טכניון מכון טכנולוגי לישראל
הטכניון מכון טכנולוגי לישראל - בית הספר ללימודי מוסמכים  
Ph.D Thesis
Ph.D StudentSchwarts-Givli Hilla
SubjectThe Effects of Delamination with and without Contact on
Sandwich Structures with a "Soft" Core
DepartmentDepartment of Civil and Environmental Engineering
Supervisors Professor Emeritus Yeoshua Frostig
Professor Oded Rabinovitch


Abstract

The study deals with the effect of delamination on the static and dynamic behaviors of sandwich panels with a soft core using a general and systematic, non-linear and high-order approach. The theoretical model accounts for the nonlinear and time-dependent real contact conditions that develop between the delaminated surfaces. In addition, the model accounts for the flexibility of the core and for the resulting high-order displacement, acceleration, and velocity fields within the core. The mathematical formulation uses the ordinary unidirectional panel theory for the face-sheets and a two-dimensional elasticity approach for the core. An approach that adopts a quadratic and cubic polynomial description for the vertical and longitudinal displacements of the core, respectively, in accordance with the exact closed form solution of the static case is developed. This approach leads to a consistent dynamic formulation with unknowns in terms of displacements only. The field equations and the corresponding boundary and continuity conditions are derived via the variational principle of virtual work for the static analysis and through the Hamilton’s principle for the dynamic analysis.

The nonlinear contact effects in cyclic loading, the free vibration behavior, and the nonlinear and time dependent real contact effects in the dynamic response are investigated quantitatively. The numerical results reveal that the non-linear geometrical behavior of the face-sheets, combined with the inertial forces and the external loads applied on the panel, lead to complex and time-dependent contact conditions at the debonded surfaces. These contact conditions significantly affect the static and dynamic response of the panel as well as its overall and localized behavior. In addition, it is shown that the predictions of the two simplified models of “with and without contact” may significantly deviate from those of the “real contact” model and do not always define the upper and the lower bounds for the “real contact” response, and neither of them can be considered as a conservative approximation for design purposes. Furthermore, the numerical examples demonstrate that the free vibration behavior is strongly affected by the assumption with regards to the contact conditions at the debonded interface and by the exact definition of the boundary conditions through the height of the section.

The generality and wide applicability of the formulation set the basis for the static and dynamic analysis of delaminated sandwich panels, and provides a general approach to the study of a broad range of problems, associated with the behavior of delaminated sandwich panels.