fibres may form an electrically conductive network whose resistance varies with deformation, while glass reinforcement may guide light whose intensity changes when fibres bend, debond or fracture.[4][5]

The term overlaps with multifunctional composite, smart material and intrinsic sensing. It is normally distinguished from systems in which a conventional strain gauge, fibre Bragg grating or piezoelectric patch is merely attached to or embedded in an otherwise passive composite. Some hybrid designs contain both intrinsic self-sensing material and discrete sensors, using the different signals to reduce ambiguity about the location or type of damage.[1]

Sensing mechanisms

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Electrical resistance and piezoresistivity

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Continuous carbon fibres are electrically conductive, whereas most polymer matrices are insulating. In a carbon-fibre composite, current therefore passes through fibres, fibre-to-fibre contacts and, in multidirectional laminates, contacts between plies. Elastic strain can reversibly change fibre resistance and contact geometry; matrix cracks, delamination and fibre rupture can irreversibly remove or rearrange conductive paths.[4][6] Resistance measurements can consequently be related to applied strain and to the onset or accumulation of damage.

Conductive fillers—including carbon nanotubes, graphene, carbon black, metallic particles and two-dimensional materials such as MXenes—are also used to create a percolating network in an insulating matrix or at a fibre–matrix interface. Such networks can provide higher strain sensitivity than the structural fibres alone, but their response depends strongly on filler dispersion, concentration, contact resistance, temperature and humidity.[1]

The resistance-based principle is also applied to self-sensing cementitious composites. Conductive fibres, particles or nanomaterials are dispersed through cement paste, mortar or concrete so that loading and cracking alter the material's electrical resistivity. Proposed uses include monitoring pavements, bridges and other civil infrastructure, although moisture, freeze–thaw exposure, mix design and electrode configuration can affect the response.[7]

Optical reinforcing fibres

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In an optical self-sensing glass-fibre composite, selected load-bearing filaments or bundles act as short-distance optical waveguides. Light is confined when the refractive index of the glass is greater than that of the surrounding coating or polymer matrix. Mechanical deformation, microbending and changes at the fibre–matrix boundary can attenuate transmitted light. Fibre fracture interrupts the optical path, while light escaping at a break can help locate the damaged region.[5][8]

This approach reduces the diameter and stiffness mismatch associated with embedding a standard telecommunications optical fibre, which is typically much larger than an individual reinforcing filament. It also makes the sensing path part of the reinforcement rather than a foreign inclusion. Its limitations include attenuation in reinforcing-grade glass, the need for stable light coupling and polished end faces, and sensitivity to the refractive indices and condition of the matrix and fibre surface.

Other and hybrid mechanisms

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Reviews published in the 2020s group fibre-based self-sensing systems into piezoresistive, optical and magnetic approaches, with capacitive, impedance-based and hybrid methods also under development.[1] Hybrid monitoring can compare an intrinsic signal with acoustic emission, thermography or another independent measurement. Acoustic emission is not itself an intrinsic property of the composite because external transducers are normally required, but it can establish when an irreversible event occurred and can help distinguish matrix cracking, interfacial failure and fibre fracture.

Related optical-sensor research at Birmingham provided complementary methods for validating and interpreting self-sensing signals. Chen, Malik, Fernando and co-workers developed a fused-tapered fibre-optic acoustic-emission sensor and demonstrated real-time detection of damage development in tensile, Mode-I delamination and composite blow-off tests.[9] Malik and co-workers also modelled the strain-transfer response of adhesively surface-mounted fibre Bragg grating sensors and validated the finite-element predictions against optical and electrical-resistance strain measurements.[10] Although these devices are distinct sensors rather than reinforcing E-glass light guides, the work supplied independent optical and acoustic measurements applicable to damage-detection experiments.

Historical development

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Reinforcing-fibre light guides

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Work in the 1990s demonstrated that selected reinforcing fibres could be made to act as light guides within a laminate. Hayes and co-workers reported quartz reinforcing fibres that combined a load-bearing role with optical damage detection.[11] Kister, Wang, Ralph and Fernando subsequently showed that conventional E-glass reinforcement could be converted into a waveguide by suitable surface preparation and a lower-refractive-index cladding.[5] In 2004, Kister, Ralph and Fernando used surface-mounted and embedded E-glass light guides to detect impact, indentation and flexural damage in glass-fibre-reinforced polymer laminates; damage location was visible from light escaping through broken guides.[8] Fernando and colleagues also used reinforcing E-glass light guides for chemical process monitoring and for observing fibre-fracture sequences.[12] In 2009, Harris, Mahendran, Malik, Fernando and their co-workers extended the concept to an integrated design combining self-sensing, self-healing and crack-arresting functions, and reported preliminary manufacture and evaluation of the proposed composite architecture.[13]

Filament-level optical damage detection

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Shoaib Ahmad Malik developed the reinforcing-fibre approach into a system for resolving the failure of individual, reinforcement-scale glass filaments in real time. His doctoral research at the University of Birmingham, supervised by Gerard Fernando, investigated both conventional E-glass and custom-made small-diameter optical fibres (SDOFs).[14]

Malik's experimental programme addressed several practical problems that had limited filament-level monitoring. It used end-tabs to protect brittle bundles in tensile-test grips, polished subminiature optical connectors to couple light into and out of the bundle, and a resin-infusion process to manufacture low-void specimens. A high-speed charge-coupled-device camera recorded the illuminated bundle end, while acoustic-emission events triggered image acquisition. Image-registration and analysis routines were then used to track the transmitted light from individual filaments and correlate its loss with mechanical loading and acoustic activity.[14][15]

Attenuation of transmitted light immediately before fracture in an E-glass filament (a–c) and a small-diameter optical fibre (d–f).

Acoustic-emission correlation and fibre-only bundles

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Earlier fibre-bundle research had established an acoustic-emission and statistical description of progressive filament failure. R'Mili, Moevus and Godin tensile-tested lubricated and unlubricated bundles containing about 2,000 E-glass filaments, used acoustic emission (AE) to detect individual breaks, and derived Weibull strength distributions from cumulative AE events and applied strain.[16] This work provided extensive evidence that fibres fail progressively according to a distribution of strengths. AE is nevertheless an indirect measurement of the elastic waves released by fracture: inter-fibre friction, multiple breaks, twists, localised fracture and events near the grips can complicate a one-to-one assignment between a recorded hit and a particular filament.[16][14]: 58–63 

Malik's programme used the earlier AE results as a reference and introduced an independent optical channel. Neat-resin specimens, unimpregnated fibre bundles and resin-infused composites were tested separately, allowing matrix cracking to be distinguished from fibre-only processes in the unimpregnated bundles. The first AE event above a specified threshold triggered the high-speed camera, and the tensile-machine load was recorded by the AE system; optical intensity, load and AE activity could therefore be compared on a common time base. AE amplitudes of 42–55 dB were associated with inter-fibre friction, 70–90 dB with fibre fracture in bundles, 60–70 dB with matrix failure and 80–100 dB with fibre fracture in composites. In three of the four bundle types, the cumulative AE-hit rate increased markedly at 90–95% of peak load, whereas silane-treated E-glass bundles showed a more gradual increase.[14]: 159–193, 228–240, 252 

The comparison produced quantitative as well as temporal agreement. For a representative as-received E-glass bundle of approximately 2,800 filaments, 526 AE hits above 60 dB were recorded before peak load and were interpreted as fibre fractures, equivalent to about 16% of the bundle. Over the same interval, transmitted optical intensity decreased by about 17%. The close values supported the attribution of most of the optical loss to fractured filaments, although the thesis noted that applied strain could also modify light propagation before failure. Across the bundle and composite tests, AE, mechanical load and transmitted-light measurements followed the same overall damage trend. The image-processing routines identified individual filaments with an accuracy of 94 ± 2%.[14]: 201–220, 228–253 

The fibre-only bundle experiments supplied the principal distinction from the preceding AE studies. Successive images showed individual load-bearing filaments ceasing to transmit light at different times, including after the bundle had reached peak load, while surviving fibres continued to carry load. This directly demonstrated a temporally sequential, non-catastrophic failure process: weaker filaments failed first according to their relative strengths, load was redistributed among the survivors, and the bundle did not fail when its first filament broke. Because the monitored gauge section was an unimpregnated bundle, the observed extinction represented fibre fracture rather than matrix cracking or delamination. Although AE initiated image capture, the evidence of each break was supplied independently by the reinforcing filament itself. The thesis characterised this as the first direct in-situ use of transmitted light through reinforcing fibres to demonstrate individual damage and successive fibre-only failure in a tensile-loaded bundle; earlier work, including that of R'Mili and co-workers, had inferred the process from AE, load curves and statistical strength distributions.[16][14]: 210–220, 252–253 

The peer-reviewed SDOF study published by Malik, Wang, Curtis and Fernando in 2016 used fibres with an overall diameter of 12 ± 2 micrometres. During tensile loading of unimpregnated bundles and resin-infused composites, the method recorded the progressive extinction of individual illuminated filaments and demonstrated the feasibility of detecting their fracture in real time.[17] The same research programme considered co-weaving SDOFs with E-glass and applied the monitoring method to conventional E-glass bundles and composites.[17][14]

Sequential fracture and load redistribution

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The optical records also provided an indication of damage before final failure. In a representative SDOF composite, approximately 7–8% of the filaments had ceased transmitting light at 76% of ultimate tensile strength, about 15 seconds before fracture of the specimen. Consecutive images recorded at 16.67-millisecond intervals then showed one filament attenuating immediately before it fractured. As that filament ceased transmitting, a neighbouring load-sharing filament attenuated and subsequently fractured. The sequence was interpreted as direct optical evidence of successive filament failure following local load redistribution, consistent with a distribution of filament failure strengths. The thesis and the later peer-reviewed paper described identification of a filament immediately before fracture as a first-reported capability.[14]: 241–246, 253–254 [17] The thesis nevertheless noted that conclusive spatial mapping of one filament failure to the next would require coherent fibre bundles and imaging at more than 60 frames per second.[14]: 245–246, 254 

Sequential fibre failure in an SDOF composite. The red- and yellow-circled filaments attenuate and then cease transmitting as neighbouring fractures redistribute load.

Malik also co-authored work in which E-glass reinforcement was used for evanescent-wave monitoring of epoxy cross-linking, extending the self-sensing concept from damage detection to manufacture and cure monitoring. A 2007 conference paper reported E-glass-based in-situ cure monitoring and detection of silane coupling agents, preceding later quantitative studies of cross-linking reactions.[18][19][20] The associated analytical programme also investigated deformation of differential-scanning-calorimetry sample pans during heating, a potential source of apparent movement in simultaneous non-contact optical and thermal measurements.[21]

Malik's 2016 study became part of the published basis for later research on reinforcing-glass light guides. Independent studies by Hegedus, Sarkadi and Czigany cited the Malik–Fernando work when developing white-light monitoring with commercial glass-fibre bundles.[3][22]

Subsequent E-glass development

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From 2017 to 2020, Hegedus and co-workers quantified the transmission properties of commercial reinforcing glass fibres and developed specimens in which a bundle selected directly from a woven E-glass fabric was illuminated with white light.[23] Their work showed reversible optical changes under subcritical tensile and compressive loading and later demonstrated that partial fibre breakage and fibre–matrix debonding produced persistent changes in transmitted optical power. Microscopic observation of the illuminated bundle end helped distinguish dark, broken filaments from other attenuation mechanisms.[3][22] These studies also showed that carefully selected commercial resin systems could support light guidance without necessarily removing the original fibre sizing.

Developments in the 2020s

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Research in the 2020s has increasingly combined structural fibres with conductive nanomaterials, multifunctional interphases and multiple sensing modes. Resistance-based carbon-fibre systems have been studied under tension, compression, bending, fatigue and impact, while fibre-based reviews also describe optical, magnetic and hybrid sensors.[6][1] Current work includes scalable manufacture, distributed interrogation, wireless acquisition and machine-learning methods that classify or predict damage from several signal channels. Reviews nevertheless describe most implementations as laboratory-scale and identify manufacturing repeatability, ageing, environmental cross-sensitivity and the scarcity of long-duration field validation as continuing barriers.[1]

Measurement and interpretation

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Self-sensing measurements are commonly expressed as a normalised change relative to an undamaged baseline. For electrical systems this may be the fractional change in resistance, while optical systems may use normalised transmitted power or the intensity of individual illuminated filaments. Calibration is material- and geometry-specific because the signal can depend on fibre orientation, volume fraction, electrode arrangement, contact resistance, resin refractive index, temperature, moisture and loading rate.[4][6]

Reversible and irreversible effects must be separated. Elastic strain, temperature or reversible microbending can change a signal without permanent damage; fibre fracture, delamination or loss of conductive paths generally causes a persistent change. Combining intrinsic measurements with acoustic emission, microscopy or mechanical load data is therefore used to assign a physical mechanism to a signal. Statistical models, including the Weibull distribution for fibre strength, may be used when many filaments fail progressively rather than in a single event.[14]

Applications

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Proposed and demonstrated applications include:

  • monitoring strain, fatigue and impact damage in aerospace, automotive, marine and wind-energy composites;
  • detecting damage or overloading in civil structures and strengthening systems;
  • tracking cure and cross-linking during composite manufacture;
  • monitoring filament or bundle failure during materials testing; and
  • providing large-area or distributed sensing without inserting a mechanically dissimilar sensor.[1][2][20]

Limitations

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No single self-sensing mechanism uniquely identifies every damage mode. Electrical measurements can be affected by temperature, moisture, contact resistance, current-path anisotropy and irreversible network rearrangement. Nanofiller systems require controlled dispersion and reproducible percolation. Optical reinforcing fibres require suitable refractive-index contrast, stable coupling and access to fibre ends, and optical loss can arise from deformation or interface changes before fracture. In all systems, adding a sensing function must not significantly reduce the mechanical performance, durability or manufacturability of the host composite.[1][6]

The translation of laboratory coupons to large structures also requires durable connections, baseline management, compensation for environmental conditions, inspection coverage, standardised calibration and evidence that the sensing response remains stable over the service life. These factors, together with cost and signal interpretation, remain active research topics.[1]

See also

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References

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  1. 1 2 3 4 5 6 7 8 9 10 Tao, Yinping; Zhang, Rongmin; Hu, Xianming; Ou, Yunfu; Ren, Musu; Sun, Jinliang; Zhang, Han; Peijs, Ton (2025). "A comprehensive review on fiber-based self-sensing polymer composites for in situ structural health monitoring". Advanced Composites and Hybrid Materials. 8: 339. doi:10.1007/s42114-025-01413-y.
  2. 1 2 Chung, Deborah D. L. (2023). "A review of self-sensing in carbon fiber structural composite materials". World Scientific Annual Review of Functional Materials. 1: 2230004. doi:10.1142/S2810922822300045.
  3. 1 2 3 Hegedus, Gergely; Sarkadi, Tamas; Czigany, Tibor (2019). "Self-Sensing Polymer Composite: White-Light-Illuminated Reinforcing Fibreglass Bundle for Deformation Monitoring". Sensors. 19 (7): 1745. doi:10.3390/s19071745.
  4. 1 2 3 Scholle, Patrick; Sinapius, Michael (2021). "A Review on the Usage of Continuous Carbon Fibers for Piezoresistive Self Strain Sensing Fiber Reinforced Plastics". Journal of Composites Science. 5 (4): 96. doi:10.3390/jcs5040096.
  5. 1 2 3 Kister, Guillaume; Wang, Liwei; Ralph, Brian; Fernando, Gerard F. (2003). "Self-sensing E-glass fibres". Optical Materials. 21 (4): 713–727. doi:10.1016/S0925-3467(02)00089-7.
  6. 1 2 3 4 Wang, Shu-Yang; Xie, Gui-Hua (2025). "A Review on Resistance-Based Self-Sensing of Carbon Fiber-Reinforced Polymer Subjected to Loads". Advanced Engineering Materials. 27 (13) 2500244. doi:10.1002/adem.202500244.
  7. ↑ Bekzhanova, Zere; Memon, Shazim Ali; Kim, Jong Ryeol (2021). "Self-Sensing Cementitious Composites: Review and Perspective". Nanomaterials. 11 (9): 2355. doi:10.3390/nano11092355.
  8. 1 2 Kister, Guillaume; Ralph, Brian; Fernando, Gerard F. (2004). "Damage detection in glass fibre-reinforced plastic composites using self-sensing E-glass fibres". Smart Materials and Structures. 13 (5): 1166–1175. doi:10.1088/0964-1726/13/5/021.
  9. ↑ Chen, R.; Theobald, P.; Gower, M.; Malik, S.; Burns, J.; Fernandes, E.; Bryce, G.; Fernando, G. F. (2008). "A novel fibre optic acoustic emission sensor". Proceedings of SPIE. 6932 693237. doi:10.1117/12.776170.
  10. ↑ Malik, S. A.; Mahendran, R. S.; Harris, D.; Paget, M.; Pandita, S. D.; Machavaram, V. R.; Collins, D.; Burns, J. M.; Wang, L.; Fernando, G. F. (2009). "Finite element modelling of fibre Bragg grating strain sensors and experimental validation". Proceedings of SPIE. 7292 72921V. doi:10.1117/12.817620.
  11. ↑ Hayes, Simon A.; Liu, Tongyu; Brooks, David; Monteith, Stephen; Ralph, Brian; Vickers, Stephen; Fernando, Gerard F. (1997). "In situ self-sensing fibre reinforced composites". Smart Materials and Structures. 6 (4): 432–440. doi:10.1088/0964-1726/6/4/007.
  12. ↑ Fernando, Gerard F.; Degamber, Balkarransingh; Wang, Liwei; Doyle, Crispin; Kister, Guillaume; Ralph, Brian (2004). "Self-Sensing Fibre Reinforced Composites". Advanced Composites Letters. 13 (2): 123–129. doi:10.1177/096369350401300203.
  13. ↑ Harris, D.; Mahendran, R. S.; Brooks, D.; Al-Khodairi, F. A. A.; Machavaram, V. R.; Reynolds, P.; Wang, L.; Pandita, S. D.; Paget, M.; Wedderburn, J.; Malik, S. A.; Ojo, S. O.; Kukureka, S. N.; Fernando, G. F. (2009). "Self-sensing, self-healing, and crack-arrestor composites". Proceedings of SPIE. 7293 72930P. doi:10.1117/12.817617.
  14. 1 2 3 4 5 6 7 8 9 10 Malik, Shoaib Ahmad (2011). Damage Detection Using Self-sensing Composites (PhD thesis). University of Birmingham. Retrieved 4 August 2026.
  15. ↑ Malik, S. A.; Wang, L.; Mahendran, R. S.; Harris, D.; Ojo, S. O.; Collins, D.; Paget, M.; Pandita, S. D.; Machavaram, V. R.; Fernando, G. F. (2009). "In-situ damage detection using self-sensing composites". Proceedings of SPIE. 7292 729204. doi:10.1117/12.817622.
  16. 1 2 3 R'Mili, M.; Moevus, M.; Godin, N. (2008). "Statistical fracture of E-glass fibres using a bundle tensile test and acoustic emission monitoring". Composites Science and Technology. 68 (7–8): 1800–1808. doi:10.1016/j.compscitech.2008.01.018.
  17. 1 2 3 Malik S. A.; Wang L.; Curtis P. T.; Fernando G. F. (2016). "Self-Sensing Composites: In-Situ Detection of Fibre Fracture". Sensors. 16 (5): Article 615. doi:10.3390/s16050615. PMID 27136555.
  18. ↑ Wang, L.; Malik, S.; Harris, D.; Fernando, G. F. (2007). "Self-sensing composites: in-situ cure monitoring". Proceedings of SPIE. 6423 64231F. doi:10.1117/12.779399.
  19. ↑ Wang, Liwei; Pandita, Surya D.; Machavaram, Venkata R.; Malik, Shoaib A.; Harris, David; Fernando, Gerard F. (2009). "Characterisation of the cross-linking process in an E-glass fibre/epoxy composite using evanescent wave spectroscopy". Composites Science and Technology. 69 (13): 2069–2074. doi:10.1016/j.compscitech.2008.11.001.
  20. 1 2 Wang, Liwei; Tomlin, Andrew; Pandita, Surya D.; Gupta, B. D.; Malik, Shoaib A.; Hudson, Martin; Curtis, Paul T.; Fernando, Gerard F. (2016). "In-situ monitoring of cross-linking reactions using E-glass fibres and evanescent wave spectroscopy". Sensors and Actuators B: Chemical. 236: 358–366. doi:10.1016/j.snb.2016.05.126.
  21. ↑ Malik, S. A.; Wang, L.; Paget, M. A.; Biddlestone, F.; Fernando, G. F. (2012). "Deformation of sample pans used in differential scanning calorimeters". Journal of Thermal Analysis and Calorimetry. 109 (1): 495–499. doi:10.1007/s10973-011-1748-6.
  22. 1 2 Hegedus, Gergely; Sarkadi, Tamas; Czigany, Tibor (2020). "Self-sensing composite: Reinforcing fiberglass bundle for damage detection". Composites Part A: Applied Science and Manufacturing. 131 105804. doi:10.1016/j.compositesa.2020.105804.
  23. ↑ Hegedus, Gergely; Sarkadi, Tamas; Czigany, Tibor (2017). "Analysis of the Light Transmission Ability of Reinforcing Glass Fibers Used in Polymer Composites". Materials. 10 (6): 637. doi:10.3390/ma10060637.

Category:Composite materials Category:Smart materials Category:Sensors Category:Structural health monitoring Category:Non-destructive testing

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