Thermo-Viscoelastic Constitutive Modelling And Forming Simulation Of Wood Composites

Because of their advantages such as environmental friendly, cheap price, light weight and recyclability, nature fiber composite materials were increasingly used in car decorative parts, and have gained great attentions in automobile industry. However, some product defects often occur during the thermoforming processes of wood composites for auto-decorative parts. By far engineers'experiences and trial and error methods are still used to solve these problems, which leads to postponement of development of new products and quality fluctuation of current products. So this work is devoted to investigate the mechanism inherent in the thermoforming of wood composite by a material characterization approach and forming simulation techniques.PP wood composite material was selected as the research object in this dissertation. Extensive tensile and compressive tests experiments with various temperature and strain rates were first carried out to obtain the basic mechanical behavior of the PP wood composite material. Their mechanical responses were shown to be sensitive both to the strain rate and temperature. Besides, it was found that raising the temperature has an equivalent effect as decreasing the strain rate. Then through the application of the viscoelastic basic principle and taking into account the structure of the PP wood composite material, a thermo-viscoelastic constitutive model was derived, and the physical interpretation of every parameter was analyzed. The influence of temperature, strain rate on the mechanical character of the wood PP composite material was described.The developed thermo-viscoelastic constitutive model for the wood composite is implemented in LS-DYNA by using its user-defined subroutine interface UMAT. Thermal compression of the wood composite was then simulated and compared with experimental data for the purpose of model validation.The predicted theoretical results coincided quite well with experimental data. Finally, Based on the developed constitutive model, the thermal forming of an auto-interior part made from the PP wood composite material was simulated This can provide some references for the inner decoration forming to a certain degree, and guide the practical producing of the automotive inner decoration- fender.