Flexural Properties And Failure Mechanism Of GLARE Laminates

The development of large aircraft brings forward the strict requirements for material selection of key structural components.GLARE laminates have been already developed as the important structural materials for aircraft fuselage and wing skin owing to their good fatigue properties,excellent resistance to impact and significant weight reduction in structural design.During flights,the bending moment on aircrafts causes a large deflection of laminates.The oversize deformation can result in the structural failure of GLARE.Therefore,it is meaningful to inquire the failure behaviors and damage mechanisms of GLARE laminates under bending load.Firstly,floating roller peel test and interlaminar shear test were conducted in this study to optimize the content of adhesive.Then the infiltration mechanism of epoxy was investigated by means of SEM observation,contact angle test,roughness measurement and lap-shear tensile test respectively.GLARE laminates with good bonding interface were prepared based on the optimized adhesive content and surface treatment process.Secondly,the influence of specimen dimension,loading nose radius,support radius and L/h ratio on flexural properties were studied by numerical simulation and experiments.Then the bending test method for GLARE laminates was gained.Moreover,the effect of fiber layup configuration and laminates structure on the failure mechanism was confirmed by the comparative study of failure behaviors of GLARE laminates during the bending experiment and the numerical simulation process.Finally,the flexural properties of GLARE laminates with different structures were measured.The evolution of flexural performance with the expansion of structure obtained in this study could provide a powerful supporting for prediction of flexural performance.Results indicated that the laminates manufactured with higher adhesive content showed higher peel strength and shear strength.The infiltration of epoxy on porous alumina surface had two modes,fully wetting and incompletely wetting.The adhesion performance could be improved by optimizing the surface treatment process.Besides,the specimen dimension and loading nose radius had no significant influence on the bending strength,while the support radius could affect the bending strength greatly.The L/h ratio,which could change the failure mode of the laminates,had the most significant impact on flexural properties.The shear failure mode was dominant at small L/h ratio.However,relative sliding between specimen and supports occurred at L/h ratio of 25.Therefore,effective bending failure occurred when L/h ratio was limited in a certain range.The bending failure behavior changed with fiber layup configuration.Moreover,structural configurations(3/2,4/3,5/4 and 6/5)affected bending strength and modulus distinctively.It was found that bending modulus decreased with structural expansion and bending strength depended on fiber layup configuration.The bending strength of unidirectional laminate increased with structural expansion,while that of other fiber layup laminates decreased.