Fatigue Damage Monitoring For Fiber Reinforced Polymer Laminates Using Acoustic Emission Technique With Scanning Electronic Microscope Image

Basalt fiber reinforced polymer (BFRP) is a structural material with superiormechanical properties. BFRP can also be used to strengthen a structure if it iswrapped or attached to the surface of structural elements in civil engineering. Theacoustic emission technique (AE) combined with the scanning electronicmicroscope (SEM) technique is employed to monitor the fatigue damage evolutionof the BFRP plates. Then, the features of AE signals are analyzed using wavelettransform, and different damage patterns of BFRP are recognised. Additionally, bycalculating the energy of received AE signals, the damage evolution of the BFRPmaterials can be obtained. The main achievements of this dissertation are desc ribedin the following.Fristly, unidirectional BFRP laminates with14layers are made with the handlay-up method in this paper. Then, three-point bending fatigue tests are performedon the BFRP plates. The acoustic emission technique and SEM technique areemployed to monitor the fatigue damage evolution of the BFRP plates in anapproximate continuous scanning way.Secondly, time-frequency analysis using the wavelet transform techniqueinstead of the peak frequency method is proposed to analyze the received AEsignals. The time frequency analysis using wavelet transform describes thepanorama of AE signals very well, while traditional peak frequency method loses alot of features. Combining the SEM images and the analysis of AE signals, thedamage of BFRP material are described.Thirdly, three main frequency bands of AE signals: low frequency band(80-160kHz), intermediate frequency band (160-300kHz) and high frequency band(above300kHz), which correspond to three different damage patterns: matrixcracking, delamination and fiber fracture, respectively. Then, seven damage patterns,that is, matrix cracking, delamination, fiber fracture and their combinations, areidentified from the time-frequency curves of the AE signals by combining theanalysis of AE signals and SEM images.Finally, The cumulative energy (obtained from wavelet coeffic ients) of variousdamage patterns of the BFRP specimens during entire fatigue tests are analyzed. The fatigue damage evolution of the BFRP specimens is presented. Delaminationplay an important role in the fatigue damage of BFRP, fiber fracture usually occursin the end of loading process. The delamination usually causes the matrix damage atthe beginning, while, with the increasing of loading time, the delamination induce sfiber fracture at the end of fatigue test.