The effects of geometrical dimensions on the failure of composite-to-composite adhesively bonded joints

ABSTRACT

As a weak link in large wind turbine blades, adhesively bonded joints have recently received unprecedented attention in the field of wind energy because they are easily damaged and have short lifetimes. This paper deals with the effects of geometrical dimensions and laminate layups on failure load and the associated failure mode of composite bonded joints for wind turbine blades. Single-lap composite-to-composite bonded joints were fabricated and tested to complete failure under tensile load, and the features of a thick adhesive layer, a large overlap length and width, and actual laminate layups were considered. The failure load and mode of bonded joints along with the geometrical dimensions and composite layups were analyzed and compared with previous studies. The results show that failure load decreases overall with adhesive thickness, while it increases rapidly with overlap length and increases slightly faster than is proportional with overlap width. A combination of both adhesive failure and thin-layer cohesive failure is prone to initiate in thick and short bonded joints, while fiber-tear failure is initiated in thin and long bonded joints. Thick adherends can enhance the bonded joint to some extent. Therefore, it is recommended that at least one unidirectional lamina is laid in the middle of the composite layups to avoid the premature failure of adherends for bonded joints in wind turbine blades.

KEYWORDS:

• Failure load
• failure mode
• geometrical dimensions
• lap-shear bonded joints
• composite adherends
• wind energy

Acknowledgements

The authors gratefully acknowledge the financial support from the National Science Foundation of China (No. 51606196), the Key Laboratory of Wind Energy Utilization of CAS (No. KLWEU-2016-0301) and the “Transformational Technologies for Clean Energy and Demonstration”, Strategic Priority Research Program of the Chinese Academy of Sciences (Grant No. XDA21050303). We are also grateful to the anonymous reviewers for their suggestions to improve this paper.

Author contributions

Zhiwen Qin conducted the analysis of the key issues and partly finished the experiments and manuscript. Ji Huang analyzed the experimental data and wrote the manuscript in part. Lixing Zhang designed the molds and fabricated the coupons. Haijun Peng contributed to finish the experiments. Ke Yang, Jihui Wang and Jianzhong Xu critically revised the paper and provided constructive criticism.

Conflicts of interest

The authors declare no conflict of interest.

Additional information

Funding

This work was supported by the National Natural Science Foundation of China [No. 51606196]; “Transformational Technologies for Clean Energy and Demonstration”, Strategic Priority Research Program of the Chinese Academy of Sciences [Grant No. XDA21050303]; Key Laboratory of Wind Energy Utilization of CAS [No. KLWEU-2016-0301].