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... composite materials with high specific stiffness and strength have been widely applied in various fields such as aerospace or industry. Simultaneously, curing methods for joining composite materials have also gone through development intensively, for examples Hot- press, Pultrusion, Resin Transfer Molding (RTM) and Vacuum Molding. During the curing process, internal damages and residual strain are the most considerable relevance to quality of product, and hence demanded careful treatment. Commonly, the internal damage of composite materials could be detected by using ultrasound scan and X-ray, but these methods, however, are significantly high cost and not on-line monitoring. It is not suitable for smart structure application. Since several recent decades, optical fiber sensors have been utilized in composite material field popularly for their predominating advantages such as small size, low cost, and capability of avoiding electromagnetic influence. In 1988, Afromowitz proposed the polymer fiber embedded into composite materials to monitor the refractive index changes in the composite materials during curing process [Afromowitz, 1988]. And one year later the authors presented Fiber Optic Fresnel Reflection Technique for supervising the curing process [Afromowitz & Lam, 1990]. In late 1980s, Fiber Bragg Grating (FBG) sensor, one kind of optical fiber sensors, has attracted considerable attentions to the applications in aerospace, structural, medical and chemical spheres. FBG sensors are small and compatible with common polymeric materials, and thereby being easily embedded close to the internal sensing site in a composite structure without introducing significant defects. In 1990, Dunphy et al. employed the Fiber Bragg Grating embedded into composite materials to monitor the vitrification during curing process [Dunphy et al., 1990]. Similarly, FBG sensors were also applied to measure strain and residual stress after curing [Dewynter- Marty et al., 1998 & Okabe et al., 2002a]. On the other hand, Kuang and collegues improved detecting effect of the sensors by embedding FBG into composite materials in different layers [Kuang et al., 2001b]. Alternatively, in 2002, Okabe et al. utilized small-diameter FBG to study residual stress with micro damage of inner structure of the composite [Okabe et al., 2002b]. Furthermore, FBG has been also used to monitor the epoxy curing, and found the glass transition temperature with intensity changes [Giordano et al., 2004 & Wang et al., 2007]. Recent studies [Okabe et al., 2002a & Kuang et al., 2001a] discovered that when FBG sensors are embedded in CFRP laminates, the reflection spectrum from the sensors splits into two peaks because of the non-axisymmetric thermal residual stresses. This deformation of the spectrum was considered defective as it would lead to misinterpretation in strain measurements or crack detection in the laminates [Menendez & Guemes, 2000; Murukeshan et al., 2000; Leng & Asundi, 2002]. According to our knowledge, most of the previous researches focus on measuring the mechanical properties of composite materials and damage evaluation, but lack of curing residual strain monitoring in different layers. The aim of current study is to apply Fiber Bragg Grating sensors to monitor the characteristics of the curing process in a Graphite/Epoxy composite. Four FBGs are embedded into different lamina of composite materials, and the curing development as well as internal residual strain during curing process would be measured. Fiber Bragg Grating Sensor consists λ of = thousands 2 n eff Λ of short period refractive index (2-1) where modulation. n eff is When the effective the broad refractive band light index source of optical lunches fiber, at Λ the is FBG, the grating the certain period wavelength which is about of the 1um. light will Fig. 1 be illutrates reflected. the The principle reflected of wavelength FBG schematically. of FBG can be expressed as following [Hill & Meltz, 1997]: λ = 2 n eff Λ (2-1) where n eff is the effective refractive index of optical fiber, Λ is the grating period which is about 1um. Fig. 1 illutrates the principle of FBG schematically. Because of thermo-optic effect and Photo-Elastic effect, the wavelength of FBG will be shifted with changes of temperature and strain. The FBG wavelength is a function of the temperature and strain and in form as following [Hill & Meltz, ...
Context 2
... composite materials with high specific stiffness and strength have been widely applied in various fields such as aerospace or industry. Simultaneously, curing methods for joining composite materials have also gone through development intensively, for examples Hot- press, Pultrusion, Resin Transfer Molding (RTM) and Vacuum Molding. During the curing process, internal damages and residual strain are the most considerable relevance to quality of product, and hence demanded careful treatment. Commonly, the internal damage of composite materials could be detected by using ultrasound scan and X-ray, but these methods, however, are significantly high cost and not on-line monitoring. It is not suitable for smart structure application. Since several recent decades, optical fiber sensors have been utilized in composite material field popularly for their predominating advantages such as small size, low cost, and capability of avoiding electromagnetic influence. In 1988, Afromowitz proposed the polymer fiber embedded into composite materials to monitor the refractive index changes in the composite materials during curing process [Afromowitz, 1988]. And one year later the authors presented Fiber Optic Fresnel Reflection Technique for supervising the curing process [Afromowitz & Lam, 1990]. In late 1980s, Fiber Bragg Grating (FBG) sensor, one kind of optical fiber sensors, has attracted considerable attentions to the applications in aerospace, structural, medical and chemical spheres. FBG sensors are small and compatible with common polymeric materials, and thereby being easily embedded close to the internal sensing site in a composite structure without introducing significant defects. In 1990, Dunphy et al. employed the Fiber Bragg Grating embedded into composite materials to monitor the vitrification during curing process [Dunphy et al., 1990]. Similarly, FBG sensors were also applied to measure strain and residual stress after curing [Dewynter- Marty et al., 1998 & Okabe et al., 2002a]. On the other hand, Kuang and collegues improved detecting effect of the sensors by embedding FBG into composite materials in different layers [Kuang et al., 2001b]. Alternatively, in 2002, Okabe et al. utilized small-diameter FBG to study residual stress with micro damage of inner structure of the composite [Okabe et al., 2002b]. Furthermore, FBG has been also used to monitor the epoxy curing, and found the glass transition temperature with intensity changes [Giordano et al., 2004 & Wang et al., 2007]. Recent studies [Okabe et al., 2002a & Kuang et al., 2001a] discovered that when FBG sensors are embedded in CFRP laminates, the reflection spectrum from the sensors splits into two peaks because of the non-axisymmetric thermal residual stresses. This deformation of the spectrum was considered defective as it would lead to misinterpretation in strain measurements or crack detection in the laminates [Menendez & Guemes, 2000; Murukeshan et al., 2000; Leng & Asundi, 2002]. According to our knowledge, most of the previous researches focus on measuring the mechanical properties of composite materials and damage evaluation, but lack of curing residual strain monitoring in different layers. The aim of current study is to apply Fiber Bragg Grating sensors to monitor the characteristics of the curing process in a Graphite/Epoxy composite. Four FBGs are embedded into different lamina of composite materials, and the curing development as well as internal residual strain during curing process would be measured. Fiber Bragg Grating Sensor consists λ of = thousands 2 n eff Λ of short period refractive index (2-1) where modulation. n eff is When the effective the broad refractive band light index source of optical lunches fiber, at Λ the is FBG, the grating the certain period wavelength which is about of the 1um. light will Fig. 1 be illutrates reflected. the The principle reflected of wavelength FBG schematically. of FBG can be expressed as following [Hill & Meltz, 1997]: λ = 2 n eff Λ (2-1) where n eff is the effective refractive index of optical fiber, Λ is the grating period which is about 1um. Fig. 1 illutrates the principle of FBG schematically. Because of thermo-optic effect and Photo-Elastic effect, the wavelength of FBG will be shifted with changes of temperature and strain. The FBG wavelength is a function of the temperature and strain and in form as following [Hill & Meltz, ...
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Structural health monitoring is of great importance for the application of composites in aircrafts. Fiber Bragg grating (FBG) sensors are very suitable for structure strain measurement. However, the strain measured by FBG sensors is different from the original strain in host materials. The relationship between them is defined as strain transfer. As...
Citations
... In addition, a crucial technological tool for tracking medium-and high-frequency vibration behavior, acceleration measurements can provide insight into the vibration environment of numerous significant installations [11][12][13]. It also has drawbacks in complex situations, such as low circuit stability and significant signal noise [14][15][16][17]. The advantages of FBG acceleration sensors over typical electrical acceleration sensors include superior sensitivity, linearity, antielectromagnetic interference, and strength. ...
... Fibercore Co. Ltd. (PS1250/1550) produced the FBG fiber with a center wavelength of 1555 ± 0.3 nm, which reflects around 99% of the light and has a fullwidth half maximum of roughly 0.175 nm. A phase mask approach, frequently used in FBG manufacturing, is employed to create the FBG fiber [26]. ...
A R T I C L E I N F O Keywords: FBG accelerometer Fiber Bragg grating Dual mass block Low-and medium-frequency vibration measurement A B S T R A C T A novel short fiber Bragg grating (FBG) accelerometer based on a dual mass block structure is presented in this paper. The sensor is established on a solid, symmetrical design comprising a V-type beam. The configuration in the FBG accelerometer causes the FBG fiber to distort twice as much when subjected to external vibration. The theoretical research and optimization of the FBG accelerometer's natural frequency and sensitivity are performed using MATLAB software, while static structural stress and modal simulation analysis are examined using ANSYS software. An experimental test is applied to evaluate the implementation of the sensors. The natural frequency of the sensor is 880 Hz, and its stability frequency response is flat in the 20-340 Hz low-to middle-frequency range. The linearity of the average sensitivity is approximately 66.95 pm/g, and the transverse anti-interference of the FBG fiber is around 6.53%. This work proposes a suitable method to observe low-and medium-frequency vibration signals in large-scale applications.
... In addition, a crucial technological tool for tracking medium-and high-frequency vibration behavior, acceleration measurements can provide insight into the vibration environment of numerous significant installations [11][12][13]. It also has drawbacks in complex situations, such as low circuit stability and significant signal noise [14][15][16][17]. The advantages of FBG acceleration sensors over typical electrical acceleration sensors include superior sensitivity, linearity, antielectromagnetic interference, and strength. ...
... FBG sensors offer the solution, which does not allow laminated structure breakdown (usually with a diameter of 125-300 micron), they are inert and sensitive to both temperature and mechanical loading. In the works [Chiang 2011, Antonucci 2006, Murukeshan 2000], FBG technologies there were used to monitor thermoactive resin curing for airspace and wing energy industries. The optoelectronic sensor system, shown in Figure 3, which consisted of two light sources: superluminescent diode for lighting Bragg grating sensor and laser diode with 1310 Nm wavelength to light the fi ber edge in the article [Antonucci 2006] there was developed. ...
An article herein considers the development of fiber-optic sensors system, based on fiber Bragg gratings. Presently, fiber-optic sensor has become world-widely known amongst sensor technologies, which is used for monitoring engineering and construction structures. The work is linked with developing the system from fiber-optic sensors on the basis of fiber optic gratings, its characteristics, deformation behavior and temperature, acting at fiber Bragg grating by means of computer modeling. The research is focused at analysis of characteristics and deformation and temperature behavior of fiber-optic Bragg sensor. Fiber-optic Bragg sensor with tilted grating is used for measuring deformation of the object, the strength of which is changed, dependent on the applied force, as well, for measuring and detecting any temperature deviations, influencing at fiber Bragg grating, which might bring to fire and accidents. In the research there was made simulation modeling in MATLAB(Simulink) software.
... A diagnostic technique based on the embedment of Fiber Bragg Grating (FBG) sensors carried by optical fibers was applied to monitor the curing process. Such a technique, which makes possible the development of a lightweight and efficient strain sensing network [33,34], has already been applied to follow the development of the strains during the curing of composites and FML's by several authors [35][36][37][38][39][40][41][42][43]. In this work, the same sensors were used to monitor the curing cycle and then fracture mechanic tests in DCB configuration, investigating the strain evolution during the crack propagation. ...
The presence of residual stresses due to the manufacturing process may influence the development of damage in the interfaces of hybrid composite/metallic elements, thus complicating the structural integrity analysis. The paper presents an integrated experimental and numerical approach to develop sufficiently accurate models for the residual stress build-up and the interface damage propagation in hybrid structures. The experimental part focuses on the effect of residual thermal stress on mode I fracture behavior in three different interfaces of co-bonded composite/metallic hybrid specimens under the DCB test. The strain evolution is monitored by FBG sensors carried by optical fibers embedded in the specimens during the manufacturing and DCB test. Strain evolution during the curing cycle is used to calibrate a cooling simulation, followed by the simulation of the mechanical tests. The resulting multistep numerical approach obtains an appreciable correlation with experimental forces, strain evolution, and final residual strain in the DCB tests. Experimental and numerical analyses indicate that residual thermal stress can affect the evolution of strains during crack propagation, the development of permanent displacements, and the forces required to propagate the cracks.
... The FBG sensors offer a solution that does not cause disruption to the laminated structure (typically 125-300 µm diameter), are chemically inert, and sensitive to both temperature and mechanical strain. Recently, there has been an increasing interest in using FBG technology for cure monitoring of thermosetting resins for aerospace and wind energy applications [9][10][11]. ...
This paper presents a new approach to model heat transfer through an optical fibre. Three thermal strain modelling procedures were evaluated for coated and uncoated FBG optical fibres, considering different layers of sensors that effect strain measurements. The compensation factors required for strain measurements were investigated. The acrylate coating was found unsuitable for thermosetting polymers due to low Tg whereas, polyimide coating was appropriate for cure monitoring due to high Tg than most thermoset resins. Three types of thermal strain models were simulated, and the results were compared with experiments. The heat transfer through the core of an optical fibre was found negligible relative to glass cladding and the coating layers. It was found that thermal strains induced by the glass cladding and protective layers become more dominant as the heating rate and temperature range increases. The uncoated FBGs were found to give better accuracy for high temperature applications.
... There is a requirement for sensors to monitor all stages of manufacture of composite materials, in particular the infusion of the resin into the preform and its subsequent cure. The monitoring of infusion and the degree of cure of the resin are currently carried out empirically [2], as pre-production measurement tools such as differential scanning calorimetry [3] are not suitable for online process monitoring, while dielectric sensors [4] are not suited to being embedded into carbon fiber reinforced composites. ...
The use of chirped long period gratings (CLPGs) for monitoring the flow, the direction of the flow and the subsequent cure of an epoxy resin is presented. The asymmetric properties of the CLPG and its sensitivity to refractive index changes were exploited to facilitate the measurement of the direction of the flow. The performances of a continuously chirped LPG (CCLPG) and a step chirped LPG (SCLPG) were compared, with the CCLPG showing improved spatial resolution. The CCLPG and SCLPG were also used to monitor changes in the refractive index of the resin during cure, with the results showing close agreement with measurements undertaken simultaneously using a fibre optic Fresnel refractometer.
... The natural frequency of the cantilever composite beams depends on their dimension and constitution, the number of embedded SMA wires, and their transformation temperatures. However, the decrease of the natural frequency of the cantilever composite beams at T > A f was mainly due to the generation of an internal compressive stress by the mismatch of thermal expansions between the layers of glass fibre/epoxy, SMA wires, and optical fibre [18,19]. Since the SMA wires and the optical fibre were not embedded in the neutral axis of the samples, the mismatch of the thermal expansion would therefore cause the bending of the sample accordingly upon heating. ...
... The damping ratio of the composite under the change of temperature can be evaluated by measuring the vibration amplitude in free vibration motion using the following damping equation [19]: ...
Embedded actuator and sensor technology provides accurate structural
health monitoring and proper structural response of a structure in any
harsh servicing situation. This paper describes the fabrication of a
smart composite by embedding shape memory alloy (SMA) wires and fibre
Bragg grating (FBG) sensors into a glass fabric reinforced polymeric
composite. Mechanical performances of the composite under martensitic
and austenitic stages of the SMA wires were studied, and its natural
frequencies were also measured accordingly. The result shows that the
shift of the natural frequency arises from temperature change, thus
changing the mechanical properties of the SMA wires. The changes of
strain, stress, curvature, and damping ratio were predicted from an
asymmetrical lamination model. It was found that this model demonstrates
certain attractive effects, including mechanical properties, the change
of shape, and the natural frequency upon activation of the SMA wires.
... The system had enough sensitivity to analyze a curing period of 28 days, where the received optical power was 5% of the initial value. Curing monitoring of composite material was also conducted by Chiang [17]. Early age curing of Portand cement paste, with a 0.50 water cement ratio (w/c) was conducted by Câmara et al. [18]. ...
A fiber Bragg grating (FBG) sensor was used to monitor the early age curing temperatures of cement paste. Additional advantages in using the sensor were highlighted. The FBG was inscribed by a Continuous Wave 244 nm argon ion laser in the photosensitivity fiber. The fabricated FBG was calibrated from room temperature to 105 degrees C. In this temperature range, the FBG was found to be good in terms of both the sensitivity and linearity which were around 9 pm/degrees C and 99.9%, respectively. A host specimen with ratio of Portland cement, sand and water of 800, 500, and 275 ml by volume was used in the experiment. Results showed that the FBG could determine the initial and the final early age setting times. The initial early age setting time for the cement paste was about 5 h and the final early age setting time was about 14 h after casting. (C) 2013 Published by Elsevier Ltd.
... There is a requirement for sensors to monitor all stages of manufacture of composite materials, in particular the infusion of the resin into the preform and its subsequent cure. The monitoring of infusion and the degree of cure of the resin are currently carried out empirically [2], as pre-production measurement tools such as differential scanning calorimetry [3] are not suitable for online process monitoring, while dielectric sensors [4] are not suited to being embedded into carbon fiber reinforced composites. ...
A chirped long period grating (LPG) is used as a directional flow sensor by monitoring the change in the transmission spectrum upon immersion in an oil of refractive index higher than that of the fibre cladding. The change in profile of an attenuation band is shown to depend on the direction of immersion, indicating the possibility of using such devices in applications such as resin flow sensing in the manufacture of fibre reinforced plastic composite structures.
