Research On Buckling Instability Characteristics Of Laminates With Free Borders On Contralates

Aircraft composite material is a complex multiphase system,and it is difficult to avoid various uncertain influencing factors in the process of material and structure forming,resulting in structural damage;these damages will seriously threaten the safe use of aircraft composite material structures.Among the many damages,delamination damage is particularly prominent.Delamination refers to the peeling phenomenon between different fiber layups,which can be caused by external impact or any possible situation.Delamination damage will reduce the critical buckling load of the laminate and weaken the bearing capacity of the laminate.The buckling and delamination expansion of the compressed laminate will cause the laminate to fail prematurely,so it is necessary to study the buckling instability of the laminate with delamination damage.At present,most researchers use shell element modeling to study the delamination expansion and buckling instability of laminates with delamination damage,but shell elements cannot well reflect the interlaminar characteristics.This thesis takes the carbon fiber/epoxy composite laminate with typical delamination damage in practical engineering as the research object,and uses the solid element to participate in the modeling to study the buckling instability of the laminate.The content and results are as follows:(1)Comparing the critical buckling theoretical value of the compressed composite laminate with the critical buckling load value calculated by the BUCKLE module in the finite element software ABAQUS,the error is 3.18%,and the numerical solution method of the BUCKLE module is reliable and effective.Without considering delamination damage,the effects of aspect ratio and laying angle on buckling instability of composite laminates are studied.When the aspect ratio is less than 1,the influence on the load value is greater;when the aspect ratio is greater than 1,with the increase of the aspect ratio,the initial change range of the two load values is larger,and the change range of the final load value is smaller and smaller,showing a convergence trend;When the angle is less than 45°,the load value gradually increases as the laying angle increases,and when the angle exceeds 45°,the load value gradually decreases.(2)The finite element software ABAQUS is used to establish the expansion evolution prediction model of the composite laminate with delamination damage,and the simulation results are compared with the experimental results.The obtained load-displacement curve is roughly consistent with the experimental curve.the errors are all within 14.37%,and the simulation modal diagram intercepted from the result file can also be consistent with the experimental phenomenon,which verifies the validity of the model.The layered expansion path is:first expand toward the free edge of the model,and then continue to expand toward the fixed edge of the model until failure.(3)The influence of different parameters on the evolution of delamination damage propagation is explored.Studies have shown that delamination damage close to the surface layer of the laminate will greatly reduce the critical load value,and will experience local buckling and mixed buckling,accompanied by delamination damage expansion;while delamination damage near the midplane has a greater impact on the bearing capacity.The influence of delamination is small,emerging the overall buckling,and there is no delamination damage expansion,and the stability is better;the delamination expansion and buckling instability are more sensitive to the delamination size,the larger the delamination size,the faster the delamination expansion,and the corresponding critical load.The smaller the value,the easier buckling instability occurs and the weaker the bearing capacity;compared with the composite laminate with through-delamination damage,the delamination of the laminate with through-delamination damage is more sensitive to the load,prone to delamination damage expansion.The critical load of the laminate with circular delamination damage is slightly smaller,and the shape of the delamination damage has little effect on the buckling behavior of the laminate.This paper provides theoretical guidance and reference for the repair of composite laminates with delamination damage.It provides theoretical guidance and reference for the repair of composite laminates with delamination damage.