Thermo-hyrgo-mechanical processes for the densification and forming of wood: Continuum-mechanical material formulation and structural simulations

几个世纪以来，木材一直被用作建造建筑结构的实木。近年来，生态和技术要求的提高导致了对建筑材料性能的改善的需求。德累斯顿理工大学钢与木材结构研究所(ISH)开发了基于原材料木材的热湿力学性能的木材成形技术。利用有限元方法对木材成形过程和由成形木材制成的结构部件的行为进行数值模拟，需要一个真实的本构模型来描述木材在有限变形时的热湿力学材料行为。目前更新建议的主要目的是准备数值工具和方法，以模拟和设计由成形木材制成的最优工业产品。数值模拟提供了深入了解成形技术应用过程中结构内部的多物理效应和现象的手段。在第一个资助期内，为模拟木材致密化和木材成形奠定了基础。为了进一步发展和验证木材大变形时的热湿各向异性材料模型，将模拟结果与ISH提供的实验数据进行了比较，并通过考虑木材原材料和束缚水的木材电流密度模型进行了进一步的发展。为此，针对成形木材的制造模拟，对水分的质量平衡质量和与位移相关的连续介质力学过程进行了修正。此外，为了模拟水分进出流动和热对流现象，建立了热吸湿有限表面单元以及相关的本构关系。此外，由于关于这项技术的定性和经验性的初步工作很少，因此对显著影响值的识别进行了参数研究。最后，对成形木材制造的结构部件进行了真实的和与工业相关的数值模拟。以论证该成形工艺及其数值模拟的实用性。

Wood has been used as solid wood for the construction of building structures since centuries. Recently, increased ecological as well as technical requirements lead to a demand for improved properties of building materials. The Institut of Steel and Timber Construction of TU Dresden (ISH) develops the technology of wood forming based on the thermo-hygro-mechanical properties of the raw material wood.The numerical simulation of the wood forming process and the behavior of structural components made from formed wood using the finite element method require a realistic constitutive model in order to describe the thermo-hygro-mechanical material behavior of wood at finite deformations.Main aim of the renewal proposal at hand is the preparation of numerical tools and methods for the simulation and design of optimal industrial products made from formed wood. The numerical simulation provides the means to achieve a deep insight into the multi-physical effects and phenomena within the structures during application of the forming technology.The basis for modelling wood densification as well as wood forming is achieved during the first funding period. In order to further develop and to validate the thermo-hygroscopic anisotropic material modelling of wood at large deformations, a comparison of simulation results with experimental data provided by ISH is carried out.Further developments are made by modelling the current density of wood under consideration of its raw material and its bound water. To this purpose, a modification of the mass balance mass of moisture and of displacement dependent continuum mechanical processes are carried out with respect to the simulation of the manufacturing of formed wood.Furthermore, a thermo-hygroscopic finite surface element is formulated as well as related constitutive laws, in order to model the moisture in- and out flow and thermal convective phenomena.Additionally, parameter studies are carried out with respect to the identification of significantly influencing values, since only few qualitative and empirical preliminary work regarding this technology is existing.Finally, realistic and industry-related numerical simulations of structural components made from formed wood are carried out and analyzed, in order to demonstrate the practical applicability of the forming technology and its numerical modelling.