Strain Transfer Research Articles

Characterization of Engineering-Suitable Optical Fiber Sensors Packaged with Glass Fiber-Reinforced Polymers

Glass fiber-reinforced polymer- (GFRP-) packaged optical fiber (OF) sensors are considered a promising engineering-suitable sensor for structural health monitoring. To date, some critical characteristics of the GFRP-packaged OF (GFRP-OF) sensors have not yet been thoroughly studied. This study aimed to systematically characterize the properties of the GFRP-OF sensors. Firstly, we proposed a dimension optimization method for GFRP-OF sensors by strain transfer theory, which is based on a symmetrical three-layered cylindrical model. Then, we experimentally investigated the properties of the GFRP-packaged fiber Bragg grating sensor and GFRP-packaged distributed optical fiber sensor, including their mechanical properties, strain/temperature sensing performance, fatigue resistance, and corrosion resistance. The experimental results showed that the shear bearing capacity of GFRP-OF sensors was more than 120 times larger than that of the other three coated OF sensors, indicating that GFRP dramatically enhanced the robustness of the OF sensor. The GFRP–OF sensors also feature excellent strain and temperature sensing performance with high linearity and repeatability. The results also demonstrated that the GFRP–OF sensors have good fatigue properties with absolute fluctuations of strain sensitivity coefficients throughout the fatigue cycles within 0.02 pm/με; repeatability error did not exceed 0.5%, and nonlinear errors were less than 2%. A case study presented in the last section also illustrates the effectiveness of the GFRP-OF sensor in a field application.

Strain transfer in porous multiferroic composites of CoFe2O4 and PbZrxTi1−xO3

This manuscript examines the mechanism of strain-coupling in a multiferroic composite of mesoporous cobalt ferrite (CFO), conformally filled with lead zirconate titanate (PZT). We find that when the composites are electrically poled, remanent strain from the piezoelectric PZT layer can be transferred to the magnetostrictive CFO layer. X-ray diffraction shows that this strain transfer is greatest in the most porous samples, in agreement with magnetometry measurements, which show the greatest change in sample saturation magnetization in the most porous samples. Strain analysis shows that porosity both accommodates greater lattice strain and mitigates the effects of substrate clamping in thin film strain-coupled composites.

High-Sensitivity Pressure Sensors Based on a Low Elastic Modulus Adhesive.

With the rapid development of intelligent applications, the demand for high-sensitivity pressure sensor is increasing. However, the simple and efficient preparation of an industrial high-sensitivity sensor is still a challenge. In this study, adhesives with different elastic moduli are used to bond pressure-sensitive elements of double-sided sensitive grids to prepare a highly sensitive and fatigue-resistant pressure sensor. It was observed that the low elastic modulus adhesive effectively produced tensile and compressive strains on both sides of the sensitive grids to induce greater strain transfer efficiency in the pressure sensor, thus improving its sensitivity. The sensitivity of the sensor was simulated by finite element analysis to verify that the low elastic modulus adhesive could enhance the sensitivity of the sensor up to 12%. The preparation of high-precision and fatigue-resistant pressure sensors based on low elastic modulus, double-sided sensitive grids makes their application more flexible and convenient, which is urgently needed in the miniaturization and integration electronics field.

Interaction of In-Plane Magnetic Skyrmions with 90∘ Magnetic Domain Walls: Micromagnetic Simulations

${90}^{\ensuremath{\circ}}$ pinned magnetic domain walls can be observed in thin magnetic layers attached to a ferroelectric substrate. The main stabilization mechanism of the noncollinear magnetic texture is the strain transfer, which is responsible for imprinting of the ferroelectic domains into the uniaxial anisotropy of the ferromagnet. Here, we investigate by means of micromagnetic simulations how the interfacial Dzyaloshinskii-Moriya interaction influences the ${90}^{\ensuremath{\circ}}$ domain-wall structure. It is shown that Dzyaloshinskii-Moriya interaction induces a large out-of-plane magnetization component, strongly dependent on the domain wall type. In particular, it is shown that this out-of-plane magnetization component is crucial for the transport of the in-plane magnetic skyrmions, also known as bimerons, through the magnetic domain walls. Based on the results of micromagnetic simulations, a concept of in-plane magnetic skyrmion valve based on two ${90}^{\ensuremath{\circ}}$ pinned magnetic domain walls is introduced.

Characterization of OFDR distributed optical fiber for crack monitoring considering fiber-coating interfacial slip

An analytical crack-strain transfer model considering interfacial bond-slip between optical fiber and fiber coating is proposed and experimentally validated for crack monitoring of structures. Interfacial shear stress-slip relationship between the optical fiber and fiber coating was determined by using pull-out tests, and a simplified trilinear three-stage interfacial shear stress-slip model was proposed. The model is incorporated into the development of a crack-strain transfer model between the structural substrate and the optical fiber, and the fiber strain distribution is analytically obtained and compared with the strain distribution as perfect bond is assumed between the fiber and fiber coating. Experiments were also conducted to validate the crack-strain transfer model by continuously monitoring corrosion-induced concrete cracking with OFDR distributed optical fiber. Compared with strain transfer models proposed by other researchers in the literature and perfect bond model, the crack-strain transfer model considering interfacial shear stress-slip mechanism between fiber and fiber coating agrees well with experimental results, especially for large crack monitoring.

Distributed fibre optic sensing: Reinforcement yielding strains and crack detection in concrete slab during column failure simulation

Flat slab systems made of reinforced concrete (RC) are popular structural solutions widely used in practical applications. The knowledge about their behaviour under extreme loading conditions, including the loss of the columns, is still being developed worldwide. Also, new materials are tested for this purpose. The research presented hereafter in the article includes the progressive collapse simulation caused by removing the external column in the flat slab system reinforced with B600B steel. One of the aims of the research was to assess the effectiveness of the applied reinforcement after losing the column, depending on the degree of horizontal tie reinforcement. The structural behaviour of the entire reinforced concrete system during the experiment was controlled using advanced reference techniques, including distributed fibre optic sensing DFOS, optical image correlation system, total station as well as conventional strain and displacement transducers. The article focuses on the possibilities of DFOS sensing in an extensive range of strains caused by the steel yielding and the cracks directly in concrete. Thanks to distributed measurements and monolithic composite sensors, it was possible to detect all the cracks and reflect their patterns during all load stages until structural failure. The article describes the methodology and discusses the results of this pioneer measurement approach. Despite the extensive state of the art in distributed sensing, the paper provides the new knowledge gained during research. It is mainly related to a DFOS-based solution for extremely high strain measurements thanks to the excellent bonding properties and strain transfer to the optical fibre, from both steel reinforcement and surrounding concrete.

Surface Displacements Mechanism of the Dobi Graben from ASAR Time-Series Analysis of InSAR: Implications for the Tectonic Setting in the Central Afar Depression, Ethiopia

The Dobi graben is a Quaternary, NW-trending continental rift found within the East-Central Block (ECB) of the Afar Depression (AD) in Ethiopia. The AD might be the only place where three active rifts meet on land. This diffused, Rift–Rift–Rift (RRR) triple junction in the ECB comprises the overlap zone between the Red Sea and the Gulf of Aden propagators. Rifting is ongoing in the Dobi graben as evidenced by the August 1989 earthquakes (of magnitude 5.7 < MW < 6.2). This study carried out a surface displacement time-series analysis to examine the kinematics of the Dobi graben and the surrounding area using 18 ascending orbit scenes (between May 2005 and March 2010) along tract 257 and 15 along the descending orbit (tract 006) of the Advanced Synthetic Aperture Radar (ASAR), C-band (λ = 5.6 cm) acquired by the ENVIronmental SATellite (ENVISAT). We utilized the Small Baseline Algorithm (SBA) techniques of the distributed scatterer, which were implemented independently to generate Line of Sight (LOS) displacement maps. These LOS displacement surface movements, identified in both geometries, can be interpreted as ± signs of predominantly vertical movement in both geometries: positive for uplifting and negative for subsidence. Additionally, opposite signs of ± horizontal movement in both geometries indicate that the movement is from East to West (or vice versa). Results from the velocity and displacement maps and time series analysis suggest that creeping is associated mainly with normal faulting and could be the primary mechanism for strain distribution for the Southeastern part of the Dobi graben. The anomalous, continuous uplifting exhibited at the rift shoulder and in the horst area might be linked to the presence of temporary reactivation of normal faulting in the region. The oblique, positive LOS signals observed in different parts of the Dobi graben might serve as a proxy for understanding how strain is accommodated as normal faulting and is distributed in a distinct northeast direction. This explanation supports both the arguments for the Northeast migration of the triple junction and the transfer of strain from the southernmost Red Sea Rift (RSR) to the Central AD.

Applicability Analysis of Strain Transfer Between Surface-Mounted Optical Fiber Sensing Component and Materials

In order to explore the coupling transfer mechanism, a multi-layer mechanical model of sensor components is constructed. The surface-mounted strain transmission coefficient formula is derived by analysing the influence between structural parameters and strain transfer coefficient. The strain transmission coefficient of the sensor structure has a positive exponential relationship with the elastic modulus of the tested material through modelling, and the growth trend is gradually reducing. The gypsum material curve is in a parabola, and the top point is 87%. The curved form of concrete and low-carbon steel materials is the same, the top point is 100%, and the concrete curve of the three strengths is close to coinciding. Through integral calculation, the average strain transmission coefficient of gypsum material is 73.5%, C20 concrete is 94.7%, C30 concrete is 95.1%, C50 concrete is 95.3%, and low-carbon steel is 97.1%. The matrix diameter negatively correlates with the strain transmission coefficient, but the influence is small. Integrating the strain transfer coefficient curve, the average strain transfer coefficient of 1.0 mm matrix diameter is 97.45%, 1.5 mm matrix diameter is 97.38%, 2.0 mm matrix diameter is 97.30%, and 2.5 mm matrix diameter is 97.25%. The 3.0 mm matrix diameter is 97.21%. Experiments have verified the rationality of the theoretical formula and the correctness of the influence relationship, which provides a reference for the application of fiber grating sensing technology in tunnel structure monitoring.

Metagenomic strain detection with SameStr: identification of a persisting core gut microbiota transferable by fecal transplantation

BackgroundThe understanding of how microbiomes assemble, function, and evolve requires metagenomic tools that can resolve microbiota compositions at the strain level. However, the identification and tracking of microbial strains in fecal metagenomes is challenging and available tools variably classify subspecies lineages, which affects their applicability to infer microbial persistence and transfer.ResultsWe introduce SameStr, a bioinformatic tool that identifies shared strains in metagenomes by determining single-nucleotide variants (SNV) in species-specific marker genes, which are compared based on a maximum variant profile similarity. We validated SameStr on mock strain populations, available human fecal metagenomes from healthy individuals and newly generated data from recurrent Clostridioides difficile infection (rCDI) patients treated with fecal microbiota transplantation (FMT). SameStr demonstrated enhanced sensitivity to detect shared dominant and subdominant strains in related samples (where strain persistence or transfer would be expected) when compared to other tools, while being robust against false-positive shared strain calls between unrelated samples (where neither strain persistence nor transfer would be expected). We applied SameStr to identify strains that are stably maintained in fecal microbiomes of healthy adults over time (strain persistence) and that successfully engraft in rCDI patients after FMT (strain engraftment). Taxonomy-dependent strain persistence and engraftment frequencies were positively correlated, indicating that a specific core microbiota of intestinal species is adapted to be competitive both in healthy microbiomes and during post-FMT microbiome assembly. We explored other use cases for strain-level microbiota profiling, as a metagenomics quality control measure and to identify individuals based on the persisting core gut microbiota.ConclusionSameStr provides for a robust identification of shared strains in metagenomic sequence data with sufficient specificity and sensitivity to examine strain persistence, transfer, and engraftment in human fecal microbiomes. Our findings identify a persisting healthy adult core gut microbiota, which should be further studied to shed light on microbiota contributions to chronic diseases.Bmxg3NA25n3myfWhCsfsJVVideo abstract

A Sensing Mechanism and the Application of a Surface-Bonded FBG Dynamometry Bolt

In the present paper, a new type of surface-bonded fiber Bragg grating (FBG) dynamometry bolt is designed. It is assumed that the adhesive layer is a linear viscoelastic material and its creep mechanical behavior is expressed by the standard linear solid model. The shear strain transfer model of the surface-bonded FBG sensor is established. Additionally, the instantaneous and quasistatic strain transfer functions of the surface-bonded FBG sensor are obtained. The functions are validated by a uniaxial tensile test and a long-term constant-load tensile test. The test results show that the strain measured by the FBG sensor has a proportional relationship with the strain measured by the resistance strain gauge. Furthermore, under the fixed load for a long period of time, the strain of the FBG sensor has a tendency to drift and the strain reduction rate is about 40.5%. Finally, the field application is carried out in a mining area. It has been proved that the ground pressure online monitoring system based on the FBG sensing technology can successfully monitor the stress of the rock bolt.

Magnetoelectric properties of three-layered composite thin film fabricated by pulsed laser deposition

Magnetostriction-piezoelectric composite films present promising application prospects due to the presence of the magnetoelectric effect. In this paper, a sandwich structure Bi4Ti3O12/CoFe2O4/Bi4Ti3O12 composite film was prepared in a pulsed laser deposition system. The morphology, EDX, XPS, ferroelectric, piezoelectric, ferromagnetic and magnetoelectric properties were investigated in detail. In the sample, the atomic percentages of Bi, Ti and O elements measured by EDX are 35.373%, 12.824% and 46.578%, respectively. The out-of-plane electric domain structure and the in-plane magnetic domain structure show that BTO and CFO phases have excellent ferroelectricity (Pr = 1.57 μC/cm−2) and ferromagnetism (Mr = 104.83 emu/cc), respectively. The piezoelectric properties are proportional to the ferroelectric properties, so the composite thin films also have good piezoelectric properties (d33max = 192 p.m./v). Moreover, a great magnetoelectric coupling coefficient (∼11.95 mV/cm·Oe) was obtained by mechanical strain transfer and interface coupling. By adding a ferroelectric layer to the composite thin film, the clamping effect can be reduced and the coupling between the ferroelectric and the ferromagnetic layers can be increased, providing the experimental basis for the research of magnetoelectric coupling effect.

Cytoprotective Effects of Lactobacilli on Mouse Epithelial Cells during Salmonella Infection

Treatment of common pathogens, such as Salmonella species, Escherichia coli, Staphylococcus aureus, etc., is a big challenge for a practitioner. Antibiotics’ side effects during their application for the treatment of infectious diseases should not be underestimated as they have many issues, such as the transfer of antibiotics-resistant genes, dysbiosis, and antibiotic-resistant strains, which is the main hurdle in the eradication of diseases. To avoid these antibiotics complications, in modern countries, the interest of using probiotics in feed supplementation to promote health and prevent or treat intestinal infectious diseases has been increasing. The purpose of the present study was to evaluate the probiotic potential of three Lactobacilli strains isolated from clinically healthy dogs for their further utilization as a dietary supplement for dogs to avoid pathogenic and antibiotic complication. After 16SrRNA sequencing, in vitro tests were conducted to assess the survival potential of Lactobacilli under simulated gastrointestinal conditions and adhesion ability to the MODE-K cell line, effects on epithelial barrier function, anti-inflammatory activities, effects on host defensin peptides (beta-defensin 3), and inhibitory effects on common pathogens. Lactobacilli showed considerable potential to survive in simulated gastrointestinal environmental conditions, low pH, and high bile salt concentrations along with good adhesion properties with MODE-K cells. Pathogenic bacterial growth and their adhesion to MODE-K cells were significantly inhibited by Lactobacilli. Real-time PCR analyses further demonstrated that the L. acidophilus strain AR1 and AR3 inhibit Salmonella-induced proinflammatory cytokine (IL-6, IL-8, IL-1β) production and reinforce the expression of tight junction protein (occludin). None of the strains induce mRNA expression of beta-defensin 3 in MODE-K cells. Based on the in vitro results, the L. acidophilus strain AR1 has the potential to be supplemented in canine feed. However, further in vivo studies investigating health-promoting effects are awaited.

High temperature effects on surface acoustic wave strain sensor

Surface acoustic wave sensors (SAW), as a wireless passive sensor, are susceptible to temperature disturbance for high-temperature strain measurements, which results in poor accuracy and repeatability of the strain sensing. This paper investigates temperature effects on SAW strain sensors. Results show that high temperature not just induces frequency drift, but also reduces strain transfer ratio due to glue softening. The resonant frequencies of the langasite (LGS) SAW sensor have a linear relationship with strain for fixed temperatures, while the strain sensitivity is greatly affected by temperature. The results also show that the difference of measured strain sensitivities between the two resonant frequencies for one device is much less affected by temperature because they suffer the same strain transfer ratio and temperature characteristics, but different strain responses. A method to eliminate temperature effects has been proposed and accurate high-temperature strain measurements with SAW sensor were conducted to extend strain range up to 380 με with high repeatability under 500 °C.

Improvement of the Supercapacitor Performance of Nickel Molybdenum Chalcogenides/Reduced Graphene Oxide Composites through Vanadium-Doping Induced Crystal Strain Relaxation and Band Gap Modification

Metal chalcogenide/reduced graphene oxide (RGO) composites have gained significant interest as promising electrode materials for supercapacitor application. Herein, the effect of different chalcogens (O, S, and Se) on nickel-based bimetallic composites along with the addition of a scanty amount of a heteroatom (V) is investigated. Different sizes and electronegativity of the chalcogens alter the morphology of the composites. However, V doping does not change the morphology but regulates the crystalline strain, band-gap energies, and charge transfer kinetics of the materials. All these factors are very important in controlling the performance of a supercapacitor device. Among all the doped and undoped composites, Se-based electrode materials exhibit the highest supercapacitor properties. In a three-electrode configuration, the V-doped Ni-Mo selenide/RGO (VNMSeR) composite electrode exhibits the highest specific capacitance of ∼610 C g–1 (1220 F g–1) at 2 A g–1 current density with a superior rate capability of ∼73.7%. An asymmetric supercapacitor device has been fabricated using VNMSeR as positive and thermally RGO as negative electrode. The device exhibits a maximum energy density of ∼60.5 Wh kg–1 at a power density of 1.47 kW kg–1 and shows ∼83.4% retention (50.5 Wh kg–1) in energy density when the power density increases by ∼8.25-fold (12.12 kW kg–1).

Multiscale Strain Transfer in Cartilage.

The transfer of stress and strain signals between the extracellular matrix (ECM) and cells is crucial for biochemical and biomechanical cues that are required for tissue morphogenesis, differentiation, growth, and homeostasis. In cartilage tissue, the heterogeneity in spatial variation of ECM molecules leads to a depth-dependent non-uniform strain transfer and alters the magnitude of forces sensed by cells in articular and fibrocartilage, influencing chondrocyte metabolism and biochemical response. It is not fully established how these nonuniform forces ultimately influence cartilage health, maintenance, and integrity. To comprehend tissue remodelling in health and disease, it is fundamental to investigate how these forces, the ECM, and cells interrelate. However, not much is known about the relationship between applied mechanical stimulus and resulting spatial variations in magnitude and sense of mechanical stimuli within the chondrocyte’s microenvironment. Investigating multiscale strain transfer and hierarchical structure-function relationships in cartilage is key to unravelling how cells receive signals and how they are transformed into biosynthetic responses. Therefore, this article first reviews different cartilage types and chondrocyte mechanosensing. Following this, multiscale strain transfer through cartilage tissue and the involvement of individual ECM components are discussed. Finally, insights to further understand multiscale strain transfer in cartilage are outlined.

Monitoring of crack opening displacement of steel structure by PPP-BOTDA-distributed fiber optical sensors: Theory and experiment

Crack opening displacement (COD) is an essential parameter in fracture analysis of steel structures, and a novel methodology was developed for measurement of COD using high-resolution distributed fiber optical sensors. Based on crack-induced strain transfer mechanism, a theoretical model was firstly proposed to explicitly determine COD of steel element by strain singularity considering both the elastic and elastoplastic behavior of the optical fiber coating. The presented theoretical COD equations consider the inclination angle between the sensor axis and crack length as well. An experimental program of a pre-cracked pure bending steel element was then conducted to confirm the feasibility of the proposed monitoring approach. The PPP-BOTDA (Pre-Pump-Pulse Brillouin optical time domain analysis) with 1-cm-level spatial resolution was used in distributed measurement of strain and determination of COD. Estimated CODs were also compared to those measured using traditional electronic digital display micrometer. The results indicate that the inclination effect of the optical fiber is slight on the COD within the inclination angle range of 30°. This proposed approach demonstrates great promise for high accuracy and sensitivity of COD monitoring applications.

Multidimensional Imaging Reveals Mechanisms Controlling Multimodal Label-Free Biosensing in Vertical 2DM-Heterostructures.

Two-dimensional materials and their van der Waals heterostructures enable a large range of applications, including label-free biosensing. Lattice mismatch and work function difference in the heterostructure material result in strain and charge transfer, often varying at a nanometer scale, that influence device performance. In this work, a multidimensional optical imaging technique is developed in order to map subdiffractional distributions for doping and strain and understand the role of those for modulation of the electronic properties of the material. As an example, vertical heterostructures comprised of monolayer graphene and single-layer flakes of transition metal dichalcogenide MoS2 were fabricated and used for biosensing. Herein, the optical label-free detection of doxorubicin, a common cancer drug, is reported via three independent optical detection channels (photoluminescence shift, Raman shift, and graphene enhanced Raman scattering). Non-uniform broadening of components of multimodal signal correlates with the statistical distribution of local optical properties of the heterostructure. Multidimensional nanoscale imaging allows one to reveal the physical origin for such a local response and propose the best strategy for the mitigation of materials variability and future device fabrication, enabling multiplexed biosensing.

Temperature and time stability of process-induced strain engineering on 2D materials

Process-induced strain engineering is an effective method of crafting the strain state in 2D materials. Much like how it has been used in the fabrication of Si-based electronics, stressed thin films are deposited onto van der Waals-bonded 2D systems where relaxation of the stressor layer causes strain transfer into the 2D materials. This type of strain engineering can be used on a device-by-device level and be controlled for strain magnitude, compression or tension, uniaxiality or biaxiality, and directionality relative to crystal structure by varying film stress or geometry. One critical question in translating this technique to 2D materials is how temperature and time stable this strain engineering process is. In this work, we explore these factors through Raman spectroscopic mapping and photoluminescence spectroscopy ranging in temperatures from 293 to 4 K. It is shown that strain engineering with thin film stressors is equally persistent at all temperatures examined and time stable for a period of at least 14 months (the period of observation). These results suggest that process-induced strain engineering may be used to tune any number of interesting low-temperature properties in 2D materials and that any devices engineered in this way will have long-term stability for applications in electronics, optoelectronics, and beyond.

Monitoring Strategic Hydraulic Infrastructures by Brillouin Distributed Fiber Optic Sensors

We present a case study of a Structural Health Monitoring (SHM) hybrid system based on Brillouin Distributed Fiber Optic Sensors (D-FOS), Vibrating Wire (VW) extensometers and temperature probes for an existing historical water penstock bridge positioned in a mountain valley in Valle d’Aosta Region, Northwestern Italy. We assessed Brillouin D-FOS performances for this kind of infrastructure, characterized by a complex structural layout and located in a harsh environment. A comparison with the more traditional strain monitoring technology offered by VW strain gauges was performed. The D-FOS strain cable has been bonded to the concrete members using a polyurethane-base adhesive, ensuring a rigid strain transfer. The raw data from all sensors are interpolated on a unique general timestamp with hourly resolution. Strain data from D-FOS and VW strain gauges are then corrected from temperature effects and compared. Considering the inherent differences between the two monitoring technologies, results show a good overall matching between strain time series collected by D-FOS and VW sensors. Brillouin D-FOS proves to be a good solution in terms of performance and economic investment for SHM systems on complex infrastructures such as hydropower plants, which involve extensive geometry combined with the need for detailed and continuous strain monitoring.

Crack detection and retardation of steel structure by smart CFRP embedding PPP-BOTDA fiber sensors

Crack detection and retardation are essential issues in the CFRP reinforcement of damaged steel structures. A smart CFRP was developed for monitoring and retarding of crack opening displacement (COD) by embedding distributed fiber optical sensors which measure the strain singularity of externally bonded CFRP in the cracking zone. Based on crack-induced strain transfer mechanism in CFRP strengthening system, a theoretical model was then proposed to obtain an explicit COD expression considering both the elastic and elasto-plastic behavior of the adhesive. An experimental program of a pre-cracked pure bending steel element was also conducted to verify the proposed COD model. The distributed measurement of strain was conducted on CFRP by the commercial PPP-BOTDA (Pre-Pump-Pulse Brillouin optical time domain analysis) sensor with high spatial resolution. The comparison of theoretical CODs and the measured ones using EDDM (electronic digital display micrometer) confirms the ability of presented model on COD estimate. The proposed method using smart CFRP embedded with distributed optical fibers demonstrates great promise for high accuracy and sensitivity of COD monitoring, and has the capability of crack retardation and detection for the strengthened structures.