以內埋式光纖光柵感測器監測碳纖維複合材料衝擊及疲勞破壞之應用

Abstract

Carbon Fiber Reinforced Plastic (CFRP) composites used today are at the leading edge of materials technology, with performance and fair costs to the applications. It is important to detect the impact fractures inside CFRP, preventing the structure from catastrophic failure. Due to its tiny size, Fiber Bragg Grating (FBG) sensors can be embedded inside the CFRP materials without significantly affecting its intensity. The purpose of this study was to discuss the feasibility of investigating impact damage by using pre-embedded FBGs in CFRP materials. Just after impact, the FBG sensor could detect the impact damage if it is in the vicinity of the impact source. For impact at a distance from the sensor, bending test was conducted to observe the relation between the peak wavelength shift and bending load charts to reveal any hysteresis phenomenon on the peak wavelength-bending load charts that could help us to infer the impact damage up to 50mm away from the sensors. For the post-impact fatigue test, it was found the characteristic Bragg wavelength gradually became buried in a wide band of wavelengths. In order words, the FBG lost its capability to act as a sensor. It was found that this phenomenon may be attributed to the highly non-uniform strain inside the CFRP specimen near the impact position induced by a combination of fatigue and impact damages. This revealed a previously undocumented phenomenon that may limit the application of FBG in damage monitoring inside composite material.