複合材料葉片之失效分析及設計改進

Abstract

本文旨在透過理論與實驗，探討葉片的失效模式(如挫屈、材料失效)，以及改良葉片承受負載能力的方法。首先分別對兩種不同疊層設計的葉片(設計A與設計B)進行實驗，檢測葉片於靜態負載下的失效模式，在實驗中分別量測葉片不同位置的應變與翼尖位移，並使用有限元素分析軟體ANSYS對葉片的變形狀況分別作線性與非線性分析，實驗結果顯示非線性分析較線性分析來的準確，其中兩種不同設計的葉片，理論與實驗應變值相近，誤差小於10%，且設計B的挫屈發生載重，理論與實驗值相差小於1.3公斤。隨後使用非線性分析配合適當的破壞準則來提升設計A的失效風壓負載，此葉片風壓負載計算方式主要根據葉片元素理論。在只考慮單一失效模式的狀況下，得到葉片於風速40m/s發生脫膠，蒙皮於風速42m/s發生挫屈，風速47m/s發生首層破壞。對葉片適當的加入肋板以增強葉片結構後，葉片的挫屈發生風速提高至85m/s，同時解決脫膠現象，且首層破壞發生於87m/s。此外，實驗室配置一套無線應變量測系統，用以測試葉片於實際風壓的應變狀況，驗證應力分析方法的正確性。

In this thesis, the failure modes such as buckling and material failure and ways for improving the load carrying capability of wind blades are studied via both theoretical and experimental approaches. First of all, we separately tested two kinds of blades with different layer designs (Designs A and B) under static loads to detect the failure modes of the blades. In the tests, the strains at different locations on the blade skin and the blade tip displacement were measured. The finite element code ANSYS is then used to analyze the linear and nonlinear deformations of the blades. It has been shown that the nonlinear finite element method can produce more accurate results that the linear one when compared with the experimental results. In particular, it has been shown that the theoretical and experimental strains are in good agreement with errors less that 10% for both blade designs. The difference between the theoretical and experimental buckling loads of the blade with Design B is less than 1.3kilograms. The nonlinear finite element together with appropriate failure criteria is then used to design the wind blade of Design A under for enhancing the failure wind load of the blade. The wind load distributed on the blade is calculated based on the blade element theory. With the consideration of only one failure mode, it has been found that debounding occurs at wind speed of 40m/s, skin buckling at 42m/s, and first-ply failure at 47m/s. After an appropriate reinforcement of the blade structure by adding webs, the blade buckling wind speed becomes 85m/s without debounding, and first-ply failure occurs at 87m/s. Furthermore, we build a wireless strain measuring system to measure strains in the blade under wind load to verify the correctness of the method for stress analysis.