Simultaneous measurement of temperature and strain in glass fiber/epoxy composites by embedded fiber optic sensors: I. Cure monitoring

In this paper (Part I) the use of fiber optic sensors for real-time monitoring of the cure kinetics of GFRP composites is explored. The proposed sensing system allows the simultaneous measurement of both temperature and strain by monitoring the change in reflected wavelength from two coupled fiber Bragg grating (FBG) sensors that have been embedded into the composite laminate. Instrumented GFRP laminates with 12, 18 and 24 reinforcing plies, respectively, were prepared by means of the vacuum bagging technique. Samples were cured in a thermally controlled oven at 80 °C and 30 kPa for 240 min (isothermal stage) and then cooled down to ambient temperature by turning off the heating source (cooling stage). The obtained results, combined with proper data post-processing, have proven the effectiveness and potentiality of the proposed sensing system to measure the progression of the composite cure kinetics. It was shown that temperature within the specimen can differ significantly from the set-point temperature inside the oven because of the heat released during the exothermal reticulation of the epoxy resin. The combined sensing system also allowed the residual strain accumulated within the composite during the cooling stage to be accurately measured. Once the laminate had been cured, the embedded optical sensing system reveals itself purposeful for real-time structural health monitoring and damage assessment of the finished component. This aspect is discussed with more detail in the accompanying paper (Part II).

[1]  Xavier E. Gros,et al.  An eddy current approach to the detection of damage caused by low-energy impacts on carbon fibre reinforced materials , 1995 .

[2]  M. Cao,et al.  Fiber-optic composite cure sensor: monitoring the curing process of composite material based on intensity modulation , 2003 .

[3]  Vadakke Matham Murukeshan,et al.  Cure monitoring of smart composites using Fiber Bragg Grating based embedded sensors , 2000 .

[4]  Andrea Cusano,et al.  Cure-induced residual strain build-up in a thermoset resin , 2006 .

[5]  John Botsis,et al.  Embedded fiber Bragg grating sensor for internal strain measurements in polymeric materials , 2005 .

[6]  Yu-Lung Lo,et al.  Measurement of Corrosion and Temperature Using a Single-Pitch Bragg Grating Fiber Sensor , 1998 .

[7]  Antonino Squillace,et al.  Non-destructive evaluation of aerospace materials with lock-in thermography , 2006 .

[8]  Gerard Franklyn Fernando,et al.  In-situ process and condition monitoring of advanced fibre-reinforced composite materials using optical fibre sensors , 1998 .

[9]  Ralph P. Tatam,et al.  Strain development in curing epoxy resin and glass fibre/epoxy composites monitored by fibre Bragg grating sensors in birefringent optical fibre , 2005 .

[10]  Nobuo Takeda,et al.  Temperature-compensated strain measurement using fiber Bragg grating sensors embedded in composite laminates , 2003 .

[11]  Libo Yuan,et al.  Thermal effects on an embedded grating sensor in an FRP structure , 2001 .

[12]  L M Sim,et al.  Damage detection and assessment in fibre-reinforced composite structures with embedded fibre optic sensors-review , 2002 .

[13]  Eric Udd.  Fiber optic smart structures , 1996 .

[14]  Li Cheng,et al.  Determination of dynamic strain profile and delamination detection of composite structures using embedded multiplexed fibre-optic sensors , 2004 .

[15]  Ivana K. Partridge,et al.  Monitoring autoclave cure in commercial carbon fibre/epoxy composites , 1998 .

[16]  Measurement of the degree of cure of glass fiber–epoxy composites using dielectrometry , 2001 .

[17]  Li Cheng,et al.  Embedded fibre Bragg grating sensors for non-uniform strain sensing in composite structures , 2005 .

[18]  Nobuo Takeda,et al.  Detection of impact damage of stiffened composite panels using embedded small-diameter optical fibers , 2004 .

[19]  Jinsong Leng,et al.  Structural health monitoring of concrete cylinders using protected fibre optic sensors , 2006 .

[20]  Andrea Cusano,et al.  Advanced cure monitoring by optoelectronic multifunction sensing system , 2004 .

[21]  L. Calabrese,et al.  The effect of a liquid CTBN rubber modifier on the thermo-kinetic parameters of an epoxy resin during a pultrusion process , 2003 .

[22]  John Botsis,et al.  Characterisation of residual stresses in a single fibre composite with FBG sensor , 2007 .

[23]  Maurice Whelan,et al.  Embedded fibre Bragg grating sensors in advanced composite materials , 2001 .

[24]  Y. Scudeller,et al.  Determination of strain distribution and temperature gradient profiles from phase measurements of embedded fibre Bragg gratings , 2006 .

[25]  I. Partridge,et al.  Dielectric monitoring of cure in a commercial carbon-fibre composite , 1995 .

[26]  Nobuo Takeda,et al.  Detection of transverse cracks in CFRP composites using embedded fiber Bragg grating sensors , 2000 .

[27]  Yun-Jiang Rao,et al.  Recent progress in applications of in-fibre Bragg grating sensors , 1999 .

[28]  Joy P. Dunkers,et al.  The application of optical coherence tomography to problems in polymer matrix composites , 2001 .

[29]  Vlastimil Matejec,et al.  In situ study of the epoxy cure process using a fibre-optic sensor , 2001 .

[30]  Francesco Aymerich,et al.  Ultrasonic evaluation of matrix damage in impacted composite laminates , 2000 .

[31]  Libo Yuan,et al.  Strain monitoring in FRP laminates and concrete beams using FBG sensors , 2001 .

[32]  T. Osswald,et al.  Theoretical analysis of fiber motion and loads during flow , 2004 .

[33]  Wei Jin,et al.  Strain monitoring in composite-strengthened concrete structures using optical fibre sensors , 2001 .

[34]  Gerard Franklyn Fernando,et al.  In situ cure monitoring of epoxy resins using optical fibre sensors , 1996 .

[35]  Li Cheng,et al.  Utilization of embedded optical fibre sensors for delamination characterization in composite laminates using a static strain method , 2005 .

[36]  Alan D. Kersey,et al.  Fiber optic sensors in concrete structures: a review , 1996 .

[37]  Yunjiang Rao,et al.  Simultaneous strain and temperature measurement of advanced 3-D braided composite materials using an improved EFPI/FBG system , 2002 .

[38]  Hyun-Kyu Kang,et al.  Simultaneous monitoring of strain and temperature during and after cure of unsymmetric composite laminate using fibre-optic sensors , 2003 .

[39]  J. A. Guemes,et al.  Response of Bragg grating fiber-optic sensors when embedded in composite laminates , 2002 .

[40]  Ralph P. Tatam,et al.  RAPID COMMUNICATION: Relating the state of cure to the real-time internal strain development in a curing composite using in-fibre Bragg gratings and dielectric sensors , 1998 .

[41]  Anand Asundi,et al.  Structural health monitoring of smart composite materials by using EFPI and FBG sensors , 2003 .

[42]  Hwa-Yaw Tam,et al.  Fundamentals and applications of optical fiber Bragg grating sensors to textile structural composites , 1998 .

[43]  Nobuo Takeda,et al.  A new approach to predicting multiple damage states in composite laminates with embedded FBG sensors , 2005 .

[44]  Werner Daum,et al.  How to reliably measure composite-embedded fibre Bragg grating sensors influenced by transverse and point-wise deformations? , 2004 .

[45]  Mojtaba Kahrizi,et al.  Characterization of a FBG strain gage array embedded in composite structure , 2005 .

[46]  Nobuo Takeda,et al.  Estimation of the damage patterns in notched laminates with embedded FBG sensors , 2006 .

[47]  Kenneth Reifsnider,et al.  Characterization and Analysis of Damage Mechanisms in Tension-Tension Fatigue of Graphite/Epoxy Laminates , 1984 .

[48]  John Botsis,et al.  On a direct determination of non-uniform internal strain fields using fibre Bragg gratings , 2005 .

[49]  E. Shafir,et al.  Practical strain isolation in embedded fiber Bragg gratings , 2005 .

[50]  Y. Okabe,et al.  Quantitative evaluation of transverse cracks in carbon fiber reinforced plastic quasi-isotropic laminates with embedded small-diameter fiber Bragg grating sensors , 2003 .

[51]  Gregory M. Glenn,et al.  Fiber-reinforced composites , 1988 .

[52]  Hyun-Kyu Kang,et al.  Strain monitoring of a filament wound composite tank using fiber Bragg grating sensors , 2002 .

[53]  Antonello Cutolo,et al.  Monitoring by a single fiber Bragg grating of the process induced chemo-physical transformations of a model thermoset , 2004 .

[54]  P. Foote,et al.  DESIGN NOTE: Optical fibre acoustic emission sensor for damage detection in carbon fibre composite structures , 2002 .