Stability of Flat Composite Shells with Environmental Reinforcement under Combined Loading Conditions

Abstract

In this study, the stability of flat composite shells with a thickness of 5 cm and element dimensions of 40 × 200 cm, arranged in a connected grid configuration, was investigated under combined axial, lateral, and external pressure loads. Using the First-Order Shear Deformation Theory (FSDT) and numerical implementation in Abaqus, two environmental reinforcement methods—temperature-dependent and external pressure-dependent—were incorporated into the modeling as controlled variables. The results of nonlinear static analysis indicated that, in the absence of reinforcement, the shells experienced sudden collapse at displacements of 7–11 cm. In contrast, with the application of temperature-induced environmental reinforcement, the yield threshold increased by up to 68%, and the structure exhibited ductile behavior with high energy absorption after passing the linear critical point. This behavior is attributed to the release of anisotropic residual stresses and a more uniform stress distribution across the composite layers. In the model incorporating environmental reinforcement via external pressure, the yield force decreased; however, the overall structural displacement was reduced by 10%, and the minimum von Mises stress decreased by 82%, indicating effective neutralization of bending stresses and enhanced stability in the plastic region. Despite their distinct mechanisms, both reinforcement methods led to a qualitative transformation in structural behavior, shifting from sudden failure to controlled deformation. The analyses demonstrated that environmental reinforcement not only increases load-bearing capacity but also transforms the failure mechanism from localized to progressive and from brittle to ductile. This approach introduces and validates, for the first time in the composite engineering literature, the concept of “environmental reinforcement” as an active design strategy that does not require internal equipment. It provides a foundation for the development of smart roofs, space structures, and systems resistant to combined loading conditions in aerospace, construction, and defense industries.