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

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

Three dimensional dynamics of laminated curved composite structures: A spectral-Tchebychev solution

Composite structures have been widely used in many diverse industries due to their high stiffness, high strength, and light-weight. Furthermore, since they exhibit directional material properties, it enables superior advantages in the design process such as achieving tailor-made characteristics. Since, these structures are subjected to dynamic excitations during operation, it is highly crucial to accurately and efficiently capture the dynamics of composite structures. This study presents a new spectral-Tchebychev (ST) solution to investigate the dynamic behavior of (curved) laminated composite structures. To derive the integral boundary value problem for each lamina, extended Hamilton principle is used. The strain energy is expressed using three-dimensional elasticity equations. To discretize the domain of the problem, Gauss-Lobatto sampling scheme is followed and the deflections (generalized coordinates) are expressed using triple expansion of Tchebychev polynomials. Then, the system matrices for each lamina is calculated using the derivative and the integral operations defined in the Tchebychev domain. To connect the individual laminae, compatibility equations are written. To incorporate the compatibility equations and to incorporate any type of boundary condition, projection matrices approach (that is based on singular value decomposition) is used. To validate the accuracy of the presented approach, two case studies (straight and curved laminated composite) are investigated. In each case the natural frequencies and the mode shapes are compared to those obtained from a commercial finite element (FE) software. The comparison indicates that presented three-dimensional spectral-Tchebychev solution technique enables the accurate and efficient prediction of the vibrational behavior of curved laminated composite structures

Microstructure and tensile mechanical properties of anisotropic rigid polyurethane foam

10.1007/s11340-008-9146-0Experimental Mechanics486763-776EXMC