Simulation of timber structures under consideration of material and structural inhomogeneities

申请人在木材力学领域的最终目标是通过有限元方法对木材结构进行逼真的数值分析。在以前的项目中，已经开发了详细描述木材力学行为的模型。这些模型与无间断的同质木材相关，并且需要确定性的材料属性。自然生长的材料木材受到结构(树枝和变化的纹理过程)和材料的不均匀性(自然变化的材料特性)的影响，这影响了木材结构构件的力学行为。在第一个项目阶段，已经建立了考虑树枝生长不均匀的模型和通过随机数据模型捕捉材料性质自然变化的方法，并将一直发展到初步项目结束。树枝作为木材的天然弱点往往会引发破坏。为了能够对木材结构进行真实的分析，现有的模拟木材破坏和损伤的方法应该得到加强，并与模拟生长不均匀的模型相结合。在压缩下，木材的破坏可以用塑性公式来很好地描述。因此，在续建项目的第一部分中，塑性模型将与描述树枝的方法相结合。与塑性力学相比，断裂力学和粘结区模型能更好地模拟拉伸和剪切破坏。因此，在续展项目的第二部分中，将加强现有的衔接要素和相关材料的描述。为了捕捉由分支引起的纵向拉伸破坏，必须扩展粘性材料模型。对于从分支开始的裂纹路径的模拟，需要开发和实施内聚单元的自适应网格划分程序。在续建项目的第三阶段，描述材料不均匀性的方法将得到加强。虽然人们普遍认为材料性质的变化可以通过随机分布来适当地映射，但关于这些分布的参数的信息是相当不同的。这种额外的不确定性不能被随机性充分捕捉到。为了利用随机数据模型的优点并能够考虑非随机不确定性，开发了一种用于木结构模拟的模糊随机有限元方法。

The final aim of the applicant in the area of timber mechanics is a realistic numerical analysis of timber structures, by means of FEM. In previous projects, models for the detailed description of the mechanical behaviour of timber have been developed. These models are related to homogenous timber without discontinuities and require deterministic material properties. The naturally grown material wood is affected by structural (branches and varying grain course) and material inhomogeneities (naturally varying material properties) which influence the mechanical behaviour of structural members made of timber. In the first project period, models to consider growth inhomogeneities in terms of branches and methods to capture the natural variation of material properties by a stochastic data model have been developed and will be developed until the preliminary project end.Branches as natural weak points in wood often initiate failure. To enable a realistic analysis of timber structures the existing methods to model failure and damage in timber should be enhanced and combined with the models to simulate growth inhomogeneities. Under compression, failure in timber can be described very well by plasticity formulations. Therefore, plasticity models will be combined with the methods to describe branches in the first part of the continuation project. Tensile and shear failure can be simulated more adequately by fracture mechanics and cohesive zone models compared to plasticity. Thus, in the second part of the continuation project, the existing cohesive elements and the related material description will be enhanced. To capture longitudinal tensile failure initiated by branches, the cohesive material model has to be extended. For the modelling of crack paths starting from branches, an adaptive meshing procedure for the cohesive elements needs to be developed and implemented. In the third period of the continuation project, the methods to describe material inhomogeneities will be enhanced. Although it is generally agreed that the variation of material properties can be mapped appropriate by stochastic distributions, the information about the parameters of these distributions are varying considerably. This additional uncertainty cannot be captured by randomness adequately. To use the advantages of a stochastic data model and be able to consider non-stochastic uncertainty, the development of a fuzzy-stochastic FEM for the simulation of timber structures is intended.