In-plane finite element approach for analyzing manufacturing defects in composite materials

Kurzfassung

Fiber composite materials provide low material weights in combination with high material stiffness and strength. The fiber stiffness and strength characterize mainly the behavior of unidirectional composites plies. The single ply behavior is highly sensitive to variations of fiber orientations, fiber misalignments or the fiber volume content. Critical phenomena for composite structures are defects caused by the manufacturing and processing technologies. It is has been shown by many authors during the last years that the analysis of manufacturing defects in composite structures is a complex problem. Critical defects being often detected are fiber misalignment and elliptical voids caused by porosities due to gas enclosures during the infiltration and curing process. These defects substantially influence the stiffness and strength of composite structures. Therefore it is very important to develop a method which is able to determine critical defects and precisely analyze the effects of these defects. The paper will present an appropriate In-plane finite element model for the analysis of the effects of fiber waviness on the stiffness of unidirectional composites under shear and tensile loading conditions. The ply and roving orientations are considered with a meso-level approach. The element coordinate system is consequently reoriented to the fiber direction according to the curvature of the fibers. The approach uses laminates with different waviness and regular fiber oriented layers. The investigation is also capable to study the effect of in-plane elliptical voids in lamina surrounded with curved fibers on the stiffness. The built-in Hashin failure and damage model in ABAQUS is utilized to model the failure of uniform fiber waviness, graded fiber waviness and the influence of elliptical voids on the strength of a composite ply under pure shear and pure tensile loading conditions along and transverse to the fiber direction. The study enables the validation of the unidirectional fiber stiffness as function of waviness with analytical approaches for two kinds of curved fibers: uniform and graded fibers waviness. Finally, we will present a multi-scale approach via the sub-modeling technique of ABAQUS-CAE. This enables the connectivity of local models in meso-level with macro-level structures and the computation of large structures for industrial purposes.