Strain measurements with fibre Bragg grating sensors under inhomogeneous deformations

Bragg grating sensors are fibre optic sensors for strain and temperature investigations with many advantages: the sensors can be embedded in plastic materials or composites and several gratings can be inscribed in one sensor. However, inhomogeneous deformation or transversal loading cause widening and splitting of the reflected wavelength peak of a fibre Bragg grating (FBG) sensor. These effects are shown in a residual stress analysis, in which the hole drilling method is adapted for FBG sensors. Additionally, a four-point bending test on three different notched aluminium beams is used to investigate the widening and splitting of the reflected peaks and their effects on the strain analysis. At each sample, a reference strain gauge sensor and two FBG sensors are applied. The two FBG sensors are loaded with different strain gradients. The unnotched beam and the beam with small strain gradient show the accuracy and reproducibility of the experiment. The beam with medium strain gradient shows no peak splitting, but the widening does influence the strain analysis. The results of the beam with high strain gradient demonstrate the peak splitting and the failure of the strain analysis methods. Initial approaches on how to deal with this widening and splitting are discussed.

Download Full-text

Preliminary View of a Smart Technique for Materials Testing in the Laboratory using FBG Sensor

MATEC Web of Conferences ◽

10.1051/matecconf/201820304001 ◽

2018 ◽

Vol 203 ◽

pp. 04001

Author(s):

Isah W. Balarabe ◽

Mohamad Hisham ◽

Ahmad R. Niraku ◽

Indra S.H. Harahap

Keyword(s):

High Resolution ◽

Bragg Grating ◽

Materials Testing ◽

Fibre Bragg Grating ◽

Fbg Sensor ◽

Perfect Correlation ◽

Fbg Sensors

Simple experiments for calibrating Fibre Bragg Grating (FBG) in order to measure strain and temperature have been successfully demonstrated in this study. This will allow convenient use of FBG sensor in the laboratory for measuring quantities. Linear curve fittings were employed for both the strain and temperature, and R2 values are determined respectively. The result showed a perfect correlation between FBG, strain and temperature. The approach can be employed with ease, simplicity in an inexpensive manner, in order harness the advantages offered by FBG sensors such as accuracy, precision, speed and high resolution.

Download Full-text

Model of the Temperature Influence on Additively Manufactured Carbon Fibre Reinforced Polymer Samples with Embedded Fibre Bragg Grating Sensors

Materials ◽

10.3390/ma15010222 ◽

2021 ◽

Vol 15 (1) ◽

pp. 222

Author(s):

Torkan Shafighfard ◽

Magdalena Mieloszyk

Keyword(s):

Numerical Simulation ◽

Composite Structures ◽

Thermal Loading ◽

Elevated Temperatures ◽

Mechanical Strain ◽

Experimental Investigations ◽

Bragg Grating ◽

Fibre Bragg Grating ◽

Reinforced Polymer ◽

Fbg Sensors

This study investigates the thermo-mechanical behaviour of additively manufactured Carbon Fiber Reinforced Polymer (CFRP) with embedded Fibre Bragg Grating (FBG) sensors with respect to their feasibility for utilising them under thermal loading. This was conducted through the Finite Element Method (FEM) inside an ABAQUS environment. Numerical simulation was complemented by several experimental investigations in order to verify the computational results achieved for the specimens exposed to thermal loading. FBG sensors, incorporated into the material by embedding technique, were employed to measure the strains of the samples subjected to elevated temperatures. It was shown that the strains given by numerical simulation were in good agreement with the experimental investigation except for a few errors due to the defects created within the layers during Additive Manufacturing (AM) process. It was concluded that the embedding FBG sensors were capable of identifying thermo-mechanical strain accurately for 3D-printed composite structures. Therefore, the findings of this article could be further developed for other types of material and loading conditions.

Download Full-text

Fatigue Crack Propagation Monitoring Using Fibre Bragg Grating Sensors

Vibration ◽

10.3390/vibration4030039 ◽

2021 ◽

Vol 4 (3) ◽

pp. 700-721

Author(s):

Magdalena Mieloszyk

Keyword(s):

Fatigue Crack ◽

Crack Propagation ◽

Acoustic Waves ◽

Crack Detection ◽

Bragg Grating ◽

Alloy Sample ◽

Fibre Bragg Grating ◽

Propagation Process ◽

Crack Propagation Process ◽

Fbg Sensors

The paper presents the analysis of the possibility of fatigue crack detection and monitoring its propagation process using fibre Bragg grating (FBG) sensors. The investigations were carried out on an aluminium alloy sample (a part of the Mi-2 helicopter rotor blade). During the fatigue test, the sample was equipped with FBG sensors applied for strain measurement and the vibration-based strain monitoring. It was observed that the strain curves determined by the FBG sensors agreed well with the fatigue force profile. However, the strain curves were almost insensitive to the crack propagation process, except in the last stage of the test, when the crack length was equal to 25 mm. The strain values and the natural frequencies of the sample that were determined experimentally were compared with the values achieved from the finite element method model, with both methods showing good agreement. Additionally, spectrogram-based analyses were performed, focused on the acoustic waves phenomena related to a crack propagation process. It was confirmed that the proposed signal processing method, based on spectrogram analyses, can be applied for the detection of fatigue crack development in metal structures.

Download Full-text

Four-Point Bending Tests to Study the So-Called Plasticity Effect on the Residual Stress Results Determined by the Hole-Drilling and Ring-Core Methods

Advanced Materials Research ◽

10.4028/www.scientific.net/amr.996.319 ◽

2014 ◽

Vol 996 ◽

pp. 319-324

Author(s):

David von Mirbach

Keyword(s):

Residual Stress ◽

Bending Test ◽

Hole Drilling ◽

Test Machine ◽

Bending Tests ◽

Hole Drilling Method ◽

Four Point Bending ◽

Drilling Method ◽

Four Point Bending Test ◽

Ring Core

The hole-drilling method (HDM) and ring core method (RCM) are limited to low residual stresses under 60% of the yield stress. This issue will experimentally analyze the method of adaptive calculation function, presented by the author on the ICRS9. With a four-point-bending test machine, a defined stress can be triggered between the middle bending. In this defined loading area, the strains in two load cases with the HDM and the RCM configuration were measured. With these measured strains the residual stress calculation will be analysed.

Download Full-text

Fibre Bragg grating sensor applications for structural health monitoring

Aircraft Engineering and Aerospace Technology ◽

10.1108/aeat-11-2017-0255 ◽

2018 ◽

Vol 92 (3) ◽

pp. 355-367

Author(s):

Cansu Karatas ◽

Boray Degerliyurt ◽

Yavuz Yaman ◽

Melin Sahin

Keyword(s):

Structural Health Monitoring ◽

Health Monitoring ◽

Composite Structures ◽

Composite Beams ◽

Strain Gauges ◽

Bragg Grating ◽

Fibre Bragg Grating ◽

Content Type ◽

Structural Health ◽

Fbg Sensors

Purpose Structural health monitoring (SHM) has become an attractive subject in aerospace engineering field considering the opportunity to avoid catastrophic failures by detecting damage in advance and to reduce maintenance costs. Fibre Bragg Grating (FBG) sensors are denoted as one of the most promising sensors for SHM applications as they are lightweight, immune to electromagnetic effects and able to be embedded between the layers of composite structures. The purpose of this paper is to research on and demonstrate the feasibility of FBG sensors for SHM of composite structures. Design/methodology/approach Applications on thin composite beams intended for SHM studies are presented. The sensor system, which includes FBG sensors and related interrogator system, and manufacturing of the beams with embedded sensors, are detailed. Static tension and torsion tests are conducted to verify the effectiveness of the system. Strain analysis results obtained from the tests are compared with the ones obtained from the finite element analyses conducted using ABAQUS® software. In addition, the comparison between the data obtained from the FBG sensors and from the strain gauges is made by also considering the noise content. Finally, fatigue test under torsion load is conducted to observe the durability of FBG sensors. Findings The results demonstrated that FBG sensors are feasible for SHM of composite structures as the strain data are accurate and less noisy compared to that obtained from the strain gauges. Furthermore, the convenience of obtaining reliable data between the layers of a composite structure using embedded FBG sensors is observed. Practical implications Observing the advantages of the FBG sensors for strain measurement will promote using FBG sensors for damage detection related to the SHM applications. Originality/value This paper presents applications of FBG sensors on thin composite beams, which reveal the suitability of FBG sensors for SHM of lightweight composite structures.

Download Full-text

A Kinematic Model to Compensate the Structural Deformations in Machine Tools Using Fibre Bragg Grating (FBG) Sensors

10.20944/preprints201612.0139.v1 ◽

2016 ◽

Author(s):

Francesco Aggogeri ◽

Alberto Borboni ◽

Rodolfo Faglia ◽

Angelo Merlo ◽

Nicola Pellegrini

Keyword(s):

Machine Tool ◽

Real Time ◽

Kinematic Model ◽

Experimental Tests ◽

Bragg Grating ◽

Fibre Bragg Grating ◽

Machining Performance ◽

Novel Approach ◽

Structural Deformations ◽

Fbg Sensors

Structural deformations are one of the most significant factor that affects machine tool (MT) positioning accuracy. These induced errors are complex to be represented by a model, nevertheless they need to be evaluated and predicted in order to increase the machining performance. This paper presents a novel approach to calibrate a machine tool in real-time, analyzing the thermo-mechanical errors through Fibre Bragg Grating (FBG) sensors embedded in the MT frame. The proposed configuration consists of an adaptronic structure of passive materials, Carbon Fibre Reinforced Polymers (CFRP), equipped by FBG sensors that are able to measure in real-time the deformed conditions of the frame. By using a proper thermo-mechanical kinematic model, the displacement of the end effector may be predicted and corrected when it is subjected to external undesired factors. By starting from a set of FE simulations to develop a model able to describe the MT structure stresses, a prototype has been fabricated and tested. The scope was to compare the numerical model with the experimental tests using FBG sensors. The experimental campaign has been performed varying the structure temperature over time and measuring the tool tip point (TTP) positions. The obtained results showed a substantial matching between the real and the predicted position of TTP confirming the effectiveness of the proposed calibration system.

Download Full-text

Structural Health Monitoring System of Composite Beams with Surface Bonded and Embedded Fibre Bragg Grating Sensors

Key Engineering Materials ◽

10.4028/www.scientific.net/kem.744.332 ◽

2017 ◽

Vol 744 ◽

pp. 332-336 ◽

Cited By ~ 3

Author(s):

Boray Değerliyurt ◽

Cansu Karataş ◽

Melin Şahin ◽

Yavuz Yaman

Keyword(s):

Structural Health Monitoring ◽

Health Monitoring ◽

Bragg Grating ◽

Fibre Bragg Grating ◽

Stress Concentrations ◽

Bending Tests ◽

Health Monitoring System ◽

Structural Health ◽

Paper Manufacturing ◽

Fbg Sensors

Fibre Bragg Grating (FBG) sensors are frequently being used for Structural Health Monitoring (SHM) of aerospace structures. One of the most important advantages of using FBG sensors is that it is possible to embed them into composites. In this paper, manufacturing methods of composite specimens with embedded FBG sensors are given. To avoid stress concentrations at ingress/egress regions of fibre optic wires, PTFE (Teflon) tubes were used during manufacturing. Moreover, FBG connectors melt at high curing temperatures. Therefore, those connectors were cut and after manufacturing, these connectors were spliced back to the FBG sensors. Embedded FBG’s were then checked and the correct wavelength data were taken. All the sensors were observed as intact and ready for bending tests. Procedure for bending tests is also explained including applied loads, boundary conditions, test setup and the peripheral equipment. Results of bending tests show that the system is an appropriate one for SHM purposes.

Download Full-text

On the Improvement of Calibration Coefficients for Hole-Drilling Integral Method: Part II—Experimental Validation of Calibration Coefficients

Journal of Engineering Materials and Technology ◽

10.1115/1.1543972 ◽

2003 ◽

Vol 125 (2) ◽

pp. 107-115 ◽

Cited By ~ 5

Author(s):

Jong-Ning Aoh ◽

Chung-Sheng Wei

Keyword(s):

Experimental Validation ◽

Three Dimensional ◽

Bending Test ◽

Hole Drilling ◽

Dimensional Model ◽

Three Dimensional Model ◽

Fem Model ◽

Hole Drilling Method ◽

Drilling Method ◽

Calibration Coefficients

Experimental validation of the calibration coefficients for integral hole-drilling method obtained from an improved three-dimensional FEM model was achieved using bending test of a cantilever beam. The experimental setup is a simple yet accurate method to validate the calibration coefficients obtained by a three-dimensional FEM model. With this experiment, we also validate the adequacy of the criterion applied for thin or thick plates in a previous work. The relieved stresses calculated from the calibration coefficients of the three-dimensional FEM model were compared with those calculated from two-dimensional model calibration coefficients. The results show that the accuracy of relieved stress calculation has been greatly improved as the calibration coefficients based on a three-dimensional model are used for integral hole-drilling method. Significant error in the residual stress measurement and calculation could be arisen if calibration coefficients for integral hole-drilling method were not chosen correctly for corresponding thin plate or thick plate cases according the results of the bending test of cantilever beam. A transitional dimensionless thickness was proposed by examining the calculated relieved stresses obtained from the calibration coefficients for different plate thickness. The probability bounds of relieved stress corresponding to both cases were also calculated to further reveal the improvement of the calibration coefficients obtained from the three-dimensional model.

Download Full-text

Structural Health Monitoring of Gantry Girder using Fibre Bragg Grating Sensors

International Journal of Engineering and Advanced Technology - Regular Issue ◽

10.35940/ijeat.a1286.109119 ◽

2019 ◽

Vol 9 (1) ◽

pp. 2956-2958

Keyword(s):

Structural Health Monitoring ◽

Fiber Bragg Grating ◽

Health Monitoring ◽

Strain Sensors ◽

Work Place ◽

Bragg Grating ◽

Fibre Bragg Grating ◽

Structural Health ◽

Fbg Sensors ◽

Heavy Loads

Most of the industries have an in-build overhead crane that helps in lifting and transportation of heavy loads from one location of work place to another. Gantry girders are provided to support the loads transmitted through the moving wheels of the overhead cranes. The paper presents the structural health monitoring (SHM) practices that can be implemented for damage detection of gantry girder using Fiber Bragg Grating (FBG) sensors that are positioned on the key parts of the crane. The sensor is designed for monitoring the stress and strain of the girder. The alternating stress was determined based on distributed fiber bragg grating strain sensors. The analysis of the signals based on finite element (FE) models helps to determine the safety condition of the crane.

Download Full-text

Optimisation of Through-Thickness Embedding Location of Fibre Bragg Grating Sensor in CFRP for Impact Damage Detection

Polymers ◽

10.3390/polym13183078 ◽

2021 ◽

Vol 13 (18) ◽

pp. 3078

Author(s):

Helena Rocha ◽

Ugo Lafont ◽

João P. Nunes

Keyword(s):

Impact Damage ◽

Large Diameter ◽

Real Life ◽

Low Velocity Impact ◽

Bragg Grating ◽

Fibre Bragg Grating ◽

Low Velocity ◽

Residual Strains ◽

Fbg Sensors ◽

The Impact

Aerospace composites are susceptible to barely visible impact damage (BVID) produced by low-velocity-impact (LVI) events. Fibre Bragg grating (FBG) sensors can detect BVID, but often FBG sensors are embedded in the mid-plan, where residual strains produced by impact damage are lower, leading to an undervaluation of the damage severity. This study compares the residual strains produced by LVI events measured by FBG embedded at the mid-plan and other through-thickness locations of carbon fibre reinforced polymer (CFRP) composites. The instrumented laminates were subjected to multiple low-velocity impacts while the FBG signals were acquired. The FBG sensor measurements allowed not only for the residual strain after damage to be measured, but also for a strain peak at the time of impact to be detected, which is an important feature to identify the nature and presence of BVID in real-life applications. The results allowed an adequate optical fibre (OF) embedding location to be selected for BVID detection. The effect of small- and large-diameter OF on the impact resistance of the CFRP was compared.

Download Full-text