Design optimization of honeycomb sandwich panels for blast load mitigation

A general process for optimization of a honeycomb core sandwich panel to minimize the effects of air blast loading is presented in this dissertation. This process can also be readily applied to other types of cellular core. The panel geometry consists of two metal face plates with a crushable honeycomb core. Metallic sandwich panel with a cellular core such as honeycomb has a great potential to absorb the impact energy of the blast by undergoing cyclic plastic buckling deformation at a nearly constant stress. The core also provides higher bending stiffness to weight ratio of the sandwich by maintaining larger gap between the face plates. The ability of the core to absorb the impact energy and provide stiffness is not only influenced by its cell size and height, but also by the thickness and shape of the face plates. Optimization is necessary as there is strong coupling between the several variables and the physics, which makes parametric studies relatively ineffective. The optimization study investigates the size and shape of the face plates, and depth and cell size of the core, to minimize dynamic deflection or acceleration of the backface plate. Constraints on total mass and on plastic strain in the face plates are imposed. A design of experiments (DOE) based response surface optimization method is used. Response equations are determined using the central composite face centered method, which are then interfaced to a gradient based optimizer in the MATLAB optimization toolbox. Function evaluations are done using LS-DYNA finite element (FE) software.;Considering the high computation time involved in the FE simulation of detailed honeycomb cells, an alternative technique is used to simplify the honeycomb core modeling and to reduce computation time. Specifically, virtual testing is used to develop a homogenized model for the stress-strain curve of the honeycomb core. The homogenized model is validated by comparison to existing results in the literature as well as to detailed FE models of test specimens. The homogenization approach can be readily applied to other types of cellular core.;For deflection minimization, results produce a stiffer front face plate which effectively distributes the blast load to a larger area of the core and also produce a stiff core by increasing both core density and core depth. For acceleration minimization, results again produce a stiffer front face plate, but accompanied by a sufficiently soft core. The mechanism of lowering the backface acceleration is by absorbing energy with low transmitted stress. Strain rate effects on the results are discussed. Further, a clear cut comparison between monolithic metal plates and sandwich plates, for the same loading and failure criteria, is presented here.