Buckling analysis of perforated stiffened composite plates with interfacial debonding under hygrothermal and in-plane edge loadings

Engineered composite structures often incorporate stiffeners to enhance the strength of perforated panels without significantly increasing their mass. However, interfacial debonding between the stiffener and skin can compromise structural integrity under external loads, potentially leading to failure. This study focuses on the buckling behaviour of stiffened perforated laminated plates with interfacial debonding, subjected to non-uniform edge loading and environmental conditions. A computationally efficient reduced-order finite element (FE) formulation has been devised using the 2D plate and 1D beam elements to minimise the computational cost. The plate and stiffener flange are modelled using a 9-noded heterosis element to address shear-locking, while a 3-noded isoparametric beam element represents the stiffener web and ribs. To account for stiffener torsional behaviour, a torsion correction factor is incorporated into the stiffener web and ribs formulation. Interfacial debonding is simulated by introducing a dummy node with an independent displacement field for the stiffener flange, connected by the fictitious spring between the plate and the penetrated flange nodes, to prevent nodal interpenetration. Displacement continuity is enforced in the bonded regions to maintain compatibility between the stiffener and plate displacement fields. The study employs a dynamic approach to evaluate buckling loads under two boundary conditions, considering operational and environmental effects. Additionally, hygrothermal-dependent material properties are considered to incorporate the effect of hygrothermal loading on the elastic behaviour of the material. A preliminary investigation identifies an optimal loading pattern and cutout geometry for enhanced buckling performance. In contrast to prior research, this work examines various stiffener configurations to evaluate the stability of perforated plates under non-uniform edge loading and determines the configuration that improves buckling capacity. The analysis indicates that the circular cutout panel incorporating the SP-3 stiffener configuration demonstrates a 42.86% improvement in buckling resistance compared to the SP-2 stiffener design. Furthermore, debonding significantly reduces the buckling capacity of the CCSS panel by 20.14%, especially at greater stiffener depths of d s /b s = 7 under hygrothermal conditions. Moreover, larger cutout sizes exacerbate stability reductions of the CCSS panel by 2.70% due to debonding under the reference hygrothermal state. In contrast, debonding under hygrothermal conditions results in a 38.44% reduction in the buckling strength of the smaller cutout SSCC panel, highlighting the impact of restraint conditions. Therefore, this study serves as a foundation for optimising designs to ensure stability, durability, and cost-effectiveness in demanding operational scenarios.