Simple, efficient mixed solid element for accurate analysis of local effects in laminated and sandwich composites

A mixed, eight-node solid element is developed with the aim to accurately and efficiently capture local stresses in composites. The nodal degrees of freedom are the three displacements and the three interlaminar stresses. Characteristic features, C⁰, tri-linear, serendipity shape functions are used to interpolate these quantities across the element volume. With this choice, the intraelement stress fields satisfy the equilibrium equations in integral form. Integration is exact. It is carried out by a symbolic calculus tool. To test the element performances, the intricate stress fields of thick sandwich composites with undamaged and damaged face layers, piezoelectrically actuated beams, thermally loaded laminates and close to a two-material wedge singularity are investigated. The element appears robust, stable and rather accurate using reasonably fine meshes. Compared to displacement-based counterpart elements, the computational effort is not larger.