Vibration-based Fatigue Life Prediction Of CFRP Composites With Delamination Damage

Fiber reinforced polymer(FRP)has advantages such as high specific strength and modulus,corrosion resistance,and strong designability,resulting in wide use in aerospace,civil engineering,and automotive manufacturing.However,FRP is a laminated structure with low interlayer strength,which is prone to cause delamination during manufacturing and use,and cause reduction in structural stiffness and service life.Therefore,it is necessary to detect and evaluate the remaining life of FRP structures containing delamination damage.This study investigates the natural frequency and compression-compression fatigue life of FRP panels with delamination.The effect of delamination damage on the natural frequency and fatigue life of FRP structures was studied,and the delamination damage and fatigue life of FRP structures were evaluated based on frequency changes.The study has combined experiment,simulation,and intelligent algorithms,and the main content are as follows:Modal experiments and compression-compression fatigue experiments were conducted on CFRP laminated specimens with different delamination.The results showed that with the increase of delamination damage,the first five natural frequencies and compression-compression fatigue life of CFRP specimens showed a downward trend.The severe is the delamination,the more obvious decrease is seen in the highorder frequencies and the fatigue life,indicating that delamination damage greatly affects the vibration frequencies and the compression-compression fatigue life of FRP structures.A modal model of CFRP laminated panels was established using ABAQUS,and a fatigue analysis model of CFRP laminated panels was established by combining UMAT subroutines,which was verified by experimental data.By setting different delamination sizes and interfaces in the finite element modal analysis model and fatigue analysis model,it was found that the natural frequency and fatigue life of CFRP laminated panels showed a downward trend with the increase of delamination,and the influence trend of delamination on both was basically consistent even for delaminations occurring at different interfaces.The experimental results were analyzed,and the simulation data was used to verify that the inherent frequency and fatigue life of CFRP laminated beams with different delamination sizes can be well fitted by an exponential function,demonstrating a quantitative relationship between the inherent frequency and fatigue life of delaminated composite materials.After analyzing the experimental and simulation data,it was found that the natural frequencies and compression-compression fatigue life of CFRP laminated panels with delamination can be fitted by an exponential function,indicating a quantitative relationship existed between them.Therefore,the fatigue life can be evaluated through the changes in vibrational frequencies.Two inverse detection methods were used to predict the fatigue life of CFRP laminated panels based on frequency shifts.One is to identify delamination damage in CFRP laminated panels using surrogate model genetic algorithm(SAGA)and artificial neural network(ANN),and then fatigue simulation of CFRP laminated panels with predicted delamination were performed to obtain the numerical fatigue life.The other is to construct an ANN algorithm with frequency changes as the input and fatigue life as the output.After training the ANN with the sample data,the fatigue life of CFRP laminated panels can be directly predicted by inputting the target frequency changes.Both methods were validated by numerical and experimental cases,and the results showed that quantitative evaluation of the fatigue life of FRP laminated structures with delamination damage based on vibration monitoring is feasible,providing a reference and support to monitor health and remaining life of in-service FRP structures with existing damage through vibration parameters.