Elastic moduli of model random three-dimensional closed-cell cellular solids

Most cellular solids are random materials, while practically all theoretical results are for periodic models. To be able to generate theoretical results for random models, the finite element method (FEM) was used to study the elastic properties of solids with a closed-cell cellular structure. We have computed the density ($\rho$) and microstructure dependence of the Young's modulus ($E$) and Poisson's ratio (PR) for several different isotropic random models based on Voronoi tessellations and level-cut Gaussian random fields. The effect of partially open cells is also considered. The results, which are best described by a power law $E\propto\rho^n$ ($1 < n <2$), show the influence of randomness and isotropy on the properties of closed-cell cellular materials, and are found to be in good agreement with experimental data.Comment: 13 pages, 13 figure

Approximation of the critical buckling factor for composite panels

This article is concerned with the approximation of the critical buckling factor for thin composite plates. A new method to improve the approximation of this critical factor is applied based on its behavior with respect to lamination parameters and loading conditions. This method allows accurate approximation of the critical buckling factor for non-orthotropic laminates under complex combined loadings (including shear loading). The influence of the stacking sequence and loading conditions is extensively studied as well as properties of the critical buckling factor behavior (e.g concavity over tensor D or out-of-plane lamination parameters). Moreover, the critical buckling factor is numerically shown to be piecewise linear for orthotropic laminates under combined loading whenever shear remains low and it is also shown to be piecewise continuous in the general case. Based on the numerically observed behavior, a new scheme for the approximation is applied that separates each buckling mode and builds linear, polynomial or rational regressions for each mode. Results of this approach and applications to structural optimization are presented

Validation of high fidelity CFD/FE FSI for full-scale high-speed planing hull with composite bottom panels slamming

High fidelity CFD/FE FSI (Computational Fluid Dynamics/Finite Element FluidStructure Interaction) code development and validation by full-scale experiments is presented, for the analysis of hydrodynamic and structural slamming responses. A fully instrumented 9 meter high speed-planing hull with sterndrive is used. Starboard and port bottom panels are constructed with different composite materials and fiber orientations, allowing for study of the relation between structural properties and slamming. The code CFDShip-Iowa is employed for CFD simulations and the commercial FE code ANSYS is used as structural solver. The hydrodynamic simulations include captive (2DOF without sterndrive) and 6DOF free running conditions for various Froude numbers in calm water and regular waves. Calm water simulations compares well with the experimental data and 1D empirical data provided by the sterndrive manufacturer for resistance, heave, pitch and roll motions. Numerical one-way coupling FSI is performed in head and following regular waves representative of sea-trial conditions, using FE models for two bottom panels. The resulting strains are compared with experimental data showing a good qualitative and quantitative agreement

Mechanical metamaterials at the theoretical limit of isotropic elastic stiffness

Acknowledgements H.N.G.W. is grateful for support for this work by the ONR (grant number N00014-15-1-2933), managed by D. Shifler, and the DARPA MCMA programme (grant number W91CRB-10-1-005), managed by J. Goldwasser.Peer reviewedPostprintPostprintPostprintPostprin