Multiscale Finite-Element-Simulation of the load carrying behaviour of fibre composite structures

该项目的最优目标是在两个尺度上计算纤维增强复合材料层合结构的承载荷载。必须开发的模型将通过出现的专业的实际问题进行测试和评估。这些是结构部件的交点，角弧，例如腹板到凸缘的过渡处，在装配范围内重叠，以及开口处的钢筋。用现有的方法，具有这些特长的整个结构是无法处理的。所有使用整体层节点自由度来获得三维应力应变状态的单元公式都是不合适的。这一说法也适用于3D全尺寸计算，因为由于计算工作量，只能处理细节问题。因此，对双比例尺模型的全局部分的一个基本要求是使用标准的5或6个节点壳自由度。在前人研究的基础上，在双尺度模型的局部部分加入几何非线性。局部模型可视为一维代表性体积元。与传统的三维RVEs相比，这大大减少了计算时间。通过扩展，可以得到与任意非线性三维材料定律的接口。脱层是层合纤维增强聚合物最重要的破坏模式。由于在层边界处使用了局部位移自由度，因此可以扩展当前的模型来描述分层。通过引入双结点或所谓的处理层，不连续的位移可以被描述。应力和切向矩阵是通过不可逆内聚律得到的。将所建立的双尺度壳模型应用于上述实际问题。对于简单的几何形状，将与现有昂贵的3D模型的结果进行比较，并进行相关评估。

The superior goal of the project is the computation of bearing loads for laminated fiber reinforced polymer structures on two scales. The model which has to be developed will be tested and evaluated by means of practical problems with appearing specialties. These are intersections of structural parts, corner arcs e.g. at a transition of a web to a flange, overlapping in assembling ranges, as well as reinforcements at openings. With existing methods whole structures with these specialties cannot be treated. All element formulations which use global layer wise nodal degrees of freedom to obtain the three dimensional stress and strain state are not suitable. This statement also holds for 3D-full scale computations, since due to the computational effort only detailed problems can be handled. Therefore an essential demand for the global part of the two-scale model is the use of the standard 5 or 6 nodal shell degrees of freedom. Basing on the previous research, geometrical nonlinearity is to be added to the local part of the two-scale model. The local model can be considered as a one-dimensional representative volume element (RVE). This comes with a significant reduction of computing time, compared with conventional three-dimensional RVEs. With the extension an interface to arbitrary nonlinear three-dimensional material laws is available.Delamination is the most important failure mode of laminated fiber reinforced polymers. Since local displacement degrees of freedom are used at the layer boundaries, it is possible to expand the current model to describe delamination. With the introduction of double nodes or so called processing layers discontinuous displacements can be described. Stresses and tangential matrices are obtained through irreversible cohesive laws. The developed two-scale shell model will be applied to above mentioned practical problems. For simple geometries comparisons with the results of existing costly 3D-models and related assessments will be performed.