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Ultrasonic Evaluation for the Detection of Contact Defects of the Timer and Fiber-reinforced Polymer (FRP)

Ramezanpour, Moein | 2022

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  1. Type of Document: M.Sc. Thesis
  2. Language: Farsi
  3. Document No: 54942 (09)
  4. University: Sharif University of Technology
  5. Department: Civil Engineering
  6. Advisor(s): Toufigh, Vahab
  7. Abstract:
  8. Fiber-reinforced polymer (FRP) composites have been used tremendously to repair and rehabilitate timber structures due to their formability, ease of use, and high specific strength. The quality of the bond between FRP and timber substrate is critical for having complete composite action. In this paper, a comprehensive set of linear and nonlinear ultrasonic methods was performed to investigate the bond between carbon-FRP (CFRP) and timber. For this purpose, one hundred and twenty-six specimens of reinforced timber were prepared. Two techniques were considered to bond CFRP and timber: 1) externally bonded reinforcement (EBR) and 2) externally bonded reinforcement on the groove (EBROG). The effect of the number of CFRP layers, adhesive types, the extent of artificial surface defects, and the depth of the groove was contemplated. By analyzing linear methods, differences in stiffness and modulus of elasticity of CFRP and timber led to velocity variation and attenuation phenomena. Higher-order harmonics were also used to investigate the nonlinear behavior of ultrasonic waves at the bond. The second harmonic generation detected microscale surface damage at CFRP and timber bond. Single-lap shear tests were employed to determine the bond strength of CFRP and timber and evaluate the accuracy of the linear and nonlinear methods. Finally, using the ultrasonic output and mechanical experiments, artificial neural network models were considered. These models revealed the correlation between destructive and nondestructive measurements. According to the results of neural network models, the nonlinear parameter provided significant performance in detecting defects at the CFRP-to-timber bond even with low-frequency.
  9. Keywords:
  10. Ultrasonic Waves ; Wave Attenuation ; Artificial Neural Network ; Fiber Reinforced Polymer (FRP) ; Carbon Fiber Reinforced Polymer (CFRP) ; Timber Structures ; Nondestructive Test

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