Research On Buckling And Delamination Growth Of Composite Laminate With An Open-hole And Embedded Delamination

The carbon fiber reinforced composite material,as a new type of composite material with excellent properties,is widely used in aerospace,shipping,transportation,medical equipment and other fields and support an effective way for increasing structure efficiency.However,in the production,manufacturing,transportation and other processing of composite materials,the external load will produce different type of damage to composite structures,especially the invisible delamination damage,and threaten the safety of structure.In the process of bolt connection and repair of composite materials,the delamination around the hole is a common type of damage during the process of drilling.At present,the influence of central hole and delamination damage on the bearing capacity of laminate are studied separately,there is a lack of research on the comprehensive effects of laminate failure process caused by central hole and delamination damage.The carbon fiber reinforced composite laminate with a central hole and delamination damage is subject for this study.And its buckling and delamination growth behavior under compression load and failure mode in different type of delamination damage and ultimate bearing capacity were studied with the method combined experiment with numerical simulation.Firstly,aiming at the shortcomings of various forms of delamination damage and the uneasy to measure,preparing specimen with an open-hole and artificial embedded delamination.Taking compression experiment with the prepared specimen under step load and the help of C scan.And observing the delamination growth and recording the experimental data when recording the buckling forms.The results of experiment indicate that under the compression load,the buckling mode of composite laminates with an open-hole and embedded delamination is presented as initial compression,local buckling and global buckling.The basic path of delamination growth during the buckling process is as follows:expand along the width direction of the specimen first,which is perpendicular to the load direction and extend to the width edge of the specimen.And then expand along the length direction of the specimen,which is parallel to the load direction until finally damage.This work provides an experimental basis for numerical simulation.Secondly,the ABAQUS Standard module is used to establish the finite element model,the solid element is used to simulate the specimen and the cohesive model is used to simulate the initial damage criterion and damage propagation criterion.It is showed when comparing the finite element results and experimental results that both in the calculation of laminates buckling load,or growth prediction of delamination,the results of numerical simulation can fit the experimental results well.It means that the proposed model in this paper can make great prediction of buckling and delamination growth of composites laminates with an open-hole and embedded delamination.According to mechanism analysis,because of stress concentration around the hole and the initial delamination grown in type I for S₁₁1 was greater than T_I.Then it grown in a mixed mode of type for S₁₁1 was greater than T_I and S₂₂ was greater than T_II.Finally,based on sensitivity analysis of delamination damage,the influence of delamination shape,size,and coupling delamination of thickness direction on the buckling and delamination propagation of composite laminates are studied.The results show that when the delaminations'location and shape are the same,the larger of the size,the smaller of the critical buckling load,and the smaller of the bearing capacity.Only change the shape of delamination makes little difference of laminates buckling mode and delamination propagation mode.When there are coupling delamination in the direction of thickness and the delamination located in the same side of neutral surface,the sublaminate upper the delamination that near surface begins local buckling first.Then the global buckling occurs until the model being destroyed.Its delamination growth mode is the same with the laminate of single delamination.When the coupling delamination located in the both sides of neutral surface,the sublaminate near the neutral surface begins local buckling first,and then the sublaminate that away from the neutral surface begins local buckling.Then the global buckling occurs until the critical buckling load.The results of this paper can provide a certain theoretical basis for the damage tolerance of composite structures,and provide basic support for the application of composite materials.