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Application of FBG sensors to monitoring of CFRP influenced by physical aging

COMPTEST 2011 14 – 16 February 2011 at EPFL, Lausanne. Application of FBG sensors to monitoring of CFRP influenced by physical aging. Shin-ichi Takeda a , Jun Koyanagi b , Shin Utsunomiya a , Yoshihiko Arao c , Hiroyuki Kawada c.

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Application of FBG sensors to monitoring of CFRP influenced by physical aging

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  1. COMPTEST 2011 14 – 16 February 2011 at EPFL, Lausanne Application of FBG sensors to monitoring of CFRP influenced by physical aging Shin-ichi Takeda a, Jun Koyanagi b, Shin Utsunomiya a, Yoshihiko Arao c, Hiroyuki Kawada c aAerospace Research and Development Directorate, Japan Aerospace Exploration Agency bInstitute of Space and Aeronautical Science, Japan Aerospace Exploration Agency cDepartment of Mechanical Engineering, Waseda University

  2. Research Background JAXA will plans to launch some scientific satellite. Large-scale Mirror (< 5m j) is needed for high resolution observation. • Requirements • Lightweight • Long-term stability • Profile irregularity • (1/10 RMS of laser wavelength ) • Surface roughness • (1/100 RMS of laser wavelength ) • CFRP (Carbon Fiber Reinforced Plastic) is promising structural material. • High specific strength • High heat conductivity

  3. Objectives • Long-term stability of CFRP is affected by some factors. • Water absorption – on ground • Physical aging – on ground, in space • Thermal residual stress relaxation – on ground, in space Physical aging is known to cause resin shrinkage in CFRP. Thermal residual strain in CFRP changes in long-term. Strain changes due to physical aging were measured by FBG sensors experimentally.

  4. Physical aging (PA) • Process of state of molecular chain reach from non-equilibrium to equilibrium with time. • Cause decrease in free volume and increase in density. Non equilibrium State Molecular chain Free Volume Aging Process Equilibrium State T0 Tg Temperature Steady state of molecular

  5. FBG sensors • Small size – 150mm including polyimide coating for this study • High sensitivity to strain measurement - 1.2 pm/me, 13 pm/˚C Tension Compression Compression Tension • Evaluation of an axial strain by wavelength shift of reflected light.

  6. Thermocouples Optical fiber Experimental Procedures - specimen • Materials • Epoxy-based carbon fiber UD prepregs • IMS60/ #133, Toho Tenax Co. Ltd. • FBGs • 15mm grating period, polyimide coating, Fujikura Ltd. 90o 0o • Manufacturing: Autoclave • 180oC, 2.5hours

  7. Confirmation of degree of cure using DSC Prepreg Cured CFRP • Heat flow showed degree of cure in present CFRP is over 95 %. • The present autoclave process was good standard.

  8. ④ ① ③ ② PC Experimental Procedures – measurement • 100oC in vacuum hot oven • Wavelength shift of reflected light: every 1 hour • Temperature: every 5 minutes ② ③ ① ④

  9. Temperature changes during strain measurement • After 120 minutes, temperature was almost uniform, 98oC to 100oC. • Compressive residual strain after 120 minutes reference value of 0 me.

  10. Reflection spectrum changes 90o 4 Plies 90o 8 Plies Birefringence 0o 4 Plies 0o 8 Plies Uniform strain • While the spectra keeping its shape, the spectra shift to lower wavelength. • Compressive residual strain increased gradually for 90o specimen.

  11. Results of strain changes – UD laminates 90o 45o 0o • Strain changes were almost same with changes in laminates thickness. • It is important to consider the strain changes due to PA.

  12. Creep test of CFRP • Specimen • Materials • Epoxy-based carbon fiber UD prepregs (same as previous tests) • Dimensions • 210 mm x 25.4 mm x t • Stacking sequences • [9016], t=2.20 mm • [02/908]s, t=2.75 mm • Test conditions • 100oC in hot oven • No load (= 0 MPa), 5.8kg (= 10 MPa) • Strain and Temp. measurements

  13. Creep test results of 90o CFRP specimen Creep strain was estimated on the assumption that shrinkage due to PA is same as that on 10MPa load. -345.6 me (avg.)

  14. Creep test results of cross-ply CFRP specimen Strain changes were calculated by CLT.

  15. Conclusions • Strain changes due to physical aging were measured by FBGs. • The strain change in 90o CFRP was largest because of resin shrinkage. • The strain changes were almost same with changes in laminates thickness. • Creep test results illustrated that it is important to consider the strain changes due to PA.

  16. Thank you for your kind attention! Jeju Island, 18th ICCM JAXA, Chofu Aerospace Center Aerodrome Branch

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