دانلود رایگان مقاله فروپاشی ساختاری کامپوزیت تیغه توربین بادی تحت ترکیب خم شدن و چرخش

Abstract

This study presents a comprehensive investigation on structural collapse of a 47 m composite blade under combined bending and torsion in a full-scale static load test. The primary focus is placed on root causes and failure mechanism of the blade collapse. The investigation consists of three parts. First, video records of the blade collapse are examined on a frame-by-frame basis. Direct evidence is presented on how the blade collapses in progressive chain events. Second, the detailed post-collapse investigation is conducted both in-situ and in laboratory. The critical failure modes and the associated stress/strain state once experienced by the blade are indentified. Third, strain measurements are analyzed to provide quantitative evidence of the process leading to the blade collapse and consequently confirm the findings of this study. It is found that longitudinal compressive crushing failure and the following delamination of the spar cap, which are driven by local buckling, are the root causes of the blade collapse. The constraint of the loading saddle and local reinforcement of the blade section also contributes to the blade collapse. Torsion loads, although exhibiting no significant effect on the blade strength, are found to affect post-collapse characteristics of the blade.

6. Conclusions and future work

This study presented a comprehensive investigation on a fullscale structural collapse of a large composite blade subject to combined bending and torsion. Video record examination, postcollapse investigation and local strain analysis were conducted to find out both qualitative and quantitative evidence which helps understand how and why the blade collapsed. Major findings of this study include: (1) The root causes of the blade collapse were indentified to be longitudinal compressive crushing failure and the following delamination of the spar cap at the suction side, which was primarily subject to compressive loads during the test. These two critical failure modes of the spar cap were directly responsible for the loss of the load-carrying capacity of the blade and determined the load level at which the ultimate strength of the blade was reached. (2) Local buckling of the spar cap in the form of bulging was found to be the dominating phenomenon driving the process to the blade collapse. The loading saddle and local reinforcement contributed to this process by causing a reverse bending in the adjacent spar cap due to their constraint effect, which leads to the increase of compressive strains at the outside portion of the spar cap and the consequent longitudinal crushing failure of the laminates. (3) This study did not find direct evidence to confirm that the torsion loads had noticeable effect on the ultimate strength of the blade. This is possibly because the magnitude of twisting moment is much smaller than that of bending moment. However, the torsion loads were found to contribute to the post-collapse characteristics once the blade lost its loadcarrying capacity due to the spar cap failure.