An Impulse excitation based numerical model

Metallic thermal protection systems (MTPS) are used to protect the base structure of hypersonic cruise vehicle from aerodynamic heating. Honeycomb core sandwich structures form integral part of these MTPS. As these honeycomb sandwich panels (HCSP) are load bearing structures and a variety of design parameters affect the stiffness, estimating the panel bending stiffness of these sandwich structures is crucial for their effective utilization. Bending stiffness is generally evaluated experimentally using a destructive 3-pt/4-pt bend test. In this study, the effect of various design parameters that affect the bending stiffness of the HCSP are evaluated using a numerical model based on the Impulse Excitation (IE) NDE technique. This method provides the advantage of evaluating the panel stiffness at the design stage without resorting to actual fabrication of panels for destructive evaluation using 3-pt or 4-pt bend tests. This study consists of three stages, in the first stage; a representative HCSP sample was fabricated and tested using IE technique to estimate the flexural resonance frequency. In the second stage, numerical model of the IE test procedure was established and validated. Taguchi based Design of Experiments (DOE) was used in the third stage to study the effect of crucial HCSP design parameters such as (a) honeycomb core cell shape (b) core cell size (c) core height (d) core sheet thickness (e) top face sheet thickness and (f) bottom face sheet thickness, sheet thickness on the bending stiffness. Analysis of Means (ANOM) was used to identify the optimum combination of the aforementioned design parameters to achieve maximum bending stiffness. Analysis of variance (ANOVA) performed to evaluate the contribution of the individual design factors towards the bending stiffness indicate that honeycomb core cell height is the most critical design factor of the honeycomb sandwich panel.

Keywords: Sandwich Structures, Bending Stiffness, Impulse Excitation, DOE, Taguchi, ANOVA.