Influence of creep on the geometrically nonlinear behavior of soft core sandwich panels

• We investigate the creep buckling of sandwich panels through a high-order theory.
• The panel is modelled as three layers structure with compatibility between them.
• The core is assumed to be linear viscoelastic and it governs the creep response.
• The model is based on a step-by-step time analysis.
• The critical creep effects on the global and local buckling capacity are revealed.

The effects of creep of the core material on the global and local geometrically nonlinear behavior of sandwich panels under axial and/or lateral loading conditions is presented, within the framework of the high-order sandwich theory (HSAPT). The theoretical model combines the concepts of the hereditary (convolution) integral of viscoelasticity based on the principle of superposition, with the HSAPT. From the expansion of the relaxation moduli into Prony series, an incremental exponential law that corresponds to the rheological generalized Maxwell model is obtained, and which allows for a step-by-step time analysis that accounts for the change in deformations and stresses with time. The results show that creep of the core leads to a significant reduction in the local and global buckling capacity of sandwich panels. It is shown that sandwich panels under a combined axial and lateral loading can undergo global buckling with time due to creep, under a sustained load that is less than 50% of their buckling load. Similar trend is also observed for the local buckling (wrinkling) of the compressed face sheet when the panel is subjected to a sustained uniformly distributed load. In both cases, buckling commenced at a relatively low stress levels but it is associated with an unlimited increase of the stresses with time that eventually lead to material failures and total failure of the sandwich panel.