Test And Prediction Model Of Fatigue Crack Propagation In GLARE

Glass fiber reinforced aluminum laminate(GLARE)has been widely used in aircraft structures due to its excellent impact resistance and fatigue crack growth characteristics.During the flight process,the initial damage position of aircraft structure usually initiates cracks,and the fatigue crack growth happens.Therefore,the research on fatigue crack growth with initial cracks is of great significance to the damage tolerance design of aircraft structure.At present,a large number of scholars have studied the fatigue crack growth mechanisms of GLARE,and have established the various fatigue crack growth prediction models.However,the existed prediction model of fatigue crack growth is not suitable for long-term fatigue crack growth,and the influence of ambient temperature is also not considered.Therefore,in this thesis,the fatigue crack growth tests of different types of GLAREs were conducted.The long crack stable growth process of GLARE under different temperature conditions was also analyzed.The correction factors of stress intensity factor(SIF)for the fatigue crack growth of GLARE were studied.The Alderliesten model was also modified to predict the fatigue crack growth.This study can provide the theoretical support for the structural design and engineering application.The fatigue crack growth tests for three types of GLAREs and aluminium plate were conducted.The effects of stress level,stress ratio and temperature on the fatigue crack growth rate were taken into account.The contribution of temperature to the fatigue crack growth rate of GLARE was analyzed.The fatigue crack growth rates of GLARE with three types of ply structures were compared.The results show that the fatigue crack growth rate increases with the increase of stress level.The fatigue crack rate of aluminum plate is much higher than that of GLARE.The boundary effect of GLARE is not obvious.The growth rate of fatigue crack growth decreases with the increase of the volume fraction of the fiber layer along the applied stress direction.The fatigue crack growth rate accelerates at the elevated temperature can process,and slows down at low temperature.In order to adapt the analysis of fatigue crack growth process of GLARE with long fatigue crack size,a finite width correction factor of SIF for the fatigue crack is required when applied the fracture mechanics.From the physical point of view,the finite width correction factor of SIF is determined by using the work ratio.The proposed correction method is also validadted by the aluminum experiment.Then,the finite width correction factor of GLARE with three types of ply structures are obtained by using this method.The theoretical extreme point of the finite width correction factor of the SIF for GLARE is given,which is related with the material modulus and thickness of constituents.The delamination characteristics of GLARE during the fatigue crack growth process are determined by using the digital image correlation test technology(DIC)in the fatigue crack growth experiments of GLAREs.A calculating the equivalent delamination area method is proposed.The relationship between the delamination area and the crack growth length is established.The work ratio of the GLARE is also calculated using the equivalent compliance method.The mathematical formulation of the delamination correction factor for the fatigue crack growth in GLARE is established.The parameters in the formula are the function of the elastic moduli of the composite layers in GLARE.Finally,based on the fatigue crack groth experiments of GLARE at elevated and room temperatures,a correction factor considering the temperature effect(temperature correction factor)is obtained by combining with the shape and delamination correction factors,and its effectiveness is verified.The shape,delamination and temperature correction factors are introduced into the SIF in the Alderliesten fatigue crack growth prediction model to predict the fatigue crack growth in GLARE.It is found that this method can accurately predict the fatigue crack growth in GLARE,and is also suitable for the fatigue crack growth prediction in GLARE at elevated temperature.The calculation method for the finite width correction factor of SIF of fatigue cracks is proposed from the physical point of view in this thesis,which can guide solving the correction factor of SIF in other material systems.In addition,the proposed fatigue crack growth prediction model can provide the theoretical basis for the damage tolerance structure design.