۱- Introduction

۲- The multiscale modeling framework

۳- Multi-scale modeling procedure

۴- Model validation

۵- Damage evolution of the wind turbine blade

۶- Conclusions

References

Abstract

Composite structures have been widely used in wind turbine equipment for their high stiffness to mass ratio and high strength. A major concern in the use of composite materials is their susceptibility to various micro damage, such as fiber breakage and matrix crack, which will lead to macroscopic structural fracture. In this paper, a multi-scale modeling strategy is proposed to investigate failure mechanisms and damage evolution of composite blades with initial defects from microscopic damage (including fiber fractures and matrix cracks) to macroscopic fracture. At the microscopic scale, an isoparametric micromechanical model is developed to calculate microscopic stresses and simulate microscopic damage. At the laminar scale, the classic laminate theory is employed to evaluate the laminate stiffness. At the structural scale, a reverse modeling technology is proposed to accurately acquire structural dimensions of a wind turbine blade, and a macroscopic 3D model is implemented into ANSYS/LS-DYNA software. By comparing with the experimental data, it is demonstrated that the proposed multi-scale method is suitable to predict mechanical properties of complex composite structures effectively.

Introduction

As one of the most abundant renewable and green resources, wind energy is increasingly playing an important role in reducing CO2 emission for environmental protection and has viable commercial values [1-3]. It has been one of the most important new energies due to its availability and accessibility. To maximize the energy that can be harvested from wind, an efficient and safe design of a wind turbine, including its strength and damage tolerance, is essential. Complex dynamic loads may lead to a catastrophic failure of wind turbine blades [4-5]. According to the data from Caithness windfarm information forum [6], blade failure is the most common accident of wind turbines, estimated at around 3800 incidents per annum. Therefore, it is crucial for researchers to have a better understanding of the failure mechanisms, which will improve the safety and reliability of wind turbines. Wind turbine blades, which are normally manufactured by continuous glass fiber-reinforced resin matrix composites, accounts for nearly one-fifth of the cost of a wind turbine. Experimental [7-8] and theoretical methods [9-10] have been used to investigate the mechanical features and damage mechanisms of composite blades. However, for a heterogeneous material, it is difficult to reveal the intrinsic relations between its macroscopic and microscopic characteristics, such as fiber arrangements and fiber shape [11-14], by experimental methods. As a result, more and more researchers are using numerical methods to study their mechanical properties and optimally design composite wind turbine blades. Haselbach et al. [15] studied ultimate failure of a 34m long blade.