Structural defects such as resin pocket area are inevitably created between surface and core of composite structures during the production of wind turbine blades using vacuum infusion process. In this article, four-point bending tests were performed on tapered sandwich composites to investigate the effect of resin pocket area on the mechanical strength, crack growth path, and failure mode. Specimens were in similar shape to wind turbine blade profiles, and a shear-dominant load was applied to the resin pocket area during the experiments. The extended finite-element method was applied in order to predict crack growth path and failure mode. The average static strength of the specimens including the small size of resin pocket area had almost no change in compare with the specimen with no resin pocket area. Moreover, the medium size of resin pocket area decreased the strength for 3.5% while the large size one enhanced it for 1.75%. Thus, it can be deduced that the defect area does not have a significant effect on the flexural strength of the sandwich composite tapered specimens, but it can arrest the crack. Therefore, the crack propagates in the opposite direction at the interface of the face and core. Although the resin pocket area arrests the crack, it was observed that the size of resin pocket area directly affects the crack growth and its path. The smaller resin pocket area leads to slower crack growth, and early collapse occurs for the larger size of defect area. So, the size of resin pocket area has considerable importance during manufacturing of such structures. Finally, numerical results have shown good agreement with experimental ones.

中文翻译：

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树脂袋面积对锥形夹芯复合材料失效的影响

在使用真空灌注工艺生产风力涡轮机叶片的过程中，在复合结构的表面和芯部之间不可避免地会产生结构缺陷，例如树脂袋区。在本文中，对锥形夹层复合材料进行了四点弯曲试验，以研究树脂袋面积对机械强度、裂纹扩展路径和失效模式的影响。试样的形状与风力涡轮机叶片轮廓相似，并且在实验过程中对树脂袋区域施加了剪切主导载荷。应用扩展有限元方法来预测裂纹扩展路径和失效模式。与没有树脂袋区域的样品相比，包括小尺寸树脂袋区域的样品的平均静态强度几乎没有变化。而且，中等尺寸树脂袋区域强度降低3.5%，而大尺寸树脂袋区域强度提高1.75%。因此，可以推断缺陷区域对夹层复合材料锥形试样的弯曲强度没有显着影响，但可以阻止裂纹。因此，裂纹在面与芯的界面处以相反的方向传播。虽然树脂袋区域阻止了裂纹，但观察到树脂袋区域的大小直接影响裂纹扩展及其路径。较小的树脂袋区域导致裂纹扩展较慢，并且较大尺寸的缺陷区域会发生早期坍塌。因此，在制造此类结构时，树脂袋区域的大小具有相当重要的意义。最后，数值结果与实验结果非常吻合。