Two-dimensional Theoretical Model And Numerical Analysis On Delamination Buckling Of Composite Laminates

Fiber reinforced composite laminates have become the most popular materials in the aerospace industry due to their excellent mechanical properties.However delamination happens frequently because of defects in manufacture or assembly and damages in application.Under small load,delamination can cause buckling of laminated structures which will induce the expansion of the delamination and lead to failure of the structure eventually.Delamination reduces the bearing capacity and service life of laminated composite structures,which is a hidden risk for composite laminates.Therefore,it is essential to investigate delamination of laminated structures.In this thesis,we study composite materials with delamination defects from two aspects: theoretical analysis and numerical simulation.A two dimensional theoretical model is developed to study the buckling and post buckling problems of composite materials with delamination under bending loads.Then the buckling behavior and delamination growth of composite laminates containing various types of delamination under bending load were studied.Main contributions of this study include:First,a two dimensional theoretical model is developed for the analysis of buckling and post buckling of laminated composite plates with delamination.The model can be used to estimate the critical buckling load,and the deformation of post buckling.Second,the buckling process of layered composite material with delamination under bending load is obtained by finite element analysis,which generally include three stages: the initial stage,top layer and bottom layer are bending down until the load increases to a certain value,which results in a sudden change on the curve of straindisplacement,where the buckling takes place;the second stage: the bending load keeps increasing together with the out-of-plane displacement of the central point until the maximum load is reached,and the structure becomes unstable;the third stage: the capacity of bearing of the material is lost.Third,the buckling behavior and delamination growth of composite laminates with various types of delamination were tested to be:1.The bearing capacity of laminates was greatly reduced by delamination defects;the buckling critical load of the laminates declines with the increase of the delaminated area;the size of the delamination does not affect the buckling mode.2.The maximum bearing capacity of the composite laminates with rectangular delamination is greater than that with circular delamination,when the areas of the two types of delamination are the same.Therefore the laminated composite plate containing rectangular delamination is more resistant to buckling.3.The critical buckling load of laminated composite plates with delamination at low temperature is the same as that under normal temperature.But the displacement mutatio due to buckling is less than that of normal temperature.The performance of the material in the initial stage of buckling is better than the normal temperature,but with the increase of the load,the maximum bearing capacity of the laminated structure at low temperature is lower than the normal temperature.In the aspect of delamination,the expanded area at low temperature is larger than the normal temperature.In this study,a two-dimensional theoretical model of composite laminates with delamination damage is proposed,which enriches the research methods of buckling and post-buckling of laminate plates under bending loads.Through the finite element analysis of composite laminates with delamination damage,the influence of geometric factor and temperature on the critical buckling load and the delamination growth path of the composite are analyzed.