Fatigue Failure Process Characterization for Carbon Fiber Sheet Reinforced Steel Rods Using the Acoustic Emission Technique

Acoustic emission (AE) technique is a widely used CM technique. In this paper, AE technique was used to characterize the fatigue failure process for carbon fiber sheet (CFS) reinforced steel rod. The AE signals at the frequency band of 50–400 kHz are detected by using AE sensors mounted on the steel rod and analyzed by both parameter analysis and spectrum analysis in order to investigate the feasibility of using the AE technique to identify various failure modes during fatigue failure process for CFS reinforced steel rods. Tension-tension fatigue experiments were carried out on both CFS reinforced and unreinforced steel rods. Based on AE energy parameter analysis using wavelet decomposition method, failure process was initially divided into three stages for unreinforced specimen and seven stages for CFS reinforced specimen. The frequency contents within the frequency band of 50–400 kHz for various failure modes in each stage including crack initiation, developing, final rupture in steel rod and matrix crack, debonding in CFS were revealed by fast Fourier transform (FFT) method. Further wavelet transform (WT) analysis was performed to illustrate the sequences of the failure modes and main failure mode in each stage by the occurrence time and longest duration time, respectively. This work indicates that the proposed method is promising for distinguishing failure stages qualitatively and identifying failure modes quantitatively in CFS reinforced steel rods.