Measurement of CFRP elastic modulus based on FBG reflectance spectrum analysis

• A novel method achieves CFRP elastic modulus measurement.
• FBG reflectance spectrum analyses are the foundations of the method.
• 3 dB bandwidth and center wavelength are chosen as reference indexes.
• Self-adaptive method is introduced to achieve experiment analyses.
• Absolute errors of reference indexes confirm the correctness of this novel method.

Based on fiber Bragg grating (FBG) reflectance spectrum analysis, one novel method to measure the elastic modulus of carbon fiber reinforced plastics (CFRP) is proposed. Basic theory of the novel method is that CFRP uniform cantilever beam produces linear gradient strain which leads to FBG reflectance spectrum broadening under external loadings. Calculation model of the basic theory is put forward and validated by finite element method (FEM) simulation. In order to obtain actual data about the relationship between elastic modulus and FBG reflectance spectrum, experiment of CFRP uniform cantilever beam under external loadings is implemented. The experiment spectrum corresponding to external weight 20 g is chosen as the specimen to explain data processing procedure by self-adaptive method. 3 dB bandwidth and center wavelength of FBG are selected as the reference indexes in the procedure. Elastic modulus of CFRP which is used in the experiment is extracted and its value is 6.617 GPa. To validate the correctness of the elastic modulus, contrastive analyses between transmission matrix theory calculation and experiment spectrums with external weights 5 g and 10 g are also carried out. Absolute errors of 3 dB bandwidth and center wavelength in the comparison are all less than 5 pm which prove the feasibility and correctness of this novel elastic modulus measurement method.