Localized effects in the nonlinear behavior of sandwich panels with a transversely flexible core

This paper presents the results of an investigation of the role of localized effects within the geometrically nonlinear domain on structural sandwich panels with a "compliant" core. Special emphasis is focused on the nonlinear response near concentrated loads and stiffened core regions. The adopted nonlinear analysis approach incorporates the effects of the vertical flexibility of the core, and it is based on the approach of the High-order Sandwich Panel Theory (HSAPT). The results demonstrate that the effects of localized loads. when taken into the geometrically nonlinear domain, change the response of the panel from a strength problem controlled by stress constraints into a stability problem With unstable limit point behavior when force-controlled loads are applied. The stability, problem emerge as the nonlinear response develops with the formation of a small number of buckling waves in the compressed face sheet in the vicinity of the localized loads. The development of the nonlinear response is demonstrated through the numerical study of three-point bending of a unidirectional sandwich panel With an unstiffened core, and with a core stiffened in the vicinity of the loads, respectively. It is shown, that the change from unstiffened to stiffened core alters the nonlinear response significantly. The nonlinear response is described in terms of deflections and stress resultants in the face sheets, as Well as in terms of the interfacial stress components at the upper and lower face-core interfaces. The overall nonlinear response is described through curves of the load versus the extreme absolute values of the aforementioned structural quantities. A very important finding of the study is that stiffening of the core may improve the performance in terms of local stresses to some extent, but at the same time it may lead to undesirable bifurcation-type or semi elastoplastic behavior in some cases.