Buckling Analysis of Variable Angle Tow Composite Plates with One Circular Delamination

Advanced carbon-fibre composite materials are increasingly used as primary structural components in aviation and aerospace industries due to their high stiffness-to-density ratio. The design of composite aerostructures is required to meet a number of safety criteria, in particular, the damage tolerance. Delaminations, which are caused by the impact of foreign objects (tool drops, runway debris, bird strikes etc) or the manufacture process, are one of the most common damage defects of laminated composite structures. The delaminations may lead to the occurrence of the local buckling and/or the global buckling before the ultimate design load, and therefore reduce the load-carrying capacity of composite structures. The mechanics of laminated composite structures containing delaminations had been extensively studied by many researchers in last two decades. With an increased understanding of the failure mechanism due to the delaminations, the damage tolerance constraints can be considered in the optimal design of composite structures. However, a finite element method using the cohesive elements or the Virtual Crack Closure Technique (VCCT) is normally very time-consuming to perform the damage analysis of composite laminates. Therefore, developing an analytical modelling to compute the residual buckling or postbuckling strength after the delaminations remains importance, not only for the availability of an efficient design tool but also for the study of physical insights of delaminations. A number of previous works had applied the analytical modelling to study the effect of a delamination or delaminations on buckling and postbuckling strength of constant stiffness composite plates. This work developed a Rayleigh-Ritz modelling to analyse the buckling behaviour of VAT plates with one circular delamination. Taking advantages of the advanced VAT laminates to improve the damage tolerance of composite structures remains great potential. However, the damage mechanics and the failure mechanism of VAT composite laminates containing delaminations have never been well studied. This work performed the parametric study of the compressive buckling load of the VAT laminates with linear variation of fibre angles. The results reveal the benefits of utilizing the variable stiffness tailoring to improve the delaminated buckling resistance of composite structures.