Engineering Research On Mechanical Models Of 3D Woven Composites And Fatigue Life Of Composite Structure

This thesis contains two relatively independent parts. In part one, micro- and meso-scale finite element models were built to obtain the average stiffness and local stresses of the three dimensional woven composites. In part two, the fatigue life of the composite strap, which warps around the cap of bottom bolt of the blade of wind turbine, was estimated.Part one:1. The micro- and meso-scale finite element models of of 3D woven composites were built. The micro model was used to calculate the average stiffness and local stresses of fiber tow, while the meso one was used to obtain those mechanical properties of three dimensional woven composites. The meso-scale unit cells for the surface area and interior area were modeled separately to investigate the discrepancy between them. The simplified meso unit model simulating bending load was specified.2. The theoretical meso-scale models of 3D woven composites were built, respectively. The average stiffness of the composites were calculated by them parallel to the numerical models. In the meso theoretical model, meso architecture was partitioned to several parts according to the local fiber direction and local fiber density. The local iso-stress or iso-strain conditions are considered between various parts. The stiffness and local stresses are estimated under in-plane tension, in-plane shear and bending. The results have been verified by those from FE model.Part two:Firstly, the safety factor of the composite strap which warps around the cap of bottom bolt of the wind turbine blade has been analyzed under equivalent fatigue load. Then, the fatigue life was estimated separately by use of safety life valuation method which based on the Palmgren Miner liner fatigue damage accumulation rule and Puke criterion. The effect of inter fiber fracture was taken into considered.