Distributed Fiber Optic Strain Sensors Research Articles

Application of Distributed Fiber Optic Strain Sensors to LMQXFA Cold Mass Welding

The future High Luminosity upgrade of the Large Hadron Collider (HL-LHC) at CERN will include the low-beta inner triplets (Q1, Q2a/b, Q3) for two LHC insertion regions. The Q1, Q3 components consist of eight 10 m-long LMQXFA cryo-assemblies fabricated by the HL-LHC Accelerator Upgrade Project. Each LMQXFA Cold mass contains two Nb3Sn magnets connected in series. A stainless-steel shell is welded around the two magnets before the insertion into the cryostat. There is a limit on how much coil preload increase induced by the shell welding is allowed. Distributed Rayleigh backscattering fiber optics sensors were used for the first time to obtain a strain map over a wide area of a Nb3Sn magnet cold mass shell. Data were collected during welding of the first LMQXFA cold mass and the results confirm that the increase of the coil pole azimuthal pre-stress after welding do not exceed requirements.

Distributed fiber optic strain sensing in axially loaded glued-in steel rods in glued-laminated timber

The rise in popularity of mass timber structures globally has increased the demand for high-performance timber connections. Glued-in rod connections which are advantageous compared to other dowel-type connections because of their high strength and stiffness, have been the subject of extensive research in the literature; However, the lack of an in-depth understanding of their behavior and a uniform set of guidelines for their design continues to limit the use of glued-in rods in practice. To develop an improved understanding of the behavior of glued-in rod connections this paper examines, for the first time, the use of distributed fiber optic sensors to measure the complete strain distribution along the length of a glued-in rod connection. Axial pullout tests were conducted on twenty-five glued-in rod connections in glued-laminated timber with varying embedment lengths and glue-line thicknesses. Results of the study demonstrate the ability of fiber optic sensors to capture the full strain distribution along the length of the steel rod and along the epoxy-adhesive interface, enabling the study of localized behavior that would be difficult to measure using conventional strain gauges. In addition, results demonstrate the ability of distributed fiber optic strain sensors to infer axial stress and force distributions along the length of a glued-in rod connection, which are compared with theoretical distributions from the Volkersen model, as well as measure bond-slip behavior.

Monitoring Flexure Behavior of Compacted Clay Beam Using High-Resolution Distributed Fiber Optic Strain Sensors

Abstract Understanding the mechanical characteristics of clayey soil is critical to estimate the stability of clay-related geotechnical engineering works. However, the distributed information of the internal deformation of clay is hard to capture through traditional methods. In this paper, a set of four-point bending tests were performed on a compacted clay beam instrumented with fiber optic strain sensors to investigate the flexure and cracking behaviors. The optical frequency domain reflectometry technique with high spatial resolution and precision was employed to establish a distributed strain sensing (DSS) system in this study. The results show that the DSS system exhibits a high accuracy in the collection of the clay deformation in terms of compression, tension, and cracking. The comparison of the internal strain profiles with the observation of particle image velocimetry analysis system verifies the feasibility of fiber optic sensing technology in the quantitative assessment of clay deformation. The performance of fiber optic sensors in the rebound deformation and creep deformation monitoring was preliminarily issued in the study. In addition, the progressive failure on the fiber–soil interface was analytically studied to evaluate the deformation compatibility between the fiber and surrounding clayed soil. The conclusions drawn in this paper can help to guide the state interpretation of clayey soil instrumented with fiber optic sensors.

Laboratory Investigation of the Structural Performance of a Corrugated Steel Culvert under Increasing Cover Depth

The performance of large diameter corrugated steel culverts/pipes under varying cover depth up to deep burial has previously not been investigated in a laboratory setting due to limitations associated with the application of overburden pressures. Using the new deep burial simulator at Queen’s University, it is now possible to test flexible pipes up to 3 m in diameter up to a simulated burial depth of approximately 17 m. In this study, a 2-m diameter corrugated steel pipe (CSP) culvert was instrumented with displacement transducers, strain gauges, and distributed fiber optic strain sensors and was tested under increasing overburden pressure up to a total of 358 kPa (equivalent to a depth of 17.9 m of soil with a unit weight of 20 kN/m3). The diameter change values along the length of the culvert were within 10% of each other, suggesting that the simulator produces approximately uniform loading. The Canadian bridge design code produced thrust estimates within 10% of the measured response but did not predict the development of localized plastic hinges seen in the experiment.

Evaluation of suturing performance in general surgery and ocular microsurgery by combining computer vision-based software and distributed fiber optic strain sensors: a proof-of-concept.

Improper suturing may cause an inadequate wound healing process and wound dehiscence as well as infection and even graft rejection in case of corneal transplantation. Hence, training surgeons in correct suturing procedures and objectively assessing their surgical skills is desirable. Two complementary methods for assessment of suturing skills in two medical fields (general surgery and ocular microsurgery) were demonstrated. Suturing quality is assessed by computer vision software. Evaluation of stitching flow of operation is based on measuring strain induced in an optical fiber that is placed in proximity to the wound and parallel thereto and is pressed and passed by wound stitches. Our software generated a score for suturing outcome in both general surgery and ocular microsurgery when the stitching was done on a patch. Every trainee received a score in the range 0-100 that describes his/her performance. Strain values were recognized when using a patch in general surgery and a rubber patch in ocular microsurgery, but were less distinct in (disqualified) human cornea. We proved a concept of an objective scoring method (based on various image processing algorithms) for assessment of suturing performance. It was also shown that fiber optic strain sensors are sensitive to the flow of stitching operation on a patch but are less sensitive to the flow of stitching operation on a human cornea. By combining these two methods, we can comprehensively evaluate the suturing performance objectively.

Novel in-situ residual strain measurements in additive manufacturing specimens by using the Optical Backscatter Reflectometry

Material extrusion (MEX) is a well established production method in additive manufacturing. However, internal residual strains are accumulated during the layer-by-layer fabrication process. They bring about shape distortions and a degradation of mechanical properties. In this paper, an in-situ distributed measurement of residual strains in MEX fabricated thermoplastic specimens is achieved for the first time. This innovative measuring system consists of an Optical Backscatter Reflectometry (OBR) interrogation unit connected to a distributed fiber optic strain sensor which is embedded during the MEX process. The characteristic residual strain distribution inside 3D printed components is revealed and numerically validated. The main mechanisms of residual strain creation and the sensing principles of in-situ OBR are described. A minimum measuring range of 4 mm and a spatial resolution of 0.15 mm were experimentally demonstrated. The potential of in-situ OBR technology for detecting invisible manufacturing defects was shown by a trial experiment.

Structural Performance of In-Service Corrugated Steel Culvert under Vehicle Loading

AbstractDynamic distributed fiber optic strain sensors were used, for the first time, to monitor the behavior of an in-service corrugated steel culvert with a span of 2.75 m and a skew angle of 45°...

Spatially continuous strain monitoring using distributed fiber optic sensors embedded in carbon fiber composites

A distributed fiber optic strain sensor based on Rayleigh backscattering, embedded in a fiber-reinforced polymer composite, has been demonstrated. The optical frequency domain reflectometry technique is used to analyze the backscattered signal. The shift in the Rayleigh backscattered spectrum is observed to be linearly related to the change in strain of the composite material. The sensor (standard single-mode fiber) is embedded between the layers of the composite laminate. A series of tensile loads is applied to the laminate using an Instron testing machine, and the corresponding strain distribution of the laminate is measured. The results show a linear response indicating a seamless integration of the optical fiber in the composite material and a good correlation with the electrical-resistance strain gauge results. The sensor is also used to evaluate the strain response of a composite-laminate-based cantilever beam. Distributed strain measurements in a composite laminate are successfully obtained using an embedded fiber optic sensor.

薄壁圆环分布式光纤测力传感器的性能

薄壁圆环分布式光纤测力传感器的性能

Skin–stringer debonding detection using distributed dispersion index features

Statistical approaches have been extensively used to detect structural damage. This article proposes a preliminary investigation on the use of a non-model-based damage identification method, implementing “dispersion feature” indicators, extracted from the differential strain signal. In detail, the method takes advantage of the elaboration of the full-spectrum acquisition, irrespective of the healthy state of the structure under test. Large variations of some selected statistical features, representative of the acquired signals, are taken as indicators of the presence of anomalous structural condition. At this stage, these features have been arbitrarily selected. In synthesis, a cumulative dispersion index is defined as the combination of the selected feature variations, contemporarily overcoming prescribed thresholds, providing a scalar output that can be used as an index to identify and possibly quantify the extension of a damage location. Experimental results confirm the envisaged potentiality of the proposed technique. In this study, damage in the form of a stringer debonding is referred to, obtained as a consequence of point impacts on a wing box stiffened panel. A distributed fiber optic strain sensor network is used to detect the input data.

Distributed Sensing of Circumferential Strain Using Fiber Optics during Full-Scale Buried Pipe Experiments

AbstractAs buried infrastructure in North America and around the world reaches the end of its service life, engineers and infrastructure managers will require an improved understanding of the performance of both deteriorated pipes and repair techniques. To develop this improved understanding, sensing technologies that enable the full pipe behavior to be measured, rather than a small number of localized discrete measurements, are required. A possible solution to this problem is to use distributed fiber optic strain sensors. To this end, a series of buried pipe tests were undertaken on steel, concrete, and high-density polyethylene (HDPE) pipes instrumented with distributed fiber optic strain sensors. The distributed measurements were in agreement with conventional strain gauges, but enabled the full strain distribution around the circumference of the pipe to be measured. This allowed localized behavior that would have been missed with conventional strain gauges to be detected and quantified. In addition, t...

Damage/Deterioration Detection for Steel Structures Using Distributed Fiber Optic Strain Sensors

Distributed fiber optic sensors have the potential to be used to detect three critical deterioration mechanisms in steel structures: (1) fatigue cracking, (2) localized damage or deterioration, and (3) distributed damage or deterioration, such as corrosion. This study investigated the strain and spatial resolution of distributed fiber optic sensors and explored the potential benefits and challenges of using distributed fiber optic strain sensors for damage/deterioration detection. The experimental program consisted of a series of axial tension tests performed on steel plate specimens with three types of simulated damage/deterioration: cracking, local cross section reduction, and distributed cross section reduction. The results indicate that similar accuracy to strain gauges can be achieved and distributed fiber optic strain sensors can provide much more detailed information about specimen behavior. The results of a finite-element analysis for each specimen were compared with the experimental measurements. There was good correlation between the two if the boundary conditions were modeled properly. However, care must be taken when selecting the sensing fiber to be used and when interpreting the results.

A Method for Detecting Deformation of Pipeline Based on Distributed Fiber Optic Strain Sensor

A method for detecting pipeline’s deformation is presented in this paper, based on distributed fiber optic strain sensor. We simplify the pipeline and analysis it as a beam. According to beam’s geometrical relational expression, pipeline’s deflection could be calculated by using discrete strain with numerical method.