Impact of interfacial degradation on flexural-torsional instability of sandwich beams

This paper investigates the impact of interfacial degradation and localized interfacial damage on the flexural–torsional nonlinear instability of sandwich beams. For that purpose, a nonlinear high-order sandwich beam model that incorporates the presence of imperfect interfaces that link the face sheets and the core with the potential evolution of lateral-flexural instability is developed. The research questions relate to the effect of such interfaces on the soft-core sandwich beam and its nonlinear response in the context of the lateral-torsional instability. The investigation refers to the formation of instabilities, the corresponding critical loads, the nonlinear post-buckling behavior, and their variation with the degradation of the interfaces. Along with the new modeling approach, the findings outlined in the paper include new quantitative insight into the complex nonlinear response and the role played by the ability of the interfaces to transfer tractions and maintain compatibility. The analysis reveals that the deterioration of the interfacial state affects not only the critical level of load but also the order of evolution of instabilities and particularly their nature: a stiffening post-buckling, a limit-point behavior, or a snap-through one. All depending on the interfacial properties. Together, they affect the rich deformation, traction, and stress fields in the sandwich structure and, correspondingly, the resilience of the sandwich beam.