Christina Völlmecke

Geometric modelling of kink banding in laminated structures

An analytical model founded on geometric and potential energy principles for kink band deformation in laminated composite struts is presented. It is adapted from an earlier successful study on confined layered structures that was formulated to model kink band formation in the folding of geological layers. This studys principal aim was to explore the underlying mechanisms governing the kinking response of flat, laminated components comprising unidirectional composite laminae. A pilot parametric study indicates that the key features of the mechanical response are captured well and that quantitative comparisons with experiments presented in the literature are highly encouraging.

Modeling of Interactive Buckling in Sandwich Struts with Functionally Graded Cores

AbstractAn analytical pilot model for interactive buckling in sandwich struts with cores made from a functionally graded material based on total potential energy principles is presented. Using a Timoshenko beam approach, a system of nonlinear differential and integral equations is derived that predicts critical and secondary instabilities. These are validated against numerical simulations performed within the commercial finite-element package Abaqus. Good agreement is found, and this offers encouragement for more elaborate models to be devised that can account for face-core delamination—a feature where functionally graded materials are known to offer distinct advantages.

Delamination growth in buckled composite struts

Existing analytical models dealing with buckling and postbuckling phenomena of delaminated composites comprise one limitation: the restriction to stationary delaminations. In the current work, an analytical framework is presented which allows to model the postbuckling response of composites without such limitation. Therefore, the well-known problem of a composite strut with a through-the-width delamination is studied. The system is fully described by a set of I generalized coordinates. The postbuckling response for a stationary delamination is modelled using the conventional total potential energy approach. The postbuckling response for a non-stationary delamination, i.e. once delamination growth occurs, is modelled using an extended total potential energy functional in which the delamination length is expressed by the generalized coordinates and the load parameters. By solving the underlying variational principle the postbuckling response is obtained. Implementing the Rayleigh–Ritz method yields a set of non-linear algebraic equations which is solved numerically. Postbuckling responses for a cross-ply laminate are provided until the strut fails. Depending on delamination depth and length additional load bearing capacities of such composite struts are documented before failure due to unstable delamination growth occurs.

Buckling and postbuckling behavior of delaminated composite struts

ABSTRACT The buckling and postbuckling behavior of composite struts under uniaxial compression is investigated. A geometrically nonlinear model comprising only four generalized coordinates is applied to multi-layered struts built up of transversally isotropic unidirectional layers. Laminates with a cross-ply layup are investigated. By minimizing the total potential energy of the system, equilibrium paths and critical buckling loads for varying lengths and depths of delamination are determined. Thus, the response of the system in the postbuckling range is analyzed and areas of stable and unstable behavior are determined. The outcome of the work provides detailed information about the influence of delaminations on the buckling behavior of composite struts.

Modelling Cracked Cross-Ply Laminates with Delamination Buckling

The mechanical behavior of cross-ply laminates loaded under in-plane compression containing matrix cracks and delaminations is investigated in order to study their influence on the structural stability behavior. This is done by employing a semi-analytical modelling approach which comprises an analytical framework for a structural stability analysis of damageable structures and the Equivalent Constrained Model for deriving reduced stiffness properties of the cracked layers. Cross-ply laminates with varying delamination depths as well as varying matrix crack densities are studied.