Bolt insertion damage and mechanical behaviors investigation of CFRP/CFRP interference fit bolted joints

Interference fit has advantages in improving fatigue behaviors of composite bolted joints; however, interference fit bolt insertion tends to cause damages in laminates weakening joint mechanical properties. Therefore, an experimental study was conducted to investigate bolt insertion damages of Carbon Fiber Reinforced Polymer (CFRP)/CFRP interference fit bolted joints. Mechanical behaviors of joints were also evaluated experimentally under both quasi-static loads and cyclic loads. Scanning Electron Microscope (SEM) and high-resolution X-ray micro-CT scan were used to examine micro damages in laminates. Damage and failure behaviors of joints were characterized. The results demonstrated that the hole entrance in upper laminate and the laminate boundary near the hole wall were the most critical regions for damages during bolt insertions. However, the influence of those damages on quasi-static failure loads and fatigue failure modes of joints was minimal. Delamination and matrix cracking occurred first in laminates following fiber and matrix fracture in quasi-static tensile tests. Interference fit could improve the fatigue resistance of the laminate hole; however, the bolt seemed to suffer a more critical local fatigue loading condition. This paper can contribute to composite structure designs, especially in understanding damage and failure behaviors of composite bolted joints.(c) 2022 Chinese Society of Aeronautics and Astronautics. Production and hosting by Elsevier Ltd. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/).

Automated summary

This paper investigates the damages caused by bolt insertion in Carbon Fiber Reinforced Polymer (CFRP) interference fit bolted joints. The mechanical behaviors of the joints under static and cyclic loads were experimentally evaluated. The results show that the hole entrance in the upper laminate and the laminate boundary near the hole wall are the most critical regions for damages during bolt insertions. However, these damages have minimal influence on the static failure loads and fatigue failure modes of the joints. The interference fit can improve the fatigue resistance of the laminate hole, but the bolt seems to experience a more critical local fatigue loading condition.