Self-sensing TFDR for damage detection of CFRP structures

Carbon fiber reinforced polymer (CFRP) composites have higher specific strength and specific stiffness than conventional metallic materials. The CFRP structures, however, are easily damaged by impact loading. It is quite difficult to detect damage of the impact loading by visual inspection. In the present paper, self-sensing Time-Frequency-Domain Reflectometry (TFDR) is proposed as a damage detection method for large CFRP structures. The TFDR uses a set of high-frequency burst signals. From the time span between the input signal and the reflected signal, the location of the damage is identified. By using the several signals of different frequencies, other information can be measured. This is the advantage of the frequency domain Reflectometry. TFDR uses both methods to locate the damage and dimension of the damage. The effect of micro structure of CFRP is investigated for the Finite Difference Time Domain (FDTD) analysis. Microstructures of CFRP of fiber direction and transverse direction are modeled and FDTD analyses are performed to check the limitation of the orthotropic homogeneous approximation of CFRP. As a result, CFRP may be considered as an orthotropic homogenous conductor when the electromagnetic wavelength is longer than 25 times of averaged CFRP microstructure. The electrical analyses showed that the TFDR was applicable to detect damage location and size of CFRP structures.