Abstract
Complex dynamic effects influence the structural response of metallic core sandwich structures. Before these structures can be used in the field, it is necessary to understand the mechanical response and failure mechanisms of the sandwich structures under possible dynamic loading conditions which they may be subjected to. In this dissertation, a corrugated core sandwich structure under dynamic in-plane compression is the focus.
The main objective of this dissertation is to investigate the structural response of the Al6061-T6 and SS304 corrugated core sandwich columns under dynamic loading, through theoretical and numerical analysis. There are two in-plane loading directions, perpendicular-to-corrugations and parallel-to-corrugations, to accommodate the anisotropic response. The investigation considers compression velocities ranging from quasi-static up to 100m/s, divided into low (up to the order of a few m/s) and high (the order of tens of m/s) velocity responses.
For low velocity response, analytical models are proposed to predict individual failure modes. Each model is dedicated to the prediction of each of the individual failure modes: global buckling failure, face wrinkling failure for sandwich columns compressed perpendicular-to-corrugations, the local plate buckling for sandwich columns compressed parallel-to-corrugations. All of those models, based on the theory of stress wave propagation, calculate the out-of-plane displacements until failure criteria are satisfied. The validity of the proposed models is confirmed by comparison with FE simulations. The models successfully describe complex phenomena such as dynamic strengthening by material strain-rate effects, inertia effects as well as imperfection sensitivity.
Using those analytical models, the dynamic effects on the failure maps are investigated. Subsequently it is successfully proven that increased rate-of-loading leads to the inertial stabilization of global buckling motion and the change of failure modes from global to local buckling.
The efficiency of the developed analytical models is highlighted in a dynamic optimization procedure. Due to the complex dynamic phenomena, the individual failure responses under low compression velocities of V=0.1 and 1m/s are approximated as a function of sandwich design parameters, which is referred to as response surface methodology. A number of numerical experiments for the response approximation are calculated using the developed analytical models, and the optimization problems are solved via a sequential quadratic programming algorithm. As a result, it is concluded that sandwich columns are superior to monolithic columns, and that beneficial sandwich concepts are more remarkable at the lower velocities due to the inertial stabilization of global buckling motion. Moreover, it is suggested that the minimum weight design of corrugated core sandwich columns with maximum impulse capacity must consider reinforcing local buckling strength under dynamic loading.
Lastly, the high velocity sandwich column response is generalized in terms of sandwich geometric dimensions and loading intensity. In this high velocity response region where considered compression velocity is of the order of tens of m/s, the response time scale is of the order of less than one round trip of a plastic wave. Thus, the high velocity column response can be accounted for by applying the theory of rate-independent elastic-plastic wave propagation with an analogy between monolithic solid columns and sandwich columns. Simplified theoretical models for each in-plane loading orientation are suggested and validated by FEM.
