Yeqing Wang

Thermal Ablation in Fiber-Reinforced Composite Laminates Subjected to Continuing Lightning Current

This work is concerned with thermal ablation modeling in carbon fiber-reinforced polymer-matrix composite laminates subjected to the lightnig strike. Both direct heat injection and Joule heating produced by the lightning current are taken into account. First, a model describing interaction of the lightning current channel with a conductive structure is presented. The model includes channel expansion and spatial and temporal distribution of the lightning current and linghtning-induced heat flux. Second, anisotropic electrical and thermal properties of the CFRP composite laminates are determined in a wide temperature range (up to the sublimation temperature of the carbon fibers) using experimental data and micromechanics considerations. Third, a nonlinear thermo-electric coupled problem is formulated and solved for a CFRP composite laminate to determine the electric-currentinduced temperature distribution and associated thermal ablation. Finally, the obtained predictions of thermal ablation in the CFRP composite laminate are compared to the reported experimental results. It is found that the predicted thermal ablation depths agree well with those reported in the experimental study.

Investigation of the Effects of Receptors on the Lightning Strike Protection of Wind Turbine Blades

Receptor plays an essential role in determining the efficiency of lightning strike protection (LSP) on wind turbine blades. To investigate the effects of receptors with different shapes and sizes on the LSP, we apply five different receptor configurations to the blade of a high-fidelity wind turbine model. The static electric field strength on the blade surfaces due to a lightning stepped leader is predicted through the development of a numerical model with finite element analysis. The interception efficiency is evaluated by comparing the predicted maximum electric field strength in the vicinity of the receptors. In addition, the locations of the predicted lightning strike attachment points match well with those obtained by experimental measurements, which validate the current numerical approach.

Lightning Analysis of Wind Turbines

Lightning strike damage accounts for one of the greatest number of losses for wind turbines and is among the top two most frequently reported causes of loss in the wind energy insurance claims in the United States (USA). The Midwest and Texas area, where the most wind power is produced in the USA, are subjected to high lightning flash activities. Also, since multi-MW wind turbines are pursued in the recent years, the corresponding wind turbine blades are becoming longer than before. The longer the blade, the greater its risk of being hit by the lightning. An increase in the blade size and extensive use of composite materials lead to significant challenges in the development of lightning strike protection systems for wind turbine blades, and a better understanding of the response of polymer-matrix composites to a lightning strike is essential for such developments. In this chapter, the basic physics of lightning strike and lightning interaction with the wind turbines are discussed. The common lightning strike protections for wind turbines as well as typical lightning damage mechanisms are introduced. In addition, the analytical and finite element numerical approach of predicting the lightning strike-induced electric field is presented. The obtained electric fields are used to estimate the lightning dielectric breakdown of the composite wind turbine blade. Furthermore, the other forms of lightning damage for wind turbine blades, including the rapid heat transfer, thermal ablation, and delamination, are also discussed. Future recommendations for such lightning research of wind turbines are provided.

Impact response of CFRP laminates with CNT buckypaper layers

In this work, the impact behavior of the electrified carbon fiber reinforced polymer (CFRP) composites with carbon nanotube (CNT) buckypaper layers has been studied. A custom-built experimental setup that allows for real time measurements of pulsed electric current, voltage, load, and velocity during coordinated application of a current pulse with an impact load was utilized. The experimental setup included a current pulse generator capable of producing a 30 millisecond current pulse with an amplitude of up to 2500 A. The application of the peak of the current pulse was coordinated with the peak of the impact load. A series of electrical, impact, and coordinated electrical-impact characterization tests were performed on three types of samples: 16-ply IM7/977-3 unidirectional laminates; laminates containing four layers of buckypaper (BP) and 12 unidirectional IM7/977-3 layers arranged as CF2/BP/CF4/BP/CF4/BP/CF4/BP/CF2; and laminates containing seven layers of buckypaper and nine unidirectional IM7/977-3 layers arranged as [CF2/BP]7/CF2. The results show that addition of buckypapers can lead to the increased impact resistance of CFRP composites.